those who live off the land, the inability to migrate may remove one of the major safety nets for distressed people.

SECTORAL APPROACHES

One promising approach to investigating the economic impacts of abrupt climate change would be to focus on individual sectors. Economic studies often have relied on the organizing framework of the national income and product accounts, in which the economy is divided into major sectors and for which both income and output data are available for most countries and numerous years (see Toth, 2000). For example, for the United States, detailed income and output data are available for 83 different sectoral breakdowns during the period 1948-1999. There is no similar accounting framework for nonmarket sectors or for ecological studies.

Agriculture

Under the sectoral approach, there are a few obvious sectors to examine. Perhaps the most important is agriculture, which is the sector most heavily affected by weather and climate. Current studies indicate that the impact of gradual climate change on agriculture over the next few decades is likely to be relatively modest for the United States. For example, a recent survey found that the impact of a 2.5°C gradual warming is likely to reduce agricultural value between 0.1-0.2 percent of global income (Nordhaus and Boyer, 2000).

Agriculture is likely to be the most accessible sector for studies on the impact of abrupt climate change because of the extensive information available and the well-developed research infrastructure in this field (Reilly, submitted). It is important to emphasize that it will be necessary to view different abrupt climate impact scenarios from a probabilistic rather than a mechanistic point of view. This applies not only to agriculture but also to other areas such as species extinction, floods, wildfires, hurricanes, human and wildlife diseases, and droughts. It is unlikely that an abrupt climate change will occur as a single abrupt event; rather, it will occur as a distribution of potential events, with increasing severity at lower probabilities. This probabilistic nature of abrupt climate change adds another layer of complexity to impact analyses and to communicating the risks and opportunities to the public.

Because of a methodological coincidence, certain approaches used to



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