On Friday, when Richard Branson offered a $25 million prize to anyone who figures out how to remove a billion tons of carbon dioxide per year from the atmosphere, Al Gore sat by his side and called it an “important and welcome” initiative. For once, Mr. Gore couldn’t be accused of hype.

$25 Million to Encourage Cleaner Air (February 10, 2007) Vacuuming up our carbon-dioxide mess sounds improbable now, but so did the idea of precisely determining a ship’s longitude in 1714, when the British government offered a prize that led to a revolutionary tool for navigators, the chronometer. Private spaceships seemed impractical a decade ago, but the $10 million Ansari X Prize spurred competitors to spend more than $100 million, and the winning design will soon be taking tourists into space.

If governments and other moguls throw in more money, the new Virgin Earth Challenge may be the start of competitions that ultimately yield nanobots or microbes capable of gobbling up carbon dioxide. As far-fetched as it seems today, removing carbon dioxide from the atmosphere could turn out to be a lot more practical than the alternative: persuading six billion people to stop putting it there.

In his film “An Inconvenient Truth,” Mr. Gore has done a brilliant job of reaching the masses by combining a sober science lecture with a horror movie: gigantic ice sheets quickly melting, seas rapidly swamping vast areas, hurricanes relentlessly battering the coasts, the Gulf Stream stopping and plunging Europe into an ice age.

But there are two problems with this approach. One is that scaring people doesn’t necessarily make their political leaders do anything substantive. The other problem is that most of the horror-movie scenarios are looking less and less plausible. Climate change will probably occur not with a bang but with a long, slow whimper, as you can see in the new report from the Intergovernmental Panel on Climate Change.

The report concludes that it’s “very likely” that humans are now the main factor warming the climate. But even as the panel’s scientists are becoming surer of the problem, and warning of grim consequences this century and beyond, they’re eschewing crowd-thrilling catastrophes. Since the last I.P.C.C. report, six years ago, they haven’t raised the estimates of future temperatures and sea levels.

While Mr. Gore’s movie shows coastlines flooded by a 20-foot rise in sea level, the report’s projections for the rise this century range from 7 inches to 23 inches. The panel says Greenland’s ice sheet will shrink and might eventually disappear, but the process could take “millennia.” The Antarctic ice sheet is projected to grow, not shrink, because of increased snowfall.

The scientists acknowledge uncertainties and worrisome new signs, like the sudden acceleration in the flow of Greenland’s glaciers several years ago. But the panel, unlike Mr. Gore, didn’t extrapolate a short-term trend into a disaster, and its caution is vindicated by a report in the current issue of Science that the flow of two of the largest glaciers abruptly decelerated last year to near the old rate.

The panel does consider it “likely” that future typhoons and hurricanes will be stronger than today’s. But it also expects fewer of these storms (albeit with “less confidence” in that projection). As for the Gulf Stream, it is “very unlikely” to undergo “a large abrupt transition during the 21st century,” according to the new report. The current is expected to slow slightly, meaning a little less heat from the tropics would reach the North Atlantic, which could be good news for Europe and North America, since that would temper some of the impact of global warming in the north.

Whatever happens, you can stop fretting about the Gulf Stream scenario in Mr. Gore’s movie and that full-fledged Hollywood disaster film “The Day After Tomorrow.” Mr. Gore’s companion book has a fold-out diagram of the Gulf Stream and warns that “some scientists are now seriously worried” about it shutting down and sending Europe into an ice age, but he must have been talking to the wrong scientists.

There wouldn’t be glaciers in the English shires even if the Gulf Stream did shut down. To understand why, you need to disregard not only the horror movies but also what you learned in grade school: that the Gulf Stream is responsible for keeping London so much warmer than New York even though England is farther north than Newfoundland.

This theory, originated by a 19th-century oceanographer, is “the earth-science equivalent of an urban legend,” in the words of Richard Seager, a climate modeler at the Lamont-Doherty Earth Observatory of Columbia University. He and other researchers have calculated that the Gulf Stream’s influence typically raises land temperatures in the north by only five degrees Fahrenheit, hardly enough to explain England’s mild winters, much less its lack of glaciers.

Moreover, as the Gulf Stream meanders northward, it delivers just about as much heat to the eastern United States and Canada as to Europe, so it can’t account for the difference between New York and London. Dr. Seager gives the credit to the prevailing westerly winds — and the Rocky Mountains.

When these winds out of the west hit the Rockies, they’re diverted south, bringing air from the Arctic down on New York (as in last week’s cold spell). After their southern detour, the westerlies swing back north, carrying subtropical heat toward London. This Rocky Mountain detour accounts for about half the difference between New York and London weather, according to Dr. Seager.

The other half is caused by to the simple fact that London sits on the east side of an ocean — just like Seattle, which has a much milder climate than Siberia, the parallel land across the Pacific. Since ocean water doesn’t cool as quickly as land in winter, or heat up as much in summer, the westerly winds blowing over the ocean moderate the winter and summer temperatures in both Seattle and London.

So unless the westerlies reverse direction or the Rockies crumble, London and the rest of Western Europe will remain relatively mild. The danger London faces isn’t an ice age but a long, inexorable warming that will keep the temperatures and sea levels gradually rising for centuries — not an action flick but a super-slow-motion documentary.

It’ll be hard to keep audiences interested, particularly since the solutions are also in slow motion. The I.P.C.C. considers options for reducing greenhouse emissions, but projects that even the most radical (and politically painful) policies wouldn’t make much difference the first two or three decades. To politicians worried about the next election, especially in poor countries, 2030 sounds like eternity.

It’s always possible that something will galvanize people around the world into taking short-term pain for long-term gain. But I suspect there’s a better chance of someone claiming that $25 million prize. Whether it’s carbon-dioxide-gobbling nanobots or something else, it’d be good to have a backup plan when 2030 rolls around.
(By JOHN TIERNEY, NYT, 13/02/2007)
http://www.nytimes.com/2007/02/13/science/earth/13tier.html?_r=2&ref=science&oref=slogin&oref=slogin