Michael Oppenheimer is a professor of geosciences and international affairs at Princeton University. Kevin Trenberth is a distinguished senior scientist at the National Center for Atmospheric Research.
In a recent op-ed for The Post, Rep. Lamar Smith (R-Tex.) offered up a reheated stew of isolated factoids and sweeping generalizations about climate science to defend the destructive status quo. We agree with the chairman of the House Committee on Science, Space and Technology that policy should be based on sound science. But Smith presented political talking points, and none of his implied conclusions is accurate.
The two of us have spent, in total, more than seven decades studying Earth’s climate, and we have joined hundreds of top climate scientists to summarize the state of knowledge for the Intergovernmental Panel on Climate Change (IPCC), the World Climate Research Program and other science-based bodies. We believe that our views are representative of the97 percent of climate scientists who agree that global warming is caused by humans. Legions of studies support the view that, left unabated, this warming will produce dangerous effects. (This commentary, like so much of our work, was a collaborative process, with input from leading climate scientists Julia Cole, Robert W. Corell, Jennifer Francis, Michael E. Mann, Jonathan Overpeck, Alan Robock, Richard C.J. Somerville and Ben Santer.)
Man-made heat-trapping gases are warming our planet and leading to increases in extreme weather events. Droughts are becoming longer and deeper in many areas. The risk of wildfires is increasing. The year 2012, the hottest on record for the United States, illustrated this risk with severe, widespread drought accompanied byextensive wildfires.
Last month, levels of carbon dioxide in the atmosphere exceeded 400 parts per million, approaching the halfway mark between preindustrial amounts and a doubling of those levels. This doubling is expected to cause a warming this century of four to seven degrees Fahrenheit. The last time atmospheric carbon dioxide reached this level was more than 3 million years ago, when Arctic lands were covered with forests. The unprecedented rate of increase has been driven entirely by human-produced emissions.
Projections from an array of scientific analyses summarized by the National Academy of Sciences and most of the world’s major scientific organizations indicate that by the end of this century, people will be experiencing higher temperatures than any known during human civilization — temperatures that our societies, crops and ecosystems are not adapted to.
Computer model projections from at least 27 groups at universities and other research institutes in nine countries have proved solid. In many cases, they have been too conservative, underestimating over the past 20 years the amounts of recent sea-level rise and Arctic sea ice melt.
Much has been made of a short-term reduction in the rate of atmospheric warming. But “global” warming requires looking at the entire planet. While the increase in atmospheric temperature has slowed, ocean warming rose dramatically after 2000. Excess heat is being trapped in Earth’s climate system, and observations of the Global Climate Observing System and others are increasingly able to locate it. Simplistic interpretations of cherry-picked data hide the realities.
In recent years, our understanding of the relationship between climate and extreme weather has sharpened, along with our appreciation of the vast damages such events cause.
Contrary to Smith’s assertions, there is conclusive evidence that climate change worsened the damage caused by Superstorm Sandy. Sea levels in New York City harbors have risen by more than a foot since the beginning of the 20th century. Had the storm surge not been riding on higher seas, there would have been less flooding and less damage. Warmer air also allows storms such as Sandy to hold more moisture and dump more rainfall, exacerbating flooding.
Smith referred to the IPCC’s special report on extremes but did not mention that the report connects several types of extreme weather to climate change, including heat waves, extreme precipitation and, in some regions, drought. Furthermore, the last major IPCC report, in 2007, stated unequivocally that Earth is warming.
While we are addressing science here, one broad policy implication is clear: Humans must reduce their greenhouse gas emissions. Since John Tyndall discovered in 1859 that carbon dioxide and other greenhouse gases cause warming, science has made great strides toward establishing the scope of that warming and its impact.
The combined impetus of observed trends in climate and weather extremes, and continuing discoveries in climate science, lay bare how ludicrous Smith’s suggestion is that since we know nothing, we should do nothing.
We know a lot, more than enough to recognize that the alarm bells are ringing.
Increases in heat waves and record high temperatures; record lows in Arctic sea ice; more severe rainstorms, droughts and wildfires; and coastal communities threatened by rising seas all offer a preview of the new normal in a warmer world. Smith’s policy plan amounts to “wait and see.” But the longer we wait — effectively, like him, closing our eyes to science — the more difficult and expensive the solutions become, and the more irreversible the damage will be.
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