New Predictions of Climate Change’s Impact on Agriculture

By Shari Lifson and Rob Mitchum

Developing countries are more likely to see a drop in agricultural productivity and increased food prices due to climate change, particularly in tropical regions, according to a set of new studies out this week. In areas with limited water resources, the impact could be doubled as farmers are forced to shift from irrigation to rain-watered crops, the researchers found.

Agriculture is arguably the sector most affected by climate change, but impact assessments differ and thus are difficult to compare. As the world’s population grows, understanding which crop types, regions, farming practices and policies will be negatively affected by climate change may make the difference between adequate food supply and food insecurity.

By comparing the predictions of multiple models, scientists can assess with more confidence future climatic effects on agricultural production.

Three new studies comparing multiple models in order to quantify the global effects of climate change on major crops, freshwater availability and agricultural economics have just been published in the Proceedings of the National Academy of Sciences. The research, coordinated by the Agricultural Model Intercomparison and Improvement Project as part of the Inter-Sectoral Impact Model Intercomparison Project and led out of Columbia University’s Earth Institute and the NASA-Goddard Institute for Space Studies, breaks new ground by offering first-time multi-model assessments that provide a more accurate picture of where and why food security will be a challenge as global temperatures continue to rise.

The locations and crops most vulnerable to decreased agricultural yields as a result of climate change were the focus of a study led by Cynthia Rosenzweig, senior research scientist at the NASA-Goddard Institute for Space Studies in New York. Researchers conducted globally consistent, protocol-based, multi-model climate change assessments for wheat, rice, corn and soybeans. Included in the study is the level of confidence, or how much uncertainty, is associated with the assessments.

Results showed strong negative effects from climate change, especially in the tropics, where developing countries are concentrated, and at higher levels of warming. Simulations that included realistic nitrogen availability resulted in much more severe impacts from climate change in both temperate and tropical zones. This implies that developing countries, where there is less use of nitrogen fertilization, will have greater challenges in creating effective adaptation strategies.

“This is the first-ever global multi-model assessment for agriculture,” Rosenzweig said. “Decision-makers can now have greater confidence in results showing strong negative impacts on crop yields in developing countries.”

Freshwater availability, vital to agriculture, was examined in a related study led by Joshua Elliott, a research scientist with the Center for Robust Decision Making on Climate and Energy Policy at the Computation Institute, a joint initiative of the University of Chicago and Argonne National Laboratory. The research team compared a multi-model ensemble of hydrological models to the multi-model ensemble of crop models and found that agricultural losses from the direct effects of climate change could double, because 20 to 60 million hectares of irrigated fields would need to revert back to rain-fed crops.

“It’s a huge effect, and an effect that’s basically on the same order of magnitude as the direct effect of climate change,” Elliott said. “So the potential is the effect of limited irrigation availability in some regions could end up doubling the effect of climate change.”

However, while the models predicted freshwater shortages in some areas of the world, such as the western United States, India and China, other regions were predicted to have a surplus of freshwater. Redistributing that excess water to add irrigation to some rain-fed crop areas could reduce some of the consequences of climate change upon irrigation and agriculture, Elliott said.

Populations facing upward pressure on food prices due to climate change will be at risk for food insecurity. A multi-model study led by Gerald Nelson, former senior research fellow at the International Food Policy Research Institute, found that the mean direct climate change effects on crop yields is a 17 percent decline in 2050 (when compared to model runs with no climate change), but with significant differences by crop, region and model.

The upward pressure on food prices depends on factors such as trade, land availability and demand. The final yield effect is an average 11 percent decline as farmers respond by altering input use and management practices on existing agricultural area, expanding production into new areas (an average increase in area globally of about 8 percent) and reduced consumption (a decline of about 3 percent).

“We knew that the models have qualitatively similar responses, but before this research we had little understanding about why the magnitudes of the model responses differed so much,” Nelson said. “The size of the changes is as important as the direction. The mean effect on crop prices is a 20 percent increase, but for some crops in some regions, prices don’t change at all, while in others the increase is over 60 percent. Differences in model results arise in assumptions made by the modeling groups in three areas – how easy is it to convert nonagricultural land to cropping, how much can farmers respond to higher prices by raising yields, and how much can international trade flows respond to the different regional climate effects.

“The results provide valuable information to both the public and private sectors as they think about policy changes and investment priorities.”

The papers are among 12 published as part of a special feature in the Proceedings of the National Academy of Sciences Dec. 17, 2013. Researchers hope the Intergovernmental Panel on Climate Change will use the studies to inform the Fifth Assessment Report, which will provide a comprehensive assessment of current scientific knowledge related to climate change, due out in 2014.

Shari Lifson is communications coordinator for the Agricultural Model Intercomparison and Improvement Project. Rob Mitchum is communication manager at the Computation Institute, a joint initiative of the University of Chicago and Argonne National Laboratory.