In the judgment of most climate scientists, Earth’s warming in recent decades has been caused primarily by human activities that have increased the amount of greenhouse gases in the Atmosphere. Greenhouse gases have increased significantly since the Industrial Revolution, mostly from the burning of fossil fuels for energy, industrial processes, and transportation. Greenhouse gases are at their highest levels in at least 400,000 years and continue to rise.
The most striking evidence of a global warming trend is closely scrutinized data that show a relatively rapid and widespread increase in temperature during the past century, 1880-2004 (see Figure BELOW).
The rising temperatures observed since 1978 are particularly noteworthy because the rate of increase is so high and because, during the same period, the energy reaching the Earth from the Sun had been measured precisely enough to conclude that Earth's warming was not due to changes in the Sun. Scientists find clear evidence of this warming trend even after removing data from urban areas where an urban heat-island effect could influence temperature readings. Furthermore, the data are consistent with other evidence of warming, such as increases in ocean temperatures, shrinking mountain glaciers, and decreasing polar ice cover.
The task of mitigating and preparing for the impacts of climate change will require worldwide collaborative inputs from a wide range of experts, including natural scientists, engineers, social scientists, medical scientists, business leaders, and economists. Society faces increasing pressure to decide how best to respond to climate change and associated global changes.
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