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A preview of the National Climate Assessment

The National Climate Assessment is required by the Global Change Research Act of 1990. The Climate Assessment is the product of thirteen federal agencies and more than 240 authors. The senior science writer helping edit this report is AAAS Fellow Susan Hassol, and the forthcoming report (now available in draft form), is the third of three that she has helped prepare. She was kind enough to give AAAS MemberCentral some background on the most recent report.

The Climate Assessment is distributed to all members of Congress and the White House, but Hassol emphasized that the report is available to everyone, and that beyond the federal government, there are people all over the country that are making decisions that should take into account the changing climate, whether it is local governments upgrading infrastructure, farmers making long term plans, or individuals deciding where to purchase a home.

The 2009 report stated that global warming was "unequivocal" and primarily man-made.

The current report has the advantage of four more years of data and shows that climate models have correctly predicted the increase in warming and other changes. Warming is much greater at higher latitudes, and one surprise is how fast the Arctic sea ice is melting, considerably faster than forecast. Less sea ice means less of the sun's rays are reflected back in space, and instead are absorbed by the ocean waters, a vicious positive feedback cycle.  Less sea ice also means less protection from the sea for coastal villages. This is compounded by the fact that coastal permafrost is warming, making the coasts crumble more easily.

The Climate Assessment shows projections of impacts primarily based on two emissions scenarios, one with relatively low carbon emissions, and a higher one; both scenarios are from a Special Report on Emissions Scenarios from the Intergovernmental Panel on Climate Change (IPCC). Hassol pointed out that the higher emission case is "not a worst-case scenario." In fact, the carbon emissions envisioned in that scenario are less than the path we are currently on. The rationale for using these particular scenarios is that they show the difference in impacts between lower and higher emissions pathways and are also the ones for which climate scientists have the best data about likely impacts.

Everybody talks about the weather but what exactly can be done about climate change? Hassol paraphrased John Holdren, science advisor to Obama, who has said there are three things we will have to do: 1) mitigate; 2) adapt and 3) suffer. The more we mitigate by reducing emissions, the less we will have to adapt, and the more we mitigate and adapt, the less we'll suffer.

Part of adaptation may involve putting less infrastructure in areas that are particularly threatened by climate change. Right now, many are doing the opposite, as more people move to the Southwest, which is already very dry and threatened by longer and deeper droughts, and also to coastal areas including South Florida, which is subject to storm surge flooding.

A changing climate does have some benefits, and indeed, our nation's farmers are experiencing longer growing seasons and adapting their planting schedules to take advantage of it. The Northwest Passage is now open during the summer, and the Arctic may provide a bonanza for oil drillers, ironic though that may be. Hassol agreed that "Yes, there are some benefits, but the society that we have, the cities and the infrastructure — the pipes, the pumps, the roads, and canals — are what they are and where they are predicated on the climate that we used to have. As the climate continues to change, we will have to make large, potentially expensive changes in our infrastructure."

There is some good news, in that carbon emissions from the United States have actually declined over the last few years.  There are a variety of reasons for the lower emission rates, but at least part of the decline is due to programs put in place by federal, state and local governments.  Unfortunately, on a global scale, carbon emissions are still increasing.

The Climate Change Assessment report does not make specific policy recommendations. According to Hassol, "Scientists can inform policy, but do not make societal decisions. More than science is involved in making those decisions, including economics, politics, and the values of the society. What we can do is to point out the choices society faces; what kind of future do you want to have? Then policy makers, armed with the science, hopefully, will make changes that will lead to a better future."

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Steven A. Edwards, Ph.D.

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