Considerable progress in understanding how global climate change is likely to affect agricultural production and forest resources has been made in recent years. In the recent Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change's (IPCC) Working Group (WG) II (IPCC, 2001), agriculture was combined in a chapter with other, less managed terrestrial and aquatic ecosystems in order to assess its response to climate change. This was intended to facilitate comparison of the impacts of climate change on basic biological and ecological processes across ecosystems (including agroecosystems and forest ecosystems) in a consistent manner. However, agroecosystems are fundamentally different from less managed ecosystems such as wetlands, tundra, and savannas: they produce economically valuable goods and services within a system of clear and enforceable property rights. Such greatly complicates understanding of their response to climate change because of intense human intervention into climate-ecosystem interactions and because responses of these ecosystems to climate change can have direct and immediate economic impacts. Hence, I focus on agriculture in this chapter.

The aim of this chapter is to distill important insights into the vulnerability, potential impacts, and adaptation prospects of agriculture in response to climate change from the IPCC's WG II TAR. Most of the discussion here is drawn from material generated for chapter 5 and reported in Easterling and App (in press). The purpose of that chapter was to review and assess scientific progress in understanding of how ecosystems (including agroecosystems) and their coupled social systems may respond and adapt to climate change, and to provide a global perspective on possible agricultural outcomes. We recognize the importance of understanding small-scale regional variation in such outcomes, but leave detailed discussion of such for others to consider.

We follow a modified version of the state-pressure-response model (to include adaptation) of the Organization for Economic Cooperation and Development (OECD) to report key findings. State refers to the status or condition and future trends in food, fiber, fuel, and fodder systems under current climate conditions. Pressure refers to environmental and social stresses, including those arising from climate change, on such systems. Response refers to the induced changes in these systems arising from the imposed pressures (including climate change). Adaptation refers to the managed changes in ecosystems and deliberate human actions aimed at adjusting to climate change. This model disciplines our synthesis of the large amount of research on the consequences of climate change by focusing the review on the following questions: What is the current state of the Earth's agricultural ecosystems, and how effectively are we meeting the demands for their goods and services? What major challenges confront the world's food and fiber sectors over the next several decades, whether the climate changes or not? What are the likely biophysical and socioeconomic effects of climate change? What are the prospects for successful adaptation by agricultural systems to those effects? How vulnerable will those systems be after accounting for the potential for adaptation to alleviate stress or take advantage of opportunity?

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