Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Donate

Twitter Facebook YouTube Pinterest

RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

Keep me logged in
New? Register here
Forgot your password?

Latest Posts


The Dai After Tomorrow

Posted on 18 February 2011 by Daniel Bailey

(or: Water, Water Everywhere and Nary a Drop to Drink)

The goal of Skeptical Science is to explain what peer reviewed science has to say about global warming. Our ability to put aside our preconceptions and beliefs and to evaluate things objectively - through the cold lens of rationality and reason - says a lot about ourselves.

Much ado has been made recently in the media and the blogosphere of recent extreme weather events around the world: the flooding in Tennessee and Pakistan, the Moscow heat waves, record drought in the Amazon, and yet more flooding in Queensland and Brazil.

So let's leave the hype and agendas behind and focus instead on one of the basic juxtapositions of the warming world we live in: the co-existence of droughts and floods.

YesterDai Once More: the 2007 IPCC Fourth Assessment Report (AR4)

As of the time the IPCC came out with the AR4, predicted extremes in precipitation and droughts were being observed:

"In a warmer future climate, most Atmosphere-Ocean General Circulation 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. Another aspect of these projected changes is that wet extremes are projected to become more severe in many areas where mean precipitation is expected to increase, and dry extremes are projected to become more severe in areas where mean precipitation is projected to decrease."

Other studies demonstrated that the percentage of Earth’s land area stricken by serious drought more than doubled from the 1970s to the early 2000s.

Today's Dai

This pattern continues today. 2010 witnessed flooding in Nashville, Pakistan, Queensland and Brazil. The Amazon experienced its 2nd once-in-a-century drought, a bare 5 years after the previous once-in-a-century drought.

It has been more than 3 years since the last assessment (IPCC AR4) and the next (IPCC AR5) is still years away. To help bridge this gap in our knowledge comes a new review study, Drought Under Global Warming, A Review, led by Aiguo Dai and his team. Together they take on the formidable task of assessing the field to date.

A common measure called the Palmer Drought Severity Index (PDSI) classifies the strength of a drought by tracking precipitation and evaporation over time and comparing them to the usual variability one would expect at a given location in the low (equatorial) and middle latitudes. The more negative the number, the more drier the conditions.

Using an ensemble of 22 computer climate models and a comprehensive index of drought conditions, as well as analyses of previously published studies, the paper finds most of the Western Hemisphere (along with large parts of Eurasia, Africa, and Australia) may be at threat of extreme drought this century. Note that in the paper they re-normalize the index to the local conditions; there would be no way to explain why the Sahara desert appears to be less arid than the USA. With the renormalization, the PDSI can thus be considered an anomaly.

Another finding of the paper is that precipitation was the dominant driver for changes in the terrestrial water budget before the early 1980's. Changes since then are not only attributed to anthropogenic greenhouse gas induced (human-induced GHG) surface warming, but that those same human-induced GHG increases have contributed to the observed drying trend since the 1980's.

It was also found that despite increased precipitation, due to increased surface temperatures and increased surface runoff, higher atmospheric demand for moisture results in drier soils.

Figure 1: Current Palmer Drought Severity Index [PDSI] 2000-2009. A reading of -4 or below is considered extreme drought. Regions that are blue or green will likely be at lower risk of drought, while those in the red and purple spectrum could face more unusually extreme drought conditions. (Courtesy University Corporation for Atmospheric Research [UCAR])

The Dai After Tomorrow

Tomorrow waits for no one. What can we expect, based on this work?

By the 2030s, the results indicated that some regions in the United States and overseas could experience particularly severe conditions, with average decadal PDSI readings potentially dropping to -4 to -6 (extreme drought) in much of the central and western United States as well as several regions overseas, and -8 or lower in parts of the Mediterranean. By the end of the century, many populated areas, including parts of the United States, could face readings in the range of -8 to -10, and much of the Mediterranean could fall to -15 to -20. Such readings would be almost unprecedented.

Figure2: PDSI 2030-2039. (Courtesy UCAR)

Extreme conditions experienced earlier are expected to continue, and even worsen. In fact, droughts may become so widespread and so severe that current drought indices may no longer be adequate to quantify them.

Figure 3: PDSI 2060-2069. (Courtesy UCAR)

If the drying is anything resembling that shown in these figures, a very large population will be severely affected in the coming decades over the whole United States, Southern Europe, Southeast Asia, Brazil, Chile, Australia and most of Africa.

Figure 4: PDSI 2090-2099. (Courtesy UCAR)

The End of Dai's

The paper closes on a somber note:The above figures are themselves based on IPCC AR4 SRES A1B (medium GHG) emission scenarios. Current Business-As-Usual (BAU) emissions are running higher than that (tracking the A1F1, or high emissions, scenario). Thus, potential exists for conditions to be worse than depicted above. And that is not a comforting thought.

Dai's of Old

Aiguo Dai is a researcher with the National Center for Atmospheric Research (NCAR). His past work includes (but is not limited to):

Further reading:

0 0

Bookmark and Share Printable Version  |  Link to this page | Repost this Article Repost This


Comments 1 to 43:

  1. I covered the Dai study as well as another on the decline in the evapotranspiration rate over land here for IPS along with some comments from Kevin Trenberth and implications. (for those looking for an easy intro to the topic).
    0 0
  2. Interesting and frightening for Australia. One puzzling aspect, given recent events, is why the lack of wet conditions in the far north of Australia in the future? I thought earlier predictions had suggested this, and intuitively you would expect, with warmer seas, more rainfall events of the kind Darwin has just seen

    But elsewhere in Australia - not only not much room for agriculture, but not much room for people at all!
    0 0
  3. This is a bit heartless, but I'm wondering if anyone has factored in the reduction of emissions as the population declines in line with lack of water and reduced crops?
    0 0
  4. Looks like it'll be much worse in other parts of the world than in Australia...

    One other thing to remember, is that while there may be increased rainfall, it may fall in shorter, more intense downfalls, with long, dry periods in between. The drought conditions lead to dry soils & little vegetation, so much of the rainfall will just run off, potentially causing flooding and enormous soil erosion problems. Those would compound soil erosion by 'dust bowl' type events, where dry soils are picked up by the wind and just blown away.

    It'll take very careful land management to keep soils productive in those sorts of conditions. It will almost certainly mean significantly reduced crop yields, which, when you combine it with projected world population of around 10 billion, is a recipe for disaster.
    0 0
  5. @Torleif - if it gets to that, it'll be too late - the amount of CO2 already emitted will 'lock in' the warming for centuries to come.
    0 0
  6. Torleif, the thrashing for survival will use more fossil fuel, not less. These are the best of times to fight climate change. We will never be richer or less panicked about food and water then right... right... NOW.
    0 0
  7. Bern. I'm scaring myself here but, we're closer than you think. Russia is banning wheat exports due to low harvest caused by record drought. As 4th largest worldwide grower of wheat this has pushed global prices up. Australia's (9th globally and globally largest exporter) wheat harvest is adversely affected by recent flooding after years of drought. Ukrain (8th globally) is affected by the same drought as Russia.

    This is just wheat. Considering that globally, intense and destructive weather events are likely to become more frequent and more intense we face a likely scenario where staple grain production cannot meet demand sometime in the near future.

    Population reduction will probably happen in the least affluent countries first and therefore have a minimal ipmact on emissions. I was just interested to see if anyone had factored it in.

    Having said all of that, you're probably right.
    0 0
  8. "the paper finds most of the Western Hemisphere (along with large parts of Eurasia, Africa, and Australia) may be at threat of extreme drought this century"

    What kind of language is that? I have read the paper and still can't figure out what's that supposed to mean. I can see (e.g. Fig. 1. & 2.) during the last thousand years not only threat of extreme drought was present over the Western Hemisphere (along with large parts of Eurasia, Africa, and Australia), but such events actually occurred multiple times over various regions. (-Off-topic snipped-).

    (-Inflammatory snipped-). Not even a much stronger version like "There will be extreme drought events in most of the Western Hemisphere (along with large parts of Eurasia, Africa, and Australia) this century" can be refuted.

    (-Off-topic snipped-)

    Extreme drought events in the historical record seem to cluster around cold spells while warm periods are generally wetter.
    (-Off-topic snipped-).
    (-Off-topic snipped-).

    (-Very off-topic soliloquy snipped-)
    0 0

    [DB] Off-topic unsupported assertions snipped.

  9. Ah yes Berenyi, the "seen it all before" approach.
    0 0
  10. I am quite familiar with this subject, yet I have no idea what BP is driving at. I see a lot of text but very little substance or coherence.
    0 0
  11. Albatross: I think BP is saying that because there have always been terrible droughts, we don't have to worry about global warming causing droughts.

    Of course, that argument ignores the fact that global warming is predicted to increase the *frequency* of such droughts, or the probability that terrible droughts will occur, which, IMHO, is quite an adverse impact.
    0 0
  12. Berényi Péter #8
    "The statement above is actually a coward one."
    You're talking a-scientific here and a bit insulting. I'm sure you know very well that hardly any absolute certainty can be found in cutting edge science. Your accusation of cowardice is really a shame and inappropiate here.
    0 0
  13. Berényi Péter #8
    It sounds as though you are arguing against the language rather than the content. We are all guilty of occasional sloppy language like "may be at threat".
    What I think the author means is "our models show that there is an increased risk". This would make it clear that the null hypothesis is the current (or past) level of risk (the current frequency of extreme precipitation events and the current frequency of extreme drought events). The authors argument is that these events are becoming more frequent and therefore there is a deviation from the null hypothesis.

    Additional commentary:
    The combination of drought and extreme precipitation events is a poor prospect for agriculture. In many areas where the water supply is already under stress, aquifers are depleted. Extreme precipitation events tend not to replenish aquifers as the water is lost in sudden run-off, rather than soaking into the lower strata.
    0 0
  14. #11 Bern at 15:39 PM on 18 February, 2011
    I think BP is saying that because there have always been terrible droughts, we don't have to worry about global warming causing droughts.

    I am saying we have to worry about droughts regardless any climate projections because we know for sure from paleoclimate records that a major volcanic eruption in the Tropics can cause multi-year cooling & drought conditions, hence widespread crop failures. This kind of event can happen any time and we have absolutely no control over its occurrence. Current global food management system is based on the (false) assumption that crop failure in a region is always compensated by good harvest elsewhere, so free trade can solve the problem even without considerable reserves.

    Of course, that argument ignores the fact that global warming is predicted to increase the *frequency* of such droughts, or the probability that terrible droughts will occur, which, IMHO, is quite an adverse impact.

    No, it is not predicted, it is projected, which is something entirely different. If it were predicted indeed, one could try to falsify it, but projections, being heavily laden with mays and mights, are essentially unfalsifiable.

    Consider for example Dai's projection for the Mediterranean.

    You can see according to Dai's projection severe drought conditions may develop over the Mediterranean by the end of this century.

    However, there is research based on actual fossil evidence that indicates otherwise.

    Geologie en Mijnbouw 70: 253-264, 1991.
    The eastern Mediterranean climate at times of sapropel formation: a review
    E.J. Rohling & F.J. Hilgen

    "We argue that increased (summer) precipitation along the northern borderlands of the eastern Mediterranean, at times of sapropel formation, was probably due to increased activity of Mediterranean (summer) depressions. Forming predominantly in the western Mediterranean and tracking eastwards, such depressions tend to lower the excess of evaporation from the eastern Mediterranean relative to that from the western basin. Picking up additional moisture along their eastward path, such depressions also redistribute freshwater within the complex eastern Mediterranean water balance."

    They say (based on analysis of sea floor sediments) that between 9000 and 6000 BP (during the Holocene climatic optimum) precipitation over NBEM (Northern Borderlands
    of the Eastern Mediterranean, where Dai expects extreme drought) was considerably higher than it is today.

    At that time NH temperatures were also higher due to increased NH summer insolation, as perihelion of Earth fell into NH summer. Global average might have been somewhat lower because of SH cooling at the same time, but there is very little interaction between weather events of the two hemispheres.

    The positive precipitation anomaly is attributed to enhanced land-sea temperature difference, which is also projected to occur under AGW scenarios. From this one can surmise there might be some problem with computational climate models. Indeed, even if they were perfect in in all other respects, their spatial resolution is insufficient to represent local features like cyclone generation over the Mediterranean.

    #12 Riccardo at 19:59 PM on 18 February, 2011
    You're talking a-scientific here and a bit insulting. I'm sure you know very well that hardly any absolute certainty can be found in cutting edge science. Your accusation of cowardice is really a shame and inappropiate here.

    No, the a-scientific statement is found in the article above. To see this clearly, consider the negation of the phrase "most of the Western Hemisphere (along with large parts of Eurasia, Africa, and Australia) may be at threat of extreme drought this century", please.

    It looks like "most of the Western Hemisphere (along with large parts of Eurasia, Africa, and Australia) can't possibly be at threat of extreme drought this century", which is obviously false under any reasonable assumption about climate. Therefore the original statement is a truism which has no place in science whatsoever.

    It belongs to rhetoric or the language of marketing as it is currently known and is very much like propositions often heard in ads such as "just massage a few drops of this stuff into your hair and it may get up to 63.12% more vibrant".

    It has nothing to do with lack of absolute certainty in cutting edge science.

    As for shamefulness and inappropriateness the preposterous statement expressed in comment #7 "Population reduction will probably happen in the least affluent countries first and therefore have a minimal ipmact on emissions." surely has these qualities.

    It is also insulting because it dares to imply population reduction by mass starvation would be a solution to a problem, if only it happened to the most affluent countries. As soon as people are dying by the hundreds of millions, no sensible person cares for emissions, one cares for people. We are not here to Save the Planet, but to save human souls. It is of course not a scientific stance but a political (or rather ethical) one, but so is speculation about saving the planet by letting people die en masse. It is just a re-dressing of the old Lebensraum theory, nothing else.

    To prevent apocalypse, we obviously have to establish massive food reserves, what has to be done anyway, regardless of scary climate scenarios. We also have to spend a lot of money on improving education level of girls in the least affluent countries.

    We should not spend any money on forced CO2 emission reduction programs, because that would cripple economic development of less affluent countries (and affluent ones as well), robbing them of the only chance to accommodate to any possible change that may come in the future. Of course we should encourage flow of venture capital into R+D programs targeted on development of new energy sources and their introduction to the market as soon as their pricing becomes competitive with no subsidies whatsoever, but never before.

    Agriculture based on current technology, if given a few years leeway by a large distributed food reserve buffer, can adapt to any changes that may be in store for us. But in order to empower people to do that we should help backward nations to improve their conditions by good education, by building infrastructure and embracing cutting edge technology, while forgetting overhyped waste policies like biofuels or windmills ASAP.

    No rocket science is needed to accomplish this plan, just some conscience and common sense. Also, it costs much less than the many trillion dollars needed to control a trace gas which has demonstrably no direct harmful effect on human health at all, while it is beneficial to plant life, especially under drought stress.
    0 0
  15. Berényi - I am greatly puzzled by your strongly worded comment "We should not spend any money on forced CO2 emission reduction programs..."

    Prevention will always be less expensive than after-the-fact adaptation. You're advocating the most expensive path with that statement.

    Secondly - "Of course we should encourage flow of venture capital into R+D programs targeted on development of new energy sources and their introduction to the market as soon as their pricing becomes competitive with no subsidies whatsoever, but never before."

    Current energy sources are strongly subsidized. Perhaps it would be more appropriate to state that new technologies should enjoy no higher subsidies than existing ones? Or to be even more fair, subsidies no higher than those technologies (like nuclear) enjoyed during their development phases, as an investment in the future? Otherwise you really aren't competing on a level field.

    Finally - a massive volcanic eruption could indeed cause widespread chaos and damage. So could an asteroid strike, a new plague, virulent crop pests, tsunamis, zombie uprisings, alien invasions, etc. But none of those low probability disaster events justify hiding our heads in the sand and not acting on high probability climate change effects.
    0 0
  16. Regarding BP's posts on this thread,

    The anti-science meme by contrarians and "skeptics" continues.

    Yes, it appears that the eastern portion of the Mediterranean very likely experienced more frequent pluvial conditions 5.5 to 9.5 thousand years ago which led to sapropel formation. That regional response, has nothing whatsoever to do with the current anthropogenic forcing of global temperatures. Is BP honestly trying to suggest that the the entire Mediterranean region will now (and in the future) respond in the same way it did 5-9 K years ago to even warmer conditions? Ludicrous.

    First, as Dai et al.(2004) have found using observations, most of the Mediterranean has experienced a drying trend under the current observed warming (see their Fig. 7b). It is already experiencing an increase in drought conditions, and there are othewrs papers which show the same. Example, Xoplaki et al. (2004):

    "The second half of the twentieth century shows a general downward trend of 2.2 mm month–1 decade–1. In particular the end of the 1980s-early 1990s are well known for general drought conditions over large parts of the Mediterranean. The first canonical mode has been found to be responsible for the decadal and long term variations in precipitation. These decadal and long- term trends follow those of the Gibraltar-Iceland NAO, thus results suggest that long-term changes in Atlantic variability govern Mediterranean precipitation."

    Second, the contrarians are assuming that the N. Atlantic SSTs are now and in the future going to be similar to what they were during 5.5 to 9.5 K ago, and as shown above, they do play a role. Recent data indicate that the current warmth in portions of the N. Atlantic, are unprecedented in the last 2000 years (Spielhagen et al. 2011).

    Third, right now global temperatures are equivalent to the warmest conditions observed during the Holocene. We will shortly almost certainly be warmer than the warmest conditions experienced in the last 10 K years.

    Fourth, even in the highly unlikely event that portions of the Mediterranean do experience increased rainfall, what about the increase dimpacts of evoporation from higher temperatures, and what about the the rest of the globe?

    Fifth, BP need to familiarize himself with the permanent wilting point, and the many studies which show that elevated CO2 does not benefit all plants equally (with those using the C4 pathway, which tend to be found in hot and drier regions, benefiting the least, if at all). Not to mention the impacts of heat stress on plants. More information debunking the CO2 is "plant food" myth can be found here, and here, and here. And let us not forget the impact of fire on vegetation-- although I concede that is a tough one to weed out because of humans initing more fires, but in regions experiencing drying, controlling those fires will be more difficult.

    If BP claims to know better than Dai et al., and claims to know what the projections should be, then I challenge him to publish a paper making his case. His posts are nothing more than an elaborate attempt to obfuscate and mislead (e.g., his comments about CO2 enrichment).
    0 0
  17. BP, a small but important point, a windmill and a wind turbine are different things which serve different purposes. And we know the game of mixing them up to demean the importance of wind turbines.

    And the ideological rant at the end of you last post @15, only acts to betray your bias and undermine your credibility. Please save that nonsense should you happen to post at WUWT (or other anti-science sites).
    0 0
  18. #15 KR at 04:34 AM on 19 February, 2011
    Prevention will always be less expensive than after-the-fact adaptation. You're advocating the most expensive path with that statement.

    That's obviously not the case. Using the precautionary principle one could easily prevent accidents by banning traffic once and for all instead of the meticulous adaptation process involving crash tests, seat belts, airbags, speed limits and the like, any of which costs money. However, if you compare this cost to that of the mindless prevention scheme mentioned above, it is negligible.
    0 0
  19. Berényi - I have replied on the economic impacts of carbon pricing thread.
    0 0
    Moderator Response: [DB] Thank you!
  20. #16 Albatross at 04:49 AM on 19 February, 2011
    debunking the CO2 is "plant food" myth

    This is how the myth looks like. Pretty, eh?

    Of course soybean is a C3 plant (uses less efficient ribulosodiphosphatcarboxylase enzyme instead of phosphoenolpyruvatcarboxylase to collect CO2 from air). Still, a rather important crop.

    In case of drought which plant could collect more water? The one with shorter (a) or longer (b) roots? Place your bets. And then the stomata thing was not even mentioned. OK, it was.
    0 0
    Moderator Response: [Daniel Bailey] Please, no more spamming of this thread. This thread is about drought in a warming world. You have already been directed to more appropriate threads for the topics you've raised here. Future off-topic comments here will be deleted. Thanks!
  21. DP@20 CO2 is not the factor limiting growth of all plants in all environments. Yes, in an atmosphere richer in CO2 a soya bean plant grown in experimental conditions with unlimited water may grow larger than a plant grown in a low CO2 atmospher. But that doesn't mean the same is true of plants grown in the natural environment where water is scarce. A better developed root system will only help a plant in drought conditions if water were plentiful enough before the drought for them to grow that large in the first place. So your argument is only valid if additional unstated assumptions are valid, which is unlikely to be univeraslly true. Like many issues in science, it is not a straightforward issue, and simplistic arguments like "CO2 is plantfood" are generally misleading.
    0 0
  22. BP,

    Please read the links that I gave you. The "myth" I am referring to is the claim that we essentially do have to worry about drought in the future because higher CO2 is beneficial to "plant life".

    The images that you posted are also a strawman, a red herring too-- but I am glad that you did, because it demonstrates yet more issues with your argument. But first, I did not contest that C3 plants do not benefit from enhanced CO2, at least under ideal conditions. you made the generalization about all "plant life", the literature suggests otherwise.

    Now to your pictures.

    First, we are a long ways off from a CO2 of 700 micromol mol-1 CO2.

    Second, you do not provide a link for the photos you produced, was it Rogers (1992). If so they say in their abstract "Results from this controlled environment investigation demonstrate....". So where were those plants grown? Were they exposed to elevated temperatures as well? Were they well watered, what about nutrient supply?

    Again, while there may be some benefits to doubling CO2 for C3 plants, but on the whole these are very likely going to be far outweighed by the cons. Have you looked up permanent wilting point yet? Those extra roots on the RHS image would be no help to a plant should the root-zone soil moisture drop below the permanent wilting point as often occurs during drought. In fact, even when the plant-available water content drops below 30% plants start to experience significant decreases in above -ground biomass growth and photosynthetic activity (e.g., Mitchell et al. 2001).

    And you know what else plants do not like? Too much water, and note that research has found that extreme precipitation events in many areas are on the increase. But I digress.
    0 0
    Moderator Response: This conversation about the specific claim that CO2 will enhance growth, probably at this point should be moved to the thread "CO2 is not a pollutant," where the comments already started addressing that topic quite a while ago.
  23. BP: "a major volcanic eruption in the Tropics can cause multi-year cooling & drought conditions, hence widespread crop failures. This kind of event can happen any time and we have absolutely no control over its occurrence."

    Sounds like something a major Alarmist might say. However, while major eruptions are certain to occur over geologic time scales, that's a gross mischaracterization of the probability of a major volcano on a human time scale.

    Ample work on volcano occurrence probability exists, all the way down to a quantitative assessment of the risk of death by volcanic eruption. For example, from Newhall and Hoblitt 2000, an individual is 5x more likely to die as a result of a hurricane, 20x in flooding and 2500x employed in mining and quarrying than from volcanic eruption.

    The occurrence of explosive eruptions (those that could potentially produce global scale cooling) is a logarithmic function, decreasing with volcanic explosivity index (VEI): VEI 5 (Mt. St. Helens) is <100 per 1000 years, VEI 6 (Krakatoa-class) is ~10 per 1000 years, VEI 7 (Tambora) 3-4 per 1000 years. A catastrophic Yellowstone event (VEI 8) is <0.05 per 1000 years.

    So it is remarkable that one can be more concerned with the negative effects of low probability explosive volcanoes than the negative effects of high probability climate change.
    0 0
  24. Berenyi I know this is a futile question to someone not wanting to worry about global warming because a volcano might erupt some time, but if, as you are suggesting, we don't have to worry about CO2 levels increasing because plant growth will increase and therefore all the extra CO2 will be removed from the air - how did we get such extreme climate change in the past?
    0 0
  25. #20 BP,

    Are you familiar with the Keeling Curve? Not just that it shows annual increasing of atmospheric CO2, but the peaks and valleys of the annual curve?

    The valleys occur in the summer when vegetation is taking in CO2. The peaks occur in winter when the decaying vegetation is releasing the CO2 they previously took in. The reason the curve is rising overall is due to the anthropogenic contribution. Yes CO2 is plant food, but plants also release that CO2 it in the winter. Plants can only take up so much CO2.
    0 0
  26. #24 David Horton at 08:48 AM on 19 February, 2011
    as you are suggesting, we don't have to worry about CO2 levels increasing because plant growth will increase and therefore all the extra CO2 will be removed from the air - how did we get such extreme climate change in the past?

    Am I suggesting such a thing? I don't think so. Where have you read it?

    As for extreme climate changes of the past like glacial-interglacial transitions, they were not caused by CO2. The science is settled, there is robust consensus over this particular issue.
    0 0
    Moderator Response: [DB] BP, that is certainly the interpretation any objective reader would have to draw based on your comment at #20 above. Please continue your disinformation campaign elsewhere.
  27. I like this site. I have read these posts hoping to see if there is valid evidence to support an incresing frequency of droughts.

    Instead some character called Berenyi Peter highjacks the entire thread, trying to nitpick an article title that is simply in effect a summary and suffers what all summaries inevitably do it generalises, because its a summary or title!

    He then waffles on about preparing for natual disasters, well off topic, gives me a headache with his constant itallics, and make claims about cost mitigation and precautionary principles without a shred of proof, but plenty of straw man arguments.

    I give up I cant be bothered Im off elswhere..
    0 0
    Moderator Response: [DB] As Marcus points out immediately below, thread hijacking, as attempted by BP on this thread, will not be allowed to succeed. Debate and even disagreement is encouraged, as long as they comply with the Comments Policy. If needed, more extreme methods exist to deal with repeated violations of the Comments Policy. For a more in-depth discussion of the science of droughts in a warming world, I encourage you, and everyone, to read the paper which is the subject of this blog post. Bring any questions about it here and someone will attempt to answer them for you. Thanks for caring enough to make a comment of your own.
  28. Nigel, I know it can be frustrating, but please don't give up-that's just handing victory to deniers like BP. That's exactly *why* they hijack sites like this. Don't worry, though, we have excellent moderators who will ensure that all future OT posts get deleted, as they deserve!
    0 0
  29. Just a thought to Daniel Bailey. When talking about a thread getting off topic the article is a good case in point. I have no idea what is going to be discussed until the last sentence of the third paragraph. I suppose that if the title of the first section was "Coexistence of Drought and Flood" a reader would have been clued in from the beginning kind of like peer reviewed papers tend to do.

    I thought BP brought up a good point in comparing what was predicted with what has happened in the past. The computer models just charged on into the far distant future with no correlation to actual future events. To bad the models weren't run backwards to correlate with the past.

    I found it interesting that India seemed to go unaffected while China was hard hit with drought. Just what makes India resistant to this effect of climate change?
    0 0
  30. Re: TOP (29)

    1. Thank you for your perspective.

    2. The study discusses in exquisite detail, replete with sourced references, the entire field of drought in a warming world up to the present day even before it attempts to look at what the future may bring. Could you explain what you mean by:
    "The computer models just charged on into the far distant future with no correlation to actual future events."
    Suggesting that we must wait until after a speeding train hits us before deciding if we should have gotten out of the way seems logically impoverished to me. As do BP's ramblings on past conditions, which occurred under far different circumstances than today.

    3. Models used in the study were the 22 coupled models used in the IPCC AR4.

    4. On pages 13-14 of the study, that is discussed. Essentially, India gets progressively wetter though increased precipitation (which in its case is expressed as more frequent precipitation, as opposed to more precipitation when it does rain):

    FIGURE 10 | Multi-model mean changes from 1980–1999 to 2080–2099 under the SRES A1B scenario in annual (a) precipitation (mm/day), (b) soil moisture (%), (c) runoff (mm/day), and (d) evaporation (mm/day). The stippling indicates where at least 80% of the models agree on the sign of the mean change. (Meehl et al 2007)

    The Yooper
    0 0
  31. Marcus #28

    Ill be back. An idea might be what RC do and allow an open thread for no holds barred discussion on anything. More on topic Im in New zealand we have just had our hottest January - Febuary on record.

    Ive been having an intersting lengthy debate wth some political hacks using SC as a reference source. Im Gandalf.
    0 0
  32. David Horton at 07:08 AM on 18 February, 2011, whilst the paper referenced, "Drought under global warming:" attempts to address global climate projections, I'm not sure how the projections in the paper for Australia, and by logical extension, Africa, India, Indonesia, all those countries bordering the Indian Ocean have been arrived at given the limited attention given to the cycles so far identified in the IO.

    Greater attention was paid to the Pacific ENSO cycles etc, the only mention of the IO was about "steady warming", put down to GHG global warming, with only one brief mention of decadal variations of SST in the IO.
    Nowhere was there any analysis of the IOD, despite it being identified over a decade ago, and much work having since been done which links the phases of the cycles to variations in the Australian climate.
    Prior to the identification of the IOD, researchers had found some correlation between droughts in Australia and the ENSO cycles finding reasonable correlation of droughts with El-Nino events, however when such findings were examined in reverse by others, only lower correlation of El-Nino events with droughts in Australia was found.
    It was only by incorporating the IOD into the calculations, that high correlation between drought events in Australia and events in both the IO and the Pacific were found.

    An extension of that was then finding the link between the various cycles that affect the other countries surrounding the IO, something that had been observed by some of the very early settlers in Australia, but only explained more recently.
    Given the significance of the IOD to the IO regional climate, I would have thought it would have been given as much attention as ENSO before any trends could be established or projected.

    I also note the early caveat in the paper, "Future efforts to predict drought will depend on models’ ability to predict tropical SSTs."
    At the moment this appears somewhat limited to perhaps one or two years out depending on the various models.

    Lastly, the statement "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." seems to not rule out the possibility that perhaps despite all the projections, it will also be natural climate variations that might determine whether persistent drought over the next similar period of time occurs or not.

    All in all, given the repeated acknowledgement given to the difficulties predicting tropical SST variations on seasonal to decadal time scales, I am left with the impression that greater understanding of what might eventuate in the time scales projected is to be found in the historical perspective examined in the paper, rather than the modeling presented.
    The author virtually acknowledges this, stating, "Further advances in model developments may make it possible to predict drought on seasonal to decadal
    time scales."

    Whilst the OP claims the paper concludes on a somber note, I feel it concludes on an uncertain note by again noting the underlying deficiencies in the models used to make the projections presented.
    0 0
  33. #12 Riccardo

    "We are not here to Save the Planet, but to save human souls." How can we save human souls without saving the planet, where are the bodies that these souls inhabit to live?
    0 0
    Moderator Response: [DB] I believe you mean BP's meanderings in his comment at 14 above.
  34. Perhaps as Lovelock says; go north or south young man. Although I doubt that any part of Antarctica would be able to support human population any time soon. Not to mention the toxins in the food chain in the Arctic.
    0 0
  35. @ Ron (34)

    Conditions will be none too pretty anywhere in the latter half of the century. Not only are the main mapped graphic projections of future conditions based on a medium emissions path (while actuals are tracking a high-emissions path), one of the vectors not taken into account in the models are the results of Schaefer et al 2011, discussed here.

    Sheafer et al 2011 further compounds this problem by being too conservative itself: it presumes all GHG emissions due to PCF (Permafrost Climate Forcing) will be in the form of CO2, while in actuality much will be in the form of CH4 (methane). Should this stand up to further scrutiny & be confirmed by subsequent studies, this means an effective CO2 doubling from PCF alone by 2200. In addition, Schaefer et al 2011 do not consider methane hydrate releases, which are currently underway in the East Siberian Arctic Sea. Needless to say, no current model begins to take this all into consideration.

    Net: Even though the field is advancing rapidly (to the point that many of the assumptions tested in studies are found to be hopelessly conservative & obsolete upon publication), the more we are finding out about how truly effed-up the situation is, the more we realize just how screwed our children are going to be.

    "Safe refuges?" In North America, I'd say Northern Labrador, due to the moderating influences of the maritime seaboard. Perhaps Northern Scandinavia, but that will be swamped by refugees from Europe. Kamchatka (if the Ring of Fire doesn't destabilize it's volcanoes somehow) should be OK for a while. New Zealand's South Island also (remoteness is a good thing!).

    The reality is that no place will be safe. By 2050, safety & security will be a condition of the past. All that will matter is a place to grow enough meager foodstuffs and the supply of ammunition to protect them.

    Such a downer today; I should just go to bed.

    The Yooper
    0 0
  36. #35 Daniel

    It's definitely going to be interesting. I think we'll really start to see things going haywire in the next 10-15 years. Should make '29 look like sanity.

    Yes go to bed and if your like most of us you'll dream that you wake to find it was all just a bad dream in the first place.

    I sit back and laugh at the irony though. I mean -- what else can one do in this situation. I've got enough grey as it is and I'll be darned if I'm going to ruin my health over the world's problems.

    Like they say talk is cheap and all I ever hear is talk. How much longer must I or anyone wait for affirmative action? People need to wake up and realize that they are in the biggest war of their lives, a war for their future survival and that of their children.
    0 0
  37. For those readers living in the Pacific Northwest of the USA, there's an interesting new study just published in PNAS:

    Drought variability in the Pacific Northwest from a 6,000-yr lake sediment record
    Nelson & Abbott 2011
    doi: 10.1073/pnas.1009194108
    (Abstract, full paper is paywalled)

    Lake bed sediment core analysis reveals that the climate of the Pacific Northwest fluctuated more or less evenly between wet and dry periods for thousands of years. Droughts tended to be lengthier, with 25 percent of dry periods during the past 6,000 years persisting for 30 years (with a maximum of 75 years duration). Wet periods tended to be shorter with only 19 percent lasting more than 30 years (with a maximum of 64 years duration).

    The most recent 1,000 years has seen these periods become longer, shifting less frequently, and ushering in more extreme conditions. The wet cycle stretching from the 1940s to approximately 2000 was the dampest in 350 years (the only wetter cycle in the 6,000 year record began around 1650).

    Lead researcher Mark Abbott, a Pitt professor of geology and planetary science, said those unusually wet years coincide with the period when western U.S. states developed water-use policies.
    "Western states happened to build dams and water systems during a period that was unusually wet compared to the past 6,000 years," he said. "Now the cycle has changed and is trending drier, which is actually normal. It will shift back to wet eventually, but probably not to the extremes seen during most of the 20th century."

    Duration of dry and wet cycles by percentage over 6,000-year period.

    Another finding: the Castor Lake core matched the Palmer Index reconstructed with tree-ring data and expanded on it by 4,500 years, suggesting that lake beds are better records of long-term climate change.

    Finally, the change in cycle regularity found by Nelson & Abbott 2011 correlates with documented activity of El Niño/La Niña. When the those patterns became more intense, wet and dry cycles in the Pacific Northwest became more erratic and lasted longer.

    Fill up those canteens now.

    The Yooper
    0 0
  38. Daniel Bailey at 02:12 AM on 25 February, 2011, the infomation in the graph below is the basis of the study referred to and helps visualise the historic perspective of the regular cycles.

    Measurement of oxygen isotope ratios (red) and grayscale (black) arranged to show drought cycle duration and intensity with 20th century wet period indicated. Credit: Mark Abbott

    Whilst this study is for what has occurred at one particular location, being linked to the El-Nino/La-Nina cycles ties it in directly to what will have occurred elsewhere in the region, and by extension neighbouring regions, because what El-Nino brings to one man is what La-Nina brings to another.

    Add to this the systems that have been identified in other oceans, also with regular cycles that do not necessarily oscillate with the same frequency or pattern, and what seems to be chaotic takes on some form that becomes more predictable.
    For example, the primary driver of the conditions most recently affecting Australia is the coinciding of a La-Nina pattern with a negative phase of the Indian Ocean Dipole, the last time both a La Nina and IOD-ve combined was in 1975, when there were three consecutive La-Nina years resulting in the overall wettest period for Australia since first settlement.

    In Australia too, some years ago the realisation come about that much of the planning for our water resources was based on a period that rather being the normal, was in fact just the opposite.
    Perhaps with the pattern that appears to be forming now, those responsible for planning may have been handed a get-out-of-gaol-free card with a generally wetter period of some decades that should allow them some breathing space to make more realistic plans for when "normal" conditions return.
    0 0
  39. A discussion on PDSI disparity, very dry & very wet at the same time in different parts of the same landmass, is being migrated here from the Review of Rough Winds article.

    I am looking to create a PDSI disparity metric to quantitatively say whether a given drought & flooding episode is unusual in the observational record.

    The discussion was about the 2011 Texas drought happening alongside flooding in other parts of the US, but the general principle could be applied around the globe using the Dai dataset at Palmer Drought Severity Index (PDSI) from NCAR.

    The data set for the US analysis is the PDSI Divisional Data linked below the map on NOAA: Historical Palmer Drought Indices.

    direct link: PDSI data (3.8 MB text file)

    The NOAA PDSI dataset is composed of 344 climate divisions.
    U.S. Climate Divisions
    division area list

    Now that the data sources are referenced, here is my concept for the disparity metric.

    1) Order the list numerically by value.

    2) Match the list off into 172 top/bottom pairs; 1-344, 2-333, ... 172, 173.

    3) Take the absolute difference between the value pairs and multiply it by the summed area of the two climate divisions.

    4) Sum the 172 values from #3.

    - reference value: 8 (difference between extreme drought, -4, and extremely moist, 4) x U.S. contiguous area

    5) Divide #4 by the reference value.

    The final result is a scalar value between 0 - 100+%. Low values mean similar dry/wet conditions across the nation, while high values indicate large areas of opposites of extremes. The metric can be greater than 100% since PDSI values are not capped.

    Any suggestions, arguments against or confusion?
    0 0
  40. Bibliovermis:

    Liu et al 2011 has a nice analysis of PDSI and 'Standardized Precipitation Index.' They forecast (using standard model scenarios) a significant increase in severity and probability of drought.

    The key is figure 12, which displays the PDFs of PDSI for the past and the future. 1950-1999 shows a near normal distribution with mean value slightly above zero, while 2050-2099 displays an abnormal PDF with mean value below zero and left tail reaching towards much lower PDSI. This indicates that future drought is likely to get more severe and frequent, as projected by SPI under A2 scenario.
    Note: PDF is probability distribution function.
    0 0
  41. I have a question on Dai's through review of drought. Your figure 1 closely resembles Dai's figure 11 (c). Much of the USA is red or orange. This is a surprise to me. Compare the other PDSI source:[]=3&beg_year=2000&end_year=2009&submitted=Submit

    USA is not so dry after all. This seems more realistic to me. Can you shed any light on this difference?
    0 0
  42. Pete, that's a good question. Perusing the paper I find this:
    "We emphasize that quantitative interpretation of the PDSI values shown in Figure 11 requires caution because many of the PDSI values, which are calibrated to the 1950–1979 model climate, are well out of the range for the current climate, based on which the PDSI was designed."
    For reference, here's Figure 11:

    A description of their methodology:
    "Here monthly PDSI pm and sc PDSI pm were computed using multi-model ensemble-mean monthly data of precipitation, surface air temperature, specific humidity, net radiation, wind speed, and air pressure from 22 coupled climate models participated in the IPCC AR4,128 and used to assess changes in aridity over global land. Thus, these PDSI values may be interpreted as for the multi-model mean climate conditions. As the PDSI is a slow varying variable, the lack of high-frequency variability in the ensemble mean climate is unlikely to induce mean biases.

    Figure 11 shows the select decadal-mean sc PDSI pm maps from the 1950s to 2090s from the IPCC 20th century (20C3M) and SRES A1B scenario simulations. Results for PDSI pm are similar with slightly larger magnitudes."
    The other graphics you link to, March 2000-March 2009 and August+September of 2011, are of much more limited snapshots in time & reflect actual measurements of PDSI.

    Hope that's more clear than mud!
    0 0
  43. Daniel, Thanks for looking into this! I'm not sure it's cleared up though. I referred to figure 11 (c) which is for 2000-2009, a period we have just lived through. The base period is 1950-1979, also familiar. I would expect the base period for the online PDSI maps at NOAA to be similar. In addition, reading Dai's paper from the top as I did, and seeing his other figures including figure 7, I still have trouble matching fig. 11 (c) to everything else. Perhaps I should ask Dai unless you have another thought. By the way how do you get these diagrams? do you have the paper as html?
    0 0

    [DB] Pete, the versions in the article above are taken directly from HQ versions hosted by UCAR (Dr. Dai works at UCAR).  My assumption is that they were re-worked to be more reflective of the depth of the data available than the pixilated versions in the final paper.  HTH.

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

The Consensus Project Website



(free to republish)



The Scientific Guide to
Global Warming Skepticism

Smartphone Apps


© Copyright 2014 John Cook
Home | Links | Translations | About Us | Contact Us