Public Release:  Carbon dioxide already in danger zone, warns study

Revised theory says levels in air must decline, not just stabilize

The Earth Institute at Columbia University

A group of 10 prominent scientists says that the level of globe-warming carbon dioxide in the air has probably already reached a point where world climate will change disastrously unless the level can be reduced in coming decades. The study is a departure from recent estimates that truly dangerous levels would be reached only later in this century. The paper appears in the current edition of the Open Atmospheric Science Journal.

"There is a bright side to this conclusion," says lead author James E. Hansen, director of the Goddard Institute for Space Studies, part of Columbia University's Earth Institute. ""By following a path that leads to lower CO2, we can alleviate a number of problems that had begun to seem inevitable." Hansen said these include expanding desertification, reduced food harvests, increased storm intensities, loss of coral reefs, and the disappearance of mountain glaciers that supply water to hundreds of millions of people.

The scientists say now that CO2 needs to be reduced to the level under which human civilization developed until the industrial age--about 350 parts per million (ppm)--to keep current warming trends from moving rapidly upward in coming years. The level is currently at 385 ppm, and rising about 2 ppm each year, mainly due to the burning of fossil fuels and incineration of forests. As a result, global temperatures have been creeping upward. The authors say that improved data on past climate changes, and the pace at which earth is changing now, especially in the polar regions, contributed to their conclusion. Among other things, ongoing observations of fast-melting ice masses that previously helped reflect solar radiation, and the release of stored-up "greenhouse" gases from warming soils and ocean waters, show that feedback processes previously thought to move slowly can occur within decades, not millennia, and thus warm the world further. Once CO2 gas is released, a large fraction of it stays in the air for hundreds of years.

The scientists, from the United States, United Kingdom and France, are optimistic that current atmospheric CO2 could be reduced if emissions from coal, the largest contributor, are largely phased out by 2030. Use of unconventional fossil-fuel sources such as tar sands also would have to be minimized, they say. They predict that oil use will probably decline anyway as reserves shrink. So-called "geoengineering" solutions that would remove CO2 from the air have been proposed by others, but the group is skeptical; they estimate that artificially removing 50ppm of CO2 from the atmosphere would cost at least $20 trillion, or twice the current U.S. national debt. They suggest that reforestation of degraded land and use of more natural fertilizers could draw down CO2 by a similar amount.

"Humanity today, collectively, must face the uncomfortable fact that industrial civilization itself has become the principal driver of global climate," says the paper. "The greatest danger is continued ignorance and denial, which would make tragic consequences unavoidable."

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The other authors are Makiko Sato and Pushker Kharecha, both also of the Earth Institute; David Beerling of the University of Sheffield (UK); Robert Berner and Mark Pagani of Yale University; Valerie Masson-Delmotte of the University of Versailles (France); Maureen Raymo of Boston University; Dana Royer of Wesleyan University; and James Zachos of the University of California, Santa Cruz.

The paper, "Target Atmospheric CO2: Where Should Humanity Aim?" is at: http://www.bentham.org/open/toascj/openaccess2.htm, pages 217-231.

Author contacts:
James Hansen: jhansen@giss.nasa.gov 212-678-5500
Makiko Sato: makis@giss.nasa.gov 212-678-5618
Pushker Kharecha: pushker@giss.nasa.gov 212-678-5630
More information: Kevin Krajick, Senior Science Writer, The Earth Institute kkrajick@ei.columbia.edu 212-854-9729

The Earth Institute at Columbia University mobilizes the sciences, education and public policy to achieve a sustainable earth. Through interdisciplinary research among more than 500 scientists in diverse fields, the Institute is adding to the knowledge necessary for addressing the challenges of the 21st century and beyond. With over two dozen associated degree curricula and a vibrant fellowship program, the Earth Institute is educating new leaders to become professionals and scholars in the growing field of sustainable development. We work alongside governments, businesses, nonprofit organizations and individuals to devise innovative strategies to protect the future of our planet. Goddard Institute for Space Studies, part of The Earth Institute at Columbia University, is the only urban laboratory of the National Aeronautic and Space Administration (NASA). The Goddard Institute is a climate research center that models and monitors earth systems, using state-of-the-art equipment to predict atmospheric and climate changes in the 21st century. It also plays an important teaching role, conducting science education programs at more than 20 universities, schools and organizations throughout metropolitan New York.

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