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Is extreme weather caused by global warming?

What the science says...

Select a level... Basic Intermediate

There is growing empirical evidence that warming temperatures cause more intense hurricanes, heavier rainfalls and flooding, increased conditions for wildfires and dangerous heat waves.

Climate Myth...

Extreme weather isn't caused by global warming
"The 30 major droughts of the 20th century were likely natural in all respects; and, hence, they are "indicative of what could also happen in the future," as Narisma et al. state in their concluding paragraph. And happen they will. Consequently, the next time a serious drought takes hold of some part of the world and the likes of Al Gore blame it on the "carbon footprints" of you and your family, ask them why just the opposite of what their hypothesis suggests actually occurred over the course of the 20th century, i.e., why, when the earth warmed - and at a rate and to a degree that they claim was unprecedented overthousands of years - the rate-of-occurrence of severe regional droughts actually declined." (source: CO2 Science)

There are numerous examples of increased extreme weather frequency already being attributed to humans in the published peer-reviewed scientific literature.  For example, Pall et al. (2011):

"Here we present a multi-step, physically based ‘probabilistic event attribution’ framework showing that it is very likely that global anthropogenic greenhouse gas emissions substantially increased the risk of flood occurrence in England and Wales in autumn 2000"

Min et al. (2011):

"Here we show that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas."

Dai et al. (2011):

"All the four forms of the PDSI show widespread drying over Africa, East and South Asia, and other areas from 1950 to 2008, and most of this drying is due to recent warming. The global percentage of dry areas has increased by about 1.74% (of global land area) per decade from 1950 to 2008."

Zwiers et al. (2011):

"Therefore, it is concluded that the influence of anthropogenic forcing has had a detectable influence on extreme temperatures that have impacts on human society and natural systems at global and regional scales"

Coumou & Rahmstorf (2012):

"Here, we review the evidence and argue that for some types of extreme — notably heatwaves, but also precipitation extremes — there is now strong evidence linking specific events or an increase in their numbers to the human influence on climate. For other types of extreme, such as storms, the available evidence is less conclusive, but based on observed trends and basic physical concepts it is nevertheless plausible to expect an increase."

Hansen et al. (2012):

"we can state, with a high degree of confidence, that extreme anomalies such as those in Texas and Oklahoma in 2011 and Moscow in 2010 were a consequence of global warming because their likelihood in the absence of global warming was exceedingly small."

Source: NASA/Goddard Space Flight Center GISS and Scientific Visualization Studio

Like Hansen et al., Donat and Alexander (2012) found that global warming has made extreme heat waves more likely to occur.

"...there is a 40% increase in more recent decades in the number of extreme temperatures defined by the warmest 5% of the 1951–1980 distribution."

Like Coumou & Rahmstorf, Otto et al. (2012) found that global warming contributed to the intensity of the extreme 2010 Russian heat wave, concluding there was

"...a three-fold increase in the risk of the 2010 threshold being exceeded, supporting the assertion that the risk of the event occurring was mainly attributable to the external trend."

While it is very difficult to attribute individual weather events to global warming, we do know that climate change will 'load the dice' and result in more frequent extreme weather events.

The IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX), also discusses the relationship between human-caused climate change and various types of extreme weather events.  For example, the SREX says:

"It is likely that anthropogenic influences have led to warming of extreme daily minimum and maximum temperatures at the global scale. There is medium confidence that anthropogenic influences have contributed to intensification of extreme precipitation at the global scale. It is likely that there has been an anthropogenic influence on increasing extreme coastal high water due to an increase in mean sea level."

and

"Extreme weather and climate events, interacting with exposed and vulnerable human and natural systems, can lead to disasters."

On drought, the SREX finds:

"There is medium confidence that some regions of the world have experienced more intense and longer droughts, in particular in southern Europe and West Africa, but in some regions droughts have become less frequent, less intense, or shorter, for example, in central North America and northwestern Australia."

The SREX also has important conclusions regarding future drought changes:

"There is medium confidence that droughts will intensify in the 21st century in some seasons and areas, due to reduced precipitation and/or increased evapotranspiration. This applies to regions including southern Europe and the Mediterranean region, central Europe, central North America, Central America and Mexico, northeast Brazil, and southern Africa."

This conclusion is supported by Dai (2010), for example:

"Regions like the United States have avoided prolonged droughts during the last 50 years due to natural climate variations, but might see persistent droughts in the next 20–50 years"

Research by Emanuel (2012), Grinsted et al. (2013), and Holland and Bruyère (2013) concluded that global warming has already led to more intense hurricanes.  Elsner et al. (2008) found that:

"With the exception of the South Pacific Ocean, all tropical cyclone basins show increases in the lifetime-maximum wind speeds of the strongest storms ... Our results are qualitatively consistent with the hypothesis that as the seas warm, the ocean has more energy to convert to tropical cyclone wind." 

As Grinsted et al. noted,

"we have probably crossed the threshold where Katrina magnitude hurricane surges are more likely caused by global warming than not."

Extreme Weather Obfuscation and Misdirection

More frequently we are seeing climate contrarians dispute that human-caused climate change is impacting extreme weather events, often through misdirection by focusing on economic losses associated with extreme weather, rather than the frequency of the events themselves.

There is a silver lining in this cloud of obfuscation - climate contrarians appear to be retreating more and more away from the "it's not happening" and "it's not us" myths, toward the "it's not bad" fallback position.

Last updated on 13 November 2013 by dana1981. View Archives

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Comments 1 to 50 out of 79:

  1. "There is growing empirical evidence that warming temperatures cause more intense hurricanes, heavier rainfalls and flooding, increased conditions for wildfires and dangerous heat waves".

    Does the above statement mean that the studies which show that there is no apparent link between temperature rise and hurricanes, rainfall, flooding, fires and heatwaves, are somehow not scientific ?
  2. BUSH ADMINISTRATION LINKS EXTREME WEATHER TO GLOBAL WARMING
    Droughts, heavy rain, heat waves, wildfires and intense hurricanes are more likely to affect North America because of global warming's effect on extreme weather, the Bush Administration's Climate Change Science Program said Thursday.
    There's high confidence that the frequency and intensity of extreme weather events has already been influenced by global warming, and even greater confidence that more expensive, damaging and deadly weather is to come as temperatures continue to rise...
    Free Republic June 20, 2008

    Always remember the extreme weather/global warming mantra: "No particular weather event...can be blamed on something so general."
  3. By mid-century, annual average river runoff and water availibility are projected to increase by 10-40% at high latitudes and in some wet tropical areas, and decrease by 10-30% over some dry regions at mid-latitudes and in the dry tropics; some of which are presently water stressed areas...
    Drought affected areas will likely increase in extent. Heavy precipitation events, which are very likely to increase in frequency, will augment flood risk.
    IPCC AR4 WGII Summary for Policymakers.

    In a warmer future climate...Models project increased summer dryness and winter wetness in most parts of the northern middle and high latitudes. Summer dryness indicates a greater risk of drought. Along with the risk of drying, there is an increased chance of intense precipitation and flooding due to the greater water-holding capacity of a warmer atmosphere. This has already been observed and is projected to continue because in a warmer world, precipitation tends to be concentrated into more intense events, with longer periods of little precipitation in between. Therefore, intense and heavy downpours would be interspersed with longer relatively dry periods...
    IPCC AR4 WGI FAQ 10.1

    The warmer climate therefore increases the risks of both drought - where it is not raining - and floods - where it is - but at different times and or places. For instance, the summer of 2oo2 in Europe brought widespread floods but was followed a year later in 2003 by record-breaking heat waves and drought. The distribution and timing of floods and drought is most profoundly affected by the cycle of EL Nino events...
    ...overall trends in precipitation are indicated by the Palmer Drought Severity Index...which is a measure of soil moisture using precipitation and crude estimates of changes in evaporation.
    (The PDSI graph shown roughly increases below the "0" line until about 1977, after which its all above the line.)
    IPCC AR4 WGI FAQ 3.2

    Drought is easier to measure (than heavy precipitation events) because of its long duration...The Palmer Drought Severity Index calculated from the middle of the 20th century shows a large drying trend over many Northern Hemisphere land areas since the mid-1950's, with widespread drying over much of southern Eurasia, northern Africa, Canada and Alaska...and an opposite trend in eastern North and South America...Decreases in precipitation over land since the 1950s are the likely main cause for the drying trends, although large surface warming during the last two to three decades has also likely contributed to the drying...
    IPCC AR4 WGI FAQ 3.3
  4. #2: Something the Bush admin said in 2008 seems to be correct?
    "As options dwindle for negotiating a global pact to fight climate change, the United Nations is pointing to today's "extreme conditions."

    "As global temperature records have been set for the early summer months, states and cities are also setting hundreds of temperature records. ... Unfortunately, climate models indicate that an average summer in 2050 will have even more days topping 90°F if global warming continues unabated."
  5. Here is a statement of what should be the new paradigm:

    Weather in a given region occurs in such a complex and unstable environment, driven by such a multitude of factors, that no single weather event can be pinned solely on climate change. In that sense, it's correct to say that the Moscow heat wave was not caused by climate change.

    However, if one frames the question slightly differently: "Would an event like the Moscow heat wave have occurred if carbon dioxide levels had remained at pre-industrial levels," the answer, Hansen asserts, is clear: "Almost certainly not."

    The frequency of extreme warm anomalies increases disproportionately as global temperature rises. "Were global temperature not increasing, the chance of an extreme heat wave such as the one Moscow experienced, though not impossible, would be small," Hansen says.


    The map on that page makes it clear exactly what is meant by extreme variability:
  6. This rebuttal lack links to actual studies which is unusual and I think should be fixed.
  7. Scaddenp, bearing in mind that I'm assuredly -not- being smart-aleck, in some ways this site is "open source" in the sense that people drag in all sorts of literature and deposit it for everybody's enjoyment. "Enjoyment" often takes the form of attacking offerings and dragging them back and forth like meat thrown to a pack of feral dogs, but that's just one possible outcome. If you should have a few minutes to spend beavering away at Google Scholar, looking for likely candidates, you can bet that what you find will be most appreciated.
  8. And now for something completely different:

    Coldest winter in 1000 years is on the way
    The change is reportedly connected with the speed of the Gulf Stream, which has shrunk in half in just the last couple of years.

    Experts dispute record weather forecast
    Although La Nina has a global influence on weather, its direct influence is limited only to the tropical Pacific region, and its influence on the weather in the mid-high latitude regions is indirect and complicated, according to the report.
  9. That first report doesn't make sense, muoncounter.

    Firstly, we have no direct evidence of temperatures going back that far, so how can it be judged the coldest in 1000 years ?
    Secondly, isn't the Little Ice Age meant to be the coldest period over the last 1000 years (according to proxies), i.e. 3-400 years ago ?
    Thirdly, wasn't there a Medieval Warm Period at various times and places, about 1000 years ago - again, according to proxies ?

    Overall, I bet the so-called skeptics are drooling at the possibility of this coming to pass, despite the fact that they will have to rely on the veracities of the instrumental temperature records and the proxy records, and ignore the LIA and MWP - just so they can scream : 'Ice-age is coming !'

    Perhaps this will be another good example of their incoherence.
  10. #9: "first report doesn't make sense"

    I don't expect headlines in newspapers to make sense. As you say, the headlines and blogposts that 'The Ice Age Cometh' will indeed be all over the place.

    Whatever happened to the old idea that Arctic melting flooded the North Atlantic with cold, fresh water, thereby shutting off the northwards-flowing Gulf Stream? Has that mechanism fallen out of favor these days?
  11. Welcome to the future...

    Strongest storm ever recorded in the Midwest smashes all-time pressure records

    Since winter storms form in response to the atmosphere's need to transport heat from the Equator to the poles, this reduced [due to global warming] temperature difference reduces the need for winter storms, and thus the models predict fewer storms will form. However, since a warmer world increases the amount of evaporation from the surface and puts more moisture in the air, these future storms drop more precipitation. During the process of creating that precipitation, the water vapor in the storm must condense into liquid or frozen water, liberating "latent heat"--the extra heat that was originally added to the water vapor to evaporate it in the first place. This latent heat intensifies the winter storm, lowering the central pressure and making the winds increase.
  12. Here's somewhere it might be worth keeping an eye on (NCAR) Attribution of Climate Events
    It appears to involve Peter Stott, Myles Allen, Martin Hoerling and Kevin Trenberth, so I'm guessing they know what they are talking about.

    So far they largely seem to be highlighting the need for more cohesive research "A clear conclusion of the meeting was that there are important research needs in
    developing an attribution service sufficiently reliable and timely to be applied routinely."
  13. #9: "Overall, I bet the so-called skeptics are drooling at the possibility of this coming to pass,"

    JMurphy, you called it. Little did we know just how much drooling is going on. Here is RC reporting this story was a fraud:

    Coldest Winter in 1000 Years Cometh – not

    This claim circulates in the internet and in many mainstream media as well: Scientists have allegedly predicted the coldest winter in 1,000 years for Europe. What is behind it? Nothing – no scientist has predicted anything like it. A Polish tabloid made up the story. ...

    The “climate sceptics” website WUWT, noted for their false reports, takes up the RT piece, presents it together with The Voice of Russia and mentions „Mikhail Kovalevski“. Watts seems to be the bridge for the story´s crossing into the western media.


    And the stampede was led by the drooler-in-chief. Makes you wonder about just how the so-called 'Climategate' propagated so quickly, too.
  14. From 2010 - Global temperature and Europe's Frigid Air:



    We live in a world of contrasts gone wild.

    In producing this map the radius of influence of a given station is limited to 250 km to allow extreme temperature anomalies to be apparent. Northern Europe had negative anomalies of more than 4°C, while the Hudson Bay region of Canada had monthly mean anomalies greater than +10°C.
  15. More news of the weird in Texas; 80+F yesterday and today (and its winter).
    Perry Issues Disaster Proclamation Over Wildfires

    The proclamation covers 244 of the state's 254 counties.

    Perry says lack of precipitation has dried grass and other vegetation across the state. He says the "significant fire danger" is expected to continue.


    And the reason 244/254 counties are in drought conditions is ... fill in the blank or see comment #5.
  16. From the disaster of US House of Representatives Climate Science/EPA hearings, some good arose:

    Francis Zwiers testimony

    Observational studies show that warm temperature extremes have become hotter since the mid 20th century, cold temperature extremes have moderated, and precipitation extremes have intensified ...
    ... human influence is now affecting the frequency and intensity of high impact events that put people and their livelihoods at risk. Moreover, studies of two specific events (the European 2003 heat wave, and flooding in the UK in the autumn of 2000) have shown that the odds of those events had been increased substantially relative to the world that would have been in the absence of human induced increases in atmospheric greenhouse gases.


    Zwiers was invited by the minority members of the committee, who issued their own memo summarizing the "background on the state of understanding of climate change science because the majority hearing memo failed to do so."
  17. Continued from here:

    But while the world has got hotter in the past 100 years, Nielsen-Gammon said, Texas rainfall has actually gone up by about 10 per cent. Much of it has come from more-frequent extreme rainfall events rather than a general increase in normal rain.

    This is the pattern that seems to be emerging: More frequent higher intensity events, rather than a monotonous increase. In the case of current droughts, long weeks and months of dry weather punctuated by heavy rain. Those 'gully washers' make the statistics even out, but mostly result in runoff rather than soaking rain.
  18. Again it would be prudent to compare what changes may be appearing now with those that confronted the Ancient Pueblo People that led to their displacement.
    This an excerpt from an article examining the Anasazi Collapse
    "Studying tree rings from 27 sites across the Southwest, Dr. Jeffrey Dean of the University of the Arizona tree-ring laboratory has found evidence of a major disruption in the area's typical rainfall. Suddenly, the customary pattern of heavy snows in the winter followed by summer monsoons had become unpredictable. Even if there was not a great drought, moisture may have been coming at the wrong times. The summer rains, so necessary to keep the spring crops from dying, were no longer reliable."
  19. johnd#18: "compare what changes may be appearing now with those that confronted the Ancient Pueblo People"

    An apples and oranges comparison. We have no idea how sensitive their civilization was to climate change; however, we may surmise that without air conditioning and turbo-diesel backup generators, they were more sensitive than we are. However, anthropology is hardly the topic of this thread; the pace and intensity of current climate change's impact on weather is.
  20. muoncounter at 11:28 AM, it will obviously seem an apples and oranges comparison if cause and effect are confused as you have done so.

    However the evidence found by Dr. Jeffrey Dean of a historical major disruption in the area's typical rainfall that I referenced, is a valid apple on apple comparison to your comments regarding present day emerging patterns, and thus also relevant to this thread.
  21. johnd#20: "cause and effect are confused ... evidence found by Dr. Jeffrey Dean of a historical major disruption in the area's typical rainfall "

    Confused? Hardly. No dispute that there was a disruption in typical rainfall. But from your link,

    Recent climatological studies by other scientists suggest that rainfall patterns were disrupted in a way that might have made the Anasazi disillusioned with their old religion. ... Suddenly, the customary pattern of heavy snows in the winter followed by summer monsoons had become unpredictable. Even if there was not a great drought, moisture may have been coming at the wrong times. The summer rains, so necessary to keep the spring crops from dying, were no longer reliable. The rain dances were not working anymore.

    Apples: the rain dances weren't working as they had. Oranges: heat waves, drought and wildfire; monsoons; cold winter with deep snow, meltwater floods. Tornadoes. Thundersnow.

    But maybe it was just like that back in Anasazi days. And so the rain dance of today, 'don't worry, nothing unusual is going on,' isn't working either.
  22. Johnd,
    The climate changes caused the Anasazi civilization to collapse. Is that what you want to happen to our civilization? Jahred Diamond used this as one of the examples in his book Collapse about how previous civilizations found changes in their environment too much to survive. Current changes are greater than the Anasazi had to deal with.
  23. This report provides further information to a discussion going on over on the A Convention for Persons Displaced by Climate Change thread :


    Interior Releases Report Highlighting Impacts of Climate Change to Western Water Resources.

    Specific projections include:

    •a temperature increase of 5-7 degrees Fahrenheit;
    •a precipitation increase over the northwestern and north-central portions of the western United States and a decrease over the southwestern and south-central areas;
    •a decrease for almost all of the April 1st snowpack, a standard benchmark measurement used to project river basin runoff; and
    •an 8 to 20 percent decrease in average annual stream flow in several river basins, including the Colorado, the Rio Grande, and the San Joaquin.



    Report available here :

    Reclamation : Managing water in the West
  24. michael sweet at 16:53 PM, by what measure have you ascertained that current changes are greater than those that occurred during the period being discussed?
    From 700 to about 1100 AD the region experienced population increases ascribed to to reliable and above average precipitation.
    This then changed over a very short period into what is described as the 300 year Great Drought.
    Given the other civilisations that apparently collapsed at about the same time, both in North and South America, also apparently due primarily to changes in precipitation patterns, perhaps the changes were more widespread.

    Whilst it seems a common feature of many of those earlier societies to believe their Gods were responsible for bringing the rains, hence the rituals and sacrifices, modern day understanding is of how it is the pattern of SST's that primarily determine precipitation patterns, with land use changes and deforestation further influencing regional climates.

    It is then not surprising that a number of different early civilisations subject to the changing conditions of the same ocean basins would have experienced similar climatic changes related to shifts in SST's and hence precipitation patterns.
    Interestingly, one of the more long lasting civilisations, the Mayans, developed and built complex systems of water management which perhaps are indicators of both their ongoing need to manage a vital but variable resource, and that success in doing so is necessary to ensure a society not only prospers, but survives.
  25. Responding to Eric the Red:

    In 1954 there were 550 tornadoes, and 36 tornado related fatalities. This compares with 1039 tornadoes to June 8th, 2011, with 525 fatalities. 1974 is a much better comparison year, but there have already been 94 more US tornadoes as of June 8th than in 1974, and 159 more fatalities. With just 75 EF3 plus tornadoes to June 8th, 2011 is unlikely, as you point out, to exceed the 121 (122?) F3 tornadoes in 1974, but the switch from the Fujita scale to the extended Fujita scale makes such comparisons tricky. None of that adresses the extraordinary quantity of tornadoes in April, with 675 confirmed tornadoes, significantly more than double the amount in April of 1974:



    It is also significantly more than the previous monthly record of 542 confirmed tornadoes in May, 2003:



    You will, of course, notice that there is a rising trend in April tornadoes, and a stronger trend in May. So, you guessed it, there is a strong rising trend in annual tornadoes as well:

  26. Tom, I would expect more tornadoes after adjusting for observation improvements. Those improvements cause most of the increase of your lower chart. The long term increase will be due to more convection and more CAPE (shown to be in a upward trend). I would not expect more strong tornadoes because of other needed ingredients: a strong jet stream for adequate storm motion and mid-level dry air for the strong downdraft (the updrafts are readily available of course). See http://www.mhartman-wx.com/fcst_tools/meso_tutorial.html for a simple explanation. The tornado season peaks well before the summer peak in heat because those other ingredients diminish in summer.

    The other ingredients with increase with global warming. Thus we would expect strong tornadoes earlier in the season when the jet stream is still in a more southerly position, primarily in the areas where dry air is available east of the Rockies. We would also expect strong tornadoes in northern locations where the jet stream stays stronger later in the season and dry air is still available from Canada. Weak tornadoes should increase under global warming especially earlier in the season.
  27. 25 Tom Curtis

    In your last tornado graph, I have read that the increase in total number is a result of the advanced tools meteorologists have for locating tornado activity and several storm chasers to find them and confirm touchdowns.
    Response:

    [DB] "I have read"

    Norman, please be advised that when making a statement such as this intended to refute someone else's comment (which itself was based on sourced, linked data) you must be prepared to then back up your statement with a verifiable link to a reliable source.

  28. Thank you DB

    Here is one experts opinion on the matter of tornadoes and the apparent increase.

    More tornadoes or better detection?.

    Smaller tornadoes on increase, larger tornadoes may be decreasing in frequency.
  29. According to the NOAA data posted at #52, strong (EF3+) tornadoes have generally decreased over the past few decades. Whether smaller tornadoes have incrased of simply been detected better is still up for debate. Doppler radar has identified many tornadoes which would probably not have been spotted in years past.
  30. #25 Tom Curtis

    Here is an explanation of the increase in tornadoes in April. Check out what is needed to form a supercell thunderstorm. A strong jet stream is required.

    Here is the April anomaly for the Globe. You can see warmer than normal air in the Gulf of Mexico while the air in Canada was well below normal.

    Conditions are right for supercell thunderstorms.

    As Eric the Red pointed out in post #26, tornado season diminishes as the Canadian air warms rapidly in the summer months. There is not the strong differential and the jet stream weakens.
  31. "A strong jet stream is required."

    Upper or low-level jet or both? And not necessarily. You are clearly talking through your hat Norman.

    You might want to wander over to Desmogblog where I have been in a technical discussion with someone who claims to be in the know about these things.

    Regardless, the experts agree that trend now and in the future in tornadoes are hard to pin down, mostly on account of the poor nature of the data and changing building codes, and monitoring platforms etc.

    What we do have confidence in is that extreme precipitation events and severe thunderstorm events are likely to increase in certain areas as low-level moisture increases (see Desmogblog post for papers). In fact, extreme rainfall events are already on the increase.
  32. Albatross,

    I did wander over to Desmogblog and read your exchange with NicholasV.

    NicholasV does hold a similar position to mine concerning the Bill McKibben video.

    I did get that jet stream info from a Accuweather piece but rather than talk through my "hat" I am interested in updating my knowledge. I did take one course in college on meteorology but that was long ago.

    Here is a resource that I found that may help update my knowledge base.

    Online weather learning site.

    Reading your posts, you do seem a very intelligent person. Thanks for taking the time to share your views and resources.
  33. Albatross,

    Here is the Accuweather article about the jet stream. The claim is they predicted the severe weather in February.

    Accuweather article.

    Quote from article: "AccuWeather.com meteorologists knew by February of this year that the upcoming spring was going to be a wild one in terms of severe weather and flooding, and it was not because climate change was ongoing.

    The combination of a weakening La Nina and the anticipated sharp temperature anomaly gradient between the northern U.S. and the southern U.S. told us that the jet stream running across the U.S. would be abnormally strong this spring. A strong jet stream leads to more powerful storms and thunderstorms, which increases the chances of large tornadoes and widespread flooding."
  34. Text from the intermediate level seems broken.
  35. "I suppose what I am getting at at what stage can we start safely matching extreme weather events to AGW?"

    Doing this scientifically requires matching observations of weather to predictions from the climate models. As I understand it, only really disruptions to the hydrological cycle (drought and extreme precipitation events) are settled science within the predictions. Hurricanes are not. AR4 discussed extreme precipitation events but there was not really a long enough record to be making strong statements. Droughts will wax and wane in cycles but the pattern of drought is consistent with predictions. I dont believe you can link any single weather event to AGW - only trends in frequency and/or intensity.
  36. "I suppose what I am getting at at what stage can we start safely matching extreme weather events to AGW?"

    One thing you can do is look at the average increase in humidity due to raised temperatures. When we say that there's 4% more moisture aloft than before, you can get hold of the weather service's measurements of precipitation leading to floods and other damage. Then do some calculations with and without that 4%.

    What height would the floodwater have reached if there had been x% less water flowing into the system? The big issue here of course is that 4% is the global average increase. Choosing - let alone justifying - a more suitable number for a specific time and place is much harder.

    But this sort of calculation can be illustrative if not definitive. Without a 4% increase in humidity, floodwaters may only have reached 2 streets from the riverbank rather than the ... distance they did.

    Not terribly scientific, but may provoke thought. And much more useful for real life. AGW may not cause certain events directly, but it can worsen the impact of those that do occur.
  37. Adelady,

    I wholeheartedly agree. AGW does not directly cause these events, but can affect the impact due to warmer temperatures and higher humidity.
  38. A response to this page being cited; not a happy camper:
    I looked through your link, an UNSCIENTIFIC source. First there was NOTHING in there that showed any changes is because of our CO2, all it shows is there is changes in the climate system. DUH!!! OF COURSE. As they ADMIT they CANNOT attribute any of those events to AGW. Only that AGW might cause amplification of extreme weather events. Except, anyone who takes meteorology knows, the violence of a storm is based on the temperature differences in weather fronts. The warmer the cold air mass is, the LESS violent the storm. The evidence is clear, there is NO evidence of weather extremes changing.
    Response: Clarification: The italicized text is a quote from someone other than itscoldoutside.

    Why do they think AGW causes only cold air, not warm air, to get warmer?

    [Sph] blockquote added to clarify intent.

  39. itscoldoutside,

    "The evidence is clear, there is NO evidence of weather extremes changing."

    Really? Here is an interesting article that disagrees with your statement.

    Here we show that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas.

    And another article, this time focussed on England and Wales.

    The precise magnitude of the anthropogenic contribution remains uncertain, but in nine out of ten cases ourmodel results indicate that twentieth century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%.
  40. @Hyperactive A response [quoted verbatim, hence the italics and caps, I encountered] to this page being cited; [as you can see they are] not a happy camper. The same author is citing CO2science as a "scientific" resource ....
  41. Ah, sorry I got a bit confused by your post.
  42. @Hyperactive, NP. BTW, They were asked to post their response here. They declined; instead posting that rant (which even I can even see is wrong at so many levels); thought you might all appreciate the reaction this site is getting :-)

    And, having a table of standard arguments makes things much easier; appreciated.
  43. itscoldoutside:

    Assuming you have cut & pasted this fine commentary from a response to one of your own comments, I was amused to see your interlocutor's comment "Except, anyone who takes meteorology knows, the violence of a storm is based on the temperature differences in weather fronts."

    I'm sure he or she was a professional or dedicated hobbyist. :)
  44. itscoldoutside:

    How about providing us with a link to the comment thread you are referencing.
  45. That @Hyperactive cites a UToronto paper is apt. http://www.thestar.com/opinion/editorialopinion/article/1070377--rolling-with-the-climate-change-punches#comments
    (Unfortunately, it isn't possible to cite posts within the thread, and the interface is terrible - why I didn't bother. The exchange is fairly predictable).
  46. More unusual weather news, courtesy Jeff Masters:

    Rare February tropical disturbance drenching the Florida Keys

    Our calendars may say it's February, but Mother Nature's calendar says it's more like May in the waters of South Florida ...
    ... today's rare tropical disturbance over South Florida is symptomatic of how whacked-out our 2012 atmosphere has been. In isolation, the strange winter weather of 2011 - 2012 could be a natural rare occurrence, but there have been way too many strange atmospheric events in the past two years for them all to be simply an unusually long run of natural extremes. Something is definitely up with the weather, and it is clear to me that over the past two years, the climate has shifted to a new state capable of delivering rare and unprecedented weather events.


    But I'm sure some will say 'its happened before.' Right.
  47. The state and variety of a given ecological system plays a huge role in desertification.

    In most arid environments there are essentially 2 seasons- wet and dry. Wet seasons in an arid environment often exhibit torrential downfalls. Dry seasons are usually characterized by extreme drought. It makes sense that increasing global temperatures would increase the landmass of "arid" regions and increase the sporadic nature of rainfall (and overall precipitation levels).

    Certain biological systems have evolved to cope with extreme variations in rainfall(notably huge herds of ruminants and deep-rooted perennial grasses characterize arid environments). Bacteria within arid environments (which are usually grasslands) primarily survive the dry season's "bacterial holocaust" by living in the rumen of a grazer. Similarly, deep rooted perennial grasses improve hydrological cycles by reducing erosion, increasing water permeation into the soil and acting as a storehouse of water during the dry bacterial winter. Large herds roaming the land effectively manage the grass; they "trim the lawn" so to speak, and also apply bacteria ridden fertilizer to the land, and their hooves "till" up the hard packed soil surface (which is common in arid regions) "planting" the seeds of native perennials and increasing the soil's permeability.

    Increasing the number of perennial grasses/square foot also help the solar cycle through increased photosynthesis which helps bacteria cycling(more sugar available to the immediate environment).

    My point is that land management is the primary factor driving current trends in desertification- not atmospheric Co2 levels. A slightly warmer world with increased precipitation and more arid land, could actually have amazing benefits, if land managers took steps to encourage the biological systems that evolved to cope with such harsh climates, and thrive within them.

    From an ecological perspective, desertification is almost strictly a land management problem. Proper planning would heavily negate the potential problems associated with higher levels of more sporadic, "extreme" rainfall.
  48. @AHuntington1 #47:

    How about some references of peer-reviewed published science that support your currently unsubstantiated assertion that "desertification is almost strictly a land management problem."

    Also what exactly do you mean when you say "from an ecological perspective"?

    Finally, do you believe that the southward expansion of the Sahara desert is a "land management problem"?
  49. Oh, when I say "arid environments" i am referring to environments with extremely sporadic, sometimes torrential rainfall contrasted with extreme drought. Not completely lacking in water but with extreme temporal variations in water level. This as opposed to a rainforest, which has (relatively) consistent temporal moisture content.
  50. AHuntington, are you aware of the relationship between the Hadley cells and desertification in the horse latitudes?

    Try Johanson & Fu (2009) for starters. From the abstract:
    Observations show that the Hadley cell has widened by about 2°–5° since 1979. This widening and the concomitant poleward displacement of the subtropical dry zones may be accompanied by large-scale drying near 30°N and 30°S. Such drying poses a risk to inhabitants of these regions who are accustomed to established rainfall patterns.

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