The heat is on

THE YEAR 2005 WAS THE HOTTEST on record. The average global surface temperature of 58.6[degrees]F was the highest since such data has been kept, beginning in 1880. January, April, September, and October of 2005 were the hottest of those months on record, while March, June, and November were the second warmest ever. In fact, the six hottest years all have occurred in the last eight years. These readings, which come from the series maintained by NASA's Goddard Institute for Space Studies, continue a trend of higher global temperatures. During the past century, temperatures rose 1.44[degrees]F 0.6[degrees] of which occurred during the last three decades, a rate unprecedented in the last millennium.

Elevated temperatures primarily are due to the buildup of greenhouse gases in the atmosphere, particularly carbon dioxide (C[O.sub.2]) from the burning of fossil fuels. Once released, C[O.sub.2] traps heat that would otherwise escape back into space--and these carbon dioxide emissions have been on the rise since the start of the Industrial Revolution in 1760.

Two recent reports demonstrate the exceptional levels of current global temperature and atmospheric C[O.sub.2]. Using records stored in ice, tree rings, and fossils, scientists have estimated that the Northern Hemisphere is warmer now than at any time in the past 1,200 years. Another study revealed that atmospheric levels of C[O.sub.2] and methane, yet a different greenhouse gas, are higher today than at any time in the A last 650,000 years.

As greenhouse gas emissions continue to build up, so, too, will the pace of climate change. By 2100, the average global temperature is projected to rise 1.4[degrees] to 5.8[degrees]C relative to the 1990 level, according to the Intergovernmental Panel on Climate Change, a global body of more than 1,500 scientists. There is little question that a global temperature increase in the upper range of predictions would be highly disruptive. As temperatures rise, so, too, do the health risks from heat waves, failing crops, infectious diseases, and other environmental changes. People already facing food insecurity particularly could be distressed because with each 1[degrees]C jump in temperature above optimal levels, wheat, rice, and corn yields fall by 10%. Even at the lowest projected temperature increases, climate change models predict more frequent and more severe storms, floods, heat waves, and droughts--all of which would affect biodiversity, human health, and economic security.

Such effects already may have begun to occur. In 2005, for example, parts of Brazil's Amazon rain forest experienced the worst drought in more than a century, thought to have been precipitated in part by abnormally high temperatures in the North Atlantic Ocean. With less rainfall, tropical forests dry out and burn more easily. Less moisture evaporates from these drier forests, leading to less precipitation, which perpetuates the problem.

The upward trend in sea surface temperatures also has contributed to a record-breaking Atlantic hurricane season, with 27 named storms and 15 hurricanes in 2005. In August of that year, Hurricane Katrina ravaged the Gulf Coast, leading to more than 1,100 deaths and displacing approximately 1,000,000 people. The U.S. suffered an estimated $75,000,000,000 in damage--the costliest natural disaster in the nation's history.

A report by the Pew Center on Global Climate Change analyzing the results of 40 previous studies found a clear link between increased temperatures and numerous changes in natural systems across the U.S. Warmer winters, more precipitation, and earlier springs are causing certain plant species to bloom several weeks ahead of schedule, disrupting insect food supplies and plant pollination cycles. Temperature changes have led to shifts in many species' habitats, as populations move north and to higher elevations in search of cooler air. Scientists estimate that about half of all wild species in the U.S. already have been affected by such changes.

Warming in the Arctic--the area around the North Pole, including parts of Alaska, Russia, Canada, Greenland, and Scandinavia--has occurred at nearly twice the global average rate. Indeed, a recent snapshot shows that the greatest warming two years ago occurred in the Arctic Circle. Warming there is enhanced by a positive feedback mechanism. Snow and ice reflect some 80% of solar radiation. When they melt, more heat is absorbed by the underlying surface, which, in turn, melts more snow and ice. From 2002-05, summer Arctic sea ice has covered 20% less area than its 1978-2000 summer average. The Arctic could be ice-free in summers by the end of this century, threatening the fate of the polar bear as melting ice shrinks its habitat and compromises access to food.

Moreover, in western Siberia, an area of permafrost spanning 1,000,000 square kilometers--the size of France and Germany combined--recently began to melt for the first time since it was formed at the end of the last ice age more than 11,000 years ago. This permafrost covers the world's largest frozen peat bog. Scientists warn that, if warming trends continue, it will release billions of tons of stored carbon into the atmosphere.