The climate models suggest that warming will be most marked in the Arctic. Already there is less sea ice and the strongest warming signal of all comes from northwestern North America, including Alaska, and northeastern Siberia. Winters in these places are milder than they were.
This is the expected response to increased carbon dioxide. It occurs because during the Arctic winter the surface radiates its absorbed heat, and the temperature plummets. Cold, dense, subsiding air produces large anticyclones. Air flows outward from the anticyclones, and the extreme cold means that the air contains little moisture. Water vapor is the most powerful of all greenhouse gases, but the air over the Arctic is so dry in winter that the greenhouse effect is very small. Consequently, adding another greenhouse gas—carbon dioxide—has a disproportionately large effect. This is why all climate models predict a strong warming effect over the Arctic.
Warming in the Arctic and in northern Canada and Eurasia will affect the wildlife of these regions. The area of tundra will decrease, perhaps by 40 percent, and the ranges of animals that move freely in winter across the frozen sea will be more restricted, because the area of sea ice will also decrease, probably by about 25 percent. Migration routes, for example of caribou (Rangifer tarandus, known as reindeer in Europe), may change.
As the winters become milder and the summers warmer and longer, many species of plants and animals will begin to move. Seeds from the trees of temperate deciduous forests will germinate and grow in higher latitudes than they do today. Grasslands will replace forests in areas that become drier. Animals will follow the plants on which they depend for food and shelter. This is a natural process that has accompanied every climate change in the past. This time, though, there is a difference. People now manage much of the land, and this may make it more difficult for species to adapt.
On the other hand, people may encourage wildlife. The forested area is expanding throughout most of the temperate regions of the Northern Hemisphere. Forests are valued as public amenities for recreation, for the variety of wildlife they sustain, and because they absorb and store large amounts of carbon. If agricultural productivity continues to increase, the food we need will be produced from a smaller area and there will be more space for wildlife. Wildlife conservation is worthwhile whether the climate changes or not, of course. We need not wait for warmer weather before deciding to make more room for other species.
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