Changes

According to evolutionary scientists, there have been many cycles of naturally-caused global warming and cooling over many millions of years (see [[climate cycles]]). Some scientists, including [[Richard Lindzen]] of [[MIT]], [[Sallie Baliunas]] of [[Harvard]] and [[Fred Singer]] (independent), say that the recent warming could be part of another natural cycle.

According to evolutionary scientists, there have been many cycles of naturally-caused global warming and cooling over many millions of years (see [[climate cycles]]). Some scientists, including [[Richard Lindzen]] of [[MIT]], [[Sallie Baliunas]] of [[Harvard]] and [[Fred Singer]] (independent), say that the recent warming could be part of another natural cycle.

==The Hockey Stick Reconstruction==

==The Hockey Stick Temperature Reconstruction==

[[Image:Hockey stick chart ipcc.jpg|right|thumb|300px|The Hockey Stick graph in 2001 IPCC report shows blue proxy values along the "shaft" with red instrumental values superimposed as the "blade"]]

[[Image:Hockey stick chart ipcc.jpg|right|thumb|300px|The Hockey Stick graph in 2001 IPCC report shows blue proxy values along the "shaft" with red instrumental values superimposed as the "blade"]]

One of the main evidence for anthropogenic global warming presented during the 3rd IPCC report was a temperature reconstruction done by climatologist Michael Mann.  The resulting graph of the Northern Hemisphere temperature is shaped like a hockey stick, and it is used as evidence for the unusualness of the earth's temperature in the past few decades.  However, Stephen McIntyre and economist Ross McKitrick later discovered a serious flaw in the statistical methods used to construct the hockey stick graph.  Because of this, the 4th Assessment Report of the IPCC included several different temperature reconstruction methods instead of favoring just one hypothesis.

One of the main evidence for anthropogenic global warming presented during the 3rd IPCC report was a temperature reconstruction done by climatologist Michael Mann.  The resulting graph of the Northern Hemisphere temperature is shaped like a hockey stick, and it is used as evidence for the unusualness of the earth's temperature in the past few decades.  However, Stephen McIntyre and economist Ross McKitrick later discovered a serious flaw in the statistical methods used to construct the hockey stick graph.  Because of this, the 4th Assessment Report of the IPCC included several different temperature reconstruction methods instead of favoring just one hypothesis.