We, the teeming billions of people on earth, are changing the earth’s climate at an unprecedented rate because we are spewing out greenhouse gases and are heading to a disaster, say most climate scientists. Not so, say the skeptics. We are just experiencing normal variations in earth’s climate and we should all take a big breath, settle down, and worry about something else. Which is it? A national debate has raged for the last several decades about whether anthropogenic (man-made) sources of carbon dioxide (CO2 ) and other so-called “greenhouse gases“ (primarily methane and nitrous oxide) are causing the world to heat up. This phenomenon is usually called “global warming,” but it is more appropriate to call it “global climate change,” since it is not simply an increase in global temperatures but rather more complex changes to the overall climate. Al Gore is a prominent spokesman for the theory that humans are causing an increase in greenhouse gases leading to global climate change. His movie and book, An Inconvenient Truth, gave the message widespread awareness and resulted in a Nobel Peace Prize for him in 2008. However, the message also led to widespread criticism. On the one hand are a few scientists and a large segment of the general American public who believe that there is no connection between increased CO2 in the atmosphere and global climate change, or if there is, it is too expensive to do anything about it, anyway. On the other hand is an overwhelming consensus of climate scientists who have produced enormous numbers of research papers demonstrating that increased CO2 is changing the earth’s climate. The scientific consensus is expressed most clearly in the Fourth Assessment Report in 2007 by the United Nations–sponsored Intergovernmental Panel on Climate Change (IPCC), the fourth in a series of reports since 1990. The IPCC began as a group of scientists meeting in Geneva in November 1988 to discuss global climate issues under the auspices of the World Meteorological Organization and the United Nations Environment Program.
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