Climate change, agriculture and food security

An interview with MIT's John Reilly 

September 12, 2014

Agriculture and climate change carry significant implications for one another. Shifts in worldwide climate have the potential to impact global food production and regional food security. Meanwhile, agriculture is a significant contributor to the causes that are believed to underlie climate change. To better understand linkages between agriculture and global climate change, Cargill interviewed John Reilly, co-director of the Massachusetts Institute of Technology’s Joint Program on the Science and Policy of Global Change. Cargill has been a sponsor of MIT's program since 2008. It is one of several university programs Cargill funds that are helping us better understand climate science, impact on crop yields, adaptability, sustainability and implications for food security.

Q: Why is MIT doing research on climate change as it impacts food security

John: Our program was created more than 20 years ago to look at climate change as an integrated set of problems. This means looking at both how to reduce climate change by mitigating human contributions such as greenhouse gases (GHGs) and also how climate change will impact society. There is no sector of society that we rely on that’s more exposed to weather than farming. So we couldn’t very well tackle the problem without thinking about food.

For us, it’s essential to look at how a variety of factors interact on a fundamental level. Food security isn’t separate from water availability. Water availability isn’t separate from energy consumption. This integrated examination is where we differentiate our research from many others.

Q: So what does your research show about how that complex of factors might impact the world’s food system? Specifically, how could climate change impact the world’s breadbaskets, like central North America, Brazil and Eastern Europe?

John: Climate change is such a broad and complex issue that understanding how certain aspects of food production will be impacted remains challenging. But there are some things the scientific community knows.

We know that higher levels of CO2 in the atmosphere benefit most crops, such as wheat and rice. The main exception is mainly maize and sorghum, which use CO2 in a different way and thus benefit less. Warmer temperatures in areas farther from the equator will extend the growing season. But higher temperatures in places near the equator will cause yields to fall. So on a global level, those gains and losses in yield may balance out. But there will be shifts, certainly, in where crops are produced, which types of crops are produced and what practices are used to manage their production. CO2 also affects weeds, with some of the world’s worst weeds benefitting more than crops. Climate change also affects insect pests, crop diseases and water.

The water situation is somewhat difficult to predict. In the U.S., many climate projections show less water availability in southern and southwestern parts of the country, and in the Plains states, areas that already rely heavily on irrigation.  Worldwide, something like 17 percent of crop land is irrigated, but that land produces about 40 percent of yields, and so what happens to water supplies for irrigation can have an effect on food supply disproportionate to the land area irrigated.

Q: I’ve heard people talk about improved practices in water use, like drip irrigation, that could reduce the amount of water used by agriculture. Do you see those advances having a strong impact on water use?

John: Yes. If you look at field efficiency, getting just the right amount of water to plants through something like drip irrigation would improve water consumption. But the thing to remember is that irrigation occurs in a river shed, and so a lot of the very inefficient use of water for agriculture occurs at the top of the basin, and that water ends up flowing back into the basin and is used again by agriculture later on. So improving the efficiency upstream doesn’t necessarily mean overall gains for the system, because that water would’ve gone back in anyway.

Having said that, sprinkler irrigation methods that lead to a lot of water evaporation mean that it probably doesn’t end up back in that basin. The same goes for ditch irrigation that causes evaporation. But it’s even more complex than that. Evaporated water doesn’t disappear—it will lead to rain somewhere, possibly on land.   There is evidence that large irrigation in the Central Valley of California has increased precipitation in the central mountain areas of the U.S.

Our models point toward mid-continental and lower-latitude areas drying, whereas regions farther away from the equator may receive more precipitation. But too much water can also cause problems with flooding.

Climate change generally speeds up the hydrological cycle, causing more evaporation, and since what goes up must come down, more precipitation. And with higher temperatures, plants need more water, so the same amount of precipitation doesn’t go as far. So all of this demonstrates the amount of complexity around just one issue: water availability.

Q: What other significant impacts could we see on food security?

John: If regions near the equator that are currently very productive suffer significant yield losses, but those are balanced out with gains in colder areas, then world prices may not change much or could fall. While not a bad outcome for global food supply, lower prices coupled with yield loss would mean that farmers in those equatorial regions will face economic hardship and dislocation. If those countries are accustomed to depending on local agriculture and they can’t generate other economic activity in order to be able to buy food, the conditions could contribute to political instability and “environmental refugees.” Or if yield losses are more widespread, then food prices could rise. Some have pointed to high food prices as a contributing factor to the Arab Spring.

Q: We’ve talked about how climate change could impact agriculture, but let’s look at the reverse. What are the largest ways that agriculture is contributing to climate change today

John: I would point to five things.

First, fossil energy is used variously in agriculture. It’s a large part of fertilizer production. Farmers use fuels to drive tractors and pump water. But that alone adds up to a fairly small fraction of global GHGs, maybe 1 or 2 percent.

Second, agriculture also produces methane and nitrous oxide, powerful GHGs. In this category of gases, agriculture contributes 40 to 60 percent of world totals produced by humans. These two categories together account for 10 to 12 percent of global GHG emissions.

The third big area is CO2 emissions from land use change. We don’t have a highly accurate sense of just how much this contributes, and it varies year to year.  Estimates put the contribution in the neighborhood of 12 percent of global GHGs for the period from 1990 to 2009. And added to the first two categories, that brings us to agriculture producing about 20 or 25 percent of global GHG totals.

The fourth area is tropospheric ozone and aerosols. These gases affect precipitation. Particularly in developing countries, you have a lot of land clearing and biomass burning. Burning an open field is a very inefficient approach that produces a lot of ozone precursors and aerosols. We think of smoke stacks as producing smog, but surprisingly, this biomass burning in agriculture may contribute up to half of the global emissions of these types of gases.

The fifth area is that when we have massive change of the planet’s surface from forest to grassland or cropland, this changes the hydrological balance of the planet and also the radiative balance. Forests are quite dark, so they absorb a lot of sunlight, which causes surface heating. If you cut down forests, open land is more reflective, so this can actually have a cooling effect.

So overall, agriculture does have a significant impact on climate change, especially when comparing the relative size of agriculture in the overall economy to other industries.

Q: From a policy standpoint, what balance should we strike between mitigating climate change and adapting to it, in order to protect global food production? Is the global food system adaptive enough to make necessary adjustments?

John: I think the worldwide food system can adapt a lot. But the balance between mitigation and adaptation isn’t just about food. In point of fact, right now we are talking a lot about mitigating GHGs, but the world is doing very little. I don’t know what the exact balance is, but clearly moving toward more mitigation is necessary to stabilize atmospheric concentrations of GHGs at a level that isn’t ridiculous. It would be nice to talk about balance, but at this point our main message is that we are not doing enough to mitigate.

The thing about adaptation is that individual farmers, companies and nations, when they see bad things happening to them, see it as in their private interest to do as much as they can to avoid these negative ramifications. Their individual actions don’t require common agreement. But on the mitigation side, no one country or actor is big enough to have much effect if others don’t follow suit. So, unfortunately, mitigation requires, if not global agreement, at least agreement among the top 10 or 20 major emitters like the U.S., China, and India, to have much of an effect.

Q: At Cargill, we talk about the necessity of trust-based free trade to establish an integrated global system of agriculture. But you also have movements that stress the importance of eating locally to mitigate climate change. And some governments also are expressing a desire for food self-sufficiency. Is one of these mindsets better than the other?

John: I’m very much in the camp that says we need pretty free and unfettered trade. With these large potential changes in where food might be produced, if you’re trying to rely on your own resources and the climate shifts against you, you’re going to be in trouble if you steadfastly pursue self-sufficiency. I think we would be better served by having a broadly operating trade system.

If you look at the run up in food prices around 2007, some people attributed that to biofuels or crop failures, but most agricultural economists agree that the crisis was highly aggravated by the fact that some governments started banning exports and hoarding food.

The challenge is for countries to feel confident that the international system they’re being asked to rely on is actually reliable.  Of course, there are some potential risks from free trade. If some countries are not protecting their forests, freer trade could move production to these countries and result in a lot of deforestation. So just a bit of a caution there—we need to attend, as equally as we can, to environmental protection worldwide so inexpensive food doesn’t mean environmental problems in another corner of the world.

Q: Do you think biofuels can help mitigate GHGs overall?

John: Practiced the right way, they can probably contribute to the solution. When you burn biofuels, it releases CO2 just like traditional fuel. But growing plants for more biofuels reabsorbs CO2. As we produce corn ethanol in the U.S. today, we use a lot of fossil energy in the distillation process. So that reduces a lot of the potential advantages.
If you are growing biofuel crops on degraded pastureland and fertilizing them, then you could have a buildup of carbon in the soil. But if you’re cutting down virgin forest for cropland to produce biofuels, that results in a big carbon release.

One really positive potential solution is cellulosic biofuels, which use biomass as energy in the distillation process. If you used that and then also captured the CO2 and stored it underground, what’s called “carbon capture storage,” you could actually make biofuels a net negative contributor of CO2.