A dark forecast
|The Earth and smoggy, sunlight-dimming cloud cover.|
In the immediate aftermath of 9/11, you'll remember that for three days, all American air flights were grounded. You may also remember that the weather was remarkably warm and bright. As it turns out, that may have given us a heads-up about a disaster likely to be far larger in scope than that of September 11, as Nova documents on this evening's "Dimming of the Sun" (PBS, check local listings). It's just an hour, but in case you haven't got time to sit down with the episode, there's some important stuff in here for you.
It turns out that particle-type air pollution -- of which planes make a great deal -- has probably been keeping a significant amount of solar radiation from reaching the planet's surface. This dimming effect has artificially reduced the impact of global warming; when the pollution diminished radically for those few days, the warming became dramatically obvious. Even a three-day pause in contrail emissions, like that after 9/11, showed a two-degree average increase in daily temperature range (hotter days, cooler nights). A jump like that is huge news in climate circles -- such a small change in the system, such a pronounced and rapid effect.
Nova does good work -- this episode's a collaboration between Boston's WGBH and a UK production house -- and I was struck repeatedly during the hour by the excellent computer graphics and gorgeous location photography. (Such a beautiful planet we've got here. Shame how we've wrecked the place.) There are some excellent interviews, including those with Dr. Gerald Stanhill and James Hanson. But what you'll get out of it, and what you should get out of it, is the accumulating data that indicates that we are not just in trouble, but in the kind of trouble that looks worse the more you investigate it.
Further tests indicated that the dimming, which both bounces sunlight back into space and shades the terrain beneath, may block as much of 30 percent of the sunlight that would normally reach the ground in some regions. This dimming offsets the obvious effects of global warming -- creating a tug of war between the two, with the actual climate in the middle. This may sound like excellent news -- system equalizing itself and so forth. Um, no.
Plane contrails aren't the only cause of pollution, of course, and some of the things we've done to combat global warming (catalytic converters, less use of aerosol sprays, end of ultra-polluting factories in certain parts of the world) have decreased our particle-pollution cover without addressing the greenhouse gases that cause global warming. In essence, we're losing what turned out to be a protective layer of schmutz -- and since previous studies of global warming factored in that dimming effect as a given, the actual effects of global warning are apt to be bigger than we expected…and they'll arrive sooner than we think.
And no, we can't just decide we're going to keep polluting our way to a "happy" medium. Not only has global dimming masked the worst of the overall warming trend, but it may be wrecking weather patterns, particularly those of monsoon season. Cooler weather means the necessary rains aren't drawn to their accustomed areas of Asia and Africa; the disastrous droughts in Ethiopia and sub-Saharan Africa were probably early indicators of the phenomenon. Now the monsoon season is coming later each year to India and South Asia. If the monsoon failure becomes chronic, the effect on world food supplies will be incalculable.
It gets worse. That particle-type pollution has been on the decline since about 1990, and scientists have been seeing an increase in the rate of warming since then. If current trends continue -- decreasing particulate pollutions without actually reducing greenhouse-gas emissions -- we get the worst possible mix, warming and no cooling. The runaway warming trend that climatologists have predicted will arrive sooner, with the global ice sheets disappearing within decades.
And remember how all the major impact from global warming was going to start showing, assuming we don't change our ways, by the end of the century? Correcting for global dimming, that tipping point is now the end of the decade. Rapid, again, is the word to take away from all this. Had we recognized the global-dimming phenomenon more rapidly, we might have had more wiggle room (and that's a major "might," considering there are still fringe elements out there claiming that global warming's not real). We didn't. Now we don't.
By the end of the century, unchecked warming could mean an 18-degree temperature rise, which will mean everything from global famine to mass release of the methane frozen at the bottom of our oceans and permafrost… which would kick the temperature up yet further. Mass extinctions and destruction of the rainforest would further worsen the problem, possibly past the point of recovery. Our species wouldn't see the end of it, in any case. (Note to planet: If you recover from this and decide to evolve life again, I'd pass on anything involving opposable thumbs.)