The polar vortex blew into 2014, coating the first couple of months with snow and record-low temperatures across the country. Some climate change skeptics said the chilly phenomenon was evidence that the Earth isn't warming, while some scientists said the dramatic pattern was actually a symptom of climate change.
The polar vortex wasn't the only event of the year that spurred debate over the existence of human-caused climate change and potential solutions. Lawmakers argued over the environmental impact of building the Keystone XL pipeline to carry Canadian oil through the United States, and President Barack Obama proposed new Environmental Protection Agency regulations on coal plants.
In November, the Intergovernmental Panel on Climate Change, a United Nations group, issued its fifth and gravest report on the future of climate change, just ahead of the UN's climate change gathering in Lima, Peru. There, nearly 200 nations committed to reduce their emissions of greenhouse gases.
Despite mounting evidence and scientific consensus that human-caused climate change is real, many Americans' skepticism and flat-out denial remains strong. A Pew Research survey from September showed 61 percent of Americans believe there is solid evidence of global warming, while 35 percent disagree.
This hasn't changed in at least 17 years, said Jon Krosnick, who researches public opinion on climate change at Stanford University.
He said the country is split into two groups: two-thirds who believe climate scientists, and one-third who don't. Growing scientific evidence hasn't affected that split much.
"Of the people who don't trust scientists, any change in the findings or conclusions or opinions of scientists are not of interest," Krosnick said. "So any change in scientists' opinions will not be consequential."
Denial remains among politicians and pundits, too, providing PolitiFact with many statements to fact-check throughout 2014. The statement "Climate change is a hoax" won PolitiFact's annual readers' poll for Lie of the Year with 31.8 percent of the vote.
That claim was the title of a five-minute video released by congressional hopeful Lenar Whitney, a Republican from Louisiana. Whitney's claim ignored consequential evidence about climate change and relied on distorted and debunked evidence.
Several climate scientists told PolitiFact that Whitney's claim was "laughable," "deeply misguided," "uninformed," "disgusting" and "absurd." PolitiFact called it Pants on Fire. Whitney, meanwhile, didn't even make the runoff.
How do we know climate change isn't a mass conspiracy to pull the wool over the world's eyes, as Whitney claimed?
Such a scenario seems near impossible, considering the overwhelming consensus among respected climate scientists that anthropogenic (human-caused) global warming is indisputable. Research also shows that climate change denial is concentrated among those who have less expertise in the subject or no scientific training at all.
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Politicians with much higher profiles than Whitney also have argued with basic climate change science, such as Sen. Marco Rubio, R-Fla., a potential 2016 presidential contender. He said in May that human activity is not "causing these dramatic changes to our climate." PolitiFact rated that claim False.
Additionally, much of climate change deniers' backup evidence is cherry-picked or too simplistic to be meaningful.
For example, Rubio said Earth's surface temperatures "have stabilized," a claim PolitiFact rated Mostly False. He has a point that there has been a pause in temperature growth over the past 15 years. But scientists say it's far too early to say temperature has stabilized, and most believe growth will pick back up again. Additionally, the past 15 years have been some of the hottest years on record, despite the pause in temperature growth.
Some deniers turn the tables and say it's the government and its scientists that are spinning the data. In June, Fox News pundit Steve Doocy said, "NASA scientists fudged the numbers to make 1998 the hottest year to overstate the extent of global warming."
First of all, Doocy distorted the blog post where he took the claim from. Second, scientists found fundamental flaws in the raw data used to make this claim. PolitiFact rated Doocy's claim Pants on Fire.
Compared to the consensus among scientists, the percentage of Americans who believe in human-caused climate change is quite low. The latest Gallup polls for 2014 show that 25 percent of Americans are skeptical of global warming, while 40 percent are "concerned believers" in global warming.
According to the poll, 80 percent of skeptics are Republicans, and 11 percent are Democrats. This partisan split carries over into Washington, said California Gov. Jerry Brown, who claimed "virtually no Republican" in Washington accepts climate change science. After finding fewer than 10 current Republican politicians who accept the science, PolitiFact rated Brown's claim Mostly True.
This will eventually cause problems for Republicans trying to court young people, said Sen. Chris Murphy, D-Conn. He said "only 3 percent of voters 18 to 34 don't believe that climate change is really happening." Murphy's claim matched up with polling data, and we rated his claim True.
Conservative radio talk show host Rush Limbaugh took pride in the fact that so many Americans share his skepticism of climate change science — saying the United States leads "with the highest amount of doubt about the conventional wisdom of climate change" in the world. Taking into account caveats about the research, which polled people in 20 countries, we rated his claim Mostly True.
Climate change skeptics' talking points have evolved since the 1990s as the scientific evidence has grown, said Riley Dunlap, an environmental sociology professor at Oklahoma State University who has been studying public opinion of climate change for 20 years. They first said the Earth wasn't warming. Then they said the Earth was warming, but it's not caused by human activity. Now, many agree with the science, but think it's not that big of a problem.
"But in (Whitney's) case," Dunlap said of the claim that climate change is a hoax, "She's reverting to some of the most primitive statements."