Dueling press releases – one says GHG's 'caused' end of last ice age, other says 'lead factor'

I noticed these press releases for the new “ramp up to Paris” paper at Eurekalert today. One is from Boston College, the other is from Oregon State University. The headlines seem about as far apart as the schools themselves.

You’d think that authors of the same paper could get their PR straight.

The certainty of the theory as they present it is typical of alarmist PR’s but the conclusion, trying to link boulder deposition to CO2 levels seems a bit rocky at best. They claim to be able to resolve when boulders were uncovered from ice and link that to CO2 levels, and thus prove CO2 levels caused the end of the ice age. Of course, nether press release tells you the paper title, the DOI, or links to the journal, because as we’ve seen so many times, the paper itself is just a ticket to media coverage, and isn’t important enough to be part of the story that will be foisted upon the public.  I’ve posted both of them below for comparison in the sequence presented above in the screencap.

As Ice Age ended, greenhouse gas rise was lead factor in melting of Earth’s glaciers

New findings have implications for recent carbon dioxide rise and melting glaciers

BOSTON COLLEGE

Chestnut Hill, MA (Aug. 21, 2015) – A fresh look at some old rocks has solved a crucial mystery of the last Ice Age, yielding an important new finding that connects to the global retreat of glaciers caused by climate change today, according to a new study by a team of climate scientists.

For decades, researchers examining the glacial meltdown that ended 11,000 years ago took into account a number of contributing factors, particularly regional influences such as solar radiation, ice sheets and ocean currents.

But a reexamination of more than 1,000 previously studied glacial boulders has produced a more accurate timetable for the pre-historic meltdown and pinpoints the rise in carbon dioxide – then naturally occurring – as the primary driving factor in the simultaneous global retreat of glaciers at the close of the last Ice Age, the researchers report in the journal Nature Communications.

“Glaciers are very sensitive to temperature. When you get the world’s glaciers retreating all at the same time, you need a broad, global reason for why the world’s thermostat is going up,” said Boston College Assistant Professor of Earth and Environmental Sciences Jeremy Shakun. “The only factor that explains glaciers melting all around the world in unison during the end of the Ice Age is the rise in greenhouse gases.”

The researchers found that regional factors caused differences in the precise timing and pace of glacier retreat from one place to another, but carbon dioxide was the major driver of the overall global meltdown, said Shakun, a co-author of the report “Regional and global forcing of glacier retreat during the last deglaciation.”

“This is a lot like today,” said Shakun. “In any given decade you can always find some areas where glaciers are holding steady or even advancing, but the big picture across the world and over the long run is clear – carbon dioxide is making the ice melt.”

While 11,000 years ago may seem far too distant for a point of comparison, it was only a moment ago in geological time. The team’s findings fix even greater certainty on scientific conclusions that the dramatic increase in manmade greenhouse gases will eradicate many of the world’s glaciers by the end of this century.

“This has relevance to today since we’ve already raised CO2 by more than it increased at the end of the Ice Age, and we’re on track to go up much higher this century — which adds credence to the view that most of the world’s glaciers will be largely gone within the next few centuries, with negative consequences such as rising sea level and depleted water resources,” said Shakun.

The team reexamined samples taken from boulders that were left by the retreating glaciers, said Shakun, who was joined in the research by experts from Oregon State University, University of Wisconsin-Madison, Purdue University and the National Center for Atmospheric Research in Boulder, Colo.

Each boulder has been exposed to cosmic radiation since the glaciers melted, an exposure that produces the isotope Beryllium-10 in the boulder. Measuring the levels of the isotope in boulder samples allows scientists to determine when glaciers melted and first uncovered the boulders.

Scientists have been using this process called surface exposure dating for more than two decades to determine when glaciers retreated, Shakun said. His team examined samples collected by multiple research teams over the years and applied an improved methodology that increased the accuracy of the boulder ages.

The team then compared their new exposure ages to the timing of the rise of carbon dioxide concentration in the atmosphere, a development recorded in air bubbles taken from ice cores. Combined with computer models, the analysis eliminated regional factors as the primary explanations for glacial melting across the globe at the end of the Ice Age. The single leading global factor that did explain the global retreat of glaciers was rising carbon dioxide levels in the air.

“Our study really removes any doubt as to the leading cause of the decline of the glaciers by 11,000 years ago – it was the rising levels of carbon dioxide in the Earth’s atmosphere,” said Shakun.

Carbon dioxide levels rose from approximately 180 parts per million to 280 parts per million at the end of the last Ice Age, which spanned nearly 7,000 years. Following more than a century of industrialization, carbon dioxide levels have now risen to approximately 400 parts per million.

“This tells us we are orchestrating something akin to the end of an Ice Age, but much faster. As the amount of carbon dioxide continues to increase, glaciers around the world will retreat,” said Shakun.

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Greenhouse gases caused glacial retreat during last Ice Age

OREGON STATE UNIVERSITY

CORVALLIS, Ore. – A recalculation of the dates at which boulders were uncovered by melting glaciers at the end of the last Ice Age has conclusively shown that the glacial retreat was due to rising levels of carbon dioxide and other greenhouse gases, as opposed to other types of forces.

Carbon dioxide levels are now significantly higher than they were at that time, as a result of the Industrial Revolution and other human activities since then. Because of that, the study confirms predictions of future glacial retreat, and that most of the world’s glaciers may disappear in the next few centuries.

The findings were published today in Nature Communications by researchers from Oregon State University, Boston College and other institutions. They erase some of the uncertainties about glacial melting that had been due to a misinterpretation of data from some of these boulders, which were exposed to the atmosphere more than 11,500 years ago.

“This shows that at the end of the last Ice Age, it was only the increase in carbon dioxide and other greenhouse gases that could have caused the loss of glaciers around the world at the same time,” said Peter Clark, a professor in the OSU College of Earth, Ocean and Atmospheric Sciences, and co-author on the study.

“This study validates predictions that future glacial loss will occur due to the ongoing increase in greenhouse gas levels from human activities,” Clark said. “We could lose 80-90 percent of the world’s glaciers in the next several centuries if greenhouse gases continue to rise at the current rate.”

Glacial loss in the future will contribute to rising sea levels and, in some cases, have impacts on local water supplies.

As the last Ice Age ended during a period of about 7,000 years, starting around 19,000 years ago, the levels of carbon dioxide in the atmosphere increased from 180 parts per million to 280 parts per million. But just in the past 150 years, they have surged from 280 to about 400 parts per million, far higher than what was required to put an end to the last Ice Age.

The new findings, Clark said, were based on a recalculation of the ages at which more than 1,100 glacial boulders from 159 glacial moraines around the world were exposed to the atmosphere after being buried for thousands of years under ice.

The exposure of the boulders to cosmic rays produced cosmogenic nuclides, which had been previously measured and used to date the event. But advances have been made in how to calibrate ages based on that data. Based on the new calculations, the rise in carbon dioxide levels – determined from ancient ice cores -matches up nicely with the time at which glacial retreat took place.

“There had been a long-standing mystery about why these boulders were uncovered at the time they were, because it didn’t properly match the increase in greenhouse gases,” said Jeremy Shakun, a professor at Boston College and lead author on the study. “We found that the previous ages assigned to this event were inaccurate. The data now show that as soon as the greenhouse gas levels began to rise, the glaciers began to melt and retreat.”

There are other forces that can also cause glacial melting on a local or regional scale, the researchers noted, such as changes in the Earth’s orbit around the sun, or shifts in ocean heat distribution. These factors probably did have localized effects. But the scientists determined that only the change in greenhouse gas levels could have explained the broader global retreat of glaciers all at the same time.

In the study of climate change, glaciers have always been of considerable interest, because their long-term behavior is a more reliable barometer that helps sort out the ups-and-downs caused by year-to-year weather variability, including short-term shifts in temperature and precipitation.

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Other collaborators on this research were from the University of Wisconsin, Purdue University, and the National Center for Atmospheric Research. The work was supported by the National Oceanic and Atmospheric Administration and the National Science Foundation.