Global Warming: Is There Still Room For Doubt?

Sorry, skeptics. Scientists say they have the smoking gun

On Oct. 13, the CEO of Exxon Corp., Lee R. Raymond, told the 15th World Petroleum Congress in Beijing three things: First, the world isn't warming. Second, even if it were, oil and gas wouldn't be the cause. Third, no one can predict the likely future temperature rise.

Many others in industry and government are skeptical of the threats posed by global warming, and they would likely agree with Raymond's conclusion: "Before we make choices about global climate policies, we need an open debate on the science, an analysis of the risks, and a careful consideration of the costs and benefits."

The call for scientific debate is 10 years too late. The costs of dealing with global warming are uncertain, but in the past decade global warming itself has become one of the most exhaustively debated subjects in science. The result is a solid consensus on the scientific facts. According to the consensus, Raymond's three assertions are wrong.

In December, 160 nations will meet in Kyoto, Japan, to consider a treaty designed to curb greenhouse gas emissions. On Oct. 22, President Clinton said he will propose reducing greenhouse gas emissions to 1990 levels sometime between 2008 and 2012, with further reductions after that. To meet that goal, he called for an emissions trading plan and $5 billion in tax credits and R&D to spur adoption of more energy-efficient technologies. Japan and Europe are pushing for even steeper cuts. The task won't be easy. U.S. emissions in 1996 were already 8.3% above 1990 levels, according to a new Energy Dept. report.

ASSESSING THE CHANGE. The scientific consensus on global warming comes from the Intergovernmental Panel on Climate Change (IPCC). It was established in 1988 by the World Meteorological Organization and the United Nations Environment Program to assess the science of climate change, determine its impacts on the environment and society, and formulate strategies to respond. More than 900 scientists from 40 countries have participated as authors or expert reviewers in the IPCC's latest report, published in 1995.

"It's absolutely the best assessment body we have," says Rosina Bierbaum, acting associate director for environment in the White House science adviser's office.

"It's a look at the state of the art---what we know about the climate system," says Gerald Meehl of the National Center for Atmospheric Research in Boulder, Colo., a lead author for one of the report's chapters. "Literally thousands of people wind up reading these things....It's the consensus view of just about everyone who's chosen to become involved." In June, some 2,400 scientists signed a letter saying they endorsed the findings.

The basics of global warming are simple. So-called greenhouse gases--including carbon dioxide and methane--build up in the atmosphere. Carbon dioxide is the most important of the greenhouse gases generated by human activity. The gases trap the sun's heat, like a car parked in the sun with the windows closed. Couple that with a basic fact: The amount of carbon dioxide in the atmosphere has risen by 30% since pre-industrial times (about 1750). The implication is that temperatures are rising, and that's what the IPCC was charged with studying.

HUMAN CULPRITS. In his speech, Raymond acknowledged that some measurements show warming but added that "satellite measurements have shown no warming trend since the late 1970s. In fact," he concluded, "the earth is cooler today than it was 20 years ago." In its 1995 report, the IPCC disagreed. It said the temperature at the earth's surface, where it matters, has increased from one-half to 1 degree F since the late 19th century. The 20th century has been at least as warm as any other century since 1400 A.D., and recent years have been among the warmest on record.

On the causes of global warming, skeptics make the argument that most of the greenhouse effect comes from water vapor and only 4% of the carbon dioxide entering the atmosphere is due to human activity. "Leaping to cut this tiny sliver of the greenhouse pie...defies common sense," as Raymond put it.

Not so, said the IPCC--the 30% rise in atmospheric carbon dioxide during the industrial era is due to human activity and is responsible for the warming so far. In cautious language generated by extensive discussion, the IPCC produced what scientists say is the smoking gun: "The balance of evidence suggests a discernible human influence on global climate."

Last, skeptics say that predictions of future warming are notoriously inaccurate. Raymond agreed, but the IPCC doesn't. Continuing improvement of computer projections "has increased our confidence in their use for projection of future climate change," it said. The IPCC concluded that by 2100, temperatures could rise 2 to 6 degrees F, depending partly upon how fast carbon dioxide levels rise. That could lead to a sea-level rise of 6 to 38 inches and changes in the frequency of drought and flooding.

The IPCC admits there are uncertainties in the science. But that doesn't undercut the IPCC's conclusions. "This is an ongoing research problem," says Meehl.

As the Kyoto meeting draws near, many in the business community are campaigning vigorously against limits on fossil fuel use, saying such curbs could stifle the economy. Environmentalists are lobbying just as hard for binding limits on greenhouse gas emissions. That's a political issue, not a scientific one. And there the IPCC has no answers.

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