Windswept_ The Story of Wind and Weather - Marq de Villiers [102]
No one, not even the most vociferous climate-change skeptic, quarrels with this analysis. Nor does anyone disagree that CO levels are elevated over historic norms. CO levels held pretty steady, around 280 parts per million, for the thousand years before 1800. Since then, as industrialization really got under way, atmospheric concentrations of CO2 began to rise. Today they are around 370 parts per million.16 Some people think this isn't very much—after all, CO is only a very small component of air, just a trace gas really, and an increase of 90 parts per million, if visualized as distance, would be less than a third of an inch in a hundred yards. On the other hand, it does represent a 30 percent increase, and most earth scientists believe that with the still-expanding fossil fuel infrastructure, it may be impractical to avoid 440 parts per million, a significant increase from present levels. It also seems to be agreed that each resident of the developed world adds around five tons of carbon to the air every year, most of it coming from exhaust pipes and smokestacks. There is less agreement about whether this increasing CO has already led to global warming, and the most commonly cited "hockey stick" shaped chart, which shows a sharp upturn in global temperatures at about the time of the industrial revolution, is still widely disputed as being the result of statistical errors; there is in fact considerable evidence that parts of the world, including Europe, have gotten cooler instead of warmer over the same period. On the other hand—and there always seems to be another hand in this debate—a careful study by James Hansen of NASA's Institute for Space Studies and other scientists has concluded that the earth's "energy imbalance," the net heat gain over heat loss, is almost one watt per square meter of earth surface (enough, the authors say, that if it were maintained for ten thousand years, it would be enough to boil the oceans). Gloomily, they go on to suggest that rapid climate change might take less than a century, while it would take at least a century to change our ways even if we started now, "implying the possibility of a system [already] out of our control."17
Clouding the debate and fuzzying up its conclusions is the role of perfectly natural short-term phenomena such as, well, clouds.
In May 2004 NASA published a study of the earth's albedo, how much light and heat the earth radiates back into space, instead of absorbing, based on differences in observed earthshine on the moon. The data showed a steady decline, or dimming, of the earth's albedo from 1984 to 2000, with a particularly sharp decrease in 1995 and 1996. From 1997 to 2000, the earth continued to dim, albeit more slowly. Less heat going out to space meant more heat on the surface, and this correlated with the observed data—there was an increase in mean global temperatures in the same period. But in the past three years, the trend has apparently reversed, and the earth now appears to be both getting more sunshine and radiating more light back into space. "Though not fully understood," the study said with some understatement, "the shift may indicate [nothing more than] a natural variability of clouds, which can reflect the sun's heat and light away from earth. The apparent change in the amount of sunlight reaching earth in the 1980s and 1990s is comparable to taking the effects of greenhouse gas warming since 1850 and doubling them. Increased reflectance since 2001 suggests change of a similar magnitude in the other direction."18
Which means that natural cycles in cloud cover can account for changing surface temperatures; changing temperatures affect winds and wind patterns; winds create weather; weather in turn affects cloud cover . . . If taken literally and narrowly, the study's results could also mean that the relatively trivial amount