Models Say Climate Change Has Already Whacked Grain Yields


A new study published in Science inputs global grain yields since 1980 and temperature increases into a model and finds that climate change has already reduced yields below what they would otherwise be. From the abstract:

Efforts to anticipate how climate change will affect future food availability can benefit from understanding the impacts of changes to date. Here, we show that in the cropping regions and growing seasons of most countries, with the important exception of the United States, temperature trends for 1980–2008 exceeded one standard deviation of historic year-to-year variability. Models that link yields of the four largest commodity crops to weather indicate that global maize and wheat production declined by 3.8% and 5.5%, respectively, compared to a counterfactual without climate trends. For soybeans and rice, winners and losers largely balanced out. Climate trends were large enough in some countries to offset a significant portion of the increases in average yields that arose from technology, CO2 fertilization, and other factors.

With regard to the new Science study, the New York Times reports:

Wheat, rice, corn and soybeans account for the majority of calories consumed by the human race, either directly or as meat from animals raised on grains. Because demand for these grains is inflexible and rising, the losses from climate change probably accounted for price increases of about 6 percent in the four major commodities, the study's authors found.

At today's grain prices, that calculation implies that climate change is costing consumers, food companies and livestock producers about $60 billion a year.

"We aren't talking about the sky falling," Dr. Lobell said. "But we are talking about billions of dollars of losses. Every little bit of production is valuable when we're trying to feed the world."

If the price estimate is correct, it makes climate change a small contributor to a large trend. The prices of many foodstuffs have doubled or tripled in recent years as a result of a host of factors, including rapidly rising food demand in Asia, government mandates to use crops for biofuel production and extreme weather that may or may not be linked to climate change.

Ah, the vexations of models. But let's assume that the results are correct. Can farmers adapt to man-made climate change over the next century? A recent fascinating study in the Proceedings of the National Academy of Sciences on the expansion of wheat growing areas in North America gives us reasons to think so. That study reports:

The Intergovernmental Panel on Climate Change (IPCC) projects that by 2100 annual mean temperatures in North America will increase by 2 to 3 °C at midlatitude coastal regions and by "up to more than" 5 °C at more northern latitudes. In the main grain-growing areas, the IPCC forecasts temperatures will rise 3 to 4 °C (1). A more recent MIT study suggests far greater changes will occur (2). There are a wide range of estimates of how climate changes will impact agricultural production (37). Numerous researchers have speculated about how farmers might change cultivars, cropping patterns, and farming methods to mitigate some of the costs of abrupt climatic changes (8). Researchers at the International Maize and Wheat Improvement Center (CIMMYT) anticipate that North American wheat farmers may extend the margin of wheat production roughly 1,000 km north into northern Canada and Alaska, whereas heat and drought will make cultivation untenable in many areas of the southern Great Plains (9). To provide perspective on these and other predictions, this paper asks how farmers responded to past climatic challenges.

The spread of wheat cultivation across North America required that farmers repeatedly adapt to unfamiliar and hostile climatic conditions. The variations in climatic conditions that settlers encountered rivaled the magnitude of the predicted changes at given locations over the next century. We quantify the extent of the geographic variations and decipher how wheat growers learned to produce in new environments. Because of the paucity of Mexican data before 1929, most of our analysis of "North America" refers to Canada and the United States. Inclusion of Mexico in the later part of the 20th century highlights the role of the Green Revolution in pushing production into hotter and drier zones.

Between 1839 and 2009, wheat output increased 26-fold in the United States and more than 270-fold in Canada. In 1839, the geographic center (mean) of North American wheat production was located in eastern Ohio. Cultivation was concentrated in Ohio and New York; relatively little wheat was grown as far west as Illinois. In 2007 the center of production had moved 1,800 km west, into west-central South Dakota . Almost all this movement occurred when plant sciences were in their infancy.

Modern plant sciences can create new cultivars much more rapidly. For example, biotech companies are just now releasing new drought tolerant varieties of corn that can boost yields by 5 to 15 percent in water limited growing areas. And please remember, farmers don't just sit there and take whatever nature deals out, they adapt.

Finally, what has been happening to global grain production? Taking USDA figures [downloadable] compiled by the Environmental Policy Institute, headed by perennial doomsayer, Lester Brown, one finds that global grain production rose from 1,429 million tons in 1980 to 2,179 million tons in 2010, an increase of 50 percent. World population rose from 4.5 billion to 6.8 billion, also about 50 percent. Putting the Science study's modeled 3.8 percent and 5.5 percent production declines over the past 30 years in context, global grain production has seen as much as a 10 percent increase from one year to the next, and a four percent decrease from one year to the next since 1980.