"Warming of the climate system now is unequivocal," the American Meteorological Society (AMS) concluded in a 2012 official statement. Measurements show that Earth's surface temperature rose by 1.4 degrees Fahrenheit (0.8 degrees Celsius) between 1901 and 2010, with most of that change (0.9 degrees F or 0.5 degrees C) occurring over the last 20 years of that period, and all 10 of the warmest years happening since 1997 [source: AMS]. While the planet has warmed and cooled before, that's the most rapid increase in the past 1,300 years [source: NASA].
So, why do so many people disbelieve global warming? There are a lot of dissenting voices out there. According to one study, an assortment of organizations, often tied to the oil industry, spent nearly $560 million between 2003 and 2010 to fund groups that deny climate change, many with links to sympathetic media and politicians [source: Drexel University]. As a result, if you listen to talk radio or peruse the comments on news Web sites, you'll find the following 10 statements that supposedly disprove global warming repeated. The problem is that they don't disprove anything. Here's why.
Whenever the temperature plunges dramatically and there's heavier snowfall than usual in some states, people will cite the arctic weather as proof that global warming is a hoax. During the cold snap in early 2014, for example, businessman Donald Trump tweeted derisively, "This very expensive GLOBAL WARMING bull---- has got to stop. Ourplanet is freezing, record low temps, and our GW scientists are stuck in ice" [source: Mooney].
That's not too surprising, actually, since psychological research has found that people's views about climate change tend to be influenced by the weather on the day that they are interviewed [source: Konnikova]. One flaw with this way of looking at things, as Columbia University atmospheric scientist Adam Sobel has pointed out, is that there's a big difference between the weather on a particular day and the climate, which is the pattern of what happens over a much longer time.
"In recent times, high-temperature records have been repeatedly broken much more often than low-temperature records," he wrote in an article for CNN.
Additionally, he noted, some scientists believe that global warming paradoxically might be causing harsher winter storms, by weakening the jet stream of fast-moving winds that normally block the frigid polar air mass from creeping southward and chilling the U.S. [source: Sobel].
In September 2013, the Daily Mail — a British newspaper that frequently publishes articles presenting climate change as a hoax — trumpeted its latest evidence, in the form of researchers' findings that the Arctic ice cap actually had increased 29 percent over the previous year. "And now it's global COOLING!" the paper's headline gleefully proclaimed [source: Rose].
On the face, increasing polar sea ice would seem to be a powerful refutation of the scary scenario presented by mainstream climate scientists, which is that the shrinking ice is causing sea levels to rise dangerously. But again, the flaw in the argument is that a single year doesn't make a trend. The amount of northern polar ice varies from year to year, but the long-term pattern is one of severe decline. From 1979 to 2014, the average ice cap in January shrank from 15.5 million square kilometers (6 million square miles) to 13.7 million square kilometers (5 million square miles). The only way that 2013 looked good was because it was a little better than 2012, which was one of the worst years on record [sources: Samenow, NSIDC].
One of the most compelling moments in the 2006 documentary "An Inconvenient Truth" was the animated sequence in which a polar bear in the Arctic Ocean was forced to keep swimming because it couldn't find ice upon which it could rest [source: Hammond]. So that's why climate change disbelievers have been gleeful about recent research suggesting that despite shrinking ice, the polar bear population in the Davis Strait area of eastern Canada actually has increased in recent years, to the point where it may be at carrying capacity — that is, the maximum number of bears that the area can support [source: Crockford].
But the polar bears' story may be a bit more complicated than it seems. For one, counting these animals is a tricky business, and the fact that the ice is breaking up weeks earlier than it did in the past (due to climate change) may actually make it easier for scientists to spot them by helicopter. This could inflate their numbers.
Even if the bear population is indeed increasing, this could be due to a 1980s European ban on the importing of baby harp seal hides, which has led to an increase in the bears' food supply. But as climate change worsens, that momentary brake on the polar bears' decline may not be enough [source: Unger].
To climate change deniers, this is the slam dunk argument. If the rise in global warming has stopped, even as human civilization has continued to pump increasing amounts of carbon dioxide emissions into the atmosphere, that should prove that the whole greenhouse effect thing is bunk, right? Radio commentator Rush Limbaugh certainly thinks so. "There is no warming, and there hasn't been for 15 years," he proclaimed in an August 2013 broadcast.
That sounds convincing, except that it isn't correct. In fact, data from the Met Office, Britain's equivalent of the U.S. National Weather Service, and the University of East Anglia's Climate Research Unit shows that the global temperature did, in fact, increase between 1997 and 2012— roughly the period Limbaugh is talking about —by 0.09 degrees Fahrenheit (0.05 degrees Celsius) [source: Parry].
It is true that the increase was relatively flat, compared to other periods in the past century. But as climate scientist and National Academies of Science member Peter Gleick has pointed out in a Forbes article, global surface temperature has had similar plateaus in the past. But the overriding trend is still that the planet is getting hotter.
If you've been following the global warming discussion at all, you probably know that scientists believe that car exhaust pipes and power plant stacks are pumping too much carbon dioxide into the atmosphere. That, in turn, increases the Earth's natural greenhouse effect, in which heat from the sun's rays is trapped in the atmosphere instead of radiating back into space.
People who don't believe that humans are causing the planet to heat up sometimes point out that even though we're spewing out more carbon dioxide than ever before, the gas still only amounts to a minute fraction of Earth's atmosphere — just 0.04 percent, to be precise [source: Gillis] . How could such a small portion of the atmosphere cause so much harm?
Focusing upon the relative concentration is like claiming that a tiny quantity of arsenic or cobra venom couldn't possibly kill you [source: Gillis]. And carbon dioxide is really good at trapping heat. While the gas only amounts to not even half of a percent of the atmosphere, it accounts for 20 percent of the greenhouse effect [source: NASA]. So increasing that tiny bit of atmospheric CO2 can have a disproportionately huge effect.
Some people who acknowledge the planet is warming insist there's no proof that humans are the cause. Instead, they discuss natural heating and cooling cycles in Earth's history, and how this period happens to be one of them.
That would be a comforting notion, except that it's incomplete. Over the past century or so, the climate has heated up at a faster rate than at any time during the previous 11,300 years, which is about as far back as scientists can calculate reliably. And our planet's actual temperature is warmer than it ever was during most of that longer period [source: Plait].
It's hard to escape the suspicion that our modern industrial civilization, which has raised levels of carbon dioxide and methane in the atmosphere to the highest levels in the past 650,000 years, might have something to do with it [source: NASA].
"While natural variations have altered the climate significantly in the past, it is very unlikely that the changes in climate observed since the mid-20th century can be explained by natural processes alone," the climate change primer on NASA's Web site explains.
Climate scientists are a fickle lot, global warming doubters assert. Sure, almost all of them now seem pretty sold on the idea that the planet is heating up. But back in the 1970s, didn't they just as confidently proclaim that that Earth was cooling down? Why should we believe them now?
Well, for starters, because the ice age meme is distortion. In an era when climate measurements and modeling were in their infancy, there were a few scientists who believed that Earth might be cooling, but they were always in the minority. A review of scientific literature from 1965 to 1979, published in the American Meteorological Society journal in 2008, revealed that 86 percent of the articles presented evidence of a warming trend, and that those articles also were the ones most often cited by other researchers.
The concern about global warming also was reflected in the findings of a 1979 panel convened by the National Research Council, which concluded that increased greenhouse gas output was a serious environmental risk. That report doesn't even mention the possibility of cooling, or an ice age [source: Peterson et al.].
A lot of disbelievers in global warming like to accuse climate researchers of faking their findings, perhaps to enrich themselves with lucrative government research grants or to wield influence over public policy. If such a conspiracy were real, it would require a vast number of scientists at universities and government agencies to act in concert.
As evidence, the climate change critics have pointed to the 13 years of e-mails written by scientists at the Climatic Research Unit at the University of East Anglia in England, which were stolen from the university's computer system by a hacker and released on the Internet in 2009. The critics have claimed that the e-mails showed, among other things, that the scientists had manipulated and suppressed data to back up their assertion that global warming was being caused by human activity [source: Adam].
But an independent investigation concluded in July 2010 that there was no evidence of such rampant scientific dishonesty. The panel found scientists had not subverted the peer review process, and data to reproduce their findings was easily available.
When it came to the supposed smoking gun—an e-mail in which the unit's head, Phil Jones, mentioned a data-massaging "trick" that was used in a graph for the World Meteorological Organization, the investigators found only minor fault, saying that the technique should have been explained in a caption or text [source: CCE Review].
When President Barack Obama promised to provide federal aid to drought-stricken California in February 2014, he and aides said the state's water problems might indicate what's in store for the rest of the nation as global warming intensifies [source: Gillis]. That immediately resulted in a fusillade of criticism from climate change skeptics, who attacked the White House for going further than scientific knowledge justified, and cited that overreach to discredit the notion of climate change itself.
To an extent, the critics had a point, since Columbia University climate scientist Richard Seager told The New York Times that the severe dry spell in California was probably just an extreme swing of the state's natural weather variability.
But it is also true that droughts in some areas are a predicted impact of global warming, even as climate shifts may cause other areas to become wetter [source: : Gillis]. A study published in Nature Climate Change in 2013, for example, predicted that global warming may lead to "severe and widespread droughts in the next 30-90 years" [source: Dai].
"There's no such thing as settled science" is the last, best line of defense for those who don't believe in global warming, because it sounds so, well, scientific. It perhaps was most eloquently articulated by Texas Gov. Rick Perry in a 2011 Republican presidential debate.
"The idea that we would put Americans' economy at jeopardy based on scientific theory that's not settled yet to me is just nonsense," Perry explained. "Just because you have a group of scientists who stood up and said, here is the fact. Galileo got outvoted for a spell" [source: Saenz].
Besides the fact that this argument doesn't really refute any of the specifics of climate change theory, there's another problem: It's a debate in search of participants. Of the 4,014 scientific papers published between 1991 and 2011 that took a position on whether humans were causing global warming, for example, 97.1 percent endorsed the idea, while only 1.9 percent rejected it, and another 1 percent were uncertain [source: Cook et al.].
Additionally, just about every major scientific academy and professional organization in the world — some 200 of them — have adopted the position that the climate is changing and humans are largely responsible [source: Ca.gov]. That may not be absolute unanimity, but it's pretty close to it.
HowStuffWorks looks at what the cleanest cities are doing to avoid a 'bad air day.'
Author's Note: 10 Things That Don't Disprove Global Warning
A few years ago, while working on a magazine story, I visited the affluent southern California enclave of Balboa Island, where sea levels have risen for decades. Residents had found that their seawall, ranging from 7.5 to 9.5 feet (2 to-3 meters) tall, built back in the mid-1930s, was no longer high enough to protect their multimillion-dollar houses against flooding in during storms, and they were looking at raising $80 million to build a new 14-foot (4 meter) wall to protect their property against future storms. To them, global warming was no longer an abstract issue. Whether or not they believed humans were to blame, the trend they could see in their harbor's tidal records was discomfiting, and the risk of not doing anything was too great. I think that's a good metaphor for the situation that the rest of the world is in.
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