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future climate. Nature, here, means the natural or unmanaged living things outdoors. Humanity, of course, is part of nature, but we use the word nature to mean the unmanaged environment. In the past the study of the outcome of climate change for nature and humanity dealt largely with the impacts, or blows, themselves. Studies have dealt, for example, with the changes a new climate would cause in the plants of an ecosystem, the yield of a crop, or the safety of a seawall, assuming little or no adaptation. Here the panel integrates projections of impacts into its discussion of how to cope (see Chapter 34).

The most severe challenge in weighing impacts, however, is to compound the outcome of a changing climate with other changes that will occur during the coming decades. These changes range from technological innovations to social changes and from increased numbers of humans to ecological impacts. We can grasp the possible magnitude of some of the kinds of changes that might happen at the same time as a climate change by looking back eight decades. In 1910 the Ottoman, Austro-Hungarian, British, and Russian empires ruled much of the world. In America there were no income taxes, women could not vote, each person commanded 1.5 horsepower, and the major polluters were the 21 million horses (Nordhaus, 1990).

Although the crystal ball for seeing future life and technology is cloudy, the magnitude of the changes of the past 80 years teaches us that we must go beyond computation of the effect of warming of 1° to 5°C on, say, today's corn or coast. We must try to foresee the adjustments in nature and human behavior that will occur in response to changing environmental conditions amidst an army of technological, social, and economic changes. If we ignore these adjustments, which are here termed adaptations, we will write a "dumb people scenario." Imposing the climate near the middle of the next century on the activities of 1990 implicitly assumes that people will dumbly ignore any new environment and circumstances for 80 years and behave as they do today.

Three classes of adaptation by humans can be distinguished (Coppock, 1990). The first might be called adjustments. These are prompt, individual, uncoordinated, and largely spontaneous, such as the changes a farmer makes in crop varieties after a couple of cold years. A second class, which might be called premeditated adaptation, begins with anticipation and information and requires planning, coordinated action, and time. This class is typified by the building of a dam for irrigation. A third class might be called interventions. These actions, typically by governments, manipulate the circumstances of choices and are exemplified by the zoning of wetlands. Here, the word adaptation encompasses all these.

An illustration of a dumb scenario is a vision of the corn varieties and husbandry of 1990 in a changed climate in 2030 and then calculation of the impact of climate change as a change from the 1990 yields. A smarter

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