For scientists watching Earth's climate change, these are truly the best of times and the worst of times. It's the best of times because they can see their predictions coming to pass. It's the worst of times because they can see their predictions coming to pass.
Many signs of the pervasive global warming have also become apparent to the proverbial "man in the street": Arctic thawing, unprecedented heat waves, and a trend toward more intense hurricanes have struck different people living in diverse locations but we are all aware of them via media reports. Beyond these obvious manifestations of a new climate are more subtle alterations of the atmosphere visible only to scientists. Last week, Science Magazine published a report of increasing moisture in the otherwise bone-dry upper atmosphere observed by satellite-borne instruments. With the climate apparently gone haywire down here, you might wonder why we care about goings-on up there.
There are two reasons: water vapor itself is a strong heat-trapping or greenhouse gas. Unlike carbon dioxide, the direct human influence on its atmospheric amount through emissions from fossil fuel burning is negligible. However, the global warming caused by carbon dioxide causes more water to evaporate from the ocean surface. Scientists have long predicted that this moisture would travel to high altitudes, trap heat, and cause an enhancement of the initial warming (called a positive feedback). And that is precisely what the Science article indicates has come to pass.
The second reason is a more personal one. The credibility of climate scientists has been challenged by so-called "contrarians," and one of their specific criticisms is that the water vapor feedback is an artifact of untrustworthy computer models. The Science report is the final nail in the coffin of these skeptics.
It would be fun to cry "we told you so" about all this, except that the stakes have become too high for gloating. Water vapor and other feedbacks more or less triple the amount of warming projected to occur from carbon dioxide alone. For example, the best estimate of warming that may occur during this century changes from a modest 2 degrees Fahrenheit to a dangerous 6 degrees when feedbacks are considered.
Furthermore, contrarianism has been the feed stock for know-nothingism in Congress and the White House. It has provided a phony but effective rationale for wait-and-see policies that have led the world into ever more perilous terrain. Since Hurricane Katrina struck, the media seem to have awakened to the stakes involved. But I still wonder how long Washington can sleep while the world is slowly burning.