Half of world’s population could face climate-driven food crisis by 2100

“Ignoring climate projections at this stage will only result in the worst form of triage.”

The headline is from the University of Washington news release on a study in Science, “Historical Warnings of Future Food Insecurity with Unprecedented Seasonal Heat.” The quote is the study’s powerful final sentence. The release explains:

Rapidly warming climate is likely to seriously alter crop yields in the tropics and subtropics by the end of this century and, without adaptation, will leave half the world’s population facing serious food shortages, new research shows….

“The stresses on global food production from temperature alone are going to be huge, and that doesn’t take into account water supplies stressed by the higher temperatures,” said David Battisti, a University of Washington atmospheric sciences professor.

Worse, the study must also be considered a serious underestimate of likely impacts since, as is common in such analyses, they based their simulations on “the ‘middle of the road’ emission scenario, A1B.” In 2100, A1B hits about 700 ppm with average global temperatures “only” about 3°C warmer than today. In fact, on our current emissions path, we are going to get much, much hotter (see Hadley Center: “Catastrophic” 5-7°C warming by 2100 on current emissions path).

Figure 2

Figure. “Histogram of summer (June, July, and August) averaged temperatures (blue) observed from 1900 to 2006 and (red) projected for 2090 for (A) France, (B) Ukraine, and (C) the Sahel. Temperature is plotted as the departure from the long-term (1900–2006) climatological mean (21). The data are normalized to represent 100 seasons in each histogram. In (A), for example, the hottest summer on record in France (2003) is 3.6°C above the long-term climatology. The average summer temperature in 2090 [assuming A1B] is projected to be 3.7°C greater than the long-term climatological average.”

The results are still alarming:

We used observational data and output from 23 global climate models to show a high probability (>90%) that growing season temperatures in the tropics and subtropics by the end of the 21st century will exceed the most extreme seasonal temperatures recorded from 1900 to 2006. In temperate regions, the hottest seasons on record will represent the future norm in many locations.

If the authors had modeled the Hadley business-as-usual scenario, then I suspect even in the temperate regions, growing season temperatures in 2100 would exceed the most extreme temperatures recorded in the past century — while the tropics and subtropics will be utterly brutalized.

In the tropics, the higher temperatures can be expected to cut yields of the primary food crops, maize and rice, by 20 to 40 percent, the researchers said. But rising temperatures also are likely to play havoc with soil moisture, cutting yields even further.

Indeed, along with the temperature rise, we face desertification of one third the planet and moderate drought over half the planet. Soil moisture drops over large parts of the planet will exceed that of the 1930s Dust Bowl!

“We have to be rethinking agriculture systems as a whole, not only thinking about new varieties but also recognizing that many people will just move out of agriculture, and even move from the lands where they live now,” Naylor said.

Currently 3 billion people live in the tropics and subtropics, and their number is expected to nearly double by the end of the century. The area stretches from the southern United States to northern Argentina and southern Brazil, from northern India and southern China to southern Australia and all of Africa….

“When all the signs point in the same direction, and in this case it’s a bad direction, you pretty much know what’s going to happen,” Battisti said. “You are talking about hundreds of millions of additional people looking for food because they won’t be able to find it where they find it now.”

The study warns that the rich countries will also suffer:

Severe heat in the summer of 2003 affected food production as well as human lives in Europe. Record high daytime and nighttime temperatures over most of the summer growing season reduced leaf and grain-filling development of key crops such as maize, fruit trees, and vineyards; accelerated crop ripening and maturity by 10 to 20 days; caused livestock to be stressed; and resulted in reduced soil moisture and increased water consumption in agriculture. Italy experienced a record drop in maize yields of 36% from a year earlier, whereas in France maize and fodder production fell by 30%, fruit harvests declined by 25%, and wheat harvests (which had nearly reached maturity by the time the heat set in) declined by 21%.

Yet, by century’s end, the summer of 2003 will be considered relatively cool. What do the authors recommend?

It will be extremely difficult to balance food deficits in one part of the world with food surpluses in another, unless major adaptation investments are made soon to develop crop varieties that are tolerant to heat and heat-induced water stress and irrigation systems suitable for diverse agroecosystems. The genetics, genomics, breeding, management, and engineering capacity for such adaptation can be developed globally but will be costly and will require political prioritization. National and international agricultural investments have been waning in recent decades and remain insufficient to meet near-term food needs in the world’s poorest countries, to say nothing of longer-term needs in the face of climate change.

Rather lamely, the study never mentions the possibility of mitigation, of keeping total global warming to far less than 3°C, as a strategy. Why? The final paragraph of the release states:

“You can let it happen and painfully adapt, or you can plan for it,” he said. “You also could mitigate it and not let it happen in the first place, but we’re not doing a very good job of that.”

Okay. Fine. Another understatement of the year.

But since the authors clearly assert in the study that we’re also not doing a very good job of adaptation or investment in agriculture, I’m not sure why it makes more sense for them to push adaptation as a solution than mitigation. In fact, we’ll need to do both, but absent serious mitigation, “climate adaptation” may be little more than cruel doubletalk for most of the world.

[Note to authors — if you diss/ignore mitigation, than you need to model an emissions scenarios that does not have much if any mitigation. Try A1F1 next time.]

If we end up with 5.5°C warming or more by century’s end, and if you throw in the desertification and sharps drops in soil moisture — plus the loss of the inland glaciers that act as reservoirs for so many major river systems around the globe — then simply developing crops “that are tolerant to heat and heat-induced water stress” along with better irrigation is likely to prove utterly inadequate and irrelevant for billions of people.

The only genuine hope for avoiding “the worst form of triage” is aggressive and immediate greenhouse gas mitigation.

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13 Responses to Half of world’s population could face climate-driven food crisis by 2100

  1. Another prescription for saving life as we know it and the planet as a fit place for habitation by our children and coming generations could be to focus more of our attention on the global challenges presented to the human family by the overpopulation of Earth by the human species.

    One of the world’s finest scientists, Dr. James E. Hansen says, “Tell Barack Obama the truth – the whole truth” about human-driven climate destabilization.

    Perhaps here and now, we will find that other great scientists, the likes of Jim Hansen and John Holdren, will speak out loudly, clearly and often to tell Barack Obama the truth – the whole truth about the apparently unforeseen and unfortunately unwelcome scientific research of human population dynamics as essentially similar to the population dynamics of other species; about absolute global human population numbers as a function of the world’s food supply; about human population numbers being determined by food availability; and about the daunting threats potentially posed to the family of humanity and life as we know it, even in these early years of Century XXI, resulting from the skyrocketing growth of human population numbers worldwide.

    For repeated references to the good science of Russell Hopfenberg, Ph.D., and David Pimentel, Ph.D., please click on the links below. Comments from one and all are invited.

    Steven Earl Salmony
    AWAREness Campaign on The Human Population,
    established 2001

  2. john says:

    Why is it that scientists are so conservative with data? For example, projecting crop loss from heat alone:

    [….cutting] yields of the primary food crops, maize and rice, by 20 to 40 percent, the researchers said. But rising temperatures also are likely to play havoc with soil moisture, cutting yields even further.

    Well, we pretty much know that soil moisture effects would seriously increase crop loss — so 20 to 40 is an understatement. We also know that A1B was outdated on the day it was released.

    This kind of “analysis” and these kinds of reports do a huge disservice, by grossly underestimating the consequences of AGW.

  3. Kathy N says:

    I so agree John that this type of report has becaome almost worthless because the outcomes are so far from whay we know is really going to happen. Also there is the problem of it being worse in certain areas long before 2100. This will give us a domino affect as far as trying to supply badly hit areas over time. They make it sound like this will be an across the board even event. Instead we will have some areas feeling this affect years before others which will stress the areas that are doing somewhat better in production. Then the mass migration of people leaving drought areas will also domino over time. We simply must start at stopping emmisions or as the climate systems are already telling us go very much out of our controll

  4. Wes Rolley says:

    The real source of much of my stress, frustration at politicians who buy in to the idea that ecology is a cost for the economic status quo and so talk about solving the problems of global warming but, when push comes to shove, adopt policies that accelerate it.

    Then they ask why the public rates Congress lower even than “W”. I want to see Reid and Pelosi have the guts to really take this issue to the people, but Reid has no courage and Pelosi only knows electoral calculus. So, nothing will happen.

    I am beginning to think that Gore and McKibben are right. It is time for people to take this issue to the streets and practice non-violent civil disobedience. Maybe then, our Congressional leaders will begin to think it is really a problem that needs action rather than words.

    They would rather pass comparatively meaningless resolutions in support of prayer at school board meetings. (111th Congress, Sen.Res. 5)
    Wes Rolley is CoChiar, EcoAction Committee, Green Party US

  5. Noted economist William Cline’s 2007 global agriculture assessment [Global Warming and Agriculture, Peterson Institute for International Economics, presented a compelling case that concluded the impact of a few degrees Celsius increase in global average temperature, coupled with declining precipitation on global agriculture, could lead to crop losses as high as 28% for Africa, 24% for Latin America, 30% to 40% for India, and 21% for all developing countries (Cline, 2007). Even industrialized nations like the United States and Australia will suffer losses, including 30% to 35% in the southeast and southwestern plains of the United States.

    Pertinent to the other CP article on Yale economist Robert Mendelsohn, Cline explains with considerable clarity why economic climate modelers like Mendelsohn (and William Nordhaus) derive results skewed towards low climate damages. For one thing, they overestimate a positive carbon”fertilization” effect on ag productivity. In a separate report published in 2007, “Global scale climate-crop yield relationships and the impacts of recent warming,” Stanford biology professor, Chris Field. director of the Carnegie Institution’s Department of Global Ecology, and his Stanford colleague, David Lobell, published a [], conclude, “Despite the complexity of global food supply, here we show that simple measures of growing season temperatures and precipitation–spatial averages based on the locations of each crop–explain about 30% or more of year-to-year variations in global average yields for the world’s six most widely grown crops. For wheat, maize, and barley, there is a clearly negative response of global yields to increased temperatures. Based on these sensitivities and observed climate trends, we estimate that warming since 1981 has resulted in annual combined losses of these three crops representing roughly 40 MT or $5 billion per year, as of 2002. While these impacts are small relative to the technological yield gains over the same period, the results demonstrate already occurring negative impacts of climate trends on crop yields at the global scale.”

  6. What population? Will we be talking half of 20 billion? Or half of 5 billion? That’s kind of the real issue the study suggests is upon us, no?

  7. Mark says:

    So, what is the planet’s temp anyway? When we talk about 5-7C increase, where are we starting from?

    That may sound dumb, but I live in Minnesota and it’s forecast to be -25F tonight. If you ask folks here, +5-7C sounds pretty good right now. Spare me, I know it’s the weather, but folks just can’t seem to wrap their head around the ‘global’ not ‘local’ thing.

    The ‘average joe’ tends to look at change relative to a known point and it seems the ‘average joe’ doesn’t know what that known point (the average global temp) is. Are we going from 10C to 15-17C or what?


    [JR: It’s an average — the land warms up more than the ocean, the northern latitude more than the tropics. Yes, as places to live go, MN will fare better than most, even with 10C warming of MN. The ideal place to live is not near a coast, not near the subtropics, but near water and arable crop land. MN makes the short list! I’ll probably do a post on this sometime this year.]

  8. Ted Caplow says:

    Hi Joe (we worked together at Cap-E, congrats on a delightfully well written blog!),

    The questions of how hot, how dry, and how food-stressed occupy just one overpopulated arena on the scientific landscape, but in our eagerness to predict the unpredictable we risk not paying nearly enough attention to developing the pragmatic remedies that will be necessary to keep people fed under almost any scenario. The fundamental question in that arena: how do we decouple food production from climate, and how do we make food production a great deal more efficient than it is today? The stable of facts on this issue includes:

    (a) the 1500 mile journey the average grocery item makes from farm to table in the US (actually this figure is from an outdated study and only applies to Iowa, but it is widely quoted, last seen popping up in Dan Kammen’s Ecopolis series on Discovery, and just about everywhere else);

    (b) The US has approximately 3 acres of agriculture per capita. But we could grow all of the vegetables you eat in a year on 2 square meters using modern hydroponic techniques.

    (c) A loaf of bread has about a ton of water baked into it, in the form of loss and runoff from field culture of wheat. Rice is even worse. Average field vegetable farming runs in the range of 120 liters of water per kg. Recirculating hydroponics can cut this to 20 liters.

    (d) We recently looked at the energy footprint of Masdar (Abu Dhabi’s emergent ecopolis) and came to the startling conclusion that air freighting in much of the food for the city’s occupants (a very popular and even necessary way to get your groceries, according to conventional wisdom in that part of the world) would use several times more energy than the entire city will save. Local, high efficiency food production could solve this problem, which is included in the One Planet Living criteria that the project aspires to. And yet, the one area that the master site plan has really not addressed at all is…food.

    Perhaps this is a plug for some of my group’s work on these issues (see or Manhattan’s Science Barge project at, but at this stage in the game I think most of us would agree that mitigating the climate problem must include mitigating the impacts.

  9. Mark says:

    Thanks, Joe, but I’m looking for a number. Something like: ‘The global average temp now is X, so when it goes up 5-7C it will by Y’.


    [JR: I’m afraid that number would be kinda meaningless out of context. Search this blog or the web for Hadley or NASA GISS.]

  10. Stuart says:

    Ted: Soylent Green! (sorry – saw that movie again the other day for the first time in years and it seems more prophetic now)

    Mark: I hear that up here in northern MN all the time. show them Lake Superior is warming faster than the land around it – see Jay Austin’s paper

    Joe: Yeah, but there won’t be any moose, and the mosquitoes will be even worse. I guess I can adopt a southern accent and learn how to catch catfish and bass.

  11. Dano says:


    So, what is the planet’s temp anyway?

    the planet’s temp will be outside of the range for the entire history of agrarian societies. meaning: outside our experience.




  12. shopa says:

    I have invented a new way to move water long distances. It can be used to bring water to areas suffering from droughts.

  13. Vernon says:

    What tripe. The fact is that there is no proof that it is any hotter now than it was during the MWP.

    Huang, Shaopeng, Henry N. Pollack and Po Yu Shen (1997). “Late Quaternary Temperature Changes Seen in Worldwide Continental Heat Flow Measurements.” Geophysical Research Letters 24: 1947—1950.) published a 1997 analysis of 6000 borehole records (boreholes drilled into the ground provide a vertical temperature profile that can be inverted to yield an estimate of the historical surface temperature sequence) from each continent, dating back 20,000 years. It showed that the MWP was much warmer than it is now.

    This was used in the IPCC Report #1 but disappeared with Mann’s Hockey Stick. No one has yet to show that tree rings can be tied to termperature, for exampe IPCC Report #4 admits that the proxie record does not match the instrumented record. If the proxies do not show current warming, what makes anyone think that warming in the past would show in the proxies?

    The whole basis of this is that it has never been this warm before and there is no proof of that.

    [JR: No, the whole basis of this is NOT that it has never been warm this warm before. The whole basis for this is that external forcings warm the planet, and we are now forcing warming at a much faster pace than has ever occurred through natural forcings. There is in fact no evidence that the MWP was a global phenomenon, but there is in fact evidence that we are now warmer than we were back then. See “Sorry deniers, hockey stick gets longer, stronger: Earth hotter now than in past 2,000 years.”