SUMITRA RAJAGOPALAN:
Global warming
CBC News Viewpoint | October 25, 2005 | More from Sumitra Rajagopalan
Sumitra Rajagopalan has been writing on science and technology and its impact on society and public policy for the last six years. To date, she has written for the Washington Post, the Globe and Mail, the Toronto Star, the Montreal Gazette and the Times of India. She is adjunct professor of mechanical engineering at McGill University. Sumitra is involved in a wide range of science outreach programs in Montreal-area schools.
Forget Kyoto. By the time Christ appeared on Earth, the planet was already belching enough gas to cause global warming.
And we have our ancestors to blame. Or thank.
William Ruddiman, a professor of environmental sciences at the University of Virginia, is behind a controversial theory suggesting that humans had a hand in warming the planet nearly 8,000 years ago, and in doing so, might have prevented another ice age.
In his new book titled Plows, Plagues, Petroleum: How Humans took Control of the Climate, Ruddiman delves further into the theory that first made waves in the winter of 2003.
“I presented my results at the American Geophysical Union in San Francisco back then,” recalls Ruddiman. His findings threw a monkey wrench into a time-honoured theory: that global warming began only 150 years ago, shortly after the Industrial Revolution.
Earth gracefully pirouettes like a ballerina around its axis. Every now and then – once in 22,000 years to be exact – the axis tilts causing the planet to wobble. This clumsy movement is enough to cause warmer summers in the Northern Hemisphere and drive methane levels up in the atmosphere through the breakdown of plant matter in the wetlands.
Then, as the Northern Hemisphere moves away from the sun, methane emissions plummet, reaching a nadir 11,000 years later. Thus waxed and waned methane throughout recorded history, up until 5,000 years ago.
Then it took a wrong turn.
As Ruddiman pored over data collected from ancient air trapped inside Antarctic ice cores, he found that the methane levels reversed directions 5,000 years ago, soaring back to 700 parts per billion when they should have ebbed to 450 ppb, akin to previous cycles.
Intrigued, he turned his attention to carbon dioxide. Here, a similar picture unfolded. During the current interglacial period, the level of CO2 peaked around 10,500 as expected and continued its slow decline through modern times.
Then, it reversed course 8,000 years ago. By the start of the industrial era, CO2 concentrations had soared to 285 parts per million, around 40 ppm higher than expected. Ruddiman suspected that these discrepancies were not driven by natural causes.
So, could humans have been responsible for this anomaly?
Ruddiman found his answers in the ancient civilizations of China and Mesopotamia.
Ruddiman found evidence from studies in archeology and human historical records to show that Europeans began clearing forests to make way for new crops like wheat, barley and peas around 8,000 years ago. “This significant deforestation would have pushed levels of CO2 upwards,” he opines.
Likewise, around 5,000 years ago, Chinese farmers began flooding lowlands near rivers to grow rice, which would have contributed to a rise in atmospheric methane.
Thus, ancient agriculture, not modern industry, was responsible for the onset of global warming.
Plows, not petroleum.
As with all radical theories, this one has its skeptics. In particular, Ruddiman found one critique that warranted a closer look.
Fortunaut Joos is a professor of environmental physics at the University of Bern, Switzerland. For the past many years, Joos has developed models of carbon cycling, thanks to which he can predict the amount of carbon dioxide in the atmosphere at a given period of time.
Joos jumped on Ruddiman’s assertions and stated that there is no way forest clearing could account for the anomalous 40 ppm rise in CO2. With the area of forestland prevalent in the day, any rise in CO2 would level off at four ppm. So, Ruddiman’s assertions were off the mark – by a factor of 10.
“Indeed,” confessed Ruddiman, “he was right. Deforestation could only account for 35-45 per cent of the anomalous CO2 rise.”
So, where did the rest of the CO2 come from?
After much rumination, Ruddiman hit upon a possible answer. “It dawned on me that, alongside human factors pushing CO2 levels up, there might be another mechanism keeping the CO2 levels from going down.”
Further research revealed a cooling trend prevalent in previous interglacial cycles. Looming sea ice in Antarctica is believed to drive down atmospheric CO2 values by reducing carbon exchanges between southern ocean surface water and the atmosphere.
This cooling mechanism is absent today, thus possibly adding to an already increased level of gas.
The critics notwithstanding, Many of Ruddiman’s colleagues have welcomed his new assertions and the resulting paradigm shift in our understanding of climate change.
Ruddiman’s theory brings up an intriguing prospect. Greenhouse gases distanced us from an impending ice age. Could this mean that global warming was a good thing?
“Ah, you’ve hit the nail on the head!” exclaims Ruddiman.
Yet today, the face of global warming is decidedly ugly: floods, melting glaciers, droughts, disease. How then to reconcile the devastating effects of global warming with this new image of greenhouse gases as a warm cuddly blanket, shielding Earth from the next ice age?
“My theory is about the past,” he emphasizes, “and we simply cannot make inferences about the beneficial effects of global warming today based on yesterday’s records.”
“If anything,” he notes, “this study should be a lesson in humility. As humans, we were able to alter the climate simply by growing food,” he muses. “Now, with all the technology at our disposal, just imagine what we can do with the climate in the near future!”
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