Glimpse to past adds weight to global warming forecasts

Impact of last interglaciation shows shape of things to come

A new examination of the period of global warming that planet Earth underwent 130,000 years ago is helping scientists to confirm the accuracy of projections for the next century – particularly over Canada's North.

A team that includes University of Calgary glaciologist Dr. Shawn Marshall – the lone Canadian – will publish results of its research in the forthcoming issue of the journal Science. The paper shows that a sophisticated climate model, which is one of several global models used in projections of future climate change, is successful in recreating the last period of significant global warming.

"If the climate model is capable of reproducing a climate scenario that is consistent with the palaeological record, that gives us more confidence that it's also giving us reliable projections for the future," says Marshall, an associate professor in the U of C's Department of Geography and second author on the paper.

Marshall, together with researchers from the U.S. National Centre for Atmospheric Research (NCAR), the University of Arizona and the University of Colorado, created a snapshot of climatic conditions 130,000 years ago using existing academic research. The synthesis draws from ice core evidence, stranded coral reefs, fossilized pollen, and the chemical makeup of ancient shells in northern lakes and ocean sediments. The investigators then tested whether the NCAR climate model was able to simulate the extreme conditions of the time, which included loss of summertime sea ice in the Arctic and global sea levels about five metres higher than present.

"The difference 130,000 years ago is that there was an increase in solar radiation over the Arctic, caused by slight changes in the Earth-Sun orbit, which is a normal cycle that occur over tens of thousands of years," Marshall says. "This time around the warming is man-made, caused by carbon dioxide emissions, but the effects on Arctic sea ice, permafrost, and icefields are forecast to be similar."

Marshall's role in the study was in the area of ice sheet modelling and the implications for rising sea levels. As a result of his work, the ice sheet modeling will formally become part of the NCAR modeling system. "The fact that these climate models are getting it right is encouraging from a scientific standpoint, but quite worrisome when you think about the implications," he says.

Current scenarios project a global temperature increase of at least two degrees Celsius over the next 100 years, which is amplified to as much as 10 degrees in polar regions due to what are known as feedback cycles. The short-term result will be melting sea ice, and in the longer term a northward encroachment of the Boreal forest, and ultimately the disappearance of the Greenland ice sheet. The authors report that at least 70 per cent of the five-metre sea level rise in the last interglaciation came from retreat of the icefields in Greenland and Arctic Canada.

"Despite the different mechanisms of warming, these results indicate that the impact on Arctic environments over the next century can be expected to be substantial if predicted future climate change comes to pass," the authors write.

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To arrange an interview with Dr. Shawn Marshall, contact Greg Harris, University of Calgary media relations, at (403) 220-3506 or cell (403) 540-7306, or email, gharris@ucalgary.ca


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