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2010 - 2011: Earth's most extreme weather since 1816?

Posted on 27 June 2011 by Jeff Masters

Every year extraordinary weather events rock the Earth. Records that have stood centuries are broken. Great floods, droughts, and storms affect millions of people, and truly exceptional weather events unprecedented in human history may occur. But the wild roller-coaster ride of incredible weather events during 2010, in my mind, makes that year the planet's most extraordinary year for extreme weather since reliable global upper-air data began in the late 1940s. Never in my 30 years as a meteorologist have I witnessed a year like 2010--the astonishing number of weather disasters and unprecedented wild swings in Earth's atmospheric circulation were like nothing I've seen. The pace of incredible extreme weather events in the U.S. over the past few months have kept me so busy that I've been unable to write-up a retrospective look at the weather events of 2010. But I've finally managed to finish, so fasten your seat belts for a tour through the top twenty most remarkable weather events of 2010. At the end, I'll reflect on what the wild weather events of 2010 and 2011 imply for our future.

Earth's hottest year on record
Unprecedented heat scorched the Earth's surface in 2010, tying 2005 for the warmest year since accurate records began in the late 1800s. Temperatures in Earth's lower atmosphere also tied for warmest year on record, according to independent satellite measurements. Earth's 2010 record warmth was unusual because it occurred during the deepest solar energy minimum since satellite measurements of the sun began in the 1970s. Unofficially, nineteen nations (plus the the U.K.'s Ascension Island) set all-time extreme heat records in 2010. This includes Asia's hottest reliably measured temperature of all-time, the remarkable 128.3°F (53.5°C) in Pakistan in May 2010. This measurement is also the hottest reliably recorded temperature anywhere on the planet except for in Death Valley, California. The countries that experienced all-time extreme highs in 2010 constituted over 20% of Earth's land surface area.

Figure 1. Climate Central and Weather Underground put together this graphic showing the nineteen nations (plus one UK territory, Ascension Island) that set new extreme heat records in 2010.

Most extreme winter Arctic atmospheric circulation on record; "Snowmageddon" results
The atmospheric circulation in the Arctic took on its most extreme configuration in 145 years of record keeping during the winter of 2009 - 2010. The Arctic is normally dominated by low pressure in winter, and a "Polar Vortex" of counter-clockwise circulating winds develops surrounding the North Pole. However, during the winter of 2009 - 2010, high pressure replaced low pressure over the Arctic, and the Polar Vortex weakened and even reversed at times, with a clockwise flow of air replacing the usual counter-clockwise flow of air. This unusual flow pattern allowed cold air to spill southwards and be replaced by warm air moving poleward. Like leaving the refrigerator door ajar, the Arctic "refrigerator" warmed, and cold Arctic air spilled out into "living room" where people live. A natural climate pattern called the North Atlantic Oscillation (NAO), and its close cousin, the Arctic Oscillation (AO) were responsible. Both of these patterns experienced their strongest-on-record negative phase, when measured as the pressure difference between the Icelandic Low and Azores High.

The extreme Arctic circulation caused a bizarre upside-down winter over North America--Canada had its warmest and driest winter on record, forcing snow to be trucked in for the Winter Olympics in Vancouver, but the U.S. had its coldest winter in 25 years. A series of remarkable snow storms pounded the Eastern U.S., with the "Snowmageddon" blizzard dumping more than two feet of snow on Baltimore and Philadelphia. Western Europe also experienced unusually cold and snowy conditions, with the UK recording its 8th coldest January. A highly extreme negative phase of the NAO and AO returned again during November 2010, and lasted into January 2011. Exceptionally cold and snowy conditions hit much of Western Europe and the Eastern U.S. again in the winter of 2010 - 2011. During these two extreme winters, New York City recorded three of its top-ten snowstorms since 1869, and Philadelphia recorded four of its top-ten snowstorms since 1884. During December 2010, the extreme Arctic circulation over Greenland created the strongest ridge of high pressure ever recorded at middle levels of the atmosphere, anywhere on the globe (since accurate records began in 1948.) New research suggests that major losses of Arctic sea ice could cause the Arctic circulation to behave so strangely, but this work is still speculative.

Figure 2. Digging out in Maryland after "Snowmageddon". Image credit: wunderphotographer chills.

Arctic sea ice: lowest volume on record, 3rd lowest extent
Sea ice in the Arctic reached its third lowest areal extent on record in September 2010. Compared to sea ice levels 30 years ago, 1/3 of the polar ice cap was missing--an area the size of the Mediterranean Sea. The Arctic has seen a steady loss of meters-thick, multi-year-old ice in recent years that has left thin, 1 - 2 year-old ice as the predominant ice type. As a result, sea ice volume in 2010 was the lowest on record. More than half of the polar icecap by volume--60%--was missing in September 2010, compared to the average from 1979 - 2010. All this melting allowed the Northwest Passage through the normally ice-choked waters of Canada to open up in 2010. The Northeast Passage along the coast of northern Russia also opened up, and this was the third consecutive year--and third time in recorded history--that both passages melted open. Two sailing expeditions--one Russian and one Norwegian--successfully navigated both the Northeast Passage and the Northwest Passage in 2010, the first time this feat has been accomplished. Mariners have been attempting to sail the Northwest Passage since 1497, and have failed to accomplish this feat without an icebreaker until the 2000s. In December 2010, Arctic sea ice fell to its lowest winter extent on record, the beginning of a 3-month streak of record lows. Canada's Hudson Bay did not freeze over until mid-January of 2011, the latest freeze-over date in recorded history.

Figure 3. The Arctic's minimum sea ice extent for 2010 was reached on September 21, and was the third lowest on record. Image credit: National Snow and Ice Data Center.

Record melting in Greenland, and a massive calving event
Greenland's climate in 2010 was marked by record-setting high air temperatures, the greatest ice loss by melting since accurate records began in 1958, the greatest mass loss of ocean-terminating glaciers on record, and the calving of a 100 square-mile ice island--the largest calving event in the Arctic since 1962. Many of these events were due to record warm water temperatures along the west coast of Greenland, which averaged 2.9°C (5.2°F) above average during October 2010, a remarkable 1.4°C above the previous record high water temperatures in 2003.

Figure 4. The 100 square-mile ice island that broke off the Petermann Glacier heads out of the Petermann Fjord in this 7-frame satellite animation. The animation begins on August 5, 2010, and ends on September 21, with images spaced about 8 days apart. The images were taken by NASA's Aqua and Terra satellites.

Second most extreme shift from El Niño to La Niña
The year 2010 opened with a strong El Niño event and exceptionally warm ocean waters in the Eastern Pacific. However, El Niño rapidly waned in the spring, and a moderate to strong La Niña developed by the end of the year, strongly cooling these ocean waters. Since accurate records began in 1950, only 1973 has seen a more extreme swing from El Niño to La Niña. The strong El Niño and La Niña events contributed to many of the record flood events seen globally in 2010, and during the first half of 2011.

Figure 5. The departure of sea surface temperatures from average at the beginning of 2010 (top) and the end of 2010 (bottom) shows the remarkable transition from strong El Niño to strong La Niña conditions that occurred during the year. Image credit: NOAA/NESDIS.

Second worst coral bleaching year
Coral reefs took their 2nd-worst beating on record in 2010, thanks to record or near-record warm summer water temperatures over much of Earth's tropical oceans. The warm waters caused the most coral bleaching since 1998, when 16 percent of the world's reefs were killed off. "Clearly, we are on track for this to be the second worst (bleaching) on record," NOAA coral expert Mark Eakin in a 2010 interview. "All we're waiting on now is the body count." The summer 2010 coral bleaching episodes were worst in the Philippines and Southeast Asia, where El Niño warming of the tropical ocean waters during the first half of the year was significant. In Indonesia's Aceh province, 80% of the bleached corals died, and Malaysia closed several popular dive sites after nearly all the coral were damaged by bleaching. In some portions of the Caribbean, such as Venezuela and Panama, coral bleaching was the worst on record.

Figure 6. An example of coral bleaching that occurred during the record-strength 1997-1998 El Niño event. Image credit: Craig Quirolo, Reef Relief/Marine Photobank, in Climate, Carbon and Coral Reefs

Wettest year over land
The year 2010 also set a new record for wettest year in Earth's recorded history over land areas. The difference in precipitation from average in 2010 was about 13% higher than that of the previous record wettest year, 1956. However, this record is not that significant, since it was due in large part to random variability of the jet stream weather patterns during 2010. The record wetness over land was counterbalanced by relatively dry conditions over the oceans.

Figure 7. Global departure of precipitation over land areas from average for 1900 - 2010. The year 2010 set a new record for wettest year over land areas in Earth's recorded history. The difference in precipitation from average in 2010 was about 13% higher than that of the previous record wettest year, 1956. Image credit: NOAA's National Climatic Data Center.

Amazon rainforest experiences its 2nd 100-year drought in 5 years
South America's Amazon rainforest experienced its second 100-year drought in five years during 2010, with the largest northern tributary of the Amazon River--the Rio Negro--dropping to thirteen feet (four meters) below its usual dry season level. This was its lowest level since record keeping began in 1902. The low water mark is all the more remarkable since the Rio Negro caused devastating flooding in 2009, when it hit an all-time record high, 53 ft (16 m) higher than the 2010 record low. The 2010 drought was similar in intensity and scope to the region's previous 100-year drought in 2005. Drought makes a regular appearance in the Amazon, with significant droughts occurring an average of once every twelve years. In the 20th century, these droughts typically occurred during El Niño years, when the unusually warm waters present along the Pacific coast of South America altered rainfall patterns. But the 2005 and 2010 droughts did not occur during El Niño conditions, and it is theorized that they were instead caused by record warm sea surface temperatures in the Atlantic.

We often hear about how important Arctic sea ice is for keeping Earth's climate cool, but a healthy Amazon is just as vital. Photosynthesis in the world's largest rainforest takes about 2 billion tons of carbon dioxide out of the air each year. However, in 2005, the drought reversed this process. The Amazon emitted 3 billion tons of CO2 to the atmosphere, causing a net 5 billion ton increase in CO2 to the atmosphere--roughly equivalent to 16 - 22% of the total CO2 emissions to the atmosphere from burning fossil fuels that year. The Amazon stores CO2 in its soils and biomass equivalent to about fifteen years of human-caused emissions, so a massive die-back of the forest could greatly accelerate global warming.

Figure 8. Hundreds of fires (red squares) generate thick smoke over a 1000 mile-wide region of the southern Amazon rain forest in this image taken by NASA's Aqua satellite on August 16, 2010. The Bolivian government declared a state of emergency in mid-August due to the out-of-control fires burning over much of the country. Image credit: NASA.

Global tropical cyclone activity lowest on record
The year 2010 was one of the strangest on record for tropical cyclones. Each year, the globe has about 92 tropical cyclones--called hurricanes in the Atlantic and Eastern Pacific, typhoons in the Western Pacific, and tropical cyclones in the Southern Hemisphere. But in 2010, we had just 68 of these storms--the fewest since the dawn of the satellite era in 1970. The previous record slowest year was 1977, when 69 tropical cyclones occurred world-wide. Both the Western Pacific and Eastern Pacific had their quietest seasons on record in 2010, but the Atlantic was hyperactive, recording its 3rd busiest season since record keeping began in 1851. The Southern Hemisphere had a slightly below average season. The Atlantic ordinarily accounts for just 13% of global cyclone activity, but accounted for 28% in 2010--the greatest proportion since accurate tropical cyclone records began in the 1970s.

A common theme of many recent publications on the future of tropical cyclones globally in a warming climate is that the total number of these storms will decrease, but the strongest storms will get stronger. For example, a 2010 review paper published in Nature Geosciences concluded that the strongest storms would increase in intensity by 2 - 11% by 2100, but the total number of storms would fall by 6 - 34%. It is interesting that 2010 saw the lowest number of global tropical cyclones on record, but an average number of very strong Category 4 and 5 storms (the 25-year average is 13 Category 4 and 5 storms, and 2010 had 14.) Fully 21% of 2010's tropical cyclones reached Category 4 or 5 strength, versus just 14% during the period 1983 - 2007. Most notably, in 2010 we had Super Typhoon Megi. Megi's sustained winds cranked up to a ferocious 190 mph and its central pressure bottomed out at 885 mb on October 16, making it the 8th most intense tropical cyclone in world history. Other notable storms in 2010 included the second strongest tropical cyclone on record in the Arabian Sea (Category 4 Cyclone Phet in June), and the strongest tropical cyclone ever to hit Myanmar/Burma (October's Tropical Cyclone Giri, an upper end Category 4 storm with 155 mph winds.)

Figure 9. Visible satellite image of Tropical Cyclone Phet on Thursday, June 3, 2010. Record heat over southern Asia in May helped heat up the Arabian Sea to 2°C above normal, and the exceptionally warm SSTs helped fuel Tropical Cyclone Phet into the second strongest tropical cyclone ever recorded in the Arabian Sea. Phet peaked at Category 4 strength with 145 mph winds, and killed 44 people and did $700 million in damage to Oman. Only Category 5 Cyclone Gonu of 2007 was a stronger Arabian Sea cyclone.

A hyperactive Atlantic hurricane season: 3rd busiest on record
Sea surface temperatures that were the hottest on record over the main development region for Atlantic hurricanes helped fuel an exceptionally active 2010 Atlantic hurricane season. The nineteen named storms were the third most since 1851; the twelve hurricanes of 2010 ranked second most. Three major hurricanes occurred in rare or unprecedented locations. Julia was the easternmost major hurricane on record, Karl was the southernmost major hurricane on record in the Gulf of Mexico, and Earl was the 4th strongest hurricane so far north. The formation of Tomas so far south and east so late in the season (October 29) was unprecedented in the historical record; no named storm had ever been present east of the Lesser Antilles (61.5°W) and south of 12°N latitude so late in the year. Tomas made the 2010 the 4th consecutive year with a November hurricane in the Atlantic--an occurrence unprecedented since records began in 1851.

Figure 10. Hurricane Earl as seen from the International Space Station on Thursday, September 2, 2010. Image credit: NASA astronaut Douglas Wheelock.

A rare tropical storm in the South Atlantic
A rare tropical storm formed in the South Atlantic off the coast of Brazil on March 10 - 11, and was named Tropical Storm Anita. Brazil has had only one landfalling tropical cyclone in its history, Cyclone Catarina of March 2004, one of only seven known tropical or subtropical cyclones to form in the South Atlantic, and the only one to reach hurricane strength. Anita of 2010 is probably the fourth strongest tropical/subtropical storm in the South Atlantic, behind Hurricane Catarina, an unnamed February 2006 storm that may have attained wind speeds of 65 mph, and a subtropical storm that brought heavy flooding to the coast of Uruguay in January 2009. Tropical cyclones rarely form in the South Atlantic Ocean, due to strong upper-level wind shear, cool water temperatures, and the lack of an initial disturbance to get things spinning (no African waves or Intertropical Convergence Zone.)

Figure 11. Visible satellite image of the Brazilian Tropical Storm Anita.

Strongest storm in Southwestern U.S. history
The most powerful low pressure system in 140 years of record keeping swept through the Southwest U.S. on January 20 - 21, 2010, bringing deadly flooding, tornadoes, hail, hurricane force winds, and blizzard conditions. The storm set all-time low pressure records over roughly 10 - 15% of the U.S.--southern Oregon, California, Nevada, Arizona, and Utah. Old records were broken by a wide margin in many locations, most notably in Los Angeles, where the old record of 29.25" set January 17, 1988, was shattered by .18" (6 mb). The record-setting low spawned an extremely intense cold front that swept through the Southwest. Winds ahead of the cold front hit sustained speeds of hurricane force--74 mph--at Apache Junction, 40 miles east of Phoenix, and wind gusts as high as 94 mph were recorded in Ajo, Arizona. High winds plunged visibility to zero in blowing dust on I-10 connecting Phoenix and Tucson, closing the Interstate.

Figure 12. Ominous clouds hover over Arizona's Superstition Mountains during Arizona's most powerful storm on record, on January 21, 2010. Image credit: wunderphotographer ChandlerMike.

Strongest non-coastal storm in U.S. history
A massive low pressure system intensified to record strength over northern Minnesota on October 26, 2010, resulting in the lowest barometric pressure readings ever recorded in the continental United States, except for from hurricanes and nor'easters affecting the Atlantic seaboard. The 955 mb sea level pressure reported from Bigfork, Minnesota beat the previous low pressure record of 958 mb set during the Great Ohio Blizzard of January 26, 1978. Both Minnesota and Wisconsin set all time low pressure readings during the October 26 storm, and International Falls beat their previous low pressure record by nearly one-half inch of mercury--a truly amazing anomaly. The massive storm spawned 67 tornadoes over a four-day period, and brought sustained winds of 68 mph to Lake Superior.

Figure 13. Visible satellite image of the October 26, 2010 superstorm taken at 5:32pm EDT. At the time, Bigfork, Minnesota was reporting the lowest pressure ever recorded in a U.S. non-coastal storm, 955 mb. Image credit: NASA/GSFC.

Weakest and latest-ending East Asian monsoon on record
The summer monsoon over China's South China Sea was the weakest and latest ending monsoon on record since detailed records began in 1951, according to the Beijing Climate Center. The monsoon did not end until late October, nearly a month later than usual. The abnormal monsoon helped lead to precipitation 30% - 80% below normal in Northern China and Mongolia, and 30 - 100% above average across a wide swath of Central China. Western China saw summer precipitation more than 200% above average, and torrential monsoon rains triggered catastrophic landslides that killed 2137 people and did $759 million in damage. Monsoon floods in China killed an additional 1911 people, affected 134 million, and did $18 billion in damage in 2010, according to the WHO Collaborating Centre for Research on the Epidemiology of Disasters (CRED). This was the 2nd most expensive flooding disaster in Chinese history, behind the $30 billion price tag of the 1998 floods that killed 3656 people. China had floods in 1915, 1931, and 1959 that killed 3 million, 3.7 million, and 2 million people, respectively, but no damage estimates are available for these floods.

Figure 14. Paramilitary policemen help evacuate residents from Wanjia village of Fuzhou City, East China's Jiangxi province, June 22, 2010. Days of heavy rain burst the Changkai Dike of Fu River on June 21, threatening the lives of 145,000 local people. Image credit: Xinhua.

No monsoon depressions in India's Southwest Monsoon for 2nd time in 134 years
The Southwest Monsoon that affects India was fairly normal in 2010, bringing India rains within 2% of average. Much of the rain that falls in India from the monsoon typically comes from large regions of low pressure that form in the Bay of Bengal and move westwards over India. Typically, seven of these lows grow strong and well-organized enough to be labelled monsoon depressions, which are similar to but larger than tropical depressions. In 2010, no monsoon depressions formed--the only year besides 2002 (since 1877) that no monsoon depressions have been observed.

The Pakistani flood: most expensive natural disaster in Pakistan's history
A large monsoon low developed over the Bay of Bengal in late July and moved west towards Pakistan, creating a strong flow of moisture that helped trigger the deadly Pakistan floods of 2010. The floods were worsened by a persistent and unusually-far southwards dip in the jet stream, which brought cold air and rain-bearing low pressure systems over Pakistan. This unusual bend in the jet stream also helped bring Russia its record heat wave and drought. The Pakistani floods were the most expensive natural disaster in Pakistani history, killing 1985 people, affecting 20 million, and doing $9.5 billion in damage.

Figure 15. Local residents attempt to cross a washed-out road during the Pakistani flood catastrophe of 2010. Image credit: Pakistan Meteorology Department.

The Russian heat wave and drought: deadliest heat wave in human history
A scorching heat wave struck Moscow in late June 2010, and steadily increased in intensity through July as the jet stream remained "stuck" in an unusual loop that kept cool air and rain-bearing low pressure systems far north of the country. By July 14, the mercury hit 31°C (87°F) in Moscow, the first day of an incredible 33-day stretch with a maximum temperatures of 30°C (86°F) or higher. Moscow's old extreme heat record, 37°C (99°F) in 1920, was equaled or exceeded five times in a two-week period from July 26 - August 6 2010, including an incredible 38.2°C (101°F) on July 29. Over a thousand Russians seeking to escape the heat drowned in swimming accidents, and thousands more died from the heat and from inhaling smoke and toxic fumes from massive wild fires. The associated drought cut Russia's wheat crop by 40%, cost the nation $15 billion, and led to a ban on grain exports. The grain export ban, in combination with bad weather elsewhere in the globe during 2010 - 2011, caused a sharp spike in world food prices that helped trigger civil unrest across much of northern Africa and the Middle East in 2011. At least 55,000 people died due to the heat wave, making it the deadliest heat wave in human history. A 2011 NOAA study concluded that "while a contribution to the heat wave from climate change could not be entirely ruled out, if it was present, it played a much smaller role than naturally occurring meteorological processes in explaining this heat wave's intensity." However, they noted that the climate models used for the study showed a rapidly increasing risk of such heat waves in western Russia, from less than 1% per year in 2010, to 10% or more per year by 2100.

Figure 16. Smoke from wildfires burning to the southeast of Moscow on August 12, 2010. Northerly winds were keeping the smoke from blowing over the city. Image credit: NASA.

Record rains trigger Australia's most expensive natural disaster in history
Australia's most expensive natural disaster in history is now the Queensland flood of 2010 - 2011, with a price tag as high as $30 billion. At least 35 were killed. The Australian Bureau of Meteorology's annual summary reported, "Sea surface temperatures in the Australian region during 2010 were the warmest value on record for the Australian region. Individual high monthly sea surface temperature records were also set during 2010 in March, April, June, September, October, November and December. Along with favourable hemispheric circulation associated with the 2010 La Niña, very warm sea surface temperatures contributed to the record rainfall and very high humidity across eastern Australia during winter and spring." In 2010, Australia had its wettest spring (September - November) since records began 111 years ago, with some sections of coastal Queensland receiving over 4 feet (1200 mm) of rain. Rainfall in Queensland and all of eastern Australia in December was the greatest on record, and the year 2010 was the rainiest year on record for Queensland. Queensland has an area the size of Germany and France combined, and 3/4 of the region was declared a disaster zone.

Figure 17. The airport, the Bruce Highway, and large swaths of Rockhampton, Australia, went under water due to flooding from the Fitzroy River on January 9, 2011. The town of 75,000 was completely cut off by road and rail, and food, water and medicine had to be brought in by boat and helicopter. Image credit: NASA.

Heaviest rains on record trigger Colombia's worst flooding disaster in history
The 2010 rainy-season rains in Colombia were the heaviest in the 42 years since Colombia's weather service was created and began taking data. Floods and landslides killed 528, did $1 billion in damage, and left 2.2 million homeless, making it Colombia's most expensive, most widespread, and 2nd deadliest flooding disaster in history. Colombia's president Juan Manuel Santos said, "the tragedy the country is going through has no precedents in our history."

Figure 18. A daring rescue of two girls stranded in a taxi by flash flood waters Barranquilla, northern Colombia on August 14, 2010.

Tennessee's 1-in-1000 year flood kills 30, does $2.4 billion in damage
Tennessee's greatest disaster since the Civil War hit on May 1 - 2, 2010, when an epic deluge of rain brought by an "atmospheric river" of moisture dumped up to 17.73" of rain on the state. Nashville had its heaviest 1-day and 2-day rainfall amounts in its history, with a remarkable 7.25" on May 2, breaking the record for most rain in a single day. Only two days into the month, the May 1 - 2 rains made it the rainiest May in Nashville's history. The record rains sent the Cumberland River in downtown Nashville surging to 51.86', 12' over flood height, and the highest level the river has reached since a flood control project was completed in the early 1960s. At least four rivers in Tennessee reached their greatest flood heights on record. Most remarkable was the Duck River at Centreville, which crested at 47', a full 25 feet above flood stage, and ten feet higher than the previous record crest, achieved in 1948.

Figure 19. A portable classroom building from a nearby high school floats past submerged cars on I-24 near Nashville, TN on May 1, 2010. One person died in the flooding in this region of I-24. Roughly 200 - 250 vehicles got submerged on this section of I-24, according to wunderphotographer laughingjester, who was a tow truck operator called in to clear out the stranded vehicles.

When was the last time global weather was so extreme?
It is difficult to say whether the weather events of a particular year are more or less extreme globally than other years, since we have no objective global index that measures extremes. However, we do for the U.S.--NOAA's Climate Extremes Index (CEI), which looks at the percentage area of the contiguous U.S. experiencing top 10% or bottom 10% monthly maximum and minimum temperatures, monthly drought, and daily precipitation. The Climate Extremes Index rated 1998 as the most extreme year of the past century in the U.S. That year was also the warmest year since accurate records began in 1895, so it makes sense that the warmest year in Earth's recorded history--2010--was also probably one of the most extreme for both temperature and precipitation. Hot years tend to generate more wet and dry extremes than cold years. This occurs since there is more energy available to fuel the evaporation that drives heavy rains and snows, and to make droughts hotter and drier in places where storms are avoiding. Looking back through the 1800s, which was a very cool period, I can't find any years that had more exceptional global extremes in weather than 2010, until I reach 1816. That was the year of the devastating "Year Without a Summer"--caused by the massive climate-altering 1815 eruption of Indonesia's Mt. Tambora, the largest volcanic eruption since at least 536 A.D. It is quite possible that 2010 was the most extreme weather year globally since 1816.

Where will Earth's climate go from here?
The pace of extreme weather events has remained remarkably high during 2011, giving rise to the question--is the "Global Weirding" of 2010 and 2011 the new normal? Has human-caused climate change destabilized the climate, bringing these extreme, unprecedented weather events? Any one of the extreme weather events of 2010 or 2011 could have occurred naturally sometime during the past 1,000 years. But it is highly improbable that the remarkable extreme weather events of 2010 and 2011 could have all happened in such a short period of time without some powerful climate-altering force at work. The best science we have right now maintains that human-caused emissions of heat-trapping gases like CO2 are the most likely cause of such a climate-altering force.

Human-caused climate change has fundamentally altered the atmosphere by adding more heat and moisture. Observations confirm that global atmospheric water vapor has increased by about 4% since 1970, which is what theory says should have happened given the observed 0.5°C (0.9°F) warming of the planet's oceans during the same period. Shifts of this magnitude are capable of significantly affecting the path and strength of the jet stream, behavior of the planet's monsoons, and paths of rain and snow-bearing weather systems. For example, the average position of the jet stream retreated poleward 270 miles (435 km) during a 22-year period ending in 2001, in line with predictions from climate models. A naturally extreme year, when embedded in such a changed atmosphere, is capable of causing dramatic, unprecedented extremes like we observed during 2010 and 2011. That's the best theory I have to explain the extreme weather events of 2010 and 2011--natural extremes of El Niño, La Niña and other natural weather patterns combined with significant shifts in atmospheric circulation and the extra heat and atmospheric moisture due to human-caused climate change to create an extraordinary period of extreme weather. However, I don't believe that years like 2010 and 2011 will become the "new normal" in the coming decade. Many of the flood disasters in 2010 - 2011 were undoubtedly heavily influenced by the strong El Niño and La Niña events that occurred, and we're due for a few quiet years without a strong El Niño or La Niña. There's also the possibility that a major volcanic eruption in the tropics or a significant quiet period on the sun could help cool the climate for a few years, cutting down on heat and flooding extremes (though major eruptions tend to increase drought.) But the ever-increasing amounts of heat-trapping gases humans are emitting into the air puts tremendous pressure on the climate system to shift to a new, radically different, warmer state, and the extreme weather of 2010 - 2011 suggests that the transition is already well underway. A warmer planet has more energy to power stronger storms, hotter heat waves, more intense droughts, heavier flooding rains, and record glacier melt that will drive accelerating sea level rise. I expect that by 20 - 30 years from now, extreme weather years like we witnessed in 2010 will become the new normal.

Finally, I'll leave you with a quote from Dr. Ricky Rood's climate change blog, in his recent post,Changing the Conversation: Extreme Weather and Climate: "Given that greenhouse gases are well known to hold energy close to the Earth, those who deny a human-caused impact on weather need to pose a viable mechanism of how the Earth can hold in more energy and the weather not be changed. Think about it."

Reposted from Weather Underground by Dr Jeff Masters, Director of Meteorology.

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Comments 251 to 300 out of 419:

  1. Norman, you seem so close to the right answer, yet you desperately try not to see it sometimes. "the mathematical model of the double pendulum is scientific since the equations can offer testable explanations about the nature of the pendulum and offer predictibility about the overall behavior of pendulum." As I'm sure Dikran intended, replace 'double pendulum' and 'pendulum' in your statement with 'climate' and you're all the way there. In what way would the 'software' model of the pendulum be different from the 'mathematical' model, if it contains exactly the same physics? And like the climate model, you can then learn an awful lot about the overall behaviour of the pendulum by running the software model for an extended period of time / many times. For example, you could learn exactly where you can stand and not be hit by the aforementioned pendulum! In fact, you could learn what the boundaries are that the pendulum won't cross. You could learn the places the pendulum is most likely to be, and the points in space it crosses most or least often; or the average velocity and acceleration of differnt parts of the pendulum. In a climate model, although the individual trajectory of the climate is not exactly predictable, we can say very well that it will fall within certain bounds. Those bounds (for temperature) head upwards as a consequence of the trajectory of CO2 forcing, in just the same way as the bounds for temperature in Brisbane will head upwards as we head towards summer. Somewhere within those bounds will be the actual temperature, which is clearly more likely to be higher in 10 years than lower in 10 years. In 50 years the chances of it being higher at BAU rise to beng almost certain. Knowing the trajectory of the bounds of temperature, along with the most likely multi-year average temperature, the likely rates of change and the states of different parts of the system, is very important indeed, just like knowing where it is safe to stand next to your pendulum, or knowing details about the movement patterns of your pendulum. Best not to confuse meteorology with climate science too - the former (in this analogy) tries to predict the exact position of the pendulum at some point in the future, the latter predicts its average trajectory and the boundaries outside which it will not travel.
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  2. Tom Curtis @ 246 There are very few tornadoes in the tropics. Lots of thunderstorms just not severe type. The tropics have some of the warmest moist air on the planet. You need more than warm moist air to form severe thunderstorms. You also need the wind shear. I also have a question about CAPE. A thunderstorm brings heat to the midlattitudes of the atmosphere. Wouldn't that tend to increase the stability of the air and suppress severe thunderstorm activity?
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  3. Tom Curtis @ 249 Not quite Tom, I am not making any claim about the predicability of any given climate model and extreme weather events. I do agree this is not the thread for climate models. There already is one on this topic. I was just answering Dikran's questions. My point was that if a model was not capable of making predictions it would not be scientific. If a model can make valid predictions it is a useful science tool.
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  4. Despite 249 " perhaps we could reserve this thread for talking about the weather (stay on topic)" Because I think understanding what it means to "predict" is on topic: 248 "A software model of the pendulum would be worthless as a science as it would not give any useful prediction of the pendulum's nature." The problem, IMHO, Norman and many people have is that they do not actually look at the nature of the problem. The words used assume (lets say) that the system under study is what I'd loosely refer to as "Newtonian"; by which I mean a system for which, given the equations, one can predict to any degree of precision you wish, at any time in the future, the phase state of the system - in constant time. Newtons equations dynamics are like that. But not all good, scientific, physical system are. In a Quantum system, the phase state is calculable, in constant time but not to any required precision. You only get probability distributions. To scientifically (and QED is one of the best scientific theories we have!) predict a quantum system is to determine correctly probability distributions... that is their nature. Gas laws are are macroscopically like Newtonian mechanics - you get volume/pressure/temporarily - but expressed as statistical mechanics, more like QM... you get probability distributions... again, that is the nature of gasses. Chaotic systems can not be calculate in flat time - since you have to calculate each iteration - and precision is problematic as different precisions is, effectively, changes in initial conditions. Chaotic system, however, behave well in terms of attractors, self-similarity metrics etc. that, again, is their nature. In each case there's an appropriate, predictable, statistically well found state description which is scientifically meaningful. It is a common error to try to apply the term 'predictable' as understood in the Newtonian sense able to systems to which it does not apply. And why is this, IMHO again, appropriate to this thread? Because extreme events in this context are not tails of normal/Gaussian distributions where you can pick some sigma and say "there! beyond that value". They are more like Pareto/Zipf distributions and other statistics apply... same difference as between Newton and Chaos.
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  5. " but a good climate model should be able to predict is a region will have more our less moisture over a given period of time. " Well yes they do (example above) and validate so long a "region" is large. Its also harder to do regions than global, but that does not mean that global models are not useful and should be replaced. At the back of idea on science is that if we understood the world sufficiently well, then we must be able to predict the outcome of an experiment. However, both chaos theory and quantum theory throw that idea out. Prediction can be limited without any loss of understanding the processes. You can predict that a system will behave chaotically within a certain proscribed phase space and that is a valid, testable prediction.
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  6. So far the best definition of "extreme" above is that it must result in safety warnings. A run-of-the-mill thunderstorm does not meet that criteria although a severe thunderstorm does. What has been lacking so far is a connection from warming and more moisture in general to specific localized severe events. Specifically the logic so far has been: 1. Global average temperature rises along with global average surface moisture 2. (this step is missing) 3. Locally severe weather results.
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  7. Norman wrote: "It would seem the mathematical model of the double pendulum is scientific since the equations can offer testable explanations about the nature of the pendulum and offer predictibility about the overall behavior of pendulum. That is if you would use the equations and run a long term simulation, the simulation would trace out the same area as an actual pendulum if this were videotaped." This is not correct. The mathematical model would only be able to trace the behaviour of the real pendulum if you could measure the initial conditions with infinite precision. If you could do that, the sofwtare model would also trace out the trajectory of the pendulum exactlty. Your comment suggests that you fundamentally do not understand the nature of chaotic systems. They can be completely deterministic, but that doesn't mean they are predictable, because their behaviour is extremely sensitive to initial conditions. "A software model of the pendulum would be worthless as a science as it would not give any useful prediction of the pendulum's nature. It gives exactly the same predictions as the mathematical model; they are equivalent. The only difference is that the software model can solve the equations from the mathematical model (which do not have explicit mathematical solutions). "The science of meterology does not try to make predictions about the weather beyond a few days because they know such activity is nonscientific and useless. The prediction means nothing. Are you saying that we can't predict climate because we can't predict weather more than a few days in advance? "One could not predict anyone actual thunderstorm in the region months in advance, but a good climate model should be able to predict is a region will have more our less moisture over a given period of time. If it can't do this and make a valid prediction, the model would not be good for much and a new one should be developed. If you make the region large enough (i.e. a scale corresponding to the grid size of the GCM), then GCMs already do provide usefully accurate projections of that nature. Modellers would not claim to be able to predict rainfall at e.g. a catchment scale, as they average over grid-boxes that are far larger than a typical catchment and so can't capture such small-scale dynamics. For sub-regional or catchment level hydrology they generally use the method of statistical downscaling.
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    Moderator Response:

    [DB] Presented without my usual fanfare:

    Double compound pendulum

  8. Eric (skeptic) @256, as I stated in 232,
    "1) Increased temperature implies increased specific humidity; 2) Increased specific humidity implies more water condenses as a result of cooling due to updrafts or frontal systems; 3) More water condensing implies more latent heat released; 4) More latent heat released implies a stronger updraft generated which: 4a) Results in greater cooling, with more water released; and 4b) Results in more air being drawn into the updraft, carrying more water with it."
    I was focussed on the prediction regarding precipitation, but to make it more general I should probably add: 4c) A stronger updraft results in stronger local winds; and 4d) A stronger updraft carries precipitated water to a greater altitude, giving it a chance to freeze and fall as hail. Also of relevance is: 5) The greater the rate of condensation, the larger the drops of condensate, which increases the risk of large hail. All of these follow straightforwardly from the increased specific humidity with increased temperature. The effects are also observationally verified by the global pattern of thunderstorms, with (contrary to Norman @252), the strongest and most frequent thunderstorms forming in the tropics. This can be seen on this plot of the average number of lightning strikes per year for the years 1995-2003 from NASA: Lightning is a good proxy for the intensity of thunderstorms, including wind strength. From my experience living in equatorial Africa (the southern end of that orange blotch) and in tropical and sub-tropical Queensland, it is also a good proxy for hail frequency, intensity and size (all much larger in Africa than in Queensland), but there may be an increased frequency of large hail in more temperate regions. As Norman correctly points out, humidity alone is not enough for a thunderstorm; but heat and humidity are both definite factors in the strength of thunderstorms. If you increase both, ceterus paribus you will increase the frequency and intensity of thunderstorms. As it happens, increased warming is also expected to increase Convective Available Potential Energy, another key factor (see maps in my 246. Consequently, every element of "severe" thunderstorms, with the possible exception of tornadoes, is expected to increase globally with a warming climate, though not in all regions. That is, we can expect more damaging winds, more large hail, more flash floods, and more lightning strikes. And tornado frequency is also predicted to increase, though I can't lay out the logic of it the way I can for thunderstorms in general.
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  9. Thanks for the reply Tom. It still seems like a big leap from average to local. How do we know that an increase in convection on average will yield locally severe convection? An alternative outcome is wider areas of diffuse convection rather than narrower areas of concentrated convection. The average convection can still rise without a rise in strong convection and locally severe weather.
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  10. In support to what Dikran wrote on the predictability of the double pendulum, a nice animated gif: it shows two solutions differing by 0.001 degrees in the initial conditions of the second mass.
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  11. Hello Tom et al., With reference to the ongoing confusion about thunderstorms...I'll write up something this afternoon that I hope will clarify matters.
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  12. Albatross @261, I'll certainly look forward to it :)
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  13. OK, Make that tonight, need to take care of some work.
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  14. 260 - now Normal might like to google something like "lyapunov exponent double pendulum" and discover some amazing, real science, behind "unpredictable" chaotic systems.
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  15. Tom Curtis @ 258 I do not think you are correct on this one about severe thunderstorms. I have been checking around for the type of thunderstorms that dominate the ITCZ. I am not sure your lightning proxy is totally valid for detemining the severity of a thunderstorm when dealing with the different kinds (like comparing apples to oranges). No doubt an air-mass thunderstorm with more lightning strokes is more severe than an air-mass thunderstorm with fewer strokes. But it would not be as severe as a super-cell thunderstorm. From article on the ITCZ: "The ITCZ is formed by vertical motion largely appearing as convective activity of thunderstorms driven by solar heating, which effectively draw air in; these are the trade winds.[2]" Article source of above quote. A quote from another article: "Supercells are the most powerful thunderstorms. By their definition, supercells are always severe. Supercells are responsible for a disproportionate amount of damage and casualties." Article source for supercell quote. The air mass storms can be intense for short periods of time but not nearly as long as a supercell. Another quote from above article link: "The air mass thunderstorm is a common and usually non-severe phenomenon that forms away from frontal systems or other synoptic-scale disturbances. They form where moist and unstable conditions exist in the atmosphere. Air mass thunderstorms are usually produced in areas of very little vertical shear. As a result, the threat for severe is small. When they do reach severe limits, the thunderstorms may produce brief high winds or hail which develop because of high instability. These storms are know as pulse severe storms. Although several storm cells can develop, each individual cell lasts about 30-60 minutes and has three stages." Another article on Thunderstroms similar to the others. Article on thunderstorms. And yet another article. Air Mass Thunderstorms are usually weak. From what I was able to find out about thunderstorms, I cannot agree with your concluding statement. "Consequently, every element of "severe" thunderstorms, with the possible exception of tornadoes, is expected to increase globally with a warming climate, though not in all regions. That is, we can expect more damaging winds, more large hail, more flash floods, and more lightning strikes. And tornado frequency is also predicted to increase, though I can't lay out the logic of it the way I can for thunderstorms in general." The following information just about goes opposite of your concluding statement. Most severe storms in US occur in spring and early summer.
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  16. Dikran Marsupial @ 257 I am wondering what you are getting at by bringing up chaotic systems. Looking at the little animations of the pendulum by DB and Riccardo. Maybe you are pointing out that if you increased the energy of this system (made the pendulum swing faster), the frequency of the various cycles would increase (based upon your point that the return rate is a way to measure extreme events: "Extreme events already have a good statistical definition, namely the return period, for instance an event might have a return period of 100 years, in laymans terms, a "once in a hundred year event". This definition has the advantage of automatically taking into account the skewness of the distribution.") My question, if that is the case, is the 0.8C temp increase and 4% moisture increase of the atmosphere enough of difference to be noticeable? That is the conclusion of Jeff Masters of which this thread is about. He belives the extremes of 2010 and 2011 (not anyone event but the aggregate of all the events) are enough to determine the pendulum is moving faster.
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  17. scaddenp @ 245 "I would say that you are making the hypothesis that there is unforced cycles in the weather pattern and these alone are enough to explain weather. An alternative hypothesis which doesnt require unexplained cycles is to use existing physics and postulate that these are result of global warming." Good point, my objection is that when I go searching for articles on past climate (and I have only hit the tip of the iceberg) I see cycles and no strong evidence (except temperature graphs) that climate (long term weather patterns in a specific region) is shifting to a new more severe pattern because of forcing caused by warming. Here is another example. Most the time I post these I am accused of cherry-picking. It would be a valid point if it was just one article. But when you find numerous articles with much the same evidence, I do not know how the cherry-picking charge remains valid. Precipitation patterns for Mid-Atlanctic region. Look at the graphs. They show cycles. I can get more. Maybe I should just compile 10 or 20 links on one post that show cycles and when going back further in time, the extremes are no longer that disturbing as for some reason this extreme pattern was able to form in a non globally warmed world. At this time I plan on researching Dikran Marsupial's concept that the proof of Global Warming being a driver in extreme weather is the frequency of the extreme events. I have been focused on intensity of events. Next study is to see if the long term historical record indicates extreme patterns are taking place more often than they did in a cooler world.
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    [DB] "when I go searching for articles on past climate (and I have only hit the tip of the iceberg) I see cycles" and "Look at the graphs.  They show cycles."

    This becomes tiresome.  Seeing "cycles" without proposed physical causatives mechanisms to explain them is little different than numerology/superstition or tilting at windmills. Your preconceptions are blinding you, despite the able help of some of the august contributors to this thread.  Eg., you can't see the forest due to all the trees in your way.

    Please refer back to the OP for this Dr. Masters quote:

    "A warmer planet has more energy to power stronger storms, hotter heat waves, more intense droughts, heavier flooding rains, and record glacier melt that will drive accelerating sea level rise. I expect that by 20 - 30 years from now, extreme weather years like we witnessed in 2010 will become the new normal."

    and this cited by Dr. Masters:

    "those who deny a human-caused impact on weather need to pose a viable mechanism of how the Earth can hold in more energy and the weather not be changed. Think about it."

    Emphasis added (to both quotes); that last bit is good advice. As for this last bit from your comment:

    "I can get more."

    Please don't.  You don't want to accept the premise of the OP, that we may be witnessing the human-caused impacts on weather now, and that extreme conditions of the present may be the new norm in 20-30 years; we get that. 

    But unless you can prove that these extremes currently being experienced are NOT due to human-influence and that you have physics-based hypothesis' supplemented by solid statistical analysis to back up your contentions, then you are just being contrarian and most here will no longer waste any of their valuable time trying to help you gain understanding.

  18. Norman, when you are talking about "cycles", then there needs to be a clear distinction between unforced cycles, which have no external driver, and forced changes. ENSO and thus any downstream influences is example of unforced cycle. The interesting question is whether there is any evidence for unforced cycles with periods longer than 30 years. These are postulated - notably Tsonis and Swanson. However, other supposed "cycles" are more likely forced by variations in TSI and aerosols. On top of that, is the question as to whether warming increases the severity of weather effects within the normal cycles. La Nina's now are warmer than El Nino's of decades past - what does that do to weather? So merely saying that there has been periods of drought,storms, etc in the past is uninteresting. The postulate is that when there are extremes, then these are on average worse/more frequent etc. The most robust prediction would be about severe precipitation events and the Min et al paper, and the papers on flood events in IPCC would both appear to bear that out. I reiterate though that it is consistent with predictions, not "proof". Now 2010 events might indeed be linked to natural cycles but the severity of them is may be increased.
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  19. Tom, Norman, EricS,and others. Gee, this thread going to get as long as the "Its not the sun" at this rate ;) I think that Dr. Masters is of the opinion that the preponderance of severe events in 2010 is consistent with the increasing trend, and a system that is increasing in sensible and especially latent energy (i.e., moisture). This post is going to focus on thunderstorms and severe thunderstorms in particular, and how they might change in a warmer and more moist planet. I have written about this at length elsewhere at SkS, so I encourage people to read the posts made here, and here. In short, the research to date suggests that severe thunderstorms will increase in intensity as the planet warms and low-level moisture increases. Some seem to think that there is a "jump" or disconnect between the observations that low-level moisture has increased (and will continue to do so) and the occurrence of severe thunderstorms. I'll show that the physics and theory support that link. First, that lightning map that Tom showed us at #258. Tom, I have to agree with Norman on this one. Lightning frequency or occurrence is not typically a good proxy for thunderstorm severity. The strongest storms are typically observed over mid-latitude land areas, not over the tropics. Thunderstorms, are of course, most frequently observed over those areas. The reason for that are simple. For a thunderstorm to form one requires the realization of three criteria (all of them, not just one or two): low-level moisture (by that we typically mean in the near surface or boundary-layer, although some storms are what we call 'elevated'), instability and a trigger to lift the air to its level of free convection (examples of triggers include surface heating, fronts, outflow boundaries, drylines etc.). These criteria are, not surprisingly, most often met over the continental tropical areas. In fact, research has shown that the the most intense thunderstorms on the planet are likely found over Argentina and the southern Great Plains of the USA. I can attest to this as someone I work with told me about how a Lear jet flying into one of the storms stalled on account of the incredibly strong updraft-- we are talking updraft speeds of 50 m/s. Now for severe weather one either requires really strong buoyancy (difference in temperature between the storm's updraft and the surrounding ambient air) and/or vertical wind shear. The wind shear has a two-fold affect on updraft-- it can organize the upraft and separate the updraft and downdraft, also it can induce non-hydrostatic pressure perturbations in the storm which can cause the updraft to accelerate. Thermodynamically, one can increase the amount of buoyancy by increasing the low-level moisture and/or by increasing the lapse rate of the environmental air. The biggest bang for you buck though in this regard is to increase the low level moisture. Now this can all be explained using theory. The moist-static energy (MSE) in the low levels is given by: MSE = gz +CpT +qL (1), where g is the gravitational constant, z the height, Cp the heat capacity of air, T the air temperature, q the specific humidity or water vapour mixing ratio, and L is the Latent heat of vapourization. Because L is such a huge term, the moisture really dominates the MSE of the air. Now a metric that is used to quantify the amount of buoyant energy in the atmosphere is the convective available potential energy (CAPE). CAPE is simply the vertical integration of the positive temperature difference between a parcel rising along the moist adiabat and the corresponding ambient air temperature between cloud base and the equilibrium level. It can be shown that the maximum updraft in a storm is given by: Wmax = (2*CAPE)^0.5 (2), Now this is a theoretical value and it ignores the decrease in the updraft strength because of entrainment of cooler/drier air into the updraft and the reduction in of updraft strength by water loading of the precipitation and other factors. Empirical observations have found that observed Wmax values are closer to 0.6-0.7 of the theoretical value. The important part. Crook (1996) showed that by manipulating equation (1)increasing the low moisture by 1 g/kg increases the CAPE by 2.5 the amount as a 1 C warming of the low-level air would. So changes in near surface specific humidity of 10% or so of typical background values can have a huge impact on the buoyancy available to a storm, and in turn the maximum updraft strength-- as found by the papers I cited in one of my posts above. Increasing low-level moisture also has another important factor, it increases the liquid water content of the updraft. For hail to develop one, in basic terms, requires strong updrafts, long residence time in the updraft (typically a longer-lived updraft), and relatively high liquid water content. As the aforementioned discussion has shown increasing the low-level moisture increases the buoyancy (i.e., updraft strength), and the liquid water content of the updraft. For a hail embryo to grow into a large stone it needs to reside in a strong (moist) updraft for a long period of time, so an organized updraft helps, and that is oftentimes (but not always as shown below) where the vertical wind shear comes into the picture. So the short of it is that increasing the low-level moisture is likely to increase the chances for more intense/severe thunderstorms, and perhaps larger hail too. Work by Botzen et al. (2010) predicts that: "Extrapolations of the historical relations between hailstorm damage and weather indicators under climate change scenarios project a considerable increase in future hailstorm damage." But what about the vertical wind shear that is supposed to decrease (note that they are not predicting it will go away) over the mid latitudes as the planet warms? Well, as the research has shown, the impacts of less wind shear are offset by the increase in CAPE. Additionally, strong vertical wind shear is not a requirement for extremely large hail. Consider this recent example from Kansas, where they had > 5 cm diameter hail on 2 July 2011. The sounding below shows that the low levels were very moist (dewpoints > 20 C), the CAPE was also near 3400 J/kg, see here. The only problem was the stable air between 900 and 800 mb (aka a capping lid)-- that had to be overcome to tap into the huge convective available energy. Note the relatively weak winds in the lowest 6 km (0-6 km AGL wind shear is often used to quantify the bulk wind shear), suggesting relatively weak vertical wind shear. To cut a long story short the capping lid was broken and this was the result: [Source] Hail with a diameter of near 7 cm. The huge CAPE on this day was clearly critical in permitting giant hail to be produced in an environment with relatively-low wind shear, and this case is by no means an outlier. And a closing, but important, note on wind shear. Research has shown (see for example the work by Markett and Allen (2003)) that the precipitation efficiency of thunderstorms increases as vertical wind shear decreases. So in the future we could see a higher incidence of torrential downpours from storms having higher precipitation efficiencies arising from any decrease in wind shear. Hardly a plus.
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  20. Norman The reason that I introduced the double pendulum into the discussion was to correct your deeply misguided view of what is science and what is not. The lack of certainty or the ability to make accurate predictions does not mean something is not good science, and the double pendulum demonstrates that. Like the weather it is chaotic and hence unpredictable, even though we can write down equations that provide a perfect characterisation of its behaviour. You had been brought to the point where you could not reasonably discuss the double pendulum any further without contradicting yourself. The fact that you tried to deflect the discussion away from the double pendulum suggests to me that you know that, are not really interested in counter arguments to your position and are just trolling. This confirms my earlier prediction that further progress in discussing the science with you was unlikely.
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  21. 267 - Norman
    "Precipitation patterns for Mid-Atlanctic region. Look at the graphs. They show cycles. "
    You have spent quote a lot of time, as 270 Dikran points out, setting very particular requirements for what is science and then make the strong statement "They show cycles" based just on the eye-ball-o-matic?!?! May I suggest this post by Tamino for how to scientifically analyse an AMO data set for cycles. That's doing science; compiling 10 or 20 links isn't.
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    Moderator Response: [Dikran Marsupial] Link fixed
  22. Albatross, can I just thank you for the superb post on thunderstorms at #269! Having just watched a 'Spanish Plume' breakdown in the UK and a day when a convective cap was not broken despite high dew points and lots of CAPE, I've learned a lot in the last 10 minutes.
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  23. #269, Albatross, thanks for that post. A couple of questions though, why are the Great Plains and/or Argentina considered continental tropical areas? Or is that not what you meant? The subtropical parts of the U.S. have the most thunderstorms (Orlando Florida), but not the most severe. Typically the missing ingredient there is cooler and/or drier air aloft. Also my question to Tom in 259 applies, where is global-local connection? You pointed out that more moisture in the low levels is a big contributor to instability. But the increase in moisture is a worldwide average, not necessarily some local area prone to thunderstorms. For example there is currently an anomalous increase in moisture in the U.S. desert SW (a weather pattern). Some storms and dust storms have resulted. But that doesn't mean there is more or less moisture anywhere else in the U.S. The patterns dictate the moisture levels, not the GAT.
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  24. Dikran, I finally read through the paper in your post 224 It is pretty clear that downscaling does not work well for extremes. There is poor correlation in the bonafide extreme events (e.g. pf90) particularly during the times of year that they matter (spring and summer). In fact almost no correlation between the model downscaling and reality. Furthermore, no matter how many times you insist, the return period statistics are not a valid analysis of increasing risk of extreme events. Sure, they are great for any particular flash-flood or river flood prone area. But to conclude anything about a broader trend in extreme events requires looking at every single possible extreme area statistic. Anything less is a cherry pick. For example, we were briefed on the Toowoomba flash floods above, and a return period statistic may inform the Toowoombians. But what about all the other places that didn't flash flood? Without adding their return period statistics (which may be decreasing) into a whole, there can be no conclusion about any trend. That is why Master's post above comes up short. Sorry to be so blunt, your statistics are strong and I appreciate your criticism of my errors. But in this particular case, I believe you are incorrect.
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  25. Eric (skeptic) Pfl90 is not a measure of ability to predict "bona fide" extreme events, it is the fraction of total precipitation due to predicted events over the observed 90th centile. You are just cherry picking the statistic to find one that gives you a reason not to accept the utility of statistical downscaling. Care to explain why the fraction of total rainfall due to events over the observed 90th centile is more informative than the prediction of the 90th centile itself (pq90)? Also for floods on the SE England, five-day precipitation is what causes floods, so why not look at px5d? I have already explained, repeatedly, that return periods can be constructed for regions as well as particular locations. It is also possible to detect trends in return periods using well understood statistical methods (Extreme Value Theory) Thus your second paragraph is (a) wrong and (b) inidcates you are not paying sufficient attention to my posts.
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  26. Dikran, I will try to pay more attention. Obviously I am still learning this area, but I think there is a forest and trees issue here (a region is still just part of the forest). Looking at each statistic from table 1, and ignoring any results: pav and pint are merely precipitation. I am not sure what pq90 means. px5d appears to be a measure of extremes, except that it is only the excessive px5d's that matter. We would need to measure separate statistics for those. pxcdd is a good measure for drought provided we compare the excessive pxcdd from the model to reality. Showing there is a good match for pxcdd for a few days does not necessarily mean there is a good match for pxcdd for 10 or 20 days (or whatever might be considered a drought). Both pf90 and pnl90 appear to be good indications of extremes or a proxy for extremes.
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  27. Eric@276 All of the indices are correlations between actual observations and the downscaled results from the GCM runs, so all are comparing the model with reality. While pav and pint are indeed "merely daily rainfall", flood events in most parts of the UK are multi-day events, so the ability to predict day-to-day rainfall is actually quite helpful in predicting extreme events leading to floods. Pq90 is a test of the ability of the system to predict the 90th centile of precipitation. In other words, it is a test of the ability of the system to model the upper tail of the distribution of rainfall. As I said, multi-day rainfall events are important for most (but not all) parts of the UK, so the relevance of px5d is faily obvious, it is those sort of events that will lead to flooding. Pnl90 is not *that* interesting - how many extreme events do we get in one season? Note for pfl90 if you have a very wet season, with rain on most days, then the fraction of rainfall due to extreme events will be lower than in a more normal season, even if the extrem events are the same. Pxcdd is a measure of the ability of the downscaled model to predict the maximum number of consecutive dry days. This is reasonable as the most extreme drought in any season will be the longest one (that is pretty much the definition of a drought). If the model predicts a maximum dry spell of a couple of days, and the observations have 10 or 20 days, then you will get a low value for the pxcdd statistic, which is exactly what you would want to see how good the model is at predicting extreme droughts. There is a good reason why all of the statistics were used in the study; they are all relevant, and it is a mistake to pick and choose as it ignores important context. I should also note that only one of the models was deliberately designed for predicting extreme events on a day-to-day basis, namely MLPR, but none of the indices used are really intended for that sort of resolution (because it isn't important in climatological studies, where it is the longer term statistcs that are of interest).
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  28. Eric @273, "Or is that not what you meant?" Correct, I did not mean that. "But the increase in moisture is a worldwide average, not necessarily some local area prone to thunderstorms." Not true. Areas prone to thunderstorms, including intense/severe thunderstorms have experienced an increase in near surface specific humidity. See references below. "The patterns dictate the moisture levels, not the GAT." Not entirely true, see references below-- increases in specific humidity are closely correlated with warming in most regions, inlcuding regions with thunderstorms. Dai (2006), noted an increase in annual surface specific humidity over most land areas, see his Fig 9b. "The data show increases in specific humidity of several percent per decade, and increases in dewpoint of several tenths of a degree per decade, over most of the country in winter, spring, and summer. Nighttime humidity trends are larger than daytime trends. The specific humidity increases are consistent with upward temperature trends." Here is a relatively old study for the USA by Gaffen and Ross (1999): "The data show increases in specific humidity of several percent per decade, and increases in dewpoint of several tenths of a degree per decade, over most of the country in winter, spring, and summer. Nighttime humidity trends are larger than daytime trends. The specific humidity increases are consistent with upward temperature trends." Here is a study for Canada by Vincent et al. (2007): "After accounting for these discontinuities, the results of trend analysis show evidence of an increase in air moisture content associated with the warming observed in the country. During winter and spring, the significant warming in the western and southern regions is accompanied by an increase in dewpoint and specific humidity and by a decrease in relative humidity; in summer, warming is observed in the southeast and it is associated with significant positive trends in dewpoint and specific humidity." And another for China by Wang and Gaffen (2001): "Moisture increases are observed over most of China. The increases are several percent per decade for specific humidity, and several tenths of a degree per decade for temperature and dewpoint."
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  29. Skywatcher @272, Thanks, and you are welcome :)
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  30. Albatross, thanks for the links. I read through Dai and it shows an upward trend in RH and paints a bigger trend for the central U.S. (fig 10a) where we have plenty of thunderstorms. On top of that trend are the fluctuations from the patterns, particularly ENSO (basically lower RH in La Nina and higher in El Nino). That may be primarily due to the relationship with temperature. I'm not sure how well severe convection correlates with the trend and the fluctuations. There are many different papers with various measurements and fluctuations but I have yet to find one with a clear or even tentative correlation with the RH trend and fluctuations shown by Dai.
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  31. DB @ 267 "But unless you can prove that these extremes currently being experienced are NOT due to human-influence and that you have physics-based hypothesis' supplemented by solid statistical analysis to back up your contentions, then you are just being contrarian and most here will no longer waste any of their valuable time trying to help you gain understanding." Good point. It does take time to develop ideas. My point of posting on this website was to gather information to learn what is already out there and progress with the concept I am developing in greater depth. I come here with some hope. Conspiracy sites are nothing but HAARP, media web sites are only some person's opinion. No depth, no science, no research. So many webpages are making the claim weather is intensifying and it is because of Global warming but no one is offering mechanisms of why they think this. I read Jeff Masters article. He is a PhD in meterology and I was hoping to read some mechanisms or behind the scenes physics but it was much the same. The idea of a warming world does go against what I have come to know about the weather via experience and observation. This does not mean that what I know is valid or correct. I may be working on a wrong assumption. I have been on this site awhile and have read many posts. It seems that many intelligent and knowledgeable people post and this would be a place to test ideas and theories. If they are wrong the errors will be pointed out. If I have become dull or "thick-headed" with my posts, I apologize. I do have reasons for them.
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  32. From my local (Northern Virginia) forecast discussion: "this will place the area on the srn periphery of stronger westerlies and nrn periphery of a moist-unstable airmass. with this setup...we will have to monitor the potential for MCS activity next week." ( Now that strong spring and early summer fronts are pretty much history, our severe weather would mostly come from thunderstorm complexes that move SE with the jet stream carrying their own supply of cooler, drier air like a well defined front would have. In contrast the next week's forecast further south (Georgia) is nothing much (too much warm air aloft for thunderstorms). This pretty much follows our pattern of a peak in severe TS in spring (early south, later north) followed by sporadic severe TS in summer.
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  33. DB and Dikran Marsupial, Research I have conducted tonight to try and demonstrate why I am of the opinion that Global warming will not necessarily increase severe weather. I do believe Global Warming will produce Climate Change. I have evidence of that every year. One half of the globe warms drastically every year and the climate changes drastically with this warming. It is a fact and one I do not argue. Severe weather is the point I am not convinced off. The physical reason behind this postiion I take. It is based upon my understanding of equilibrium. Example of Chemical equilibrium. The above is an example of chemical equilibrium but in my view I think it is a Universal concept that applies to many branches of science. When a system is far from equilibrium the reaction rate is more intense, as the system approaches equilibrium things slow down, the reaction rate slows down until it final show no action. Weather is driven by a system far from equilibrium. Very cold poles in relation to a warm equator. Cold air get dense and heavy while warmer air gets lighter and rises. These differences in air density vs temperature drive the weather patterns. Adding moisture to the mix increases the complexity but does not change the fundamentals of equilibrium science. Air moves from the north (at ground level) to the south as it is heavier (in Northern Hemisphere) and south to north in the upper atmophere and drives the weather cycles. If all points on Earth were at the same temperature there would be no weather since it would have reached equilibrium. Now to determine if the physics behind this thinking have any relationship to the real world. I went to the NOAA site to get the average temperature of the US. (The region of the US is the test field to demonstrate that the physics of equilibrium does play a strong role in weather). Page I obtained average US monthly temps. Jan: 32.5 F (all temps in Fahrenheit scale) Feb: 34.7 (20th Century Mean temps) March: 42.4 April: 52.0 May: 61.0 June: 69.3 July: 74.2 August: 72.8 Sept: 65.4 Oct: 54.8 Nov: 42.5 Dec: 33.4 Because the month's of July and August and have the most atmospheric energy, Jeff Masters hypothesis would indicate that these two months should have the most severe storms. Further information to reinforce this concept. In Albatross's excellent post on thunderstorms above in 269 "The important part. Crook (1996) showed that by manipulating equation (1)increasing the low moisture by 1 g/kg increases the CAPE by 2.5 the amount as a 1 C warming of the low-level air would. So changes in near surface specific humidity of 10% or so of typical background values can have a huge impact on the buoyancy available to a storm, and in turn the maximum updraft strength-- as found by the papers I cited in one of my posts above." And his conclusion based upon this data. "So the short of it is that increasing the low-level moisture is likely to increase the chances for more intense/severe thunderstorms, and perhaps larger hail too." Here are two more links with Albatross's information. Check chart with Gulf of Mexico water temp. This chart shows July and August have the warmest Gulf Coast water. Next data group. Humidity in 100 US cities. Humidity of 100 US cities by month. If you click on May and August then check out Kansas City it is 54% for both months. I am using Kansas city as one point in an overall thesis to demonstrate a point. Any city will do I have already listed the average temps of the US above. This spot check is for moisture related test. Kansas City monthly temps. Fairly similar to the National average. Local temp May is 12 F cooler than August. National average May is 11.8 F cooer than August. This is significant when considering Albatross's quote on severe thunderstorms. Kansas City Monthly precipitation. Kansas City has almost an inch more of rain in May and June as compared to July and August. July and August would have much more potential energy for more severe weather than May. The Relative Humidity of May and August are the same but the temp is over 12F warmer. That means the August air is holding much more moisture and latent energy that can drive storms. Yet the preciptiation is lower. Also the source of the fuel, the gulf stream, is warmer meaning more moisture can be evaporated for storms in August. Now back to the National stats. I have posted the National monthly average temperature above. Now here is a really good proxy for severe thunderstorms. Number of tornadoes. Look at May and June then at July and August (this is for the whole Nation so it is not the isolated Kansas City topic) Total count of tornadoes in the US. So May has many more tornadoes than August, yet August has far more energy than May. What causes this? My understanding of weather and most physical systems is that as they get closer to equilibrium, intensity is diminished. To demonstrate. The average May temp of Yellowknife, Canada (way up North) is 41F. Atlanta, Georgia (one of the warm southern spots that air moves across to fuel severe storms) is 69.75F. Difference in temp is 28.75F In July the diference between these points 19.5F and in August it is 20.9F. The difference between the hot and cold air is less and is closer to equilibrium. That is why I feel the weather will not get more intense. I think the number of severe storms in May and June bring up a lot of latent heat to higher elevation warming that air mass. This reduces the instability of the air. The air was cooled during winter and as the warm moist air from the Gulf moves into this unstable air (cold uppper level air that allows for strong upward acceleration of warm moist air). So the very nature of the most severe thunderstorms, bringing latent heat to upper levels of the troposphere, actually bring equilibrium and suppress what should be the most severe weather in July and August as this is the air with the most potential energy. Also the temperature difference between Northern and Southern air is more extreme in May than August. This will lead to stronger winds that are moving to achieve an equilibrium. As the air masses come closer in temperature the winds are not as intense and there are less supercell storm formation. That is why I have a very difficult time accepting the models that project more intense storms as the globe warms. That was my point with Dikran Marsupial and science. If a climate model cannot predict in the range it is designed for then it is a useless scientific tool. Even if I am not adept at chaos theory or it subtle behavior, my lack of knowledge of this subject would not make a bad model good. With the nature of CO2 forced warming, it is acting in a way that should very much suppress, not inflate severe weather patterns. The poles are warming faster than the equator. This means the air is reaching an equilibrium state faster than seasonal cycles will propel it.
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    [DB] "One half of the globe warms drastically every year and the climate changes drastically with this warming."

    You refer to the seasons here, which are part and parcel of the climate, and do not change it.  You set up a straw man and proceed with tedium to knock it down.  Think not that you can convince through dissembling volume what you cannot achieve through logic and merit of argument.

    Until you can mount a position of substance based on sound analysis and rooted in physical processes, which you have not yet demonstrated to date, others would be well advised to ignore your contrarian efforts to further derail this thread.

  34. Side note I almost forgot about. Half the globe experiences extreme global warming every year. 41.4 F in US from Winter to Summer. We can observe the behavior of extreme global warming every year. I have not yet seen a tipping point in any yearly cycle. Everything seems to change gradually. It is not winter one day then spring then summer. All the changes are gradual. There is not a light switch flip on climate change to every indicate the realtiy of a tipping point mechanism. There may be a few days that are way above normal or below in the gradual cycle but no tipping point at all.
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  35. Albatross @ 269 "Extrapolations of the historical relations between hailstorm damage and weather indicators under climate change scenarios project a considerable increase in future hailstorm damage." I am not sure how this gentleman came up with this conclusion. Based upon what actually is happening with hail... "Hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of 11,000 feet (3,400 m).[13] Movement of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the atmosphere over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.[14]" Hail. Based upon the places hail falls, it would seem a warmer climate would inhibit hail from reaching the ground.
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  36. "I have not yet seen a tipping point in any yearly cycle. Everything seems to change gradually." Why would you expect otherwise? CO2 changes gradually too. "Tipping point" ideas arent really mainstream science. Best one I can think of would be arctic melt where beyond a certain point, change in albedo might make for feedback loop that would require substantial drop in other forcing to reverse. Another might be catastrophic release of hydrates but these are highly debatable points. I see no expectation of tipping points in original article or in these discussions.
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  37. Norman @285, Sigh. Some of us have tried really, really hard to inform you on the science, but its seems a lost cause I'm afraid. Norman, I know hail pretty damn well. I can't say why that is, but I urge you to please take my word for it. Now with that in mind, you are glibly dismissing a peer-reviewed journal paper because of something that you read on Wikipedia. Wikipedia can be OK, but the following statement is not accurate and perpetuates at least two popular myths (can you spot them?): "Unlike ice pellets, hail stones are layered and can be irregular and clumped together. Hail is composed of transparent ice or alternating layers of transparent and translucent ice at least 1 millimetre (0.039 in) thick, which are deposited upon the hail stone as it cycles through the cloud, suspended aloft by air with strong upward motion until its weight overcomes the updraft and falls to the ground". As for the claim about freezing levels, that is true, but only to a point and in fact when one actually looks at the physics and thermodynamics the freezing level is not that critical severe hail because the high terminal velocities of the large hailstones results in them having a relatively short residence time below the melting level. Florida storms have produced severe hail with ridiculously high freezing levels and relatively weak ambient lapse rates. And last but not least Norman, had you bothered to look at the sounding I showed in my post @269 (you know the one for the almost 3 inch diameter hail), you will have noticed that the ambient freezing level was over 14400 ft! One reason for the paucity of hail in the tropical regions is that those environments have very weak lapse rates (especially over the oceans) and as a result they have what we call "skinny CAPE", which means that the CAPE is distributed over a great depth and that the mean difference between the updraft temperature and the ambient air is relatively small-- the end result is relatively weak updrafts despite high CAPE. Any hail that is then produced in the short-lived updraft is relatively small and much more likely to melt before reaching the ground. I can back this all up with references, but I am not willing to waste more time on this only to have contrarians repeatedly and glibly dismiss the science. Now I suppose someone in the know is going to have to try and fix that Wikipedia page....
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  38. With reference to the post 283 - Norman*. "The above is an example of chemical equilibrium but in my view I think it is a Universal concept that applies to many branches of science." For a start; not all chemical reactions are equilibrium; and for those who are fond of Wiki... Non-equilibrium thermodynamics is a branch of thermodynamics that deals with systems that are not in thermodynamic equilibrium. Most systems found in nature are not in thermodynamic equilibrium "My understanding of weather and most physical systems is that as they get closer to equilibrium, intensity is diminished." In physics two kinds of dynamics exist which may be though of as static equilibrium and dynamic equilibrium. An example of the former is a bicycle at rest; its stable point is when it falls on its side. An example of the latter is a bicycle in motion; it's stable point - upright - is still a minimum but requires work input. There's no natural fact of the matter that all systems are one or there other (any more than all systems are 'predictable' as in Newtonian dynamics). Often, but not always, non-equilibrium dynamics is closely linked to chaotic systems. Due to friction etc., most systems which exhibit chaotic dynamics will drop out of chaotic mode unless energy is input... but when energy is input; the systems can remain around fixed attractors ... they are in dynamic equilibrium. I'd suggest that the weather is, indeed, a dynamic system with many equilibria points amongst which bits of it switch. IMHO appeal to and faith in equilibrium dynamics is equivalent to the same error as the 'predictability' discussion. *Note: I'm not addressing this to Norman since it's clear that when people post things which contradict his fundamental understanding of how the world works, he just ignores it; as in the case of the predictability of systems. This is for general discussion and consideration of the general reader.
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  39. Albatross @269, first and most importantly, thanks. However, I still have some questions. It has always been my understanding that the US midwest has the most severe thunderstorms on Earth, something I could have been clearer about in my 258. However, I have also understood this to be a more or less unique feature of the US as a result of its unusual geography, specifically the very cold canadian arctic linked to the very warm caribbean. I notice that the Argentine plains are also noted for intense storms. However, I suspect that this is again due to peculiarities of geography, specifically the conjunction of cold dry winds aloft due to the Humboldt current and the Andes, and warm humid conditions below due, in part, to the Brazil Current. My question is, to what extent do these regions owe there intense thunderstorms to their peculiar geography, and to what extent to their mid-latitude location? Or perhaps better, are storms more frequent and intense in the tropics except under unusual geographical circumstances which promote thunderstorm and tornado formation? I continue to believe the lightning map gives a reasonable representation of thunderstorm frequency and intensity. As can be seen above, within the US lightning frequency (top) correlates well with tornado frequency (bottom). (Norman should also note that tornado frequency increases with greater warmth, and also with proximity to the Rockies.) Clearly it needs to be interpreted more cautiously than I did before, in that either different types of storms having different frequencies of strikes, and/or differences of seasonality can distort the result, especially given the clearly stronger CAPE in tropical regions:
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  40. Albatross, in this post on a related thread you mentioned Stanley Changnon. His paper on hail trends is here: First the caveats: he has the typical selection bias found in many studies: "high quality". That's unfortunately often different from "randomly selected" or "representative". Second, his study shows hail increasing in the Plains and SE U.S. where hail is more common. Third, the study period ends in 1995. Fourth it's all hail, not severe hail. That said, he claims that overall U.S. hail incidences peaked in mid-century.
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  41. Tom, #289, I would note that the Canadian Arctic is not as cold as it used to be last century. If that temperature is truly a factor in our severe weather, it could help explain why the incidence of strong tornadoes is dropping.
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  42. Norman @283, while accepting the point about equilibrium, I should point out that although the temperatures peak in August, the difference in temperatures between north and south is greatest in winter, and greater in Spring than in Summer. I just made the comparison between Austin, Texas, and Chicago, Illinois (below); but I suspect it is a general feature: (Austin Temp - black; Precipitation - olive; Chicago Temp - red; Precipitation - Green) Therefore we would expect the forces driving climate towards equilibrium would be stronger in winter and spring than in summer in the American mid-west. Despite this, thunderstorms and tornadoes are generally associated with warmer weather. The logical conclusion is that they will be more frequent in spring than in summer, ie, when it is warm enough for super cells to form, but before the strong north south temperature gradient dissipates.
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  43. Here's an interesting paper about hail trends in China: While the long term trend in CAPE is up, the freezing level heights are also rising and vertical sheer is dropping. Consequently the long term trend in annual hail days is down.
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  44. Tom, That is precisely why more severe weather occurs in the spring. The warm, moist gulf air collides with the cold, dry air from the Rockies. This sets up the potential for supercell formation. Severe weather typically occurs in March in the deep south, and gradually works north through June. The potential stills exists for extreme weather later in summer, but is greatest in spring. Global warming would increase the warm, moist air component, but decrease the cold, dry air. The net result is probably more rain, but less severe storms.
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  45. EricS @293, You have not accurately represented the findings of the Xie et al. paper that you found-- particularly with respect to the role of vertical wind shear (interestingly, the authors do not appear to understand the role of the shear, thinking that it is involved with the triggering of storms rather than the organization of the storms, not sure how the reviewers missed that), and the possible causes for the decline in the number of hail days. Whenever a 'skeptic' cites a paper, especially when they do not use quotes, always go to the original (H/T to Peter Hadfield). With regards to the decline of hail days in this region, the authors state that: "....the vertical shear seems not to have played a dominant role in the observed down trend in hail frequency in China since a similar weakening trend in the annual mean vertical shear is found for the stations with and without down AHD trends. The long-term change in CAPE seems to have little correlation with the down trend in hail frequency, however. We considered that although the CAPE increased in the past, the annual mean precipitation and extreme precipitation events in north and northeast of China decreased as a result of the weakening of the East-Asian summer monsoon [Wang and Zhou, 2005], leading to a decreasing trend in hail frequency in these regions. On the other hand, the rising in freezing-level and the increase in aerosols may offset or even dominate the positive effect of CAPE, resulting in little trend in hail frequency in south China. The results from this study may imply a possible reduction of hail occurrence under the global warming due to the increase in freezing-level height in China." Not quite as simple as your post claimed, and a few untested hypotheses as well. Also, as they authors noted, the huge increase in aerosols in the region over recent decades complicates matters even further. Finally, the paper speaks only to the occurrence of hail days, not severe hail days. I need to give it a proper read before commenting further though.
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  46. For crying out loud guys, this repeated focus on the traditional paradigm of "tornadoes are caused when cold air from Canada meets warm air from the south" has been addressed before. Has it ever occurred to you that the storms are following the heat (and jet stream) as the warming progresses northwards as the seasons change? On the Canadian prairies, for example, the severe storm season peaks in July when baroclinicity is at an ebb and cold Arctic air is in short supply.
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  47. Interesting that Xie et al. (2008) paper cited by a 'skeptic' at #293 was loudly trumpeted over the denialosphere and is in the discredited NIPCC report. Here are the findings from another study by Xie et al. (2010): "The climatology and long-term trend of hail size in four regions of China are documented for the period of 1980–2005 using the maximum hail diameter (MHD) data obtained from the Meteorological Administrations of Xinjiang Uygur Autonomous Region (XUAR), the Inner Mongolia Autonomous Region (IMAR), Guizhou Province, and Hebei Province. The reported MHD is mainly around 10 mm in the four regions. Guizhou (in southwestern China) has the largest proportion of severe hail (MHD greater than 15 mm) among the four regions. Severe hail in southwestern China mainly occurs between February and June, while in northern China it occurs in summer (from May to August) with the peak in June. During the period studied, the size of severe hail shows a slight downtrend in Guizhou and IMAR, whereas it shows an uptrend and a flat trend in Hebei and XUAR, respectively. However, none of the trends is statistically significant. Results from sensitivity experiments using a one-dimensional numerical model show that hail size is sensitive to the freezing level height, the maximum updraft, and column cloud liquid water—all working together to determine the geographic distribution and long-term trend of the observed hail size in China." I'd be interested to know what the 1D model is that they used.
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  48. Tom @289, I'll reply later if you don't mind.
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  49. Yes Albatross, As you notice the peak for severe storms in the northern U.S. is June. Hence, the peak in Canada occurs in July. This is precisely as pointed out previously when the maximum gradient between warm and cold air occurs. Thanks for comfirming our posts.
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  50. Re "This is precisely as pointed out previously when the maximum gradient between warm and cold air occurs." No, not always. You and others, once again, insist on making sweeping and gross generalizations when severe thunderstorms are very much about the details. And Re #299, This is such a site, pity you fail to recognize that. But as you volunteered on another thread, you are not particularly interested in the importance of physics. So I find your hyperbole and innuendo uncalled for, it only goes to show the weakness of your alleged 'arguments'.
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