Study Strengthens Global Warming Theory

SANTA CRUZ, California, October 24, 2003 (ENS) - Scientists say they have filled in a key piece of the global climate puzzle for a period 55 million years ago that is considered one of the most abrupt and extreme episodes of global warming in Earth's history. The findings reinforce climate theory that suggests increasing greenhouse gas emissions will cause temperatures to rise all over the planet - with greater increases in sea surface temperatures at high latitudes than at low latitudes.

"The predictions from the models seem to be consistent with the geologic record, so I would say greenhouse climate theory is alive and well," said study leader James Zachos, a professor of Earth sciences at the University of California at Santa Cruz.

The study was published online Thursday by "Science Express" and will appear in a later print edition of "Science" magazine.

Zachos and his colleagues analyzed sediment cores deposited on the ocean floor some 55 million years ago during a period known as the Paleocene-Eocene Thermal Maximum, which lasted about 150,000 years.

This period is marked by a massive release of heat trapping greenhouse gases that caused global temperatures to rise.

The sediment cores used in the study were obtained at the Shatsky Rise in the tropical Pacific. (Photo courtesy the Ocean Drilling Program)

For reasons still unclear, the clathrates suddenly began to decompose, releasing an estimated 2 trillion tons of methane. Once released, the methane would have reacted with dissolved oxygen in the ocean to produce massive amounts of carbon dioxide (CO2), another greenhouse gas.

The large increase of these two gases raised temperatures worldwide and is reflected in dramatic changes in the fossil record of life in the ocean and on land.

"This event is the best example of greenhouse warming in the geologic record, and for the first time we have been able to document the climate response on a relatively broad planetary scale, from the tropics to polar latitudes," Zachos said.

The new study centers on the combination of the first reliable estimates of the change in tropical sea surface temperatures during this period with existing records of sea surface temperatures at high latitudes.

The researchers report that average global temperatures increased by about 5 degrees Celsius, while sea surface temperatures increased 8 to 10 degrees Celsius at high latitudes. The study shows an increase of 4 to 5 degree Celsius in tropical sea surface temperatures.

The researchers analyzed shells of microscopic plankton preserved in seafloor sediments from a site called Shatsky Rise in the tropical Pacific.

Zachos says the cores provided a complete sequence of deposits representing the boundary between the Paleocene and Eocene epochs.

"There are not many places in the Pacific where you can recover sediments of this age in which the fossils are not so recrystallized that they have lost their original geochemical signatures," Zachos said.

The chemical composition of the plankton's calcite shells reflects the temperature of the water in which they were formed.

The researchers explain that a key measurement examined in this study was the ratio of magnesium to calcium, which increases exponentially with the temperature at which the shells formed.

They found that ratio in seawater is relatively constant over the timescale of the Paleocene-Eocene Thermal Maximum event, leaving the ratio in the shells as sensitive to only one variable - the calcification temperature.

The study provides important backing for the climate models that scientists are using to predict the effects of the current rise in atmospheric CO2 due to industrial emissions, Zachos said.

Most scientists are convinced that greenhouse gas emissions are causing the planet's climate to change. (Photo courtesy the David Suzuki Foundation)

The release of this study comes as the United States is engaged in a fierce debate over climate change.

On Thursday, a dozen states, two cities and more than a dozen environmental groups filed suit in federal court challenging the Bush administration's decision not to regulate emissions of greenhouse gases as pollutants under the Clean Air Act.

President George W. Bush is loathe to enforce mandatory C02 reductions on American industries and has repeatedly questioned the science that points to the effects of greenhouse gas emissions on the climate.

Many scientists believe that there is ample evidence manmade greenhouse gas emissions are causing the climate to warm, and if left unchecked, could cause rising sea levels, the melting of the polar icecaps, and a host of other environmental problems that could have far reaching impacts.

The administration has instead called for more study of climate change and has pushed forward with a voluntary program to cut the nation's greenhouse gas intensity - the ratio of emissions to economic output - by 18 percent.

Critics believe this approach will do little to reduce emissions and note that the United Nations released data this year that found U.S. greenhouse gas emissions rose some 14 percent from 1990 to 2000.

U.S. greenhouse gas emissions are expected to increase another 12 percent by 2012.