Let's Talk Drought

By Keith Kloor | October 20, 2010 8:13 am

Drought, like global warming, is a slow motion event that humans can’t get seem to get ahead of. Or properly grasp. For a good historical case study examining how the Maya, the Vikings, and the U.S. (in the lead-up to the Dust Bowl) each responded to drought, see this paper by Ben Orlove, who observes:

From the comparative history of the past, it can be seen how fragile human societies can be and how resistant they can be to changing established patterns of action; it can also be seen that most people somehow survive in both a biological and a cultural sense.

The big difference today, obviously, is that we know this history and also have some ability to see into the future, as this new study suggests:

The United States and many other heavily populated countries face a growing threat of severe and prolonged drought in coming decades.

What’s notable about this research by Aiguo Dai, a scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, is that there’s a global warming angle:

The detailed analysis concludes that warming temperatures associated with climate change will likely create increasingly dry conditions across much of the globe in the next 30 years, possibly reaching a scale in some regions by the end of the century that has rarely, if ever, been observed in modern times.

Before going any further, it’s important to point out that modern times (especially in the U.S.) are not the best measuring stick, which this definitive paper succinctly explains in its abstract:

Severe drought is the greatest recurring natural disaster to strike North America. A remarkable network of centuries-long annual tree-ring chronologies has now allowed for the reconstruction of past drought over North America covering the past 1000 or more years in most regions. These reconstructions reveal the occurrence of past “megadroughts” of unprecedented severity and duration, ones that have never been experienced by modern societies in North America.

This in no way diminishes the threat of natural occurring droughts worsened by anthropogenic global warming, which NCAR’s Dai lays out in his new study. Those findings are bound to make a splash in the media and blogosphere today. To understand why, here’s Dai in an early MSNBC report:

We are facing the possibility of widespread drought in the coming decades, but this has yet to be fully recognized by both the public and the climate change research community. If the projections in this study come even close to being realized, the consequences for society worldwide will be enormous.

So it’s a safe bet that the hook to this story is going to be climate change. Fair enough. Dai makes that explicit in his paper (which people should read). But he also concludes on this note:

Given the dire predictions for drought, adaptation measures for future climate changes should consider the possibility of increased aridity and widespread drought in coming decades.

I don’t expect that message to be emphasized in the spot reporting of the study or much discussed by climate bloggers, but given the history of prolonged droughts and civilization, here’s hoping it echoes in the halls of policymakers and planners.

CATEGORIZED UNDER: climate change, drought
MORE ABOUT: climate change, drought
  • grypo

    What’s gotten missed is the number of studies that have come out over the last 5 years that give a better understanding of how the Earth responds to the energy imbalance created by emissions.   If I were the man in charge of messaging, this is the risk I would highlight.  Global warming would have been called “Planetary Energy Imbalance” from the beginning because, the Warming, the Change, and the Disruption are all symptoms of this.   The obsession with temperature and sensitivity numbers, which are important obviously (to understand how bad these symptoms will be), take a back seat to real world impacts of water and food shortages.

  • http://collide-a-scape.com Keith Kloor


    I understand the concept but Planetary Energy Imbalance is quite a mouthful and probably meaningless to people with less than a rudimentary grasp of climate change issues.

    When something gets tagged with a label, it’s usually simplistic but it works as shorthand. Personally, I think “climate disruption” covers all the bases for the argument that climate concerned folk are making today.

  • http://thingsbreak.wordpress.com/ thingsbreak

    That part of the world hasn’t been particularly kind to societies that move in and expand during the “green” times.

    From the best of my recollections the medieval megadrought period(s) were thought to be the result of persistent La Niña-like conditions in the tropical Pacific, modulated somewhat by warm North Atlantic SST patterns (e.g. positive AMO).

    This is interesting because there had been quite a bit of debate back in the day about whether anthropogenic warming would end up looking more like the Pliocene in terms of a persistent El Niño, more like the Medieval Climate Anomaly/MWP, or not preferentially either. There were many claims from “skeptics” that because this question was unresolved, projections of future drought regimes for the American southwest were essentially worthless- and this attack makes a superficial kind of sense, if these were the only pieces of the puzzle you had.

    But the projections for drought under anthropogenic warming aren’t based on changes to these multidecadal ocean-atmosphere oscillations, but rather the further drying of the subtropics (due to the intensification of the hydro cycle), and poleward expansion of both the mid-latitude storm tracks as well as the Hadley Cell. These behaviors are pretty robust across climate models, regardless of what mode of ENSO variability, if any, they favor as we heat up. So the take away seems to be that irrespective of whatever curveballs nature was going to throw (or not) anyway, there’s an awful lot of drought in the West’s future under unchecked emissions.

    My question would be- has anyone tried to see what happens when you induce persistent La Niña-like conditions + positive AMO in a 2100 world of unchecked emissions growth? Are tropical Pacific SSTs just too warm to facilitate the kind of change that the MCA is associated with, or do you get a nightmare-atop-nightmare scenario of medieval megadroughts striking an already near-permanently-in-drought region?

  • Hector M.

    Global warming may cause decreased precipitation in some areas, but its overall effect is an increase in rainfall, due to the increase in evaporation from the seas (and other water bodies) caused by warming. Global projections in the IPCC AR4 report (2007) as well as specific studies on water balance (availability vs withdrawals) do not support the claim of impending generalized and persistent dry/arid conditions (see some refs below). Some areas may become drier and other would become wetter, but one has to pay attention to the details: in many areas (e.g. the tropical Andes regions) there would be a significant increase in precipitation during the wet season, that is when crops are grown, and a small decrease in precipitation during the normally dry season in which no crops are grown. See for instance Fig. 11.15 and Fig TS30 in the AR4  WG1 report.

    This regards habitual or average climate, and does not preclude the possibility of  droughts (as opposed to drier climate) in areas prone to them, since it is generally believed that climate change may involve an increase in extreme events, but that is a different question (and also contested).

    Alcamo, Joseph, Petra Döll, Thomas Henrichs, Frank Kaspar, Bernhard Lehner, Thomas Rösch & Stefan Siebert, 2003a. Development and testing of the WaterGAP 2 global model of water use and availability. Hydrological Sciences Journal 48(3):317-337.

    Alcamo, Joseph, Petra Döll, Thomas Henrichs, Frank Kaspar, Bernhard Lehner, Thomas Rösch & Stefan Siebert, 2003b. Global estimates of water withdrawals and availability under current and future business-as-usual conditions. Hydrological Sciences Journal 48(3):339″“348.

    Alcamo, Joseph; Martina Flörke & Michael Märker, 2007. Future long-term changes in global water resources driven by socio-economic and climatic changes. Hydrological Sciences Journal 52(2): 247-275.

    Döll, Petra & Stefan Siebert, 2001. Global modeling of irrigation water requirements, Water Resources Research 8(4):1029″“1035.

    Döll, Petra, 2002. Impact of climate change and variability on irrigation requirements: a global perspective. Climatic Change 54:269″“293.

    Fischer, Günther, Francesco N.Tubiello, Harrij van Velthuizen & David A. Wiberg, 2007. Climate change im­pacts on irrigation water requirements: effects of mitigation, 1990-2080. Technological Forecasting & Social Change 74:1083-1107. Available at http://pubs.giss.nasa.gov/abstracts/2007/Fischer_etal.html.

  • Hector M.

    Regarding the possibility of a persistent El Niño conditions due to warming, the jury is still out but chances are it would not happen. For instance the team headed by Eric Guilyardi has attempted to replicate Pliocene conditions, and even more (more than one order of magnitude above baseline CO2 concentrations, i.e. more than 10xCO2, without seeing any trend towards a persistent El Niño (see refs). Up to now, the conclusion of AR4, that no evidence exists of any trend in ENSO associated with GW, is still valid.
    Guilyardi, Eric, 2006. El Niño”“mean state”“seasonal cycle interactions in a multi-model ensemble. Climate Dyn­amics 26:329-348.
    Guilyardi, Eric, A.Wittenberg, A.Fedorov, M.Collins, C.Wang, A.Capotondi, G.J. van Oldenborgh & T. Stock­dale, 2009a. Understanding El Niño in Ocean-Atmosphere General Circulation Models: progress and challenges. Bulletin of the American Meteorological Society. http://www.met.rdg.ac.uk/~ericg/publications.html.
    Guilyardi, Eric, Pascale Braconnot, Fei-Fei Jin, Seon Tae Kim, Michel Kolasinski, Tim Li & Ionela Musat, 2009b. Atmospheric feedbacks during ENSO in a coupled GCM with a modified atmospheric convec­tion scheme. Journal of Climate 22:5698-5718, doi:10.1175/2009JCLI2815.1.

  • http://thingsbreak.wordpress.com/ thingsbreak

    Hector- yes, I am aware. The point was not that the “permanent AGW El Niño” is still or ever reached the consensus stage, but that it was interesting question for this specific issue. I’ve butted heads with plenty of “skeptics” who claim that the permanent El Niño was a central prediction of “AGW theory” and is another example of falsified “alarmism”, e.g. Matt Rogers (Capital Weather Gang). Believe me, I’m not making that claim.

    Also, who is making the claim of global “impending generalized and persistent dry/arid conditions”? The press release and what media coverage I’ve read have been pretty faithfully conveying the widespread but regional-scale aspect of this paper. Is there a specific claim from a media piece that you’re disagreeing with?

  • cagw_skeptic99

    Rising sea levels with drowning polar bears, increased hurricane intensity and frequency, ocean acidification, and more haven’t worked well.  Let’s hope that the next naturally occurring drought cycle happens to correspond with a CAGW prediction so the voters in the US will buy what you are trying so hard to sell.
    Better up the pressure quickly as the more likely scenario for the next thirty years or so is a return to colder temperatures.  But if you keep swinging for the fences with predictions of catastrophe caused by CO2, there is still the possibility that you will get lucky.

  • cagw_skeptic99


    Carbon Dioxide is not a pollutant.  On the contrary it makes crops and forests grow faster.  Mapping by satellite shows that the earth has become about 6% greener overall in the past two decades, with forests expanding into arid regions.  The Amazon rain forest was the biggest gainer, with two tons of additional biomass per acre per year.  Certainly climate change does not help every region equally, but careful studies predict overall benefit, fewer storms, more rain, better crop yields, longer growing seasons, milder winters and decreasing heating costs in colder climates.  The news is certainly not bad and on balance may be rather good.

    Someday the world will wake up and laugh when they finally understand that the entire pursuit of economic ruin in the name of saving the planet from increasing carbon dioxide is in fact a terrible joke.  You see it is an unarguable fact that the portion of the Earth’s greenhouse gas envelope contributed by man is barely one tenth of one per cent of the total.  Do the numbers your self.  CO2 is no more than 4% of the total (with water vapor being over 90% followed by methane and sulpher and nitrous oxides).  Of that 4% man contributes only a little over 3%.  Elementary school arithmetic says that 3% of 4% is .12% and for that we are sentencing the planet to a wealth of damaging economic impacts.

    If greenhouse gases were responsible for increases in global temperature of recent decades then atmospheric physics shows that higher levels of our atmosphere would show greater warming than lower levels.  This was not found to be true during the 1978 to 1998 period of .3 degrees centigrade warming.

    Some 900,000 years of ice core temperature records and carbon dioxide content records show that CO2 increases follow rather than lead increases in Earth temperature which is logical because the oceans are the primary source of CO2 and they hold more CO2 when cool than when warm, so warming causes the oceans to release more CO2.

    While temperatures have fluctuated over the past 5000 years, today’s earth temperature is below average for the past 5000 years.

    Click here to read all of Lehr’s easy to digest points

  • http://gryposaurus.wordpress.com/ grypo

    —–Do the numbers your self.  CO2 is no more than 4% of the total (with water vapor being over 90% followed by methane and sulpher and nitrous oxides).  Of that 4% man contributes only a little over 3%.  Elementary school arithmetic says that 3% of 4% is .12% and for that we are sentencing the planet to a wealth of damaging economic impacts.—-
    Did you hear everybody!   The scientists totally missed it!  And we were all worrying.  All that was needed was “elementary maths”.   Thank God for the internet!

  • http://nigguraths.wordpress.com Shub

    So, thingsbreak, anyone who questions why the consensus tries to smuggle in the concept of an anthropogenic permanent El Nino is a ‘ “skeptic” ‘, but the layering of conjecture upon conjecture required to arrive at catastrophic drought scenario for North America is alright?

  • Brian Angliss

    “Better crop yields.”  I guess that means that the studies that found increasing plant mass but decreasing protein content in rice, corn, potatoes, barley, and wheat, can be ignored. 

    So can the studies that found cassava (a staple for nearly a billion people) yields dropped and what was left became more poisonous to both people eating the tubers and livestock eating the leaves.

    While we’re ignoring factors, let’s also ignore the fact that crop yields are affected by the fact that “fewer storms” combined with “more rain” means more severe storms and more intense precipitation, aka flooding.  I guess flooding and hail doesn’t cause crop loss.

    Let’s also ignore the logical fallacy implied in the “CO2 lags” quote, namely “it’s always worked this way in the past, so it HAS to work this way now too,” even if the conditions that drove the past don’t apply to the present.  And we can ignore the multiple independent datasets that show the troposphere did warm as expected from basic physics (ie “heat rises”) and neglect to mention that the GHG signature of simultaneous stratospheric cooling has also been measured.

    Facts?  Data?  Bah! Who needs those?!

  • http://nigguraths.wordpress.com Shub

    Dear Brian,
    The paper you cited about protein content does not support the kind of conclusions you are trying to reach.

    Global NPP has risen in the second half of the 20th century, there is ample data to support this conclusion.

    It would be a problem if plant mass *and* protein were to fall with rising CO2 and ozone, no?

  • Hector M.

    @6. thingsbreak October 20th, 2010 at 11:33 am
    Dear Thingsbreak, look at this paragraph transcribed by Keith in his post:
    “We are facing the possibility of widespread drought in the coming decades, but this has yet to be fully recognized by both the public and the climate change research community. If the projections in this study come even close to being realized, the consequences for society worldwide will be enormous.”
    The paragraph clearly raises the implication that “widespread drought” will be a generalized phenomenon with “worldwide” consequences. That is only one example, but there are many in the “alarmist” literature (not in the IPCC AR4 report, except in some isolated passages of WG2, but after reading the IAC assessment one has to take WG2 with a grain of salt…

  • Steve Bloom

    Hector M.:  “no evidence exists of any trend in ENSO associated with GW, is still valid.”

    El Nino modoki, anyone? 

    It’s the same story with Hector’s drought citations.

    Selective quotation of the literature to score political points is very, very tiresome.

  • http://www.scholarsandrogues.com Brian Angliss

    I’m not questioning NPP, Shub, but rather pointing out that NPP rising doesn’t necessarily mean that the nutritional value of the crops is going to rise at the same rate as productivity.  More and larger seeds/tubers that are less nutritious means that increased crop yields due to NPP don’t necessarily mean anything.  Using wheat as an example (15% reduction in protein content), if yields don’t rise 15%, then the loss of nutritional value counteracts the gain in yield.
    Furthermore, people would have to eat more wheat to get the same nutritional value as today.  This means eating more carbohydrates for a given amount of protein, and thus worsening health problems like obesity, diabetes, and heart disease.  It might be a boon to areas that are calorie-limited, but only if their climate can support growing the particular crop.

  • http://www.scholarsandrogues.com Brian Angliss

    Hector – “widespread” drought doesn’t necessarily mean “worldwide” drought.  It’s a non sequitor.  However, the consequences of widespread drought could easily be worldwide – poleward migrations of refugees, shifting growing regions northward, political instability due to water hoarding between nations, that sort of thing.
    Those consequences could very easily be worldwide and result from regional but widespread drought.

  • Hector M.

    A cautionary word on methodology: effect of warming on crops is too often evaluated by taking one crop grown today, and growing it (ceteris paribus) under higher temp (with higher or lower water availability). As most crops (and cultivars of those crops) are already chosen because they are adapted to local conditions, many alterations of those conditions would probably mean that crops yield less grain.
    Two main objections to this method are:
    (1) that it does not account for the effect of increased CO2 concentrations, causing 20-40% increase in yields in C3 plants such as wheat or rice, along with lower increase –up to 20%– but strong reduction in water requirements in C4 plants such as maize.
    (2) that it ignores the interactive nature of agriculture, which makes the ceteris paribus clause moot: as climate changes, plant response would change and also farmer behaviour. Agriculture is not like wild vegetation: it is a result of interaction between Man and Nature. If the climate becomes unbearably dry or hot for current crops in one area, farmers would not keep robotically planting the same cultivars with the same technology for three or four generations into the future. They would, as they usually do, change the cultivars or the species grown, change their techniques of cultivation (e.g. advancing date of planting, making irrigation more efficient, adding more fertilizer or whatever), or even changing land use, or the crop would then be grown in a more agreeable zone nearby where the climate is 1°-2° cooler, whilst the original area is devoted to more suitable crops under the new climate. It happens all the time.  These responses are not the result of planned adaptation but simply spontaneous and adaptive farmer behavior. Just as the plants “respond” to a changed climate, so do farmers. Potential impact of climate change on agriculture (potential=not considering adaptation, in IPCC jargon) cannot be even defined without considering spontaneous adaptation by farmers. It could be defined for wild vegetation, upon which adaptation measures are exogenous, but not for farming. In farming, exogenous adaptations (to be kept out of potential impact assessments) regard only major interventions from outside such as  public investments in R&D, roads, or new irrigation dams, which may or may not be undertaken. But a farmer choosing shorter-cycle varieties and being thus able to grow two crops per season once the growing season becomes longer and winters milder, is just the stuff of agriculture.

  • Hector M.

    Steve Bloom, my mention of uncertainty about any change in El Niño intensity or frequency, and much more about becoming permanent, are simply taken from the IPCC AR4 report and the main scientific team formulating and running models on ENSO. Those models do not assume a certain ENSO behavior, but are GCMs from which changes in ENSO emerge (or fail to emerge) as a consequence. They do not emerge, even under very extreme emission scenarios (above 10xC2). I do not know of other studies with the same level of detail (perhaps you do).
    This said, let me add that even the complex models of Guilyardi et al, as all the others, are not reality but simulation, and thus model-dependent and fraught with large uncertainties. Therefore I am not saying that a more frequent, more intense or permanent El Niño es not possible. Just that there is no indication as yet that it would be so, according to the consensus reflected in the IPCC WG1 2007 report and the results attained lately by most studies on the subject. Up to now, during the latest 200 years the strongest multidecadal El Niño cycle on record is still 1885-1915, followed by a lull of small ups and downs during several decades, and lately  a period of increased activity since the 1980s, now apparently entering a new lull. ENSO is all full of decadal and multidecadal cycles with no definite tendency, experts say, but who knows.

  • Steve Bloom
  • Hector M.

    widespread where? Several parts of the Sahel (eg Mauritania) are actually becoming wetter lately, reversing a drying tendency observed in previous decades (sorry, I do not have the reference at hand now, but I could find it). However, the Sahel is a horrid place to live, and there will be fierce fighting there for sources of water, as there already is, and emigration would continue, driven not necessarily by global warming but by poverty and high fertility.
    Emigration towards developed countries (driven not by drought necessarily, but coming also from wetter countries in central Africa or Ecuador, or even from China, Pakistan, Indonesia or India) would continue. In fact, Europe and the US actually need tens of millions of immigrants in the coming decades to cope with ageing and very low fertility, and those migrations would thus probably happen, with or without climate change.
    Migrations, let me add, are not an intrinsically bad thing: they usually improve the conditions and prospects of the migrants, and also the economic conditions and prospects both at origin and destination countries.

  • Steve Bloom

    Hector, you need to bear in mind that both climate change and our understanding of it are advancing at a rapid pace, and that the AR4 is getting a bit long in the tooth.  Note that the Copenhagen Diagnosis is a much more up-to-date consensus document.  What does it say on this subject? 

  • http://nigguraths.wordpress.com Shub

    I’ve seen that Science magazine paper, Steve B. Their values for evapotranspiration parameter q10 are under question.

  • Steve Bloom

    Hector, you seem to be limiting your reference horizon.  Try here e.g.  Better yet, take some time with Google Scholar to actually find all the relevant research.

  • http://nigguraths.wordpress.com Shub

    Low nitrogen content of plant protein under increased conditions of CO2, considering the fact that we are talking about plant-derived edible protein, only implies a growth state where the plants are relatively nitrogen-starved.

    Why not provide more fertilizer? The paper you cited offers this suggestion.

  • http://gryposaurus.wordpress.com/ grypo

    —-Keith Kloor Says:
    I understand the concept but Planetary Energy Imbalance is quite a mouthful and probably meaningless to people with less than a rudimentary grasp of climate change issues. When something gets tagged with a label, it’s usually simplistic but it works as shorthand. Personally, I think “climate disruption” covers all the bases for the argument that climate concerned folk are making today.—–
    The mouthful point is a good one, you’re right, but I’m not really concerned about that name as much as I am about the concept, and the fact we’ve been naming off different symptoms of a problem instead of actually calling the problem what it is.   Climate disruption, while being the better choice between that and Warming still does not take into account acidifying oceans, mass extinction, etc.  People do not associate “climate” with “problem”, this has become very obvious to me.  The point is being that Earth is out of balance in many different ways (even beyond CO2 use), and I think the words we use should reflect that in holistic manner.    But the point is moot anyway, it’s a bit late in the game for this conversation.

  • Hector M.

    Brian, let me add that the IPCC envisages increased wetness over the Amazon basin and the Andes mountains, as well as the arable plains of Brazil and Argentina. In the case of Argentina, displacement of rainfall isolines to the West, and  (much less) movement of temperature isolines to the South have already caused previously semiarid lands (formerly devoted to extensive low-productivity grazing) are now regularly cultivated with cereals and oilseeds, or cultivated pasture. A map of the change in rainfall isolines is actually reproduced in the 2006 assessment of climatic change in Latin America published by UNEP (see ref, p.46-47). Precipitation in the Buenos Aires area steadily climbed from 850mm/yr in the 1920s to about 1200 mm/yr in the 1990s (ibidem).
    The UNEP says in the cited report (p.46) that “”the agricultural frontier has advanced westwards [and] productivity has increased in the Pampas region” due to these climate changes, chiefly caused by increased evaporation in the South Atlantic. Precipitation over the Argentine Pampas region increased by about 20% between 1950-69 and 1980-99, and isolines were displaced about 200 km to the West. Nearly 2 million Ha were opened for cultivation, and productivity increased in about 40m Ha. in the same region. Similar effects have also happened in Uruguay, Brazil, Northern Argentina and parts of Bolivia (Northern Highlands, Andean Valleys and Eastern Lowlands regions), as they are also being observed in Northern latitudes (Canada, Northern Europe, Northern US, Russia). According to IPCC predictions this process would continue as the climate warms up. Some already arid and semi-arid places will become drier and less hospitable, of course, while others become more productive. Integrated assessments of the impact of climate change on agriculture and prospects for agriculture at the end of the 21st century are on the whole positive (more food per person, few people undernourished), not counting expected decline in fertility not included in AR4 population projections); in all these assessments the percent (net) impact of climate change on the 2080-2100 world agriculture is positive, and relatively small, compared with other factors driving agricultural production: see Fischer et al (refs). Assessment using Ricardian models (instead of integrated assessment techniques), like those by Mendelsohn and associates (refs) come to similar conclusions.
    This does not mean that all will be for the best in the best possible world. Climate change may be disruptive, like other phenomena such as violence or economic downturns. Life is not easy. But one has to figure out things in the more accurate manner possible.
    PNUMA, Programa de Naciones Unidas para el Medio Ambiente (UNEP, United Nations Environment Programme), 2006. Impactos y vulnerabilidad al cambio climático en la región (Chapter IV) in: El cambio climático en América Latina y el Caribe. http://www.crid.or.cr/digitalizacion/pdf/spa/doc16604/doc16604-3a.pdf.
    Fischer G., M.Shah & H. van Velthuizen, 2002a. Climate change and agricultural vulnerability. A special report, prepared by IIASA as a contribution to the World Summit on Sustainable Development, Johannesburg. Laxenburg (Austria): IIASA. http://www.iiasa.ac.at/Admin/PUB/Documents/XO-02-001.pdf.
    Fischer, Günther; Harrij van Velthuizen; Mahendra Shah & Freddy O.Nachtergaele, 2002b. Global agro-ecolo­gi­cal assessment for agriculture in the 21st century: methodology and results. IIASA RR-02-02. Laxen­burg, Austria: IIASA. http://www.iiasa.ac.at/Admin/PUB/Documents/RR-02-002.pdf
    Fischer, G., M.Shah, F.N.Tubiello & H.van Velthuizen, 2005. Socio-economic and climate change impacts on agriculture: an integrated assessment, 1990″“2080. Philosophical Transactions of the Royal Society, Series B, 360:2067-2083.
    Mendelsohn, Robert & Michelle Reinsborough. 2007. A Ricardian analysis of US and Canadian farmland. Climatic Change 81:9″“17.
    Mendelsohn, Robert & William D. Nordhaus. 1999. The impact of global warming on agriculture: A Ricardian analysis: Reply. American Economic Review 89(4): 1053″“1055.
    Mendelsohn, Robert, 2000. Measuring the effect of climate change on developing-country agriculture. In FAO 2000, Two essays on climate change and agriculture – A developing country perspective. FAO Economic and Social Development Papers No.145. Fao, Rome. http://www.fao.org/docrep/003/x8044e/x8044e00.htm.
    Mendelsohn, Robert & Ariel Dinar, 2009. Climate change and agriculture: An economic analysis of global impacts, adaptation and distributional effects. Cheltenham (UK): Eduard Elgar.

  • Steve Bloom

    “Under question” by who, Shub?

  • http://www.scholarsandrogues.com Brian Angliss

    Shub – Fertilizer is not necessarily a good long term solution, although it could certainly help over the short term.  The long term problem with fertilizer is not climate related, however, but is rather an issue of sustainable agriculture and nutrient flux into waterways.
    There is a climate related issue, however, which comes down to “how many societies can afford to buy fertilizer?”  I don’t know the answer to that question, but it’s probably a reasonable starting point to guess that areas were subsistence farming is common probably don’t have enough wealth to rely on fertilizer.  Instead they need to rely on nitrogen fixing bacteria, and there’s been some recent research that indicates that the loss of nitrogen fixing in the tropics due to rising temperatures will more than offset the gains in fixing in the temperate regions.  It’s still relatively new research and I haven’t revisited it to see if the research is still solid.
    Hector – I wasn’t thinking specific locations, just taking issue with your suggestion (perhaps unintentional) that widespread problems couldn’t have global ramifications.  However, if you look at the graphs at the link Kieth provided, they show that the tropics are expected to dry significantly while the extratropics are expected to get wetter.  I haven’t yet read the paper to say much beyond that, however.

  • Steve Bloom

    “the IPCC envisages increased wetness over the Amazon basin and the Andes mountains”

    Um, not exactly, Hector.   And does that long list of citations actually represent the state of the science?

  • Steve Bloom

    Brian, note also that there appears to be a phosphates problem on the horizon.  FYI I haven’t researched beyond that article.

  • Hector M.

    the problems that climate change may cause to subsistence agriculture would happen mostly in the second half of the 21st century. Even in tropical zones a moderate warming of 1-2° may be beneficial, although higher temp increases may be harmful.
    Now, this means that the children or grandchildren of today’s subsistence farmers would have to deal with that problem, say in 2070, with the per capita income they would have at that time, and the technology available at that time.
    I have done some calculations about economic and demographic growth for those areas, of a very conservative nature, using currently available UN population projections (that still do not account for the extent of fertility declines observed, and are very conservative about migration), and using very conservative projections of GDP growth, something like one third of the growth rates observed during the latest 60, 40 or 20 years. The results are that very poor countries (such as Haiti and many African countries) will be approaching the per capita GDP levels of today’s Western Europe, and that, allowing for an (improbable) worsening of today’s income distribution, the lowest decile’s average income would be about two to four times the meagre World Bank daily poverty line of $2.50 (international purchasing power parity dollars), more than enough to access sufficient food. Societies even below that level of development have today nearly zero undernourishment (as per FAO definition) and negligible malnutrition (as per the anthropometric WHO definition), and infrasubsistence farmers are practically non existent, in the sense that farmers are reduced to a minority in a predominantly urban population, and rely mostly on the market for their income and consumption (as they already do in most of Africa, Asia and Latin America). Food security, as defined by the World Food Summits, is all about access to food, rather than being able to grow your own food. Access meaning physical and economic access; since physical availability and access is not generally a problem, and less so in the future according to available projections, the possible problem would be economic access, and this is practically ensured once economies pass a level of about $12,000 per capita (again in PPP international dollars). Whatever may climate change do to subsistence farmers, there would be few of them around by 2100 who depend on their own food production to subsist. Of course, these are projections, not reality, but far more reliable than many climate projections, I surmise, especially because they are all built on the worst possible scenario for economic growth (if growth in the developing countries continues at past rates, and I mean outside China, these projections would be rapidly surpassed).
    A personal note: two of my own grandparents were subsistence farmers in Southern Italy in the 1900s, when like so many millions they escaped poverty-stricken Europe to make a new life in the New World. Neither them in their new home, or any of their children, to say nothing of grandchildren, were subsistence farmers anymore. Neither were those relatives of theirs who remained in Europe, e.g. in Italy: their region of origin is now thriving at about $40,000 per capita, with no poverty to speak of. The story would be probably similar for the Haitian and Senegalese and Filipino migrants of our days, whose lives are better than ever in their new residence countries, and whose remittances keep their people in the old country going along as well, and this is only the first generation migrants for most of them: wait for the second or third generation of European or American immigrant families. Ceteris will never be paribus for them.

  • Hector M.

    Steve Bloom (October 20th, 2010 at 3:58 pm):
    Please have a look at Figure TS30 and the central panel of Figure 11.15, in the WG1 AR4 report. Please remember that the Western Amazon (the core rainforest) does not have a dry season (except in the Andean springs of its rivers), and that the Central and Eastern Amazon region drier (not dry) season occurs in May-September.
    Some models ASSUMING an intensification of El Niño have predicted a drier Amazon, but you cannot assume that, especially in the relatively short term of one century or so.
    Regarding my citations: about  climate change impact on agriculture evaluated through Integrated Assessment and/or Ricardian models (the only valid methods I know of, especially the first kind mentioned), the references cited are the central ones. If you know of other studies of the kind, that refute these and conclude otherwise, please bring them to my notice: I would be quite interested. I know of several reports on the matter, addressed to a wide audience, but I mean hands-on scholarly research.

  • Hector M.

    fertilizer could be realiable also in the long term, provided you do not give farmers extraordinary subsidies allowing them to pour nearly a ton of fertilizer per hectare per year, as they do in many parts of Western Europe nowadays. If plants take nitrogen from the soil, and not all crops are leguminous plants (able to take Nitrogen from the air), you need to restore N levels to the soil, in the amounts necessary for crops to prosper, and no more. You cannot blame fertilizer for the excesses, just as you cannot blame car-makers and prudent drivers (or for that matter, gasoline) for the disasters caused by drunken morons driving at outrageously high speeds.

  • Steve Bloom

    I was just looking at the annuals, Hector.  Based on that, your statement is still incorrect.  I haven’t looked into the details of your claim about the models, but the moment you add that caveat you’re no longer quoting the AR4, are you?  Personally I would look to more recent work since things have changed since then, but if you’re going to call on the AR4’s authority you need to do so in a consistent, transparent way.

    Just out of curiosity, of that long string of papers, which do you feel does the best job of summarizing the state of things?  If you can’t narrow it down enough so that someone won’t be wasting a lot of time checking, you’re just engaged in a Gish Gallop.  Best would be to use direct references to and quotes from those papers.

  • http://nigguraths.wordpress.com Shub

    You’ve done a wide extrapolation of a meta-analysis of studies that looked at protein content of plants yielding grain, with scant data for the crop grown under differing N2 conditions, presented in a Bland-Altman plot, which has a significant amount of variation, as is clearly evident in the graph (figure 4).

    There is only so much you can conclude from results such as those presented in figure 4. I wouldn’t make much of it. But…

    Steve B,
    The IPCC itself does not place much stock in precipitation trends arrived at by models; different parts of the AR4 can be taken to mean whatever the reader fancies. The WGI contains model projections of precipitation; compare that with the Eliasch review model outputs; the conclusions are the exact opposite. Look at Jupp et al, 2010. Look at Bombardi and Carvalho, 2010. The long-term TRMM data does not show any significant decline. Zhang et al, 2009 (Science) has a positive value for ‘anthropogenic contribution in Amazon rainfall”. Hector is probably referring to the WG2 statement, referring to increased precipitation trends observed in parts of South America.

    And values from q10, as used in the paper you linked to, are at odds with Mahecha et al, 2010 (Science mag).

  • Jack Hughes

    Hi dudes,
    “Drought” is an Anglo-Saxon word. Does anybody here think they invented a word for something they had never seen – just in case ….

  • Hector M.

    Steve Bloom suggested (at
    that the IPCC did not quite foresee that the Amazon would become wetter due to climate change. I have already referred him to the specific figures (and accompanying text)  in the AR4 WG1 report  showing exactly what I had said. But I have also looked at the reference to the IPCC kindly provided by Steve as showing that the IPCC had a different opinion. It is in section of the WG1 report, and the relevant paragraph says:
    “Several land cover change studies have explicitly assessed the potential impacts (limited to biophysical effects) associated with specific future SRES land cover change scenarios, and the interaction between land cover change and greenhouse gas forcings (De Fries et al., 2002; Maynard and Royer, 2004a; Feddema et al., 2005; Sitch et al., 2005; Voldoire, 2006). In the A2 scenario, large-scale Amazon deforestation could double the expected warming in the region (De Fries et al., 2002; Feddema et al., 2005).”
    Now, this is mostly about deforestation, which in turn may enhance the effects of warming, and refers specifically to wholesale (“large scale”) deforestation. There have been other studies (like Nepstad 2008) also hypothesizing mass deforestation leading to more forest fires in a context of increased drought (supposed to be caused by an assumed enhancing of El Niño).
    But apart from no sign having been identified of such intensification of El Niño in projections up to 2100 or beyond, the fact is that deforestation on a large scale is simply not occurring. The historical rate of deforestation in the past is inthe order of 0.22 percent per year, occurring mostly at the savannas and open bush areas at the borders of the basin; due to new plantations and regrowth, net change in forest area proceeds even slower, at about 0.1% per year. Moreover, the rate is declining and could not be maintained for long anyway, since additional suitable land for grazing or crops is becoming relatively scarce in the Amazon. The vast rainforest “core” of the region is not suitable at all, except on a very limited scale in specific areas.
    Besides, the Brazilian government has developed a wide array of policies to stop deforestation, which is now proceeding at extremely low rates and still falling, concentrated mostly in one single State (Pará) where it is also declining. The average annual deforestation of about 21,000 sq.km per year prevailing in the 1980s (a year is here the 12 months to mid-year) were reduced to an average 14,000 sq km in the 1990s, increased to about 24,000 sq.km/yr in 2003 and 2004, but started rapidly to decline to 16000 sq.km/yr in 2005 and 2006, about 11000 sq./yr in 2007-08, and 7400 sq km in 2009.  Results for 2010 are not yet available from the Brazilian government satellite-based PRODES program (http://www.obt.inpe.br/prodes/index.html) but monthly preliminary data about deforestation “alerts” for their DETER program (http://www.obt.inpe.br/deter/) suggest an even lower level for this year (to be published probably by November). This decline is not accidental but due to an energetic policy of creating federal reserve areas and enforcing the law in the Amazon area, and also policies discouraging would-be settlers. In fact, total agricultural land in Brazil (for crops or grazing) remains practically unchanged since the mid 1990s in spite of large increases of crops over previously grazing lands in the Cerrado (savannas) region to the East of the Amazon.
    Therefore the prospect of “large scale” deforestation taking place in the coming decades is not a serious probability. It is even not even theoretically admissible since most of the core rainforest region is not suitable for agriculture or livestock, except in very specific locations. Only the fringe savannas and bushes are. The Nepstad idea that in severe and prolonged droughts there would be widespread forest fires wiping out large portions of the forest is also quite far-fetched. Even more are the ideas one can find in the IPCC WG2 report, of Amazongate fame, that even “a slight decline” in Amazon precipitation (let alone a prolonged drought) could cause widespread mortality of trees and tip the scale towards the savannisation of much of the forest. The only “evidence” for that was an experiment in which some hectares of forest were roofed with plastic to keep them without any rainfall for several years, after which of course many trees suffered and tree mortality increased. Never mind that several years of total rainfall deprivation are unheard of in the Amazon, nor foreseen by the IPCC projections. But one can write anything on paper.
    Thus I stand by my original contention that climate change is envisaged by the IPCC to cause increased wetness and precipitation over the Amazon. I also add that wholesale Amazon deforestation is just not occurring, and unlikely to occur in the near future.

  • Hector M.

    My precedent comment on the Amazon refers to S.Bloom comment at October 20th, 2010 at 3:58 pm.

  • Hector M.

    Shub says that “Hector is probably referring to the WG2 statement, referring to increased precipitation trends observed in parts of South America.”
    No, I was referring to WG1 precipitation projections, which are for increased rainfall over the Amazon (Fig 15.3 and TS30), and accompanying text. My main argument is derived from AR4 WG1, even if I am not a blind believer in everything contained therein. WG2, not in my sole opinion but on many others’ including the IAC, is not of the same quality level, and most particularly regarding some topics such as Himalayan glaciers and Amazon dieback. Which does not mean that everything is rubbish there, either.

  • Hector M.

    Steve asks me: “of that long string of papers, which do you feel does the best job of summarizing the state of things?”
    Steve, about impact on agriculture and food security I would refer you to Fischer et al 2002a,b, and (for a model including water and irrigation) 2007. Mendelsohn 2000 contains an assessment of the whole world agriculture, using Ricardian models based on aggregated (district) data, while Mendelsohn & Dinar 2009 use relatively small samples of farms in several countries (with less statistical significance all in all, I daresay), and do not contain an overall planet-level assessment as does Mendelsohn 2000, which is a pity. However, this is not a matter to be summarized in one paper or one soundbite, I’m afraid.

  • Steve Bloom

    Shub, you didn’t even notice that Zhang and Running considered more than one value for Q10, did you?  Do you even understand what the differences mean, especially since the two papers were looking at different things using different data?  Note also that Z+R ran in Science the week after Mahecha et al. did, that there was a second related paper (Beer et al.) published with Mehecha and a commentary on both, and that all of these folks are rather close colleagues, all of which points at there not being a meaningful discrepancy of the sort you infer?

    I’ll respond to Hector directly.  What bothers me is the misquote of the AR4 WG1 he put right up front.     


  • Hector M.

    Regarding the IPCC projections of precipitation over the Amazon basin, and after I referred him to two figures in the AR4 WG1 report, Steve Bloom Says (October 20th, 2010 at 5:35 pm): “I was just looking at the annuals, Hector.  Based on that, your statement is still incorrect.”
    Well, it is not so, I humbly dare to insist. Look again, Steve, at the lower panel (projections) in Figure TS30, showing an annual increase in wetness over the Amazon, and the same when you look at Fig 11.15 (the left map of the central panel). Notice also that the latter  figure central panel gives rainfall in percent variation, not millimeters, but one can easily figure out that the decline in precipitation in June-August over some parts of the Eastern Amazon (about -10%) correspond to a decline of about 1-2 mm per month, while the corresponding increases in the wet season (Dec to Feb), about +10-20%, correspond to about 20-40 mm per month. Thus the annual average increase. It’s not Holy Scripture, it’s just the IPCC, but there you are.

  • Steve Bloom

    Drat, the software just ate my reply to Hector.  I’ll have to reconstruct it, which I can’t until later.  Also, in my reply to Shub that should be Zhao, not Zhang.

  • Shub

    Steve B
    While your social network analysis is interesting,  it is quite easily observable that the Amazon dieback community and journals keep things ‘interesting’ by publishing countervailing papers one after the other.

    Everyone knows scientists play these games. But how should that concern us?

    The fact remains that Zhao and Running derive reductions in NPP over the past decade using q10=2 or a formula that will yield q10 values higher than 2, whereas Mahecha et al, derive from observations,  a value of ~1.4, in other words, less than 2,  seems to have been overlooked by you.

    Do you know what that means, in the context of the droughts that we are discussing?

    You are right that the WG2 report only briefly and patchily reviews rainfall projections over South America. But even they note the varied outputs for precipitation by the different GCMs.

  • Hector M.

    Shub, quite right. But the projections shown by WG1 in the figures I cited were only those on which more than two thirds of all models agreed.

  • Steve Bloom

    Sorry, Shub, I asked you first.  Now we find out if you can read and comprehend these papers.

  • dbleader61

    @43 Steve Bloom Says:

    Drat, the software just ate my reply to Hector.  I’ll have to reconstruct it, which I can’t until later.  Also, in my reply to Shub that should be Zhao, not Zhang.

    I think your software is doing a favour for you, Steve.  Hector has you beat, hands down.  He’s got you with logic, detail, sources, and ability to summarize.       

    You should concede on this one.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     

  • Ed Forbes

    As the world cools, water is trapped in the glaciers, as the world warms, the earth sees more rain. Very basic, very well known. The world dries out and sees large  deserts being formed during periods of large scale glacier advance. 

    A warm world is a wet world in any situation seen in earths history over the last many millions of years.


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Collide-a-Scape is an archived Discover blog. Keep up with Keith's current work at http://www.keithkloor.com/

About Keith Kloor

Keith Kloor is a NYC-based journalist, and an adjunct professor of journalism at New York University. His work has appeared in Slate, Science, Discover, and the Washington Post magazine, among other outlets. From 2000 to 2008, he was a senior editor at Audubon Magazine. In 2008-2009, he was a Fellow at the University of Colorado’s Center for Environmental Journalism, in Boulder, where he studied how a changing environment (including climate change) influenced prehistoric societies in the U.S. Southwest. He covers a wide range of topics, from conservation biology and biotechnology to urban planning and archaeology.


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