Humans began changing climate 7,000 years ago "I'm really certain that I'm right," says Ruddiman.
by : Will Goldsmith
When William Ruddiman stepped away from the classroom in 2001, he expected to be more retired by now. But eight years later, the UVA emeritus professor of environmental sciences just can’t seem to stop working, all because of a little idea of his that humans haven’t just been changing the planet’s climate over the last 200 years—but starting 7,000 years ago.
UVA Professor Emeritus William Ruddiman has recently published a paper that argues that anthropogenic climate change began thousands of years earlier than the first coal plant or combustion engine. “I’m really certain that I’m right,” Ruddiman muses. “And I usually wouldn’t say that.”
“My hypothesis is drawing a lot of attention,” says Ruddiman, who though retired, co-authored a paper published in August that further refines his notion that anthropogenic climate change happened thousands of years earlier than the first coal plant or combustion engine. “A good bit of [the attention] is favorable, and some of it is decidedly not favorable.” Ruddiman isn’t the stereotypical kooky old professor trying to stir the pot. He’s decidedly not Pat Michaels, the retired UVA professor who regularly bashes global warming alarmists and doesn’t think climate change is so bad. Ruddiman holds mainstream scientific beliefs about climate change over the last 200 years, and thinks it’s “risky,” but avoids policy issues. As an author of one of the most popular textbooks on the earth’s climate, he treads lightly around the controversial political subject. “The last thing I want to do is write a book that misleads thousands of students with a biased case, so that’s given me reason to track the global warming issue very carefully,” he says.
Nevertheless, Ruddiman has become entangled in the fray by virtue of his recent work. Originally, he was simply trying to make sense of polar ice core samples, which provide a sort of historic record of the earth’s climate through the air bubbles they trap. Ruddiman couldn’t understand why methane levels went up several thousand years ago when the natural trend was down. Looking for reasons why, he stumbled on literature about what humans were up to starting 7,000 years ago—clearing forest, flooding rice paddies, and producing enough food to explode the populations of both people and domestic animals—and a lot more people and animals meant a lot more methane and carbon dioxide.
“They weren’t just putting a little methane and a little CO2 in the atmosphere, they were putting enough to reverse a natural downward trend in those gases,” says Ruddiman. “They had a huge effect. …Natural cycles don’t explain that.” Ruddiman believes that those raised levels were enough to offset a cooling trend that would have made life nastier for humans at that time. That aspect of his work attracted the attention of the global warming skeptics, who have alternately cheered and disparaged Ruddiman’s work. _______________________________________________________________
Now hold on there partner, maybe you should look a little further!
Professor Ruddiman’s hypothesis that man began to change climate 7,000 years ago by emitting greenhouse gases is intriguing. Certainly, changing land use by irrigation, draining swamps, etc will change local climate. No doubt, Professor Ruddiman is influenced by the ice core graphs used by the UN Intergovernmental Panel on Climate Change (IPCC) indicating changes in greenhouse gases for the past 10,000 years. These show a steady increase in the gases starting about 7,000 years ago and a sharp rise during the 20tth Century.
Strangely, the IPCC, Professor Ruddiman, and the committee of the Geological Society of America, which he headed, which issued a statement that man is the principal cause of climate change, fail to consider temperature changes measured from these ice cores.
These temperature data, confirmed by many other studies, show that 7,000 years ago the earth was in the hottest period of the last 10,000 years – called the Holocene Climate Optimum. By 4,000 years ago, temperatures began to plunge even though greenhouse gases continued to increase. Temperatures have varied since, peaking again about 1,000 years ago, warmer than today, but not as warm as the Holocene. Greenhouse gases fail to explain the history of climate change for the past 10,000 years, past 1,000 years, or past 100 years – contradicting Professor Ruddiman’s hypothesis.
The reports of the Nongovernmental International Panel on Climate Change (NIPCC 2008, 2009), never scientifically refuted, include many of these ignored studies and conclude that Nature, Not Human Activity, Rules the Climate. There is no scientific basis for claiming that man’s emissions of these gases caused the recent warming – or for declaring these gases pollutants.
Kenneth A. Haapala
Virginia Scientists and Engineers for
Energy and Environment