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Climate Change Accelerates
The year 2007 tied with 1998 as the second warmest year on record, with an average global temperature of 14.57 degrees Celsius (see Figure 1), according to NASA’s Goddard Institute for Space Studies.1 The average global temperature in 2007 was nearly 0.6 degrees Celsius greater than the average between 1951 and 1980 and more than 0.8 degrees Celsius above the average recorded from 1881 to 1910.2 The World Meteorological Association ranks 1998–2007 as the warmest decade on record.3
That 2007 was so warm is particularly significant because throughout the year important cooling influences prevailed. These included low solar irradiance (the energy Earth receives from the Sun) and a strong La Niña in the Pacific. These natural processes were counteracted by the build-up of greenhouse gases caused principally by the combustion of fossil fuels, with other important contributions from agriculture, land use change, and industrial gases.4 (See Figure 2.) In 2007, the concentration of atmospheric carbon dioxide (CO2) climbed to a new high of 383.6 parts per million.5 (See Figure 3.)
The Intergovernmental Panel on Climate Change (IPCC) released its Fourth Assessment Report in 2007, in which it concluded with greater than 90 percent certainty that emissions of CO2 and other greenhouse gases from human activities are driving climate change.6 The report, which represents the work of thousands of experts and scientists, describes a litany of impacts to natural and managed systems that are already happening or are likely to occur if we continue with business as usual.7
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