Scientists at Capitol Hill Briefing Deliver Troubling News on Global Warming

The retreat of glaciers worldwide, from Alaska and China to the mountains of Peru, offers solid evidence that human-induced global warming is real, a leading scientist told a 4 May Capitol Hill briefing arranged by the AAAS Center for Science, Technology and Congress and the AAAS journal Science.

Lonnie Thompson, a professor of geological sciences at Ohio State University, described the dramatic loss of ice on Mt. Kilimanjaro in Tanzania, Africa. In 1912, he said, there were about 4.3 square miles of ice fields atop the mountain. By 2000, the fields had shrunk to 0.94 square miles. At the current rate of decrease, he said, "some time before 2020, all the ice fields on Kilimanjaro will disappear."

Closer to home, the picture is no better. Ice fields are retreating rapidly in Glacier National Park in Montana. "It's estimated that within 30 years, there will be no glaciers in Glacier Park," Thompson said. In southeast Alaska, the massive Muir glacier has retreated more than 9 miles since 1941.

In the Andes mountains of Peru, the Qori Kalis glacier—which had been retreating about 5 yards per year from 1963 to 1978—now is retreating nearly 220 yards per year, or more than 40 times faster. Thompson's research group also found beds of preserved plants that have been uncovered as Peru's Quelccaya ice cap retreats. Dating of the plants suggests the climate in that part of the world had been frigid for at least 5,200 years and perhaps as long as 50,000 years. Now, all that is changing.

Worldwide, Thompson said, mountain glaciers had been increasing only in Norway and Sweden, where storms that used to dump snow in the Alps moved northward. But since 1999, he said, even those Scandinavian glaciers have been shrinking.

F. Sherwood Rowland, a Nobel laureate in chemistry who spoke at the briefing, said the mechanisms driving global warming are clear. Gas molecules composed of more than two atoms, such as the carbon dioxide released in the burning of oil, coal and natural gas, have the ability to trap infrared radiation and prevent heat from being radiated to space. The greenhouse gases also include methane, nitrous oxide, chlorofluorocarbons, ozone and water vapor, Rowland said.

The scientists at the briefing said global warming is not as controversial as sometimes portrayed by skeptics. Those who study the issue agree that human industrial activity is having an impact on climate, they said, and policy makers need to understand the depth of scientific consensus on key issues.

Jerry Meehl, senior scientist at the National Center for Atmospheric Research, spoke of what he calls the "climate change commitment" that will result from the greenhouse gases we already have put into the system. Even if greenhouse concentrations were stabilized at 2000 levels, he said, we would still face warmer temperatures and rising sea levels for decades to come.

The computer models estimate that right now we are committed to an additional 1 degree Fahrenheit rise in globally averaged surface air temperatures by 2100. This is about the temperature increase already measured during the 20th century, Meehl said. Further, we are committed to about three times more sea level rise beyond the half foot or so that already has occurred in the 20th century, he said, with no sign of the committed sea level rise leveling off by 2100.

The climate change commitment will occur because the oceans take much longer to heat up than the atmosphere. There is a lag in the system, Meehl said, as warming water expands to produce sea level increases. "With each passing day, we are committed to more climate change in the future," Meehl said. "The longer we wait to do something, the worse the problem gets."

Christopher Field, an ecologist at the Carnegie Institution of Washington, described some ecological effects of climate change that already are apparent. He cited a 2003 study which found that in North America and Europe, signs of spring—animal breeding and blooming of flowers—had occurred an average of 2.3 days earlier over the course of each decade for the past half century.

Most plants and animals that are able to move have been shifting north by about 4 miles per decade, Field said, into areas that used to be cooler. Rare or endangered species often have the most difficulty shifting their range, he said, while invasive plant species do much better.

Although some climate change skeptics have argued that a little warming would be good for agriculture, Field said one study found that for every increase in temperature of 1 degree Fahrenheit, the crop yield of corn and soybeans in the U.S. is likely to decrease by 9 percent.

Donald Kennedy, the editor-in-chief of Science and president emeritus of Stanford University, said accounts of current impacts of climate change, such as the glacier retreat and altered growing cycles of plants, are more persuasive for the average person than stories on computer projections of future climate change.

And while there remain uncertainties in those computer models, Field said they point to some stark changes if greenhouse emissions are not controlled. He mentioned a study last year projecting that California's mountain snow pack could be reduced 89 per cent by the end of this century if greenhouse emissions continue on a "business as usual" trajectory.

Presentations of the climate science experts from the May 2005 AAAS Climate Change Congressional Briefing are now available here.

Earl Lane

10 May 2005