By David Lobell
David Lobell is an Assistant Professor at Stanford University in Environmental Earth System Science, and Associate Director of Stanford's Center on Food Security and the Environment. His research focuses on identifying opportunities to raise crop yields in major agricultural regions, with a particular emphasis on adaptation to climate change.
For all of the talk about the need to adapt to climate change, we still know fairly little about two basic questions: what works best, and how much can adaptation deliver? It‘s time to learn quickly.
Why don’t we know more? It would be easy to blame our ignorance on complacency. There is a tendency to marvel at the progress made in agriculture in the past 50 years, and assume it can handle anything. For example, the USDA declared in the early 1970s that new technologies meant “man has reduced variation in yields in both good and bad weather.” This optimism quietly faded after a series of bad harvests in the late 1970’s and 1980’s, including the big drought of 1988. People realized that a period of unusually benign weather, and not the technological gains themselves, had limited volatility during the middle of the 20th century.
It is also tempting to blame ignorance on inexperience. After all, many people continue to view climate change as something to deal with in the future. But the evidence is clear that climate has already been changing over the past 30 years in most agricultural areas, and farmers are doubtlessly trying to adapt. Up until now, the United States was an exception to that trend. But the 2012 drought has changed that, and projections indicate that years like this will be increasingly common in the coming decades.
With widespread evidence for climate change and its impacts, complacency and inexperience should give way to rigorous evaluations of what has happened. For example, why was US agriculture not better prepared for the 2012 drought? And did anything work well that can be scaled up?
A lot has changed in US agriculture since the 1988 drought, and many of the changes were textbook examples of what should help to reduce impacts of hot summers. Farmers now sow corn and soybeans more than a week earlier on average, and use longer maturing varieties than in 1988. Advances in cold tolerance along with spring warming trends allowed corn to expand in northern states where temperatures are cooler. For example, North and South Dakota increased corn area by more than 35% (nearly 2.5 million acres) just since 2009. Carbon dioxide levels, which improve crop water use efficiency, have increased by more than 10% since 1988. And farmers have begun to grow drought tolerant seeds that were unavailable in 1988.
Yet when the 2012 drought arrived, with fairly similar characteristics to 1988, impacts on crop yields were roughly the same. Corn yields are expected to be about 25% below trend, close to the 28% drop in 1988.
What can we learn from this experience? It is too early to say anything definitive, but two explanations seem plausible. First, it may be that some of the above changes were truly beneficial, but were counteracted by other changes making agriculture more, not less, sensitive to weather. For example, breeding progress in corn has generally been faster for good conditions than bad. As farmers become even better at eliminating yield losses from pests, nutrient stress, and other factors, the benefits of having favorable rainfall and temperature become that much greater, and the relative damages of not having them become that much worse.
A second possibility, of course, is that the adaptive changes in agriculture simply did not help much in dealing with adverse weather. For example, migrating corn northward may help, but the vast majority of corn production remains where it has been for decades, so the quantitative effect is small.
Hopefully researchers will quickly distinguish between these and other explanations, and the lessons can help guide efforts to further adapt. But any explanation will likely imply that there are limits to how much adaptation can reduce impacts of climate change. This fact does not diminish the urgency and importance of efforts to adapt to climate variability and change throughout the world. But it is a reminder that greenhouse gas mitigation is pivotal in any strategy to reduce impacts of climate change. Adaptation can only do so much.