Global Warming's US Impacts and "Permanent Drying" in the Southwest

A major new report warns that on our current emissions path, we face the severe risk of abrupt climate change impacts. The basic conclusions themselves are nothing new — see "Startling new sea level rise research: "Most likely" 0.8 to 2.0 meters by 2100" and "Australia faces the "permanent dry" — as do we."

But what is stunning is that these warnings come from the United States Geological Survey — the Bush Administration (!). This new science-based report, Abrupt Climate Change, is thus a sobering book-end to the fantasy-based talking points released by the Administration today on how the President has "Taken Constructive Steps To Confront Climate Change."

This is a first-rate report from the USGS’s Climate Change Science Program. I highly recommend reading, Chapter 2, "Rapid Changes in Glaciers and Ice Sheets and their Impacts on Sea Level," and Chapter 3, "Hydrological Variability and Change." The chapters are much more readable than the IPCC reports, and the two together will make anyone an expert on what are perhaps the two most dangerous climate impacts that threaten this country.

The sea level rise conclusion, "based on an assessment of the published scientific literature" is:

Recent rapid changes at the edges of the Greenland and West Antarctic ice sheets show acceleration of flow and thinning, with the velocity of some glaciers increasing more than twofold. Glacier accelerations causing this imbalance have been related to enhanced surface meltwater production penetrating to the bed to lubricate glacier motion, and to ice-shelf removal, ice-front retreat, and glacier ungrounding that reduce resistance to flow. The present generation of models does not capture these processes. It is unclear whether this imbalance is a short-term natural adjustment or a response to recent climate change, but processes causing accelerations are enabled by warming, so these adjustments will very likely become more frequent in a warmer climate. The regions likely to experience future rapid changes in ice volume are those where ice is grounded well below sea level such as the West Antarctic Ice Sheet or large glaciers in Greenland like the Jakobshavn Isbrae that flow into the sea through a deep channel reaching far inland. Inclusion of these processes in models will likely lead to sea-level projections for the end of the 21st century that substantially exceed the projections presented in the IPCC AR4 report (0.28 ± 0.10 m to 0.42 ± 0.16 m rise).

Again, the recent post-IPCC literature has been quite consistent in warning of sea level rise of one meter or more by 2100. Beside the 2008 Science study noted above, a Science article from 2007 used empirical data from last century to project that sea levels could be up to 5 feet higher in 2100 and rising 6 inches a decade (see Inundated with Information on Sea Level Rise) and another 2007 study from Nature Geoscience came to the same conclusion (see "Sea levels may rise 5 feet by 2100"). But now we have the U.S. government acknowledging the inadequacy of the IPCC conclusion.

[Note: The UK Guardian’s headline "Sea level rise could top 1.5m by 2099, experts warn," is quite a stretch. You won’t find that in the study.]

A key drought conclusion is:

The serious hydrological changes and impacts known to have occurred in both historic and prehistoric times over North America reflect large-scale changes in the climate system that can develop in a matter of years and, in the case of the more severe past megadroughts, persist for decades. Such hydrological changes fit the definition of abrupt change because they occur faster than the time scales needed for human and natural systems to adapt, leading to substantial disruptions in those systems. In the Southwest, for example, the models project a permanent drying by the mid-21st century that reaches the level of aridity seen in historical droughts, and a quarter of the projections may reach this level of aridity much earlier.

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