Eleven Earth and space scientists, including one from Scripps Institution of Oceanography at the University of California, San Diego, say that a recent paper attributing most climate change on Earth to cosmic rays is incorrect and based on questionable methodology. Writing in the January 27 issue of Eos, published by the American Geophysical Union, Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research and colleagues in Canada, France, Germany, Switzerland, and the United States challenge the cosmic ray hypothesis.
In July 2003, astrophysicist Nir Shaviv and geologist Jan Veizer wrote in GSA Today that they had established a correlation between cosmic rays and temperature evolution over hundreds of millions of years. They also claimed that current global warming is not primarily caused by human emissions of carbon dioxide. Their findings have been widely reported in international news media.
According to Rahmstorf, Shaviv and Veizer's analyses-and especially their conclusions-are scientifically ill-founded. The data on cosmic rays and temperature so far in the past are extremely uncertain, he says. Further, their reconstruction of ancient cosmic rays is based on only 50 meteorites, and most other experts interpret their significance in a very different way, he says. He adds that two curves presented in the article show an apparent statistical correlation only because the authors adjusted the data, in one case by 40 million years. In short, say the authors of the Eos article, Shaviv and Veizer have not shown that there is any correlation between cosmic rays and climate.
As for the influence of carbon dioxide in climate change, many climatologists were surprised by Shaviv and Veizer's claim that their results disproved that current global warming was caused by human emissions, Rahmstorf says.
Even if their analysis were methodologically correct, their work applied to time scales of several million years.
The current climate warming has, however, occurred during just the past one hundred years, for which completely different mechanisms are relevant, he says. For example, over millions of years, the shifting of continents influences climate, while over hundreds of thousands of years, small changes in Earth's orbit can initiate or terminate ice ages. But for time periods of years, decades, or centuries, these processes are irrelevant. Volcanic eruptions, changes in solar activity, and the concentration of greenhouse gases, as well as internal oscillations of the climate system, are crucial on this scale.
The 11 authors of the Eos article affirm that the strong increase of carbon dioxide and some other greenhouse gases in the atmosphere due to manmade emissions is most probably the main cause of the global warming of the last few decades. The most important physical processes are well understood, they say, and model calculations as well as data analyses both come to the conclusion that the human contribution to the global warming of the 20th century was dominant.
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Notes for journalists:
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Title: "Cosmic Rays, Carbon Dioxide, and Climate"
Citation: Rahmstorf, S. et al., Cosmic rays, carbon dioxide, and climate, Eos, Trans. AGU, 85(4), 38, 41, 2004.
Authors and contact information:
Stefan Rahmstorf, Potsdam Institute for Climate Impact Research,
Potsdam University, Potsdam, Germany:
firstname.lastname@example.org or +49-331-288-2688
David Archer, Department of Geophysical Sciences, University of
Chicago, Chicago, Illinois, USA: email@example.com or 773/702-0823
Denton S. Ebel, Department of Earth and Planetary Science,
American Museum of Natural History, New York, New York,
USA: Contact through Robin Lloyd, AMNH Communications
Office: firstname.lastname@example.org or 212/496-3419
Otto Eugster, Department of Space Research and Planetology,
Physics Institute, University of Bern, Bern, Switzerland:
email@example.com or +41 31-6314418
Jean Jouzel, Director, Pierre Simon Laplace Institute, University of
Versailles, Saint-Quentin-en-Yvelines, France:
firstname.lastname@example.org or +33 684759682
Douglas Maraun, Institute of Physics, University of Potsdam,
Potsdam, Germany: email@example.com or +49 331-977-1364
Urs Neu, ProClim-, Swiss Forum for Climate and Global Change,
Swiss Academy of Sciences, Bern, Switzerland:
firstname.lastname@example.org or +41 31-328-23-26
Gavin A. Schmidt, NASA Goddard Institute for Space Studies and
Columbia University Center for Climate Systems Research, New
York, New York, USA: email@example.com or 212/678-5627
Jeffrey P. Severinghaus, Geosciences Research Division, Scripps
Institution of Oceanography, La Jolla, California, USA:
firstname.lastname@example.org or 858/822-2483
Andrew J. Weaver, School of Earth and Ocean Sciences,
University of Victoria, Victoria, British Columbia, Canada:
email@example.com or 250/472-4001
Jim Zachos, Director, Center for the Study of the Dynamics and
Evolution of the Land-Sea Interface, University of California,
Santa Cruz, California, USA: firstname.lastname@example.org or 831/459-4644
Scripps Institution of Oceanography on the web: http://scripps.ucsd.edu
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