The Big Picture 

:Is Human Activity changing the climate? 

Temperature measurements have been compiled from land- and ship-based weather stations
located around the world into a 130-year record of the globally and annually averaged
temperature of the surface of the Earth. This record shows that the average surface
temperature has risen by a little more than half a degree Celsius. When compared with
indirect estimates of surface temperature over the past several centuries, this record shows
that the 20th century has been the warmest of any since at least the 15th century and possibly
for several thousand years.

However, climate varies naturally and confidently attributing observed changes to human
causes is difficult. Nonetheless, the Intergovernmental Panel on Climate Change (IPCC), an
international scientific body charged by the United Nations with providing comprehensive
surveys of climate change science, concluded recently that "the balance of evidence suggests
a discernible human influence on global climate". The question of how much of the observed
temperature rise has been due to human influence cannot yet be determined. Over time,
detection and attribution of the greenhouse signal are expected to become less ambiguous.

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*Global Change   

  Online Journal on climate Change and Ozone Depletion

*N.Y.Times Global Warming Archive