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Prominent Scientist Explains the Physics of Climate Change


Michael E. Mann talked climate change projections.
Photo by Chris Gosier

On April 30, a research professor at the center of the so-called “climate wars” gave a physics department talk on the science that shows carbon dioxide emissions need to be curtailed.

Michael E. Mann, Ph.D., director of the Earth System Science Center at Pennsylvania State University, helped the Intergovernmental Panel on Climate Change secure a Nobel Peace Prize in 2007 and has authored two books on the topic. Mann has been the target of climate change deniers, who hacked into his email account in an attempt to discredit him.

Mann, who was introduced by Stephen Holler, Ph.D., assistant professor of physics, started with a basic description of greenhouse effect, caused by the buildup of carbon dioxide that “traps” part of the infrared radiation emitted by the Earth. The resulting warming is amplified by feedback mechanisms such as increased evaporation, which boosts the amount of airborne water vapor that, in turn, acts as a greenhouse gas as well, he said.

In 2013, carbon dioxide concentration in the atmosphere surpassed 400 parts per million for the first time, he said. If there’s no change in the burning of fossil fuels, levels will reach 450 parts per million in a matter of just decades. By the mid-21st century, it will be be double the level that existed in preindustrial times. Meanwhile, he said, the earth’s temperature has ticked up just as expected.

“Everything I told you thus far wasn’t based on climate models; it was based on simple physics that we’ve known about for two centuries—irrefutable measurements that tell us we’re changing the composition of the atmosphere in an unprecedented manner and that the Earth is warming up as we expect it to,” he said.

“Scientists around the world would be completely stumped … if the earth were not warming up,” he said.

Mann discussed climate change projections based on computer models, saying that one of the more benign projections—that the Earth will experience an increase in global temperatures of two degrees Celsius, compared to preindustrial times, if nothing is done—“puts us firmly into the danger zone.”

“You start to see bad things happen when you talk about human health, water resources, food, national security, our economy, biodiversity, and across the board,” he said.
Such an increase could be three degrees higher, he said—“the difference between a problem that would be moderate, and which we could adapt to, and a problem that would be catastrophic.”

“Some people say, ‘Well, it’s uncertain—maybe we’ll be lucky,’” he said. “It’s true, maybe we’ll get lucky. But maybe we’ll get unlucky.”

Invoking the example of a cost-benefit analysis, he said, “we buy fire insurance not because we think our homes are going to burn down, but because if they did burn down it would be catastrophic,” he said. “It’s a very low-probability event with an effectively infinite cost to us [because]it ruins our lives if it happens.”

“I would argue that reducing greenhouse gas emission is a planetary insurance policy” because of the possibility that the worst projections could come true, he said.


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