More than 80 percent of U.S. climate scientists believe human activity is contributing to climate change, according to a poll conducted by the Statistical Assessment Service at George Mason University in April.

Beliefs on the extent it will harm the Earth, however, still vary.

Based on current trends, 41 percent of the scientists polled believe global climate change will pose a very great danger to the Earth in the next 50 to 100 years, compared with 44 percent who see it as moderately dangerous and 13 percent who said it poses relatively little danger.

A recent book highlights those who fall into the last category and those who don't connect climate change with human activity, arguing there is still life left in those cool to climate change "alarmism."

"It may well be that the majority of the world's top scientists disagree with the Al Gore view of the world," said Lawrence Solomon, author of the new book "The Deniers," which profiles scientists who question common beliefs on climate.

Robert Cahalan, head of the climate and radiation branch at NASA Goddard, counters, "The consensus on the explanation of the global warming we're witnessing is that it's due primarily to greenhouse gas emissions."

Ongoing research continues to support this view, Cahalan told United Press International, and the scientific community has largely stuck by it because no better explanation has emerged.

"We're always open to alternative hypotheses," Cahalan said.

Policymakers certainly seem convinced by the reigning hypothesis, with the international community gearing up to negotiate a replacement for the current global agreement on climate change, the Kyoto Protocol. In the United States, President-elect Barack Obama and the incoming Congress are also sending clear messages they intend to pass greenhouse gas emissions regulations. But Solomon, who's also director and founder of the Energy Probe Research Foundation, a Canadian environmental and public policy institute, backs up his claim of skepticism with an impressive list of thinkers, including Eigil Friis-Christensen, director of the Danish National Space Center, and Richard Lindzen, professor of atmospheric science at the Massachusetts Institute of Technology.

The Earth is clearly experiencing a warming period, but it's not entirely certain what's causing it or how to stop it, Solomon said, and policy decisions based on such iffy science could have unintended consequences. For instance, there's debate about whether planting more trees adds to or detracts from the warming trend.

While plant matter absorbs carbon dioxide through photosynthesis -- decreasing the amount of greenhouse gases in the atmosphere -- tree cover in northern regions obstructs large swaths of snow that decrease world temperatures by reflecting sunlight, instead of absorbing it like darker colors. It's not clear how to balance these two conflicting forces, Solomon said, and this is just one example of the multitudes of uncertainty that surround plans for climate-change mitigation.

Science always involves some level of uncertainty, though, said Jay Gulledge, senior scientist at the Pew Center on Global Climate Change. The real question is not whether everyone agrees on climate science but whether enough consensus exists to warrant action, he said.

"We're going to have to decide as a society if what the science says is a plausible outcome is acceptable," Gulledge said.

Part of the problem with Solomon's book, Gulledge said, is that it examines whether different scientists believe a "catastrophe" will result from the current warming trend.

"Science doesn't tell us what doom is or a catastrophe," Gulledge said.

That lies in the realm of policy.

But before legislators can make decisions, there needs to be a better understanding about the causes, impacts and mitigation of climate change, Solomon said, which means the debate needs to take a bigger role in public and political discussions.

"It's not acceptable that there's a debate only in scientific circles, because the public is making decisions that involve hundreds of billions of dollars," he said.

Pressure from funding sources tends to stymie that debate, though, said Edward Wegman, one of the scientists profiled in Solomon's book and a professor at George Mason University.

"If you're too much of a skeptic, you're not going to get funding from the National Oceanic and Atmospheric Administration, and you're not going to get funding from the National Science Foundation," Wegman told UPI.

"At NOAA, a funding proposal is reviewed impartially by a panel of six to 12 scientific peers who separately give it a score with a written justification based on the strength of its written narrative and its scientific merit," said Scott Smullen, NOAA's deputy director of communications.

"Scientists are by nature skeptical, and that's healthy," he said.

Proposals ranked the highest receive funding first, and so on down the line until research funds are depleted.

Wegman has other concerns about the science surrounding climate change, though. Certain aspects have been distorted or escaped proper peer review, he said, pointing to the controversy that surrounds the "hockey stick" graph used by Al Gore to demonstrate a recent increase in the mean temperature changes in the Northern Hemisphere.

In 2006 Congress asked the National Academy of Sciences to examine the validity of the graph, and the team reported it had reservations about the methodology used by Michael Mann, the scientist who created it. However, controversial studies or graphs such as Mann's do not mean global temperatures aren't rising or that human activity isn't driving climate change, said Wegman, who also testified before Congress about the graph. Nor does Wegman necessarily oppose policy proposals to halt climate change.

"I think things like mandatory reductions in emissions from automobiles and power plants and establishing wind farms and improving solar panels are good things," he said.

But major energy policy changes, particularly mandatory emissions reductions, will hit the poorest people hardest, and that's unfair, when science hasn't entirely proven the outcomes of increased carbon dioxide emissions, said Bonner Cohen, senior fellow at the National Center for Public Policy Research, a conservative think tank.

"It will raise the cost of energy for everyone," Cohen told UPI. "I cannot imagine a better way to perpetuate poverty and disease than to adopt a Kyoto Protocol-type agreement for the poorest countries in the world."

Ethicist Donald Brown, a professor at Penn State University, says while climate change mitigation policies do have costs, the world's poor will suffer much more if policy fails to prevent warming and it occurs on the scale many have projected. As a result, inaction is unethical because those who will be hit the hardest are also those who have contributed the least.

"Those most vulnerable to climate change are often the least able to afford adaptation measures such as dikes, irrigation to compensate for droughts (or) moving away from flood- or storm-prone areas," Brown wrote in a paper he co-authored on the topic.

Policymakers should take action precisely because there is uncertainty, he said.

"If government waits until all uncertainties about climate change impacts are resolved … it is likely to be too late to prevent potentially catastrophic damages," Brown said. "To ignore risks is to decide to expose human health and the environment to a legitimate threat."

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