analyze the effects of gradual climate change on agriculture can be applied for abrupt climate change. Many early studies of the impact of gradual climate change on agriculture used what came to be referred to as the “dumb-farmer” scenario. Under this approach, farmers were assumed to take only the most limited steps to adapt to climate change. For the “dumbest” of scenarios, even with a 3-6°C warming over a century, farmers would plant the same crops in the same place with the same fertilizers and the same planting and harvesting dates. These assumptions were criticized by those advocating a “smart-farmer” world. Increasingly, studies now allow for extensive adaptation, including the “Ricardian approach” (relying on cross-sectional data on land prices; Mendelsohn et al., 1994), which assumes virtually complete adaptation to climate change.
Ironically, studies that were undertaken using a non-adaptation approach are ideal to investigate the impacts of abrupt climate change. This is particularly true if the abrupt climate change is unforeseen, widespread, and sudden, for in such a case farmers could only undertake very limited adaptation. With full adaptation, linked economic-climate models project essentially no impact on the economic value of global agriculture even for globally averaged temperature changes of as much as 4°C (Figure 5.9).6 With very limited adaptation, as is likely to occur with abrupt climate change, the costs are substantial, ranging from $100 billion to $250 billion depending on the climate scenario (Figure 5.9). Moreover, these scenarios are likely to underestimate the damages from abrupt climate change because they predict relatively smooth regional changes, whereas evidence suggests that abrupt climate change will produce abrupt, magnified changes at local scales. Note that this figure shows exactly the kind of pattern of impact that was illustrated hypothetically in Figure 5.9.
A second priority sector for research is forests. This sector may be affected more than agriculture by abrupt climate change because forests are highly climate-sensitive, with long-lived ecological and economic capital stocks. Most ecological studies of the impact of climate change on forests have been limited to describing long-term equilibrium effects (Mendelsohn, 2001). The models predict ecological changes that will occur in two or