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7. Climate change is part of a natural cycle
"How can we, petty little humans that we are, possibly alter something as huge in scope as the planet's climate? After all, when you think about just how complex the Earth really is, we're just not that important. So why should we change our habits?"
That might have been true until about two centuries ago, when the Industrial Age came along and we first started burning massive quantities of filthy, CO2-producing coal. Since then, as technology has advanced and our population has multiplied to over 6 billion people, we've gotten a bit big for our britches, pushing the limits of just how much pollution we can pump into the air before seeing catastrophic global effects.
There's no doubt that historically, temperatures and greenhouse gas levels have fluctuated naturally, but those fluctuations are nothing compared to what we've seen in the past century (see "Reconstructed Temperature" chart).
6. Temperature data is unreliable
Skeptics like to claim that temperature records showing a warming trend are unreliable because weather stations are often located in areas that absorb and radiate heat, like rooftops and asphalt parking lots. But in reality, the Urban Heat Island Effect has had a very small influence on temperature readings, and climate scientists adjust the data to account for it.
All major temperature reconstructions for the past 1,000 years published in peer-reviewed journals show some variability in surface temperatures over centuries, with a dip in the Little Ice Age—and a huge uptick during the past century. Even if those reconstructions are excluded and we only look at the last 150 years, there's a significant rise.
When it comes down to it, surface temperature records are far from the only evidence of global warming. Grist, the environmental website, notes that borehole analysis, weather balloon temperature data, satellite measurements, glacial melt observations, sea level rise and other indicators can be used completely independently of surface temps.
5. Antarctica is actually gaining ice, not losing it
Melting at the Earth's poles has long been considered a major warning sign of global warming, so when two recent studies indicated a slowing of overall surface warming across Antarctica—and even some ice gain—skeptics took it as solid proof of their point. The problem is, NASA satellite data shows that Antarctica has been losing more than 24 cubic miles of ice each year since 2002.
The "discrepancy" boils down to two things: First, there's a big difference between land ice and sea ice. Sea ice is increasing, but it's not because Antarctica is cooling—in fact, the Southern Ocean is warming faster than any other ocean on the planet. It's due to a series of events including the hole in the ozone layer and wind currents pushing sea ice around.
Second, scientists suspect that Antarctic ice shelves are being eroded from underneath by warming seas, and satellites can't measure under the ice. While there's not much happening in East Antarctica, which is a high, dry desert making up two-thirds of the continent, West Antarctica—a series of ice-covered islands that rest on the ocean floor—is retreating at a dramatic pace, especially along the southern portion of the Antarctic Peninsula.
The Peninsula is the farthest point from the South Pole, so its deterioration could be a sign of what's to come for the rest of the continent.
4. 'Climategate' proves it's all an elaborate scam
When hackers stole e-mails written by England climate scientists at the University of East Anglia's Climatic Research Unit (CRU) in November 2009, skeptics hailed it as "the final nail in the coffin for global warming." To much of the public, the content of some of the e-mails seemed damning: The scientists, including Phil Jones, joked about physically harming opponents and referred to their work in terms that seemed to boast of intentionally manipulating data.
But the quotes were clearly taken out of context. Few people took the time to read the e-mails in full before deciding that their contents proved global warming to be a scam.
While Jones himself admits that the personal attacks in some of the e-mails were "awful," an extensive independent examination of all 1,073 e-mails by The Associated Press and a panel of moderate climate scientists found no evidence whatsoever that the science of global warming was faked.
A British panel in July rebuked the scientists for their behavior, but found the same thing. In fact, a New York Times story that came out after the British panel issued its decision noted that after a handful of separate investigations, "All five investigations have come down largely on the side of the climate researchers, rejecting a number of criticisms raised by global-warming skeptics."
When "Climategate" fizzled, skeptics homed in on a new target: a few minor errors in a report by the Intergovernmental Panel on Climate Change (IPCC). That's an entire article in itself; to get the facts—including at least one high-profile retraction of a story by London's Sunday Times—see realclimate.org.