As Earth Day approaches, climate change is climbing back into the public consciousness. But though most climatologists agree that humans are driving global warming, surveys suggest that public concern about climate change is waning.
According to a recent survey from the Center for Climate Change Communication at George Mason University, a majority, 61 percent, of TV weathercasters think there is disagreement among scientists on global warming.
Although 54 percent said it is occurring, 25 percent said it isn't and 21 percent said they weren't sure.
Those inclined to skepticism don't necessarily subscribe to the same exact set of claims, but their arguments do seem to cluster around a few key points. Here are five of the most common ones.
As January's cold weather and blizzards set records, some politicians and pundits argued global warming couldn't be occurring given what they could see happening outside their front doors.
As the cap-and-trade debate heated up in Washington, D.C., the Virginia GOP used a January "snowpocalypse" to attack two Democratic candidates.
In the online video "12 Inches of Global Warming," the group mocked Rep. Rick Boucher, D-Va., and Rep. Tom Perriello, D-Va., for supporting cap-and-trade climate change legislation.
The video, which included snippets from local weather reports and footage of cars covered in snow, ended with the narrator urging viewers to: "Call Boucher and Perriello and tell them how much global warming you got this weekend."
"The argument that the temperature's not rising right now is a very easy one to dismiss, but it's also a very compelling one for the average person," he said.
The confusion arises as people observe short-term variability in the weather, but he said, "The climate trend is a very slow-moving and long-term thing."
Abnormally cold days or especially severe storms are just single data points, while global temperature trends are measured over long stretches of time, he said.
Climate scientists add that this past winter's East Coast storms are consistent with what climate models expect to happen as temperatures warm and the amount of moisture in the atmosphere increases.
Beck added that during his five years blogging about climate change, he's come across skeptics who dismiss the theory on the basis of the temperature record.
A 2009 report written by Anthony Watts, a former television meteorologist who maintains a popular skeptical climate blog, reviewed the quality of data from the National Weather Service's network of stations and concluded that the U.S. record is unreliable.
The report found that 89 percent of the stations did not meet the weather service's requirements and argued that since the U.S. record was so poor, other countries must have similarly shoddy records.
Beck said others argue the record is flawed because of differing equipment, changing technology and varying altitudes.
But he said while it may be true that the record could be improved, the hundreds of thousands of measurements taken all over the world in different ways and over more than 100 years overcome the difficulties.
"It's difficult to establish a confident temperature trend," he said. "But there's no reason to believe that scientists haven't handled that problem."
So goes the theory of global warming: The average surface temperature of Earth is gradually getting warmer partly because of increases in human-caused greenhouse gases in the atmosphere.
But some of the most highly-trained skeptical scientists argue that the climate isn't as sensitive to the key greenhouse gas carbon dioxide as the greater scientific community thinks.
"I believe the fundamental basis, which is that CO2 is a greenhouse gas and we are adding it to the atmosphere," said Roy Spencer, a principal research scientist at the University of Alabama in Huntsville. "Where I depart is on this issue of how sensitive is the climate system to that little bit of warming."
Based on satellite observations of Earth, he said he's found evidence that the climate is very insensitive.
Spencer said it makes a big difference. If the climate system isn't as sensitive to carbon dioxide and the temperature change isn't as significant, he said, "then human caused global warming becomes a false alarm."
But others in the scientific community argue that the climate sensitivity hypotheses don't fully explain global temperature trends.
Jay Gulledge, the senior scientist and director the Science and Impacts Program at the Pew Center on Global Climate Change, said this argument is the most common one maintained by the most skeptical of the qualified scientists. But he emphasized that when examined by peers, it has not gained traction.
"It has failed in their eyes to explain their observations," he said.
The research published by scientists who subscribe to this argument gets published in journals and is legitimate, he said, but the theory can't explain key historical temperature changes.
Another common claim is that solar activity is causing global warming. Skeptics who subscribe to this claim argue that the sun's output is driving the upward global temperature trend.
But Gulledge said that scientists have collected large amounts of data on the sun's activity. Some data goes back 30 years, some goes back as far as 600 years, he said, and none of it supports the theory.
"Every single measurement of what the sun is doing shows that the sun is changing in the opposite direction of what would be required to produce a warming of the earth," he said.
As the so-called "climategate" scandal unraveled over the past few months, some skeptics went from challenging the science to challenging the messengers.
In November, thousands of hacked e-mails from a leading climate research center in the U.K. fueled debate.
Some skeptics saw them as evidence that researchers were exaggerating their claims and burying opposing evidence.
At the time, conservative blogger Michelle Malkin said it promised "to be the global warming scandal of the century."
"Right now, the biggest thing is just the attacks on the climate science community," said Beck.
But he pointed out that recent investigations have found that scientists' work was not compromised.
"I think it's really a lot of smoke but no fire," he said.
A panel convened by the British House of Commons to investigate the e-mails of Professor Phil Jones and his colleagues at the Climatic Research Unit of the University of East Anglia (CRU) found that the science was strong.
"Within our limited inquiry and the evidence we took, the scientific reputation of Professor Jones and CRU remains intact," the report said. "We have found no reason in this unfortunate episode to challenge the scientific consensus as expressed by [Prof. John Beddington, Chief Scientific Adviser to the British government], that 'global warming is happening [and] that it is induced by human activity.'"
The report did, however, criticize the scientists for not being more open about their work.
Another independent investigation conducted by the University of East Anglia also found no evidence of "deliberate scientific malpractice" in the group's work.