American Geophysical Union NEWS

Contact:
Harvey Leifert, +1 (202) 777-7507,

For Immediate Release: 21 January 2004

AGU Release No. 04-05

Cosmic Rays Are Not the Cause of Climate Change, Scientists Say

WASHINGTON -- Eleven Earth and space scientists 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 a 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:

Journalists (only) may obtain an advance pdf copy of this paper upon request to
Kara LeBeau: . Please provide your name, name of publication,
phone, and email address. The paper and this press release are not under embargo.

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.

Contact information for the authors:

Stefan Rahmstorf
Potsdam Institute for Climate Impact Research
Potsdam University, Potsdam, Germany
or +49-331-288-2688

David Archer
Department of Geophysical Sciences
University of Chicago, Chicago, Illinois, USA
or +1 773-702-0823

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:
or +1 212-496-3419

Otto Eugster
Department of Space Research and Planetology, Physics Institute
University of Bern, Bern, Switzerland
or +41 31-6314418

Jean Jouzel
Director, Pierre Simon Laplace Institute
University of Versailles, Saint-Quentin-en-Yvelines, France
or +33 684759682

Douglas Maraun
Institute of Physics
University of Potsdam, Potsdam, Germany
or +49 331-977-1364

Urs Neu
ProClim-, Swiss Forum for Climate and Global Change
Swiss Academy of Sciences, Bern, Switzerland
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
or +1 212-678-5627

Jeffrey P. Severinghaus
Geoscience Research Division
Scripps Institution of Oceanography, La Jolla, California, USA
or +1 858-822-2483

Andrew J. Weaver
School of Earth and Ocean Sciences
University of Victoria, Victoria, British Columbia, Canada
or +1 250-472-4001

Jim Zachos
Director, Center for the study of the Dynamics and Evolution of the Land-Sea
Interface
University of California, Santa Cruz, California, USA
or +1 831-459-4644