Global warming's impacts evident worldwide.

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 decline substantially once they reach maturity or are again logged or cleared.

Similar trends can be seen worldwide. Trees are leafing earlier throughout Europe, while fall colors appear later. Some species, such as warm-water fish, are flourishing, but cold-adapted species are in decline, leading to significant shifts in some animal communities. Globally, plants now bloom an average of 5.2 days earlier each decade, according to Terry Root of Stanford University. Mountain glaciers are shrinking at ever-faster rates, threatening water supplies for millions of people and species. And average global sea levels have risen 20-25 centimeters since 1901, due mainly to thermal expansion; more than one-tenth of this rise occurred over the past decade. A 2003 study linked changing sea temperatures associated with global warming to droughts across the United States, Southern Europe, and Southwest Asia.

A recent study by the Hadley Centre for Climate Prediction and Research, published in Nature, is one of the first to link human-induced climate change to specific injuries. It found that burning of fossil fuels, which has increased atmospheric greenhouse gas levels, has more than doubled the risk of record-breaking hot summers in Europe, such as the 2003 heat wave that killed as many as 35,000 people and devastated much of Europe's agricultural sector. The World Health Organization estimates that global climate change already accounts for more than 160,000 deaths annually.