NCPA - National Center for Policy Analysis


November 10, 2006

In recent years, scientists have made sizable gains in what was once considered an impossible art -- reconstructing the history of Earth's atmosphere back into the dim past. They can now peer across more than a half billion years.

At issue is whether the findings back or undermine the prevailing view on global warming.  One side foresees a looming crisis of planetary heating; the other, temperature increases that would be more nuisance than catastrophe.

Perhaps surprisingly, both hail from the same camp: scientists who study the big picture of Earth's past, including geologists and paleoclimatologists:

  • Most public discussions of global warming concentrate on evidence from the last few hundred or, at most, few thousand years and some climate scientists remain unconvinced that data from the deep past are solid enough to be relevant to the debates.
  • But the experts who peer back millions of years, though they may debate what their work means, do agree on the relevance of their findings.
  • They also agree that the eon known as the Phanerozoic, a lengthy span from the present to 550 million years ago, the dawn of complex life, typically bore concentrations of carbon dioxide that were up to 18 times the levels present in the short reign of Homo sapiens.
  • The carbon dioxide, the scientists agree, came from volcanoes and other natural sources, as on Mars and Venus; the levels have generally dropped over the ages, as the carbon became a building block of many rock formations and all living things.

Moreover, the opponents tend to agree on why the early Earth's high carbon dioxide levels failed to roast the planet: 

  • The Sun was dimmer in its youth. 
  • As the gas concentrations increase, its heat trapping capacity slows and reaches a plateau.

Source: William J. Broad, "In Ancient Fossils, Seeds of a New Debate on Warming," New York Times, November 7, 2006.

For text (subscription required):


Browse more articles on Environment Issues