Climate Stabilization Targets - Climate Change and Food Security

temporal coverage to formulate sensible and remarkably skillful predictive ...... the climate signal in primary production and other ecosystem properties may ... O2. Climate change could accelerate coastal hypoxia via surface warming.
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Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia

Committee on Stabilization Targets for Atmospheric Greenhouse Gas Concentrations; National Research Council

ISBN 978-0-309-15176-4 298 pages 7 x 10 PAPERBACK (2011)

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Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia

5 Impacts in the Next Few Decades and Coming Centuries

5.1  FOOD PRODUCTION, PRICES, AND HUNGER Even in the most highly mechanized agricultural systems, food production is very dependent on weather. Concern about the potential impacts of climate change on food production, and associated effects on food prices and hunger, have existed since the earliest days of climate change research. Although there is still much to learn, several important findings have emerged from more than three decades of research. It is clear, for example, that higher CO2 levels are beneficial for many crop and forage yields, for two reasons. In species with a C3 photosynthetic pathway, including rice and wheat, higher CO2 directly stimulates photosynthetic rates, although this mechanism does not affect C4 crops like maize. Secondly, higher CO2 allows leaf pores, called stomata, to shrink, which results in reduced water stress for all crops. The net effect on yields for C3 crops has been measured as an average increase of 14% for 580 ppm relative to 370 ppm (Ainsworth et al., 2008). For C4 species such as maize and sorghum, very few experiments have been conducted but the observed effect is much smaller and often statistically insignificant (Leakey, 2009). Rivaling the direct CO2 effects are the impacts of climate changes caused by CO2, in particular changes in air temperature and available soil moisture. Many mechanisms of temperature response have been identified, with the relative importance of different mechanisms varying by location, season, and crop. Among the most critical responses are that crops develop more quickly under warmer temperatures, leading to shorter growing periods and lower yields, and that higher temperatures drive faster evaporation of water from soils and transpiration of water from crops. Exposure to extremely high temperatures (e.g., > 35°C) can also cause damage in photosynthetic, reproductive, and other cells, and recent evidence suggests that even short exposures to high temperatures can be crucial for final yield (Schlenker and Roberts, 2009; Wassmann et al., 2009).

159 Copyright © National Academy of Sciences. All rights reserved.

Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia

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CLIMATE STABILIZATION TARGETS

A wide variety of approaches have been used in an attempt to quantify yield losses for different climate scenarios. Some models represent individual processes in detail, while others rely on statistical models that, in theory, should capture all relevant processes that have influenced historical variations in crop production. Figure 5.1 shows model estimates of the combined effect of warming and CO2 on yields for different levels of global temperature