The IPCC 4th Assessment Report

On February 2, the IPCC, an international group of scientists charged with reviewing the evidence on global climate change, issued “Climate Change 2007: The Physical Science Basis,” a summary for policymakers. The summary describes progress in understanding the human and natural drivers of climate change. The report is available for download at http://www.ipcc.ch/.

As has been widely reported, the new report states clearly that the earth’s climate is changing, and it attributes the bulk of these changes to human activities. Specifically, the IPCC report states that warming is “unequivocal,’ humans are “very likely” responsible (defined as more than 90% probability) and the earth’s climate is “very unlikely” to be so insensitive as to render future warming inconsequential.

The latest report from the IPCC is important for several reasons. First, it represents a consensus of scientists from around the world on the state of the science. Six-hundred authors nominated by 40 countries contributed, and representatives from 113 countries gathered to review the final draft before its release. Thus it represents an extraordinary agreement among the top climate scientists in the world on the certainty and seriousness of human-caused global climate change.

Second, this report highlights the amount and quality of new scientific evidence on the size, causes, and growing impacts of climate change. The last IPCC report, issued in early 2001, was full of uncertainties about the likelihood that human activities were behind most of the warming, and potential future warming. Here is what John Holdren, president of the AAAS, says in reflecting on the 2007 assessment: “…since 2001 there has been a torrent of new scientific evidence on the magnitude, human origins, and growing impacts of climatic changes that are underway. In overwhelming proportions, this evidence has been in the direction of showing faster change, more danger, and greater confidence about the dominant role of carbon dioxide from fossil-fuel burning and tropical deforestation in causing the changes that are being observed.”

Finally, the IPCC Fourth Assessment Report seems to be adding strength to a growing movement among scientists and others to call for immediate and serious action to begin to tackle the growing climate crisis. On February 18, the board of the AAAS issued a consensus statement declaring global climate change a growing threat to society, and calling for immediate action to rapidly reduce greenhouse gas emissions; see http://www.aaas.org/news/releases/2007/0218am_statement.shtml
AAAS president John Holdren issued a compelling argument as well: Read the full statement.

Other News

Here’s one other interesting item from the Feb 2 issue of Science magazine:
Trying to predict ecological responses to climate change may be trickier than previously thought: The summary below describes a paper published in the Feb 2, 2007 issue of Science magazine.
Most forecasts of ecological responses to climate change assume that these can be based on individual species tolerances for changing moisture or temperature regimes. Suttle et al. (p. 640; see the Perspective by Walther) challenge this assumption. In a 5-year experiment, they examined the consequences of alternative climate change scenarios in a grassland ecosystem in California, USA. Manipulation of rainfall over replicated 10-m diameter plots showed that higher-order species interactions dictate responses throughout the community. The effects on plant and arthropod abundance and diversity were the reverse of what would have been predicted based on individual species responses. Click here for article abstract.