Yukon

Fires and beetle infestations are devastating northern forestsin a cycle that is both caused by and promoting climate change, reports Charles J. Hanley of the Associated Press. As the climate warms, forests in Siberia, Europe, Alaska and northern Canada will grow weaker while pests grow stronger with milder winters. These boreal forests are key in absorbing carbon dioxide, but as they succumb to warming, they would become a source of greenhouse gases as they decay and burn.

Change is already happening in western North America, where a mountain pine beetle epidemic has killed 6.5 million acres of forest from Colorado to Washington and 35 million acres in British Columbia. The spruce bark beetle has already consumed 1 million acres in the Yukon during a 15-year epidemic. Scientists say these unprecedented epidemics are signs the climate is already changing, especially in the north.

Plant life in the north is also shifting, as warmer temperatures double the amount of shrubs and grasses on tundra, according to Bob Weber of the Canadian Press. Because the shrubby vegetation is darker, it would absorb more solar energy, possibly increasing the rate of global warming even more.

– Emily Linroth

As Vancouver, B.C., watches Fraser River stocks of sockeye fail, the count of steelhead passing the Bonneville Dam in Vancouver, Wash., is soaring. And while low Alaskan Yukon runs of king and chum salmon predict a devastating winter for subsistence fishermen, salmon are even making a comeback in the Seine, as InvestigateWest reported last week. What differences could account for these drastic population changes?

Multiple environmental factors could be affecting populations. Warmer weather can heat up rivers, especially those overdrawn by humans, and discourage the cold-water-loving fish from heading upstream. Shifting ocean currents or other predator influences could be altering food sources. Pollutants from stormwater can accumulate in the fish. Overfishing can deplete numbers. Sea lice from farmed salmon could be transferring to wild salmon, weakening them and increasing the likelihood of succumbing to disease or predators. Even superb returns from previous years could be problematic, as too many fish spawning and then decomposing could produce excess bacteria, possibly resulting in disease.