January 19, 2009

Dead On Arrival: EPA/CCSP Sea Level Rise Report Already Outdated

[update 1/20/09: for more on sea level rise see our post over at the new blog masterresource.org]

On Friday, the U.S. Environmental Protection Agency (EPA) released a report on the implications of future sea level rise on the mid-Atlantic coast (from North Carolina to New York). The report was one of the series of 21-reports commissioned by the U.S. Climate Change Research Program (recall our less than favorable reviews of another recent CCSP product). As with most climate change “assessment reports” from large government and intergovernmental efforts, the science in the report is stale and out-of-date by the time the report is finally published (the EPA’s recent documents in support of its “Advanced Notice of Propsed Rulemaking: Regulating Greenhouse Gas Emissions under the Clean Air Act” is a prime example).

Here is how the EPA describes the sea level rise scenarios considered in their latest report Coastal Sensitivity to Sea-Level Rise: A Focus on the Mid-Atlantic Region:

• Scenario 1: the twentieth century rate, which is generally 3 to 4 millimeters per year in the mid-Atlantic region (30 to 40 centimeters total by the year 2100);

• Scenario 2: the twentieth century rate plus 2 millimeters per year acceleration (up to 50 centimeters total by 2100);

• Scenario 3: the twentieth century rate plus 7 millimeters per year acceleration (up to 100 centimeters total by 2100).

The twentieth century rate of sea-level rise refers to the local long-term rate of relative sea-level rise [i.e., it includes geologic processes which has resulted in sinking land levels] that has been observed at NOAA National Ocean Service (NOS) tide gauges in the mid-Atlantic study region. Scenario 1 assesses the impacts if future sea level rise occurs at the same rate as was observed over the twentieth century at a particular location. Scenarios 1 and 2 are within the range of those reported in the recent IPCC Report Climate Change 2007: The Physical Science Basis, specifically in the chapter Observations: Oceanic Climate Change and Sea Level, while Scenario 3 exceeds the IPCC scenario range by up to 40 centimeters by 2100. Higher estimates, as suggested by some recent publications, are the basis for Scenario 3. In addition to these three scenarios, some chapters refer to even higher sea-level rise scenarios, such as a 200 centimeter rise over the next few hundred years (a high but plausible estimate if ice sheet melting on Greenland and West Antarctica exceeds IPCC model estimates).

The “higher estimates, as suggested by recent publications” have in fact, been un-suggested by recent-er publications.

Perhaps the recent-est publication applicable to future sea level rise was published on-line last week in Nature Geosciences by researchers Faezeh Nick, Andreas Vieli, Ina Howat, and Ian Joughin—folks who have been examining the processes governing glacial flow rates across Greenland. After collecting observations on the behavior of Greenland’s glaciers as well as on recent climate, Nick and colleagues developed one of the first computer models of dynamic glacial flows. From this model, they could examine the impact that various processes had on flow rate. The primary processes which have been hypothesized to control the flow rate include:

1) basal lubrication—a process by which surface meltwater drains down to the glacier/bedrock interface and increases the flow rates by decreasing the friction at bottom of the glacier. This is a favorite of Al Gore (recall his picture of a moulin on a Greenland glacier with a “massive torrent of fresh meltwater tunneling straight down to the bedrock below the ice”);

2) surface thinning at the glacial margin—a process by which the glacial surface melts from above with leads to a thinning at the end of the glacier which decreases the back pressure and thus allows for faster flow;

3) basal thinning at the glacier margin—a process by which the bottom of a marine-terminating glacier is melted by warming ocean waters leading to a decrease in back pressure (or a release from the ocean floor) and an increase in flow rate and ice discharge.

After carefully working with their model, and relating the modeled glacier behavior to the observed behavior of glaciers for the past several years/decades, Nick et al. came to the conclusion that basal lubrication was not the reason of the increased glacial ice loss in recent years, “our modeling does not support enhanced basal lubrication as the governing process for the observed changes” (Sorry Al). Instead, they found “that the dynamics of outlet glaciers are highly sensitive to near-front conditions and that the recent years of atmospheric or oceanic warming are probably a direct forcing of synchronous dynamic changes observed for many Greenland outlet glaciers.”

So, global warming has apparently been responsible for the recent increase in ice loss from Greenland’s glaciers and contributing to sea level rise—perhaps even to a greater degree than included in the IPCC projections.

Is this a sign of worse things to come? Is the EPA justified in worrying about a sea level rise that far exceeds the IPCC’s upper range of guidance?

Don’t sell the beach house just yet. Nick and colleagues go on to find that short-term rapid increases in discharge rates (such as the ones currently observed) are not stable and that “such extreme mass loss cannot be dynamically maintained in the long term.” In fact, for the one glacier that they studied (Helheim glacier), their model predicts that over the next 50 years, dynamic discharge only exceeds steady-state discharge by about 2%” and that “we suggest that in the long term, non-dynamical processes, such as direct surface melt under a warming climate, may dominate the future mass loss of the Greenland ice sheet.”

For those keeping score, the IPCC estimates that “non-dynamical processes, such as direct surface melt under a warming climate” will be responsible for between 1 and 12 centimeters (0.4 to 4.7 inches) of sea level rise from the Greenland ice sheet this century.

Thus, pointing at Greenland an exclaiming “The sky is…” er, I mean “The sea is rising!” (to any scary degree) is not telling the whole story.

According to the latest recommendations in the scientific literature as given by Nick et al. “Our results imply that the recent rates of mass loss in Greenland’s outlet glaciers are transient and should not be extrapolated into the future.” [emphasis added]

Advice clearly not taken to heart by the EPA/CCSP.

Reference:

Nick, F.M., et al., 2009. Large-scale changes in Greenland outlet glacier dynamics triggered at the terminus. Nature Geoscience, doi:10.1038/NGEO394, published on-line January 11, 2009.




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