6 global warming skeptics who changed their minds

With 2010 shaping up as the warmest year on record and unprecedented heat waves gripping the planet, global warming skeptics have suffered another blow with the defection of the "most high-profile" member of their camp, author Bjorn Lomborg. But Lomborg isn't the first doubter to accept the scientific consensus that human carbon emissions are warming the planet and need to be curtailed. Here, a review of several prominent cases:

1. Bjorn Lomborg, Danish academic

Lomborg made waves with his 2001 book, The Skeptical Environmentalist, which argued that global warming was no big deal, and fighting it would be a waste of money. This month, he's publishing Smart Solutions to Climate Change, which argues that a global carbon tax should be imposed to raise $150 billion a year to address global warming.

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Before quote: "In 20 years' time, we’ll look back and wonder why we worried so much." (2002)

After quote: "We actually have only one option: we all need to start seriously focusing, right now, on the most effective ways to fix global warming." (2010)

2. Dmitri Medvedev, Russian president

Russian leaders are famously skeptical of global warming, with then–President Vladimir Putin quipping in 2003 that a warmer Russia "wouldn't be so bad" because "we could spend less on fur coats, and the grain harvest would go up." Then Russia caught fire this summer, choking Moscow with deadly smoke, devastating agricultural production, and convincing Medvedev and other leaders that perhaps global warming is a threat, after all.

Before quote: Climate change is "some kind of tricky campaign made up by some commercial structures to promote their business projects." (2009)

After quote: "Unfortunately, what is happening now in our central regions is evidence of this global climate change, because we have never in our history faced such weather conditions in the past." (2010)

3. Michael Hanlon, British science journalist

Hanlon, science editor for The Daily Mail, was a self-professed skeptic on climate change until a recent trip to Greenland, where he witnessed the accelerated disintegration of the country's massive ice sheet. A few days on the melting ice floes, he says, "is certainly enough to blow a few skeptical cobwebs away."

Before quote: "Global warming, indeed much of environmentalism, has become a new religion. Like the old religions, environmentalism preaches much good sense, is well meaning, but has a worrying lack of logic at its core." (2000)

After quote: "I have long been something of a climate-change sceptic, but my views in recent years have shifted. For me, the most convincing evidence that something worrying is going on lies right here in the Arctic." (2010)

4. Michael Shermer, publisher of Skeptic Magazine

In 2001, Shermer hosted a Skeptics Society debate on global warming, prompted by Lomborg's Skeptical Environmentalist. He sided, predictably, with the skeptics. Then he looked at the science, and in 2006 reached a "flipping point," acknowledging the "overwhelming evidence for anthropogenic global warming."

Before quote: "Scientists like Bjorn Lomborg in The Skeptical Environmentalist have, in my opinion, properly nailed environmental extremists for these exaggerated scenarios." (2008, referring to 2001)

After quote: "Because of the complexity of the problem, environmental skepticism was once tenable. No longer. It is time to flip from skepticism to activism." (2006)

5. Gregg Easterbrook, American journalist and author

Easterbrook was an early skeptic of global warming, writing an influential book, A Moment on the Earth, in 1995 that was dismissive of mankind's role in climate change. By 2006, he'd been swayed by the decade of climate research, and wrote an essay entitled "Case Closed: The Debate About Global Warming is Over."

Before quote: "Instant-doomsday hyperbole caused the world’s attention to focus on the hypothetical threat of global warming to the exclusion of environmental menaces that are real, palpable, and awful right now." (1995, PDF)

After quote: "The science has changed from ambiguous to near-unanimous... Based on the data I'm now switching sides regarding global warming, from skeptic to convert." (2006)

6. Stu Ostro, Weather Channel senior meteorologist

A recent survey found that many meteorologists and TV weathercasters are skeptical (or even "cynical") about anthropogenic global warming (AGW), and Ostro used to fit in that camp. Now he regularly explains the connection between man-made climate change and the extreme weather roiling the world.

Before quote: Large swings in temperature "happened long before humans had a chance to influence the environment, [and] typically occurred within a 10-year period, indicating that drastic climate change can occur through natural means, and quickly." (1999)

After quote: "When it comes to skepticism about AGW, you could say I have street cred," but "it could be said that I 'converted' and became a 'believer.'" (2010)