such as labor and water flows, capital stocks produce most of the world’s valuable market and non-market services such as food, recreation, water, erosion control, and many other environmentally related goods and services (sometimes termed “ecosystem services”).

Serious impacts to ecological or economic capital stocks can occur when they are disrupted in a manner preventing their timely replacement, repair, or adaptation. It is generally believed that gradual climate change would allow much of the economic capital stocks to roll over without major disruption. By contrast, a significant fraction of these stocks probably would be rendered obsolete if there were abrupt and unanticipated climate change. For example, a rapid sea-level rise could inundate or threaten coastal build-ings; abrupt changes in climate, particularly droughts or frosts, could destroy many perennial crops, such as forests, vineyards, or fruit trees; changes in river runoff patterns could reduce the value of river facilities and flood-plain properties; warming could make ski resorts less valuable and change the value of recreational capital; and rapid changes in climate could reduce the value of improperly insulated, heated, and cooled houses. There may also be an impact on more intangible investments such as health, technological, and “taste” capital, although these are more speculative.

Similarly, ecological systems are vulnerable to abrupt climate change because they have long-lived natural capital stocks, they are often relatively immobile and migrate slowly, and they do not have the capacity of humans to adapt to or reduce vulnerability to major environmental changes. Ecological systems are also vulnerable because of anthropogenic influences on the environment, which repeatedly alter ecosystems and limit species abundance and composition as a result of habitat disturbance, fragmentation, and loss. Past examples of ecosystem vulnerability to rapid climate change, such as the Younger Dryas cooling, illustrate the fragility of species diversity at one location as forests experienced rapid change. In southern New England, trees such as spruce, fir, and paper birch experienced local extinctions within a period of 50 years at the close of the Younger Dryas (Peteet et al., 1993). North American extinctions of horses, mastodons, mammoths, saber-toothed tigers, and many other animals were greater at this time than at any other extinction event over millions of years (Meltzer and Mead, 1983). The reasons for this extinction have been linked to both climate and early human impacts (Martin, 1984).

The vulnerability of ecological and economic capital stocks to abrupt climate change arises because these stocks are often specific to particular locations and are adapted to particular climates. Demographic rates of mi-

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