New research led by Carnegie's Julia Pongratz, and supported by FSE center fellow David Lobell, examines the potential effects that geoengineering the climate could have on global food production. The team concludes that sunshade geoengineering would be more likely to improve rather than threaten food security. Their work was published online by Nature Climate Change on January 22.

A new study out of Stanford University finds extreme temperatures are cutting wheat yields by 20 to as much as 50 percent, a finding worse than previously estimated. FSE center fellow David Lobell and his colleagues used nine years of satellite measurements of wheat growth in northern India's breadbasket, the Indo-Gangetic Plains, to analyze rates of wheat ageing after exposure to temperatures higher than 34 degrees Celsius. 

Extreme heat beyond the plant's tolerance zone damages photosynthetic cells. This causes wheat to age faster, reducing the length of the growing season and the amount and size of the wheat grains. The team's crop models found that a two degree increase in temperatures would reduce the growing season by nine days, yielding 20 percent less wheat.

As the world's second-biggest crop, lost wheat yields may become a major threat to global food security. Especially given the projection that global yields need to rise 50 percent by 2050 to feed a growing, more affluent population. The results imply that warming presents an even greater challenge to wheat than previous studies estimated, and that the effectiveness of adaptations will depend on how well they reduce crop sensitivity to very hot days, particularly in areas of the world such as India already experiencing warming conditions.

The demand for food, feed and fuel will continue to rise as the world population grows and becomes more affluent. Meeting this demand will be especially challenging because of global warming, say climate experts, and the impacts of climate variability could make food markets even more volatile, adds Rosamond L. Naylor, professor of environmental Earth system science at Stanford University.

Naylor led a symposium on the compound effects of climate change and climate variability on food security at the annual meeting of the American Association for the Advancement of Science (AAAS) February 17th.

The symposium focused on two examples of climate variability: changes in growing-season temperature extremes beyond the range observed in the historical record, and changes in the El Niño–Southern Oscillation (ENSO) phenomenon – the most energetic form of year-to-year climate variability known.

Panelist David S. Battisti, professor of atmospheric sciences at the University of Washington, addressed key challenges in assessing the impact of extreme temperatures in coming decades. According to Battisti, global warming models forcast that temperature variability will increase as the average temperature warms, greatly compounding the likelihood of extreme heat and droughts. Unfortunately, these models typically have too much temperature variability in their simulations of present-day climate, he said. Battisti's talk focused on the cause of these modeling biases and their impact on climate forecasting.

Panelist Daniel J. Vimont, associate professor of atmospheric and oceanic sciences at the University of Wisconsin-Madison, discussed the impacts of El Niño in a warmer world. ENSO impacts can be severe in regions in and surrounding the tropical Pacific, and can extend around the globe, he said. ENSO variability – its return period and intensity – are very sensitive to changes in mean conditions in the tropical Pacific, he added, but these conditions are notoriously difficult to simulate using the present generation of global climate models. Vimont presented results from the linear ocean atmosphere model (LOAM), a new scientific tool for estimating global warming's impact on ENSO variability.

Naylor addressed the impacts of climate on global markets for major staple commodities, which are already under pressure from increased population-, income-, and energy-driven demands. She outlined the potential effects of climate variability on regional trade patterns, price volatility, policy responses and human welfare. 

 

Mark Shwartz is the Communications/Writer at Precourt Institute for Energy at Stanford University.

When it comes to climate change and its impacts on agriculture, we may know less than we think.

But according to David Lobell, Assistant Professor in Stanford’s Department of Environmental Earth System Science, acknowledging the gaps in our understanding could help us to more effectively prepare the world’s food system for a warmer future.

Lobell, who has built an impressive career around the study of climate change and its implications for global food security, addressed the topic of agricultural adaptation during a two-hour symposium held on the Stanford campus in early December. His presentation summarized the strengths and weaknesses of climate models in the context of global agriculture, and suggested broad strategies for preparing agriculture for climate change’s inevitable impacts.

Lobell began his talk by reaffirming some common beliefs. The Earth as a whole is unquestionably warming, he said. Precipitation intensity is increasing in high-rainfall areas, and the world’s driest regions are becoming drier.

“Think about the hottest day we currently experience in a 20-year period,” Lobell told listeners. “By mid-century, we’ll be seeing that hottest day every year, as opposed to every 20 years.” During the same period, soil moisture content in many of the world’s major agricultural areas will decrease by as much as 10 to 15 percent, while annual precipitation at the equator and high latitudes will increase by several inches per year.

At the global scale, Lobell said, climate change will have a net negative impact on existing agricultural systems. The world’s rainfed farms will become increasingly vulnerable to heat and water stress.  Growing ranges and seasons for heat-intolerant crops, such as wheat and sorghum, will contract. Although the high latitudes may see some gains from warmer temperatures and CO2 fertilization of certain crops, low-latitude regions – including South Asia and much of Africa – will suffer disproportionate yield losses as temperatures rise.

However, Lobell said that impacts aimed at local and national scales, as opposed to broad regions or the world as a whole, are much more difficult to predict. A moderate change in average rainfall across a continent could translate to drastic increases or decreases in individual countries. For example, while climate models suggest that Africa’s annual rainfall will change by less than 10 percent over the next 50 years, model projections show rainfall in the nation of Sengal changing by anywhere from five to 40 percent over the same period.

Additionally, Lobell said, forecasts of increasing climate variability are frequently overstated. “The number one misperception I hear is that climate change is going to mean more variability,” he noted.  In fact, model projections of year-to-year variability in temperature and precipitation cover a wide range. Some models do show large increases in variability over the next century – but others show a slight decrease.

Because we understand climate impacts best at the long-term and global scales, Lobell said, global responses that address long-term trends are the most likely to serve our future needs. He cautioned against approaches that prepare farmers for short-term variability, such as sudden floods or droughts, but fail to acknowledging the effects of steadily rising average temperatures. He also stressed the value of globally coordinated efforts, particularly those aimed at developing better heat and drought-tolerant crop varieties, to supplement local infrastructure projects.

 “We’re in a world where local resilience depends on global systems,” Lobell noted. He said that the interconnectedness of modern global food markets makes global trends, and global responses, increasingly relevant for local food security.

At both local and global levels, an effective response to climate change will require robust social institutions. Dr. Fatima Denton, Program Leader for Climate Change Adaptation in Africa for the Consultative Group on International Agricultural research, stressed this point in her comments on Lobell’s presentation. “Climate change has really unmasked our governance challenges and the weaknesses in our institutions,” Denton said. “This is not just about biophysical processes…it’s about the development pathways that we choose.”

Lobell agreed. Climate change, he said, presents “an important opportunity for transformation.” He encouraged present and future leaders to think critically about all aspects of the relevant science and policy. “Be skeptical of what you hear,” he advised, “and educate yourself about what we do and don’t know.”

This was the sixth talk in FSE's Global Food Policy and Food Security Symposium Series.