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Planet Earth

Global Warming: Cretaceous Quote-Mining

The LoomBy Carl ZimmerApril 2, 2007 11:40 PM


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There's nothing more grating for a science writer than see your work get cut and pasted to give people precisely the wrong impression. My latest irritation: "Ten Questions For Al Gore and the Global Warming Crowd", which appeared Friday on the conservative web site The author is John Hawkins, who describes himself as a professional blogger who runs Right Wing News. Hawkins claims that he is skeptical that humans are causing global warming because, in his words, "'the Earth-is-going-to-burn-us-alive' crowd cannot answer the most basic questions about the theory that they haughtily insist is so beyond reproach that there should be no more need for debate." He then offers ten questions for the "global warming crowd," claiming that "if the proponents of the manmade global warming theory can come up with good answers to questions like these, you can expect everyone, including me, to accept their theory." Questions seem inherently innocent--they're just simple quests for knowledge, right? But in the hands of someone like Hawkins, they also have the potential to spread quite a lot of misinformation... Take, for example, Hawkins's second question:

2) If greenhouse gasses produced by mankind are behind the roughly one degree increase in temperature over the last century, then why did the global temperature go down from roughly 1940 to 1975 even though mankind's production of greenhouse gasses was skyrocketing during that same time period?

Funny how Hawkins doesn't mention in his questions the well-established fact that burning fossil fuels creates emissions that can both absorb heat and cool the atmosphere (the latter happens when pollution seeds clouds that bounce incoming radiation back to space). Over the course of the twentieth century, cooling effects increased and then faded as dirty pollution was cleaned up and the lingering gases in the atmosphere got washed out. Meanwhile, however, heat-trapping gases continued their increase. In the mid-1900s the cooling and warming effect of human emissions roughly canceled each other out. Computer models that include the historical records of all these gases show a mid-century stall in the rise of global temperatures. See this excellent picture, based on a 2004 study in the Journal of Climate. For a more recent update, see the new Intergovernmental Panel on Climate Change report, figure 4 (pdf). (via Real Climate.) Before Hawkins delivered this question to the world, he could have found the answer with a few minutes of Googling. I don't know if he didn't have the time, or if he already knew and didn't want to draw people's attention to it. Hard to tell exactly what happened. But I do have a better idea of what happened when he invoked an article by me down in question nine. And it's pretty ridiculous. Indulge me as I quote Hawkins quoting myself--I do have a reason for it...

9) As Carl Zimmer has noted in Discover, at times in the earth's past, we've had considerably more carbon dioxide in the air that we do today, and yet it's debatable whether the temperature was significantly warmer, "During the Ordovician Period, 440 million years ago, there seems to have been 16 times as much carbon dioxide in the atmosphere as there is today--and yet, judging from the gravelly deposits it left behind, there was also an ice sheet near the South Pole that was four-fifths the size of present-day Antarctica. The second exception is even more troubling. The Cretaceous Period, when dinosaurs ruled the Earth and CO2 levels were about eight times what they are today, has been one of the most popular case studies for global warming forecasters. And everyone knows what the climate was like during the dinosaurs' heyday: steamy. Or was it? The latest evidence, reported just this past summer by British researchers, suggests that temperatures in the tropics 95 million years ago were no higher than they are now; and while it was a lot warmer at the poles than it is today, it was still freezing cold." Doesn't this suggest that there isn't anywhere near as much of a close relationship between greenhouse gasses like carbon dioxide and the temperature as many people seem to believe?

Now, if you read the article itself at the Discover web site, you'll see--in the very next paragraph--that this paradox did not cause climate scientists to reject the link between greenhouse gases and climate. Why not? Because the Earth millions of years ago was different in a couple important ways. For one thing, it got less light 440 million years ago, because the sun was dimmer. For another, the geography was different. In the Ordovician, for example, many of the continents were rammed together and situated partly over the south pole. The climate scientists I wrote about in the article were running computer models that indicated that this arrangement allowed glaciers to grow even while the planet heated up. In the article I also explained how the arrangement of continents in the Cretaceous allowed cooling clouds to form over the interiors of the continents. If the continents were going to slam into each other in the next century, the climate 440 million years ago might give us some pause about whether the planet is going to warm. But the continents are just going to creep along, while the carbon dioxide is going to shoot up, perhaps doubling or even tripling. What makes quoting my article particularly funny is that it's not--shall we say--springtime fresh. It may sound like I'm delivering the newest research with lines like, "the latest evidence." But when I first saw myself quoted in Hawkins's piece, I thought, "Hey--I remember that story. When did I write it?" Fortunately, the Discover web site reminded me. 1994. Thank you, Mr. Hawkins, for taking me back to my cub days as a science writer, to the early days of the Clinton administration, to the year that Netscape Navigator was released and Dakota Fanning was born. I just have to wonder, why did you have to reach back thirteen years for the latest understanding on climate science? Did you think that climate scientists shut their computers off in 1994? Did you think that they stopped looking for better estimates for temperatures and carbon dioxide levels in the past? You might have looked at this 2006 study on the Cretaceous, or this 2004 model of the Ordovician (pdf), which is far more complex than anything done in 1994, and sheds more light on how glaciers form in a high-CO2 world. Scientists still have a lot to learn about the climate of the ancient world. The further back in time they go, the worse their record of temperature and greenhouse gases becomes. Drifting continents make the problem even more complex. But they are making headway, not by rejecting the role of greenhouse gases in the climate but by learning more about the other factors at play in the past. The most revealing features of Earth's climate history come from the more recent past--the past few million years, for which scientists have found some excellent records in ice cores and other materials. The more recent past is also useful because the continents were in the same arrangement as they are today. And studies on the recent past support computer models that project a 3 degree C rise in response to a doubling of carbon dioxide. It's nice to know that someone's still digging back into my archives. Too bad it's Hawkins, slicing and dicing them so that readers end up misinformed.

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