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Research Studies Timing, Impact of Arctic Melt

Aerial view of ice shrinkage in the Arctic Sea
September 2012 marked a modern record in the size of sea ice in the Arctic, with levels 48.5 percent below the mean average. Now a new study in Nature reveals that the large methane release that could be causes by arctic sea ice melting could accelerate by 15 to 35 years the arrival of the date when the global mean average temperature exceeds preindustrial levels by 2°C—creating $60 trillion in economic damage. NASA/Goddard Space Flight Center Scientific Visualization Studio and NASA Earth Observatory/Jess Allen

Two papers published recently examine how quickly Arctic ice is disappearing and the economic consequences of a possible release of methane as a result.

August 6, 2013—Two scholarly papers published recently examine how quickly and extensively ice cover conditions are changing in the Arctic and the enormous economic consequences those changes could have on the global economy if thawing soils release the massive methane deposits beneath the East Siberian Arctic Shelf.

Climate Science: Vast Costs of Arctic Change” was published in July by Nature. The authors are Gail Whiteman, Ph.D., a professor of sustainability, management, and climate change at Erasmus University Rotterdam; Chris Hope, Ph.D., a reader in policy modeling at the University of Cambridge; and Peter Wadhams, Ph.D., Sc.D., a professor of ocean physics at the University of Cambridge. The team used computer modeling to calculate the global economic impacts of a methane release from melting permafrost.

There is an approximately 50 gigaton reservoir of methane under the seabed in East Siberia, and scientists believe that as the seabed thaws, the methane could escape through newly formed cracks into the atmosphere, either suddenly, or over a period of half a century.

The team utilized the PAGE09 integrated assessment model, an updated program that takes into account the latest scientific and economic information, primarily from the 4th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2007). The team conducted 10,000 program runs to assess different scenarios and their impacts through the year 2200. The research indicates that such a methane release would accelerate by 15 to 35 years the arrival of the date when the global mean average temperature exceeds preindustrial levels by 2°C. This methane release could add $60 trillion to the costs of climate change. The model indicates developing nations would be disproportionately impacted.

“In parts of Africa, where at present agriculture might just be manageable, those areas would no longer be able to have productive agriculture. It would mean that parts of Asia, particularly Bangladesh and other low-lying areas—where we already see quite devastating floods—floods would occur more frequently and be more devastating,” said Hope, in written comments to Civil Engineering online.

“The fact that the Arctic is changing rapidly is relatively well known,” said Whiteman, in written comments to Civil Engineering online. “However, among world leaders this issue is most often discussed in relation to short-term economic gains from extraction and new shipping routes.The flip side has not received enough attention, and this was a driving motivation for this study.”

The authors are beginning a new study with a larger team to further investigate the topic, including if the model is underestimating the impact of a methane release.

“There is some evidence that such a large pulse in the Arctic would take longer to disperse than more diffuse emissions elsewhere,” Hope said. “[The model] also assumes the temperature rise from the methane pulse does not trigger other methane releases that would not otherwise have occurred. This may also lead to an underestimation of the effects.”

The latest climate models vary widely on ice melt rates in the Arctic and when the area will be free of ice in September. September 2012 marked a modern record in the extent of sea ice in the Arctic, with levels 48.5 percent below the mean average. The ice is thinning as well. Still, models predict the date when ice will disappear in the Arctic in September from 2011 to 2098.

Reducing Spread in Climate Model Projections of a September Ice-Free Arctic” was published in July in the Proceedings of the National Academy of Sciences. A team of researchers lead by Jiping Liu, Ph.D., assistant professor in the Department of Atmospheric and Environmental Science at the State University of New York, Albany, examined discrepancies between 30 climate models that are utilized by researchers attempting to discern a date when the Arctic might be ice free in September.

The team used two approaches to narrow the vast spread the models produce for the date of an ice-free September in the Arctic.

“The first approach is model selection,” Liu says. “We analyzed 30 climate models [and] removed the outlier models outside a range of criteria using [actual] observations” from 1979 to present. By selecting a subset of models that aligned with observations, the team deemed their projections likely to be more reliable in the future. The team developed an average projection from this subset.

The team also used a method known as constrained estimation that is based on a “strong and persistent relationship between present and future sea ice conditions.

“The idea is that the models with excessive sea ice at present tend to retain the ice for a relatively long period,” Liu says. “The models with insufficient sea ice at present tend to lose ice relatively quickly. We used this relationship to constrain the model’s bias.

“Encouragingly, these two different methods gave us similar ice-free timing, from 2054 to 2058,” Liu says. “So we narrow this large spread from 2011 to 2098 to this five-year window. This is the best estimation we can get from the current generation of climate models.”

Liu notes that climate models are not perfect. The models still have problems representing some important physical processes of the intricate climate system. For example, because sea ice is thinning as well as shrinking, sunlight can penetrate the thinning ice to warm the water beneath it, possibly accelerating melting. Thus the Arctic could be ice free earlier than anticipated.


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