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As the climate warms, outbreaks of spruce bark beetles in the northwest U. S. and Canada are prevalent. Spruce bark beetles have killed more than three million acres of spruce trees in Alaska in the past 15 years. They are not an invasive species in those areas, but their population had been held at low levels by very cold winters. Photo shows beetle-killed stand of spruce extending up the side of Porphyry Mountain near McCarthy in Wrangell-St. Elias National Preserve in Alaska. (Photo: Adam Watson, University of Alaska Fairbanks)

Report Shows 'Unequivocal' Climate Warming

An important update on global warming, Global Climate Change: Its Impacts in the United States, has been completed. This work, done by a team of climate experts from across the country and Canada, has been co-chaired and co-edited by Jerry Melillo, senior scientist and co-director of the Ecosystems Center, and Thomas R. Karl and Thomas C. Peterson, both of NOAA’s National Climatic Data Center in Ashville, North Carolina.

The report was commissioned by the U. S. Government’s Climate Change Science Program one year ago to summarize what is known about the science of climate change and the impacts of climate change on the United States. It discusses climate-related impacts for various societal and environmental sectors and regions across the nation, with the goal of better informing public and private decision making at all levels.

Observations show that warming of the climate system is now unequivocal. &ldquoWe now have strong evidence that the global warming observed over the past 50 years is due primarily to human-induced emissions of heat-trapping gases,” Dr. Melillo said. These emissions come primarily from the burning of fossil fuels (coal, oil and gas), with additional major contributions from the clearing of forests and agricultural activities.

The report indicates that warming over this century is projected to be considerably greater than over the past century. The global average temperature since 1900 has risen by about 1.5 degrees Fahrenheit. By 2100, it is projected to rise another 2 to 10 degrees Fahrenheit. Temperatures in the United States have risen by a comparable amount and are likely to rise more than the global average over this century. Several factors will determine future temperature increases, including the amount of emissions of heat-trapping gases to the atmosphere. Dr. Melillo noted that, “increases at the lower end of the range are more likely if global heat-trapping gas emissions are cut substantially, and at the upper end if emissions continue to rise at or near current rates.”

Climate-related changes already have been observed globally and in the United States. These include increases in air and water temperatures, reduced frost days, increased frequency and intensity of heavy downpours, a rise in sea level, and reduced snow cover, glaciers, and sea ice. A longer ice-free period on lakes and rivers, lengthening of the growing season, and increased water vapor in the atmosphere have also been observed.

The report indicates that these changes are expected to increase and will impact human health, water supply, agriculture, coastal areas, and many other aspects if society and the natural environment. Some of the changes that are likely for the United States and surrounding coastal waters are of particular concern to coastal New England include more intense hurricanes and related increases in wind, rain and storm surges.

Dr. Melillo stressed that an important message of the report is the “need to begin to focus our attention on the issue of adaptation. What we might do for the climate change that is inevitable, beyond slowing down emissions? What are our adaptation options?” One example is to establish zoning policies that do not allow people to build new structure in low-lying coastal areas or in the flood plains of major rivers.