Global climate change, created by the effects of human activity, is already happening. That's the conclusion of an international panel created by the United Nations to examine the problem of human impact on the world's climate.

Ice core samples show that the level of carbon dioxide in the atmosphere is 30 percent higher now than before the industrial revolution early in the nineteenth century, and it continues to rise. Carbon dioxide is one of the so-called greenhouse gases that contribute to a general warming of the earth's climate.

A recent workshop in Vancouver on climate change looked at the results from several computer models designed to predict the rate of global warming and the pattern of effects.

It's not a simple thing to predict, says Joan Eamer a biologist with the Canadian Wildlife Service in Whitehorse. Some of the gases given off by industrial activity have a warming effect, while others have a cooling effect. The impact within particular regions is also affected by air circulation patterns, ocean currents, and latitude.

"They have to balance these things out," she says.

Although they differ on details, most models predict that carbon dioxide levels in the atmosphere will be double pre-industrial levels within the next one to two generations. Among the likely effects are an over-all increase in global temperatures, rising sea levels, and a general increase in extreme weather events like winter storms and drought.

"In fact, there is an observed increase in extreme events in the northern hemisphere now," says Eamer.

In the southern Yukon, winter temperatures could increase from two to five degrees and summer temperatures by about three to six degrees over the next couple of generations. Winter temperatures on the North Slope could go up by as much as eight degrees, Eamer says, but the summer increase would be much smaller because of the moderating effect of the Arctic Ocean.

Some of the changes that might result include a decrease in sea ice, more extreme weather events, shorter snow and ice seasons, a rise in sea level on the Beaufort coast, increased streamflow, earlier spring runoff, the melting of glaciers and permafrost.

All these changes to the land and the water have an impact on animals, plants, and people, but that impact is not easy to predict. For example, warmer and longer summers, along with the melting of some permafrost, could result in some plant and animal species moving northward. Other species that need northern or alpine habitat might move to higher altitudes or even run out of habitat and disappear.

Warmer summers might also be drier summers, Eamer says, because of increased evaporation. The composition of Yukon forests could change, with more white spruce and lodgepole pine moving in. In particularly dry areas, however, further loss of moisture might cause the forests to shrink.

Warmer winters are not necessarily a good thing. If they include heavier snowfall, which many models predict, life would be much more difficult for animals, like caribou, that scrape through the snow to find their winter food.

The severity of the impact of climate change depends partly on how quickly it happens, says Eamer.

"If things change slowly, animals and plants tend to adapt," she says. "If the change is fast, they might not be able to."

People, too, will have to adapt. Changes in the level and timing of spring water flows affect aquatic habitat, flood potential, and the design of structures like bridges and dams. Melting permafrost leads to land instability that affects buildings and structures like the Dempster Highway. Changes to the growing season affect agriculture. Changes to the precipitation and evaporation rates affect wetlands.

Reducing the quantity of greenhouse gases produced by human activity would help reduce the scale of future climate change, but not eliminate it, Eamer says. The clear message at the Vancouver workshop was that the risk is real, although the magnitude is uncertain.

For more information on global climate change and its effects, contact Environment Canada in Whitehorse.