Every 6 years, the Intergovernmental Panel on Climate Change releases a three part assessment report on climate change. The second part of the fifth of these reports was released on March 31st, and its focus is on the effect of climate change on ecosystems, economy and human society in general. Chapter 7, which the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS) has condensed into a brief analysis paper, is focused on impacts on food and agriculture.
The big take-home message is that climate change depresses yields. Even moderate climate change, anticipated in the next few decades, is associated with yield losses. By the second half of the century two-thirds of simulations project yield decreases of more than 10%. The previous IPCC report thought that warmer climates should mean longer growing seasons, and more carbon should mean an increased rate of photosynthesis. This updated report confirms that tropical cereals are experiencing a decline in yields, and that increased carbon dioxide has had no effect on the rate of photo synthesis. The news continues to be bad for tropical zone crops and the projections look more bleak in temperate zones where improved technology may only keep up with climate change effects, which leaves big gaps.To quote CCAFS, for which Emerging has done several projects: “Maize yields in the USA increased 600% over the 20th century
. Looking forward, scientists argue that yield increases of 45-70% are possible
for most crops through improved nutrient management and increased use of irrigation. Climate change may exert a drag on yield growth, but perhaps technology and careful use of resources can more than compensate.
The report suggests unfortunately that technology may not be able to keep up, with a great hit to tropical agriculture. “Simulations for the 2040s and 2050s that include on-farm adaptations – changes in planting date, fertilizer, irrigation, cultivar or other agronomic practices – give a yield benefit of 14% for temperate crops, but no discernible benefit for tropical crops,” summarizes CCAFS.
The report can be found here. The Economist’s coverage of the report can be found here.
The synthesis, also published independently as A meta-analysis of crop yield under climate change and adaptation, by Andy Challinor, James Watson, David Lobell, Mark Howden, Daniel Smith and Netra Chhetri, distills the consensus among modellers on future yields of the major food security crops – rice, wheat and maize – that provide half the food we consume.