New and much improved “Unified Synthesis Report” is open for a second round of public comment


The U.S. Climate Change Science Program has released a second iteration of a report that synthesizes and describes in lay terms the current scientific understanding of global climate disruption.  Major improvements over a heavily criticized initial draft released in July 2008 have been made by a set of authors and a review team comprised of an impressive group of scientists and experts with impeccable credentials.  We encourage readers to review this report and submit comments by the February 27 deadline.  We hope the Obama administration will publish it expeditiously and embrace it as a significant assessment of the potential consequences of climate change for the United States.     

Post by Anne Polansky

Based on a brief overview before we review it in greater detail, this 200-page report appears to be a thorough, tightly written, compelling and credible overview of the many ways that global climate disruption is affecting human populations and the natural environment and ecosystems.  The author team and “blue ribbon reviewers” (of which is Dr. John Holdren, named to be the President’s next science advisor, is one) for this second draft are among the best of the nation’s scientists and climate researchers. 

This version is a significant improvement from the first draft, issued in July 2008, which was criticized by many in the climate science community (see the peer review comments and hundreds of public comments, both with responses by the authors) for containing too many generalizations and lacking sufficient accuracy.  The report also became a target for the denialist community; for example, the US Chamber of Commerce complained that the primary reference source for the report—the set of 21 Synthesis and Assessment Products comprising the primary work product of the CCSP—was only partially completed and published (see our previous post),  a red herring issue in our view since the primary sources for the SAPs were in the published, peer-reviewed scientific literature. 

Once this second round of comments is collected and considered, the Obama administration would do well to finalize and release this report, holding it up as the good work of a stellar group of editors, authors, and reviewers, several of whom have indicated to us that the effort has been held to the highest scientific standards, conducted and managed entirely outside the realm of politics or political considerations, and in the spirit of good stewardship and statesmanship, on an issue of serious gravity and consequence for the nation. 

Climate Science Watch will be submitting substantive review comments and will post them here; we encourage others to review and comment as well (instructions). 

The main conclusions of the report are as follows:

1. Global warming is unequivocal and primarily human-induced.

There is no question that global temperature has increased over the past 50 years. This observed increase is due primarily to human-induced emissions of heat-trapping gases. (p. 13)

2. Climate changes are underway in the United States and are projected to grow.

Climate-related changes are already observed in the United States and its coastal waters. These include increases in temperature, sea level, and heavy downpours, rapidly retreating glaciers, thawing permafrost, lengthening growing seasons, lengthening ice-free seasons in the ocean and on lakes and rivers, earlier snowmelt, and alterations in river
flows. These changes are projected to grow larger. (p. 27)

3. Widespread climate-related impacts are occurring now and are expected to increase.

Climate changes are already affecting water, energy, transportation, agriculture, ecosystems, and health. These impacts are different from region to region and will grow under projected climate change. (p. 41-108, 109-156)

4. Climate change will stress water resources.

Water is an issue in every region, but the nature of the potential impacts varies. Drought, related to reduced precipitation and increases in evapotranspiration, is an important issue in many regions, especially in the West. Floods and water quality problems are likely to be amplified by climate change in most regions. Declines in mountain snowpack
are important in the Northwest, Southwest, and Alaska where snowpack provides vital natural water storage. (p. 41, 133, 139, 143)

5. Crop and livestock production will be increasingly challenged.

Agriculture is considered one of the sectors most able to adapt to climate change. However, increased heat, pests, diseases, and weather extremes will pose adaptation challenges for crop and livestock production. (p. 71)

6. Coastal areas are at increasing risk from sea-level rise and storm surge.

Sea-level rise and storm surge place many U.S. coastal regions at increasing risk of erosion and flooding, especially along the Atlantic and Gulf Coasts, Pacific Islands, and parts of Alaska. Energy and transportation infrastructure in coastal cities is very likely to be adversely affected. (p. 153)

7. Threats to human health will increase.

Health impacts of climate change are related to heat stress, water-borne diseases, reduced air quality, extreme weather events, and diseases transmitted by insects and rodents. Robust public health infrastructure can reduce the potential for negative impacts. (p. 91)

8. Climate change will interact with many social and environmental stresses.

Climate change will combine with pollution, population growth, overuse of resources, urbanization, and other social, economic, and environmental stresses to create larger impacts than any one of these alone. (p. 101)

9. Rapid, irreversible, and unanticipated changes are likely as a result of crossing key thresholds.

Some aspects of climate change and its impacts are likely to be unanticipated as complex systems respond to ongoing changes in unforeseen ways. Such changes have already been observed. Some changes in climate and associated ecological responses are likely to be rapid and irreversible as tipping points are reached. (p. 26, 159)

10. Future climate change and its impacts depend on choices made today.

The amount and rate of future climate change depends primarily on current and future human-caused emissions of heat-trapping gases and airborne particles. Responses involve reducing emissions to limit future warming, and adapting to the changes that are unavoidable. Adaptation examples include water conservation and modified land use planning in areas with high flood and fire risks. (p. 142, 151, 156)


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