The change in climate is not only affecting the arctic and diminishing the population of polar bears but is also destroying the boreal - or far northern - forest, explained the Arctic Climate Impact Assessment report.
According to the report, stress related to high temperatures is reducing the ability of the forest to store carbon dioxide at the same levels as the past.
'The boreal forest is dying,' said Glenn Patrick Juday, a professor of forest ecology at the University of Alaska Fairbanks. 'Temperature rise directly reduces growth of boreal tree species.'
He was testifying along with three other witnesses Wednesday before the House Committee on Science and Technology's investigations and oversight subcommittee.
Juday explained that increase in temperature leads to dryer conditions and wild-land fires. Over the years, fires have increased and burned a fourth to a third of all forest land in the northeast quarter of Alaska.
High temperatures also trigger outbreaks of forest-damaging insects such as the spruce budworm that feed on foliage. That leaves the tree unable to survive, Juday said.
In addition to destruction of the boreal forest, global warming is also affecting the Arctic. Sea-ice has decreased in area and thickness, with ice lost equal to twice the size of Texas from 1979 to 2005, according to Alley's statement.
Polar bears are dependant on the arctic sea-ice habitat for survival. They use the sea ice to hunt seals, to migrate to their land den areas and for mating. The decrease in ice leads to lower survival of the polar bears caused by a shorter hunting season and a reduction in ice-dependant prey such as the seals, said Kassie Siegel, the climate, air, and energy program director at the Center for Biological Diversity's California office.
According to the Arctic Climate Impact Assessment report, although some climate changes may have been due to natural sources, in recent decades changes resulting from human activity have become dominant.
'There is no question that we are going through a worrying trend. The major concern is if it is caused by human activity,' said Rep. Dana Rohrabacher R-Calif., a member of the subcommittee.
Richard B. Alley, a professor in geosciences at Pennsylvania State University, answered that recent assessments have pointed to human activities altering the composition of the earth's atmosphere through gases from industries and other sources such as vehicles.
The other question, raised by subcommittee chair Rep. Jeff Miller R-Fla., is what individuals can do to reduce pollution.
'Reducing the pollutants carbon dioxide, methane and black carbon can buy some time and presents our best opportunity for slowing and reversing the Arctic melting before it is too late,' Siegel said.
This pollution can be reduced by replacing carbon-based fuels with natural options, better vehicle maintenance to prevent emitting gases and making them energy efficient, Siegel said. 'If we do all this we will start seeing progress in January 2009.'