The following trends support some important conclusions.

First, changes to natural ecosystems are occurring on a large scale than ever before, involving entire landscapes. Such large-scale landscape changes -- through deforestation, expansion of agricultural land, and urban and suburban growth -- will likely dictate the physical condition and extent of terrestrial ecosystems in the next several decades. Fragmentation of the world´s remaining forest blocks; buildup in coastal areas; and the spread of cities, suburbs, and infrastructure over once-rural tracts will do much to degrade the habitat and watershed values of these areas.

Second, the very scale of these landscape-level changes, as well as the increasing intensity of industrial and agricultural processes, are inducing changes in the global systems and cycles -- such as the atmosphere and the nitrogen cycle -- that underpin the functioning of ecosystems. These changes in what can be called the "global commons" represent long-term environmental threats of a profound and far-reaching nature. Global warming from the buildup of greenhouse gases is the best-known example, with the potential for large-scale disruption of natural ecosystems, agriculture, and human settlements due to changes in rainfall and temperature patterns and rising sea levels.

Third, threats to biodiversity from all sources are quickly reaching a critical level that may precipitate widespread changes in the number and distribution of species, as well as the functioning of ecosystems. Current extinction rates are 100 to 1,000 times higher than prehuman levels, and projected losses of habitat from land conversion, as well as increasing competition from nonnative species, will probably push this rate higher still.

Even as these trends indicate the environmental challenges ahead, it is important to remember that they can be modified with human resolve. Already, the transition to more environmentally benign ways of growing food, producing goods and services, managing watersheds, and accommodating urban growth has begun in many far-sighted communities and companies. How fast this transition to more "sustainable: forms of production and environmental management will proceed, and whether it can effectively mitigate the effects of large-scale environmental change, is the real question.