Feeding the world as the climate continues to change will require a more diverse array of crops as well as global investment to help communities adapt to warmer temperatures, unexpected cold snaps, heavy rainfall, drought, and other extremes, experts reported 16 June on Capitol Hill.
At the AAAS-sponsored briefing, Paul Gepts, a geneticist and professor of agronomy at the University of California, Davis, warned that inadequate crop biodiversity in the United States could hamstring American farmers as climate change intensifies.
Switching crops is the easiest way for farmers to respond to changing conditions, Gepts noted. For example, “cool-season crops” such as lettuce, broccoli and spinach can be replaced during warmer periods with more heat-tolerant crops, including tomatoes, cucumbers, peppers, and sweet corn.
But much of the world’s agricultural biodiversity is located outside of the United States, Gepts explained, and the United States has signed but not ratified a key international treaty called the Convention on Biological Diversity.
“Access to agricultural biodiversity resources will become much more difficult,” Gepts said. “If we have some catastrophic [crop] diseases showing up, where are we going to find biodiversity? Either from the gene banks of the U.S. Department of Agriculture, or from other countries. That presents a security aspect.”
Speaker Gerald Nelson, a senior research fellow at the International Food Policy Research Institute (IFPRI), said that investments of $7.1 billion to $7.3 billion annually are urgently needed to help offset the negative impacts of climate change on the health of children in developing regions. His presentation drew upon an October 2009 IFPRI report, which notes that climate change will trigger a decline in yields for most important crops in the developing world, with South Asia likely to be hardest hit.
At the same time, he noted, the world’s population is predicted to rise by 50% between 1999 and 2045. “For every two of you in the room today, there will be three in the room by 2050,” he told attendees at the AAAS event. “If we don’t do anything, our projections suggest that unchecked climate change [will result in] a 20% increase in the number of malnourished children in 2050, over the number that would exist without climate change.”
Additional investment in global agricultural productivity would support much-needed research as well as improved irrigation and rural roads, Nelson said.
Cynthia Rosenzweig, a senior research fellow at NASA Goddard Institute for Space Studies, agreed that climate change is likely to threaten the world’s food supply, posing security risks for the United States and many other nations.
“There is the potential for strong shocks on any nation’s agricultural production,” she said. Extreme climate events will affect livestock as well as crop yields and agricultural pests.
In addition, Nelson said, “Water already is causing battles around the world, and that’s likely to be exacerbated by global climate change.”
Fossil-fuel burning and deforestation are primarily responsible for rising levels of greenhouse gases, which trap heat near the Earth’s surface, warming the planet and causing other climate changes. But agricultural activities also play a role, Rosenzweig explained. Methane, for example, is generated by vast rice paddies, and by the digestive processes of “ruminant” livestock such as cattle, sheep, buffalo, and goats. Fertilizers emit nitrous oxide, and land-tilling and deforestation generate carbon dioxide.
Forestry and other agricultural activities also can help mitigate climate-change impacts by absorbing carbon dioxide, Rosenzweig noted. In addition, changes in growing conditions may benefit specific regions. So questions about specific climate-farming mechanisms can be complex, but it’s clear that climate change will have a negative overall impact on global food production, she said.
In central California, Gepts said, fruit and nut trees have already suffered a 25% decrease in “chilling hours”—essential winter cooling periods that are expected to taper off by another 25% over the next five decades. The trees might then have only 300 to 400 chilling hours per year, compared with 1,200 hours in 1950.
Gepts described five strategies for easing the impacts of climate change on agriculture, assuming that greenhouse gas emissions also can be reduced. In addition to switching crops in response to climate change, for example, he noted that breeding new varieties capable of withstanding droughts or heavy rainfall will be essential in the future.
Average global temperatures have already increased by 1.5 degrees Fahrenheit (0.8 degrees Celsius) since 1880, according to a January 2010 NASA report. By 2100, the Intergovernmental Panel on Global Climate Change has predicted continued temperature increases between 2 degrees F and 11.5 degrees Fahrenheit (1.1 to 6.4 degrees Celsius) over 1990 levels.
César Izaurralde, a laboratory fellow with the Joint Global Change Research Institute, explained how high carbon dioxide levels can damage corn, maize, and wheat as water becomes trapped in the distribution pores, or stomata of the plants. Over the next 30 years, climate change is expected to cause a 3% loss in the yield of corn crops in key growing regions of America, he said.
Grasslands as well as livestock also will face major challenges in adapting to environmental changes. “The normal behavior of animals may be altered, their immunology may be altered, and their biophysiology may be altered” by climate change, said Izaurralde, who cited the U.S. Climate Change Science Program’s Synthesis & Assessment Product report.
The AAAS event was co-sponsored by the American Society of Agronomy, the Council on Food, Agricultural, and Resource Economics, the Crop Science Society of America, and the Soil Science Society of America. Speakers’ slides are now online. The Hill event also was covered by Scientific American and Climatewire.
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