Global warming's impacts evident worldwide.

• Author: Sawin, Janet L.
• Position: ENVIRONMENTAL Intelligence

Global warming is already affecting humans, plants, and animals worldwide, and these impacts are arriving faster than many climate scientists predicted.

The Arctic Climate Impact Assessment [Environmental Intelligence, January/February 2005] already documented the Arctic-warming effect in cold-climate species. The Pew Center for Global Climate Change recently released a report detailing changes around the United States in a wide variety of species and ecosystems, ranging from mountain flowers to grasses and trees, butterflies and birds, and sea urchins and red foxes. A few weeks later, the Wildlife Society released its own report with similar findings. More than half of the 40 studies reviewed for the Pew report provide evidence of a direct link between climate change and observed ecological impacts over the past 20 to 140 years.

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Average U.S. temperatures have risen 0.6 degrees C (1 degree F) over the past century, and precipitation is up an average of 5 to 10 percent, although the greater volumes of rain and snow have fallen to Earth concentrated in fewer, but more extreme, events. As a result, a number of species have shifted northward or to higher elevations, while others have completely disappeared from the United States. Scientists have documented changes in the timing of animal and insect life cycles, including breeding and migratory seasons, in conjunction with changes in climate. Even carbon cycling and storage processes have been altered. In much of Alaska, tundra and boreal forests that once absorbed more carbon dioxide than they emitted have now become net sources. Many of the forests in the lower 48 states have become net carbon sinks due to regrowth, but their ability to absorb carbon will...