Climate Change and Global Food Production: Q&A with David Lobell

By Alyson Kenward

Rice harvest in Java, Indonesia. Credit: Martijn Nijenhuis/Flickr

With  2011 already off to such a wet start in many parts of the world, concerns of what flooding will do to food prices and availability in the coming months are starting to creep into the news. In Sri Lanka, flooding has devastated rice crops, and in North Dakota, heavy rain and snow is already threatening the spring wheat crop. And all this after last summer’s Russian drought and heat wave helped drive global wheat prices higher.

But while farmers have always had to contend with the vagaries of the weather, a question of increasing importance is how agriculture will be affected by the climate changes projected to occur over the next century. Many scientists are studying which regions of the world may be impacted the most by increasing temperatures and changing precipitation regimes, and what is bound to happen to the supplies of the world’s biggest cash crops, like wheat, corn, rice and soybeans.

A new report, The Food Gap, was released last week from the Universal Ecological Fund, and it has muddied the waters even further. The report reviews how global climate change will affect the fate of crop yields and food prices in 2020. Unfortunately, the report actually misinterpreted the connection between atmospheric concentrations of greenhouse gases like carbon dioxide (CO2) and expected global temperature increases — despite the fact that recent reports from the U.N. Intergovernmental Panel on Climate Change and the National Academy of Sciences clearly identify the most current peer-reviewed understanding of this. The food study suggests that within 9 years, average global temperatures will be an average of 2.4°C warmer than during preindustrial times — or almost 1.5°C warmer than it was just last year.


This exceptionally high temperature projection is completely baseless, as NASA climate modeler Gavin Schmidt explained on the RealClimate blog — it’s more likely that the planet will experience this kind of temperature change over 100 years, not merely one decade. Nevertheless, a number of news outlets published stories on the report’s projections of how this dramatic climate change could impact the global food supply by 2020. Some publications posted corrections to their own stories, but I thought it would be helpful to take a step back and examine climate change and food security in 2020 and beyond. I spoke with Stanford University’s David Lobell, who studies how climate change affects crop yields and food prices. He helped clarify what the current research says about climate change and food security.

Q. The report, the Food Gap, suggests that changes in temperature and precipitation in the next 10 years will dramatically influence how much food is produced in many parts of the world. What are the ways in which climate is connected to food production?

Lobell: Firstly, it’s important to point out that when it comes to crops, there are always going to be troubles brought about by natural variability — we’ll continue to see extreme high and low temperatures and we will also still see droughts and floods. There is no doubt that there will be regional variations in temperature and precipitation in the future, and every region is going to have issues of some kind. That being said, for many parts of the world, consistently rising temperatures will be a problem. In the short term, I’m less convinced that total rainfall will be a big factor, but if precipitation starts to come in less frequent but heavier rainfall events, as is predicted in some regions like India, this could be a problem.

When rain comes in a quick and heavy downpour, as it’s been happening in Australia, most of it just runs off into rivers, so the water isn’t available for the crops. Plus, there is the direct damage from flooding. As a result, over the average growing season for different crops, both the change in average global temperatures and the frequency of heavy rainfall events seem to be getting worse for crops as the overall climate changes. But over just a ten-year period, like what this report is suggesting, it’s very unlikely that any trend due to climate change will be significant relative to natural variation.

Q: The report also says that in the next 10 years, the global production of wheat and corn, for example, won’t meet overall demand for these crops. How specific can you be about how crops will fare?

Lobell: We can’t pinpoint to a specific percentage, how the production of these crops will be in 10 years. It all depends on many factors, like how much land is used to grow crops, what the food prices are, as well as global climate. Yes, in some regions, the land is becoming less suitable for growing crops as temperatures increase. But in other areas, the land is becoming more suitable, so it is tough to predict how much food will be available. Higher temperatures around the world are going to be somewhat damaging for plants. They will lower crop yields and shorten the growing season in the tropics because water will evaporate from the ground faster.

When you look at most regions of the world, one degree of warming will translate to a general loss of five to ten percent crop yield. So, if the global average temperatures change by a couple of degrees, a 15 percent loss in crop yield is feasible, but it just doesn’t look like we will be anywhere near this in the next 10 years, or even the next 20 or 30 years.

 Q: What about the idea that food prices go up by 20 percent by 2020? How much can food prices increase because of climate change?

Lobell: Food prices are determined by all kinds of things. The global population is growing, people are getting richer and eating more meat and dairy. The demand for biofuels is rising. Trade agreements between countries also matter. Climate change is an additional factor on top of all that. One question we've asked is, if you hold everything else constant and just change the climate, what does that do to global prices? Looking at the most plausible climate scenarios, our best guess is that food prices won’t change too much by 2030 because of climate change. But if things are towards the more pessimistic end of what we think is plausible, price increases could be as much 50 percent higher relative to the climate back in 1990. 


David Lobell. Credit: Stanford University

 Q: Don’t plants consume carbon dioxide? So, aren’t they benefiting as atmospheric levels of CO2 increase?

Lobell: Yes, plants do love CO2 — if everything else stayed the same in the future and only CO2 increased, then the plants would benefit. But of course, CO2 isn’t the thing that is changing. As concentrations increase, the climate is also going to change. And if you’re in extreme heat or an extreme drought, having some extra CO2 isn’t going to be much consolation. Plants can only take advantage of more CO2 if they’ve also got all the other nutrients, water, and proper growing conditions they need, and all those other aspects are linked in to climate change. But the main point is yes, higher CO2 helps. Most models that are predicting future food supplies and prices include this beneficial CO2 effect, which is the main reason why we only expect small price changes from rising CO2 emissions in the next couple of decades. 

Q: In terms of which crops will be affected by climate change, what is the biggest concern in the United States?

Lobell: For me, in the U.S., corn is the big question mark. It turns out that the metabolism and growth of corn is not really helped a lot by having more CO2 in the atmosphere, so corn crops aren’t going to see much of that benefit. On the other hand, there are a lot of studies that show pretty clearly that corn crops don’t do well as temperatures increase, in most regions of the country, so there is a big question as to how much corn can continue to thrive.

One of the most interesting things about corn in the U.S. is that there is so much research devoted to this one crop, because it is so vital to our economy, that there is real potential that people will find a way to help the crops adapt to future climate change. It’s a really interesting crop to watch for looking forward.

Q: The report’s predictions are thrown off by the (unlikely) assumption that in the next 10 years, global temperatures will rise 2.4°C higher than the preindustrial average. But if the temperature does increase that much over a longer period of time, like 100 years from now, aren’t all these trends still important?

Lobell: Just getting the general trend correct isn’t good enough for these sorts of reports. The timescale is one of the most important parts of predicting how crops supplies and food prices are going to change. The challenge for those of us working in the field is to understand what all the risks are that we should worry about and which ones are likely to hit first. We need to have a sense of the proper timeline so we can figure out how best to allocate resources to prepare. So to get things right in a general sense, but wrong in terms of timescale is, in some ways, worse than saying nothing at all. When it comes to climate change, scientists already have a picture of all the things we have to worry about in the future and the story is bad enough. There isn’t any need to embellish it with far-fetched, non peer-reviewed claims — it’s just not helpful.