Current Climate Change with an Eye on Historical Glacier Melt

I am Sunday Morning Forum co-chair at the Unitarian Universalist Church of Tippecanoe County (in West Lafayette, IN). On January 29,we showed a video, Mega Cities Under Water/Rising Sea Level, . It predicts a sea level rise of 4-6 feet by the end of this century caused by melting polar ice and warming oceans. This would doom many of the coastal cities and much of Florida as its porous limestone bedrock negates the use of levees. New Orleans would not fare much better as much of it is now below sea level. After Katrina, when much of the city flooded, the Army Corp of Engineers started a $15 billion flood wall project to keep the water out. It is good up to 6 feet, and, after that, it will have to be raised. According to the video, San Francisco can be saved by building a levee just outside the Golden Gate Bridge where the water is 130 feet deep. Lots of jobs and money is wrapped up in all that construction. It was shown that, currently in Bangladesh, millions of people live at about three feet above sea level. India built a wall to keep out the rising sea. Many of the rivers in Asia have adjoining rice fields now just above sea level which can eventually flood and cause a significant drop in the food supply. Our future will be beset by major catastrophes caused by greenhouse gas emissions.

The speed of the ice melt can be estimated by looking at the historical record of the last ice age melt 20,000 years ago. Sea levels rose 390 feet then and settled about where they now are. Scientists have analyzed the data and found sea levels rose about 65 feet in 500 years, about 13.5 feet per century.

After watching the 40-minute video, we had a 20-minute discussion during which someone asked what caused the ice to melt 20,000 years ago. I guessed CO2. Afterwards, I was curious and googled the cause of the melt and found that indeed CO2 was the cause. This from quoted below.

As Ice Age Ended, Greenhouse Gas Rise Was Lead Factor in Melting of Earth's Glaciers
“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, a paleoclimatologist who was joined by researchers from Oregon State University, University of Wisconsin-Madison, Purdue University* (emphasis by Lafayette Independent) 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 the glacier 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 in the atmosphere recorded in air bubbles 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 Ice Age, which spanned nearly 7,000 years. Following more than a century of industrialization, carbon dioxide has 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.

Reading that sent me looking for more information and I found this chart:

Tom McConville, Lafayette Independent

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