BOSTON (MainStreet) — This spring put climate change back on the mainstream media radar.
It started in March, when the American Association for the Advancement of Science released a report on climate change titled What We Know to kick off an initiative to raise awareness on the issue. It makes clear that not only is human-caused climate change real and happening, but that we need to take quick and direct action to rein in greenhouse gas emissions to avert likely catastrophe. Now the the United Nation's Intergovernmental Panel on Climate Change has released a grim report acknowledging that global carbon emissions have continued accelerate even with the recent spike in political rhetoric on tackling the issue.
Despite the growing alarm in the scientific community on climate change, deniers have continued to raise their voices to drown out concern. Two arguments most often used by climate skeptics are that climate change is part of the planet's natural cycle and climate variability and that climate projections rely on fallible computer models. A study released this month in the peer-review journal Climate Dynamics, though, should put these arguments to rest.
Conducted by geophysicist Dr. Shaun Lovejoy of McGill University in Montreal, the study analyzed temperature data collected since 1500, paying particular attention to changes in the past 125 years, since the onset of the Industrial Revolution. Lovejoy considered these temperature changes in the context of longer-term climate fluctuations and looked at records of tree rings, ice cores, cores of the ocean floor and lake sediments. This kind of data offers insight into hemispheric and global climate fluctuations over hundreds, thousands or in some cases even hundreds of thousands of years. For instance, some ice cores from the South Pole can offer a blueprint of climate fluctuations over the past 800,000 years.
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After a review of these geological climate records, Lovejoy applied a "fluctuation-analysis technique" — a method for determining the probability of a given event — to understand temperature variations over wide ranges of time. He concluded that a global warming event such as the one we have been experiencing over the past century has an incredibly small likelihood, at least one in 1,000. If a bell curve analysis is applied to the data, that likelihood would become even more minuscule, ranging from one in 100,000 to one in 10 million. Lovejoy's study indicates with a confidence greater than 99% that the rate of climate change that has taken place over the past 125 years cannot be ascribed to natural cycles.
"[Climate skeptics] often try to make it appear as though there is a debate on this issue. That's what this study is going to change," Lovejoy says. "I think it's game over for the climate deniers. We can't mess around for another 10 or 20 years."
Lovejoy's research, which was unfunded, uses carbon dioxide as a surrogate for other human-caused and natural events associated with climate fluctuations, including land-use changes and aerosol pollution from volcanic eruptions — variables that can often stump computer models.
Even with his more rudimentary form of analysis, Lovejoy notes, his results are pretty much in line with estimates by the IPCC and National Academies of Science. The study predicts that doubling carbon dioxide levels in the atmosphere would cause the climate to warm by between 2.5 and 4.2 degrees Celsius; the IPCC's projection was for an increase of 1.5 to 4.5 degrees Celsius under the same scenario.
"Increases in CO2 is strongly linked to global economic activity," Lovejoy says. "To a good approximation, if you double the economy, you double the emissions — and, therefore, you double the effects."
There was some criticisms of Lovejoy's research from the climate skeptic camp for his inclusion of tree ring data for climate reconstructions, which some studies suggest can deviate widely from thermometer-based temperature readings, and for not considering other warmer periods in the planet's recent history, such as the so-called "Medieval Warming Period" of 1,000 years ago.
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Lovejoy notes that tree ring records make up only one very small facet of his review among many other factors, and that his results would be more or less the same if tree ring data were exempted. As for other warming events in the past several thousand years, he points out that it is important to understand that those were probably more regional or continental in nature rather than global. But even global scale temperatures can change by large amounts as long as their rate of increase is small enough. In other words, what makes the current climate change we are experiencing so remarkable is that it is happening very quickly over an extremely short time and over the entire globe.
Maureen Raymo, a paloeclimatologist and marine scientist from Columbia University and the Lamont Doherty Earth Observatory who has spent decades studying our planet's natural climate variability, agrees.
"What we're seeing right now is not natural," says Raymo on a Yale Forum video. "Right now, we're living in a world of a Pliocene atmosphere. But the whole rest of the climate system — the oceans are trying to catch up, the ice sheets are waning and everything is trying to catch up to this Pliocene atmosphere."
Raymo clarified that none of the recent changes in the climate can be explained by the Earth's distance to the sun, solar output or our planet's elliptical orbit. If anything, the climate community has often underestimated and understated the rate of climate change and its projected impacts, she says.
As Lovejoy puts it, "How bad [climate change] is going to be, we don't exactly know, whether it's really bad or somewhat bad. But we should be starting to wean ourselves off of fossil fuels and begin investing in carbon-free technologies immediately."
— By Laura Kiesel