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Demise of Laurentide ice sheet was triggered by increasing solar activity and CO2 levels

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Posted June 25, 2015

Researchers at Oregon State University were researching  the massive Laurentide ice sheet of the last ice age and found that at first it began shrinking through calving of icebergs and then suddenly shifted into a new regime where melting on the continent took precedence. It eventually led to demise of the Laurentide ice sheet, which covered lands of Canada. Scientists say that these results are extremely important, because they may give better idea of how ice sheets on Greenland and Antarctica may respond to a warming climate today.

Shrinking ice sheets, like this one in Greenland, are hard to observe and predict. Therefore, scientists need to research the ice sheets of the last ice age, to understand how such ice fields melt, what triggers these processes and what consequences it may have. Image credit: oregonstate.edu.

Shrinking ice sheets, like this one in Greenland, are hard to observe and predict. Therefore, scientists need to research the ice sheets of the last ice age, to understand how such ice fields melt, what triggers these processes and what consequences it may have. Image credit: oregonstate.edu.

Scientists say that a shift in “radiative forcing” in the Laurentide ice sheet began prior to 9,000 years ago and kicked the deglaciation into overdrive.  David Ullman, lead author on the study, noted that there are two mechanisms through which ice sheets diminish – dynamically, from the jettisoning of icebergs at the fringes, or by a negative “surface mass balance,” which compares the amount of snow accumulation relative to melting. The surface mass balance is positive when more snow accumulates than melts.

Scientists said that “during most of the deglaciation, the surface mass balance of the Laurentide Ice Sheet was generally positive,” and that scientists know that the ice sheet was disappearing; therefore the causes must have been dynamic. But scientists also found that there was a shift before 9,000 years ago and the deck of the ice sheet became stacked, because sunlight levels were high because of the Earth’s orbit and CO2 increased.

Scientists note that although they consider these CO2 levels to be rather high, they were about equal to pre-industrial measurements. It means, they were much lower than those of today. However, the solar intensity then was higher than today. It was still enough to trigger the switch to a new state of metling. Ice sheet was pulling back from the coast, so the calving of icebergs diminished. Surface started to melt because of solar activity and increased CO2 levels, which led to final deglaciation.

Scientists say that the findings are particularly relevant today, because they show how sensitive the ice sheet systems are. They noted that there are big shifts in the surface mass balance that occur from only very small changes in radiative forcing Examples of such forcing could be solar radiation or greenhouse gases, which are particularly relevant today, when scientists and world leaders are showing increasing attention to controlling climate change.

During the study scientists examined ice cores dating back some 800,000 years and have documented numerous times when increases in summer insolation took place. However, not all of them resulted in deglaciation to present-day ice volumes. The researchers presume that such high-volume deglacion needs an extra kick or trigger, such as today’s CO2 levels and pollution.

This research just once again shows that ice sheets are particularly sensitive to environmental conditions. Climate change is a well-known problem and there are less and less sceptics, who say that it is not a problem or human activity does not do its toll on Earth’s climate. Researches of the last ice age can show what trigger the melting of ice sheets and what consequences it may have in the near future.

Source: oregonstate.edu

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