Global Warming Isn't Natural: To Remaining Climate Change Skeptics, This Study 'Will Be A Blow'

By Ben Wolford on April 11, 2014 2:44 PM EDT

A physicist says his analysis of climate change rules out skeptics' arguments that global warming is a natural fluctuation. (Photo: Shutterstock)

A physicist says his analysis of climate change rules out skeptics' arguments that global warming is a natural fluctuation. (Photo: Shutterstock)

The author of a new climate change study says his conclusions "will be a blow" to anyone who still believes global warming is caused by nature.

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In this month's issue of the journal Climate Dynamics, McGill University physicist Shaun Lovejoy reports with more than 99 percent confidence that climate change is happening because of greenhouse gas emissions related to human activities. His research was based on a probability analysis of temperature data going back to 1500. In a statement, Lovejoy says the statistical confidence is "most likely greater than 99.9 percent."

Scientists have been fairly certain for a while that carbon dioxide from industrial technology and other greenhouse gases were causing the sun's heat to be trapped in the atmosphere. The Swedish chemist Svante Arrhenius predicted climate change as early as 1896. In March, the United Nations' climate agency even went so far as to say extreme weather in 2013 — including specific storms, droughts, and a tornado in Oklahoma — "were consistent with what we would expect as a result of human-induced climate change."

With so much consensus, is Lovejoy late to the party? He doesn't believe so. He writes that most previous research has relied on computerized models called "general circulation models," or GCMs. These are based on theoretical assumptions about carbon concentration that can't actually be measured in real life, he says. "An unfortunate side effect of this reliance on models is that it allows GCM skeptics to bring into question the anthropogenic causation of the warming," according to Lovejoy. Here's one website, for example, that calls climate change a "scientific fad."

So Lovejoy made his own model based strictly on observed temperatures. He compared temperature fluctuations before the dawn of the Industrial Revolution in 1880 with fluctuation after. To measure the climate before 1880, he used natural indicators like tree rings, layers of ice, and lake sediments that are responsive to temperature changes. Then he threw man-made carbon dioxide into the equation and calculated the probability that warming since 1880 could've happened without those emissions.

"We've had a fluctuation in average temperature that's just huge since 1880 — on the order of about 0.9 degrees Celsius," Lovejoy says. "This study shows that the odds of that being caused by natural fluctuations are less than one in a hundred and are likely to be less than one in a thousand."

It's not solid proof by itself, he says, but it complements the other research: "While the statistical rejection of a hypothesis can't generally be used to conclude the truth of any specific alternative, in many cases — including this one — the rejection of one greatly enhances the credibility of the other." He went on to predict what would happen if the amount of carbon in the atmosphere doubled, based on his measurements. The answer was that temperatures would increase between 2.5 and 4.2 degrees Celsius, which, Lovejoy observes, is within the ranged predicted by the U.N.'s Intergovernmental Panel on Climate Change.

Above photo courtesy of Shutterstock

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