Oreskes has found there is a "scientific consensus" on global warming - that is, it is real and it is being caused by humans.

Oreskes' paper's strength is its simplicity. It is something everyone can understand, without knowing the chemistry of carbon dioxide in the atmosphere.

She looked at nearly 1,000 technical papers in the peer-reviewed scientific literature and could not find a single one that disagreed with "the basic consensus statement, that CO2 is increasing, that it is changing the chemistry of the atmosphere, and it's having discernible effects," she told UPI. Further, she added, these CO2 increases are the result of human activity.

There has been an avalanche of evidence indicating the effects of warming are being felt more and more on the planet. In only the last six months:

-The Arctic Climate Impact Assessment found winter temperatures in the Arctic have increased by 4 degrees to 7 degrees Fahrenheit (2 degrees to 4 degrees Celsius) in the past 50 years and should go up about twice that much more in the next hundred;

-Arctic summer sea ice will decline by 50 percent by the end of the 21st century, the ACIA found, with some models predicting complete disappearance of summer sea ice;

-Coastal native villages in the Arctic are eroding, requiring relocating their inhabitants further inland;

-Climate change is affecting the migration patterns, habitat preferen ces and ecology of hundreds of animal species in the United States, according a report by the Pew Foundation;

-Floating ice shelves in Antarctica, stable for the past 13,000 years, have collapsed;

-Glaciers around the world are melting at rates unprecedented for thousands of years;

-Glaciers in Antarctica - previously thought to be relatively immune from warming trends - are thinning and speeding up dramatically.

"We're beginning to push past the normal range of climate variability of the Holocene (post-Ice-Age period)," said Ted Scambos, a glaciologist at the Snow and Ice Data Center in Denver. "We're seeing the first few steps, the first few responses of a globally warming world. People will point back to these first few years of the 21st century and say that this is when we saw it in the polar regions."

The polar changes could mean a dramatic increase in sea-level rise, he said , well beyond current projections.

"I don't want to mince words," Scambos told Climate. "It looks to me like we are headed toward a more rapid sea-level rise than projected by the IPCC (Intergovernmental Panel on Climate Change) report."

In 2001, the panel had predicted a range of 4 inches to 30 inches (11 centimeters to 77 centimeters) in sea-level rise between the years 1990 and 2100.

Each piece has its critics, of course, but taken as a whole, across many disciplines, the mounting evidence presents a strong case global warming is real and it already is causing tangible effects that are at least potentially serious.

Whether the effects are serious and damaging enough to warrant potentially expensive actions - such as attempting to curtail CO2 emissions - should now become the focus of the debate in the United States and elsewhere.

Because the Oreskes paper is easy to understand, an d because she did not find even a single paper dissenting from the consensus position, there has a flurry of Internet commentary downplaying the meaning of this consensus.

Roger Pielke Jr., of the University of Colorado's Center for Science and Technology Policy Research, wrote in "Prometheus: The Science Policy Weblog," that "I am amazed by the recent attention being paid to the issue of a scientific consensus on climate change. Naomi Oreskes wrote an article a few weeks back in (the journal) Science, claiming that a literature review shows that a central statement of consensus reported in the IPCC is indeed a consensus. Since that article was published, debate and discussion has taken place on, among other things, whether it is in fact a unanimous perspective rather than the overwhelming view of most scientists."

Roy Spencer, of the University of Alabama-Huntsville, argued on the Web site TechCentral Station that Oreskes' definition of w hat issue on which everyone apparently agreed was so weak it was nearly meaningless.

"Let's be honest about what that consensus refers to," Spencer wrote, "that 'humans influence the climate.' Not that 'global warming is a serious threat to mankind.'"

Interpretations aside, the studies included in the Oreskes paper also show the costs and benefits of climate change are not distributed evenly. The climate will change differently for different regions. Some studies indicate the United States, for instance, may come out a net winner from a warmer climate. On the other hand, the burden is expected to fall heavily on poor and developing countries. What else is new?

Even if humanity strides through the changes unbowed, other residents of Planet Earth might not fare so well - polar bears dependent on vanishing Arctic sea ice, for example, or pikas at alpine altitudes with a lifestyle evolved to survive in near-permanent snow cover.

Hard-headed and pragmatic policymakers usually give short shrift to policy recommendation that cannot be measured in dollars, but these softer issues of human responsibility to the rest of creation have been an important driver of many environmental polices over the past 35 years. Global warming quickly may become another one of these arenas.

Climate is a weekly series examining the science behind and potential impact of global climate change, by Dan Whipple, who covers environmental issues for UPI Science News.

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