Page - 169 - in Water, Energy, and Environment - A Primer

reached 410ppm.Based on scientific estimates, thismaybe the highest level inmillions of years. The impact on global temperature is shown in the so-called ‘hockey stick chart’ (65),which has been called byTheAtlantic magazine ‘The most controversial chart in science’ (see Figure 10.2). The sharp jump in the temperature curve from about 1900 to the present is the basis of the hockey stick analogy.When the chart was released in 1999 it was repeatedly attacked, and so were the authors of the accompanying article. Eventually, the USCongress got involved, no doubt encouraged by supporters of fossil fuels, and it was only after the National Academy of Sciences reviewed the issue in 2006, and declared the hockey stick to be good science, did the attacks begin to taper off. Today, research on the potential impacts of adding greenhouse gases to the atmosphere (which includes gases such asN2Oand chlorofluorocarbons in addition to CO2 and CH4), and their timing, are major foci of government and academic research. While there is some current opposition to such research by Figure 10.1 Carbon dioxide concentrations over time. (Source: U.S. NationalAeronauticsandSpaceAdministration) Policy considerations 169