Research Associate, World Wildlife Fund’Conservation Foundation, Washington, D.C.

Current human population and development pressures are breaking wild biological communities into fragments surrounded by human-dominated urban or agricultural lands. The result is that many wild species, perhaps hundreds of thousands by the end of this century, will be lost because of habitat disturbance (Lovejoy, 1980; Myers, 1979). Recent advances in conservation biology have demonstrated that even some species we thought would be protected within reserves may still be lost because the reserves are too small to maintain viable populations of all the species within them (Frankel and Soulé, 1981; Schonewald-Cox et al., 1983; Soulé, 1986; Soulé and Wilcox, 1980). To this daunting picture must be added a newly recognized threat, one with potentially disastrous consequences for biological diversity. This threat is global warming, commonly called the greenhouse effect.

It now seems very likely that ecologically significant climate change will occur within the next century and that many natural populations of wild organisms will be unable to exist within their present ranges. They will be lost, unless they are able to colonize new habitat where the climate is suitable, either on their own or with human help. Simply because many species survived past natural climate changes does not mean that they will survive this one without aid. The coming change promises to be very big and very fast, and because human activities will increasingly fragment and isolate populations, it will be more difficult for many species to successfully colonize new habitat when the old one becomes unsuitable.

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