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The latest and best reconstruction of temperatures near Greenland over that last 450,000 years shows that much of Greenland's vast ice sheet could melt from sustained warming of less than one degree. That means that the world risks triggering a devastating 7 meters (23 feet) of sea-level rise before the end of this century.
Writing in the prestigious Proceedings of the National Academy of Sciences (PNAS), researchers at the University of Bergen, Norway, and at Rutgers University, New Brunswick, New Jersey, analyze 450,000 years of sea surface temperatures off the coast of Greenland. They were able to track four interglacial (warm) periods, during one of which Greenland's southern ice sheet completely disappeared. During that 30,000-year-long warm period centered around 400,000 years ago, temperatures were only slightly higher than they are today--within one degree C--and well within the projections of climate models for the end of this century--if we continue on a business-as-usual trajectory.
Comparing the four warm periods it became clear that the amount of warming was not the only factor impacting how much of Greenland's ice melted. The other key was the duration of the warming. Even with temperatures just 0.8 degrees C warmer than today, the longer duration of the warm period centered around 400,000 years ago led to almost complete melting of Greenland's southern ice sheet.
According to the authors, their findings support climate models that find a tipping point somewhere between 0.8 and 3.2 degrees C warmer than today, beyond which melting of Greenland's ice sheet is inevitable even if temperatures go back down. Paleoclimatologist Nil Irvali, at the University of Bergen, explains that the tipping point occurs when melting reduces the altitude of the ice surface to the point where the even-warmer temperatures at the lower elevation guarantees runaway melting. "The elevation effect becomes dominant over time," she says, "melting accelerates, and may even continue even though the climate cools again."
The risk, she clarifies, is not that the Greenland Ice Sheet will melt before the end of the century, but that by the end of the century atmospheric warming caused by a continuation of current policies and emissions could easily trigger irreversible melting and an eventual, and devastating, 7-meter sea-level rise.
Actually, Irvali points out, it's even worse than that, since both atmospheric carbon dioxide and warmer ocean waters have extremely long lifetimes. "It is also important to note that CO2 we put into the atmosphere will have a long lifetime even if we cut emissions, and as more and more heat accumulates in the ocean it commits us to a longer timescale of warming," she says, "So our current activities will impact climate for millennia to come."
The authors conclude, "Notably, the critical temperature threshold for past [Greenland Ice Sheet] decay will likely be surpassed this century. The duration for which this threshold is exceeded will determine Greenland's fate."
To which we must add, and the fate of millions of Americans and hundreds of millions of people worldwide.**
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**In case this paleo-historical study seems too theoretical, recent observations by a completely different set of researchers show that Greenland is losing ice 7 times faster than it was two decades ago, in line with the IPCC's worst-case scenario, putting some 400 million people at risk of coastal flooding by 2100.
REA
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If you liked the post, please use the links to the right to follow or subscribe for email alerts from zerospinzone.blogspot.com.
Greenland Ice Sheet at Risk
Credit: cake@cake0
Writing in the prestigious Proceedings of the National Academy of Sciences (PNAS), researchers at the University of Bergen, Norway, and at Rutgers University, New Brunswick, New Jersey, analyze 450,000 years of sea surface temperatures off the coast of Greenland. They were able to track four interglacial (warm) periods, during one of which Greenland's southern ice sheet completely disappeared. During that 30,000-year-long warm period centered around 400,000 years ago, temperatures were only slightly higher than they are today--within one degree C--and well within the projections of climate models for the end of this century--if we continue on a business-as-usual trajectory.
Comparing the four warm periods it became clear that the amount of warming was not the only factor impacting how much of Greenland's ice melted. The other key was the duration of the warming. Even with temperatures just 0.8 degrees C warmer than today, the longer duration of the warm period centered around 400,000 years ago led to almost complete melting of Greenland's southern ice sheet.
According to the authors, their findings support climate models that find a tipping point somewhere between 0.8 and 3.2 degrees C warmer than today, beyond which melting of Greenland's ice sheet is inevitable even if temperatures go back down. Paleoclimatologist Nil Irvali, at the University of Bergen, explains that the tipping point occurs when melting reduces the altitude of the ice surface to the point where the even-warmer temperatures at the lower elevation guarantees runaway melting. "The elevation effect becomes dominant over time," she says, "melting accelerates, and may even continue even though the climate cools again."
The risk, she clarifies, is not that the Greenland Ice Sheet will melt before the end of the century, but that by the end of the century atmospheric warming caused by a continuation of current policies and emissions could easily trigger irreversible melting and an eventual, and devastating, 7-meter sea-level rise.
Actually, Irvali points out, it's even worse than that, since both atmospheric carbon dioxide and warmer ocean waters have extremely long lifetimes. "It is also important to note that CO2 we put into the atmosphere will have a long lifetime even if we cut emissions, and as more and more heat accumulates in the ocean it commits us to a longer timescale of warming," she says, "So our current activities will impact climate for millennia to come."
The authors conclude, "Notably, the critical temperature threshold for past [Greenland Ice Sheet] decay will likely be surpassed this century. The duration for which this threshold is exceeded will determine Greenland's fate."
To which we must add, and the fate of millions of Americans and hundreds of millions of people worldwide.**
-----
**In case this paleo-historical study seems too theoretical, recent observations by a completely different set of researchers show that Greenland is losing ice 7 times faster than it was two decades ago, in line with the IPCC's worst-case scenario, putting some 400 million people at risk of coastal flooding by 2100.
REA
-----
If you liked the post, please use the links to the right to follow or subscribe for email alerts from zerospinzone.blogspot.com.
