FIGURE 5.7 Illustration of difference between impacts with and without adaptation. The upper line shows the impact of climate change with full adaptation where farmers can change crops and irrigate, where leisure facilities can be replaced, and where forests regenerate. The lower line shows the impacts without adaptation, as is likely to occur with abrupt climate change. Note that for managed systems without externalities, the line without adaptation will lie everywhere below the adaptation line, indicating the costs are likely to be lower with adaptation. We have also shown a break in the no-adaptation line to reflect the potential for sharp threshold effects, such as those due to floods or fire.

smoothly from an initial state to a warmer one. In reality, it is likely that the impacts of abrupt climate change will be both larger and more acute than those under gradual climate change. The major reason for this difference, as discussed previously, is that economies and ecological systems usually will have an easier time adapting to more gradual and better anticipated changes. The net effect of small gradual climatic changes on the economy, as is indicated by most current economic studies for developed countries, is likely to be small relative to the overall economy (Figure 5.7). On the other hand, where economies cannot adapt, impacts resulting from abrupt climate change are likely to be larger and there may be threshold effects if the abrupt climate change triggers fires, water shortages, or exceeds the normal safety margins built into structures or policies.

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