19 de abril de 2012

are we warming the planet? that is the key question.

A tourist sits at the Old Fortresss in Cartagena, Colombia during sunset on April 14, 2012.
Eitan Abramovich/AFP/Getty Images
by Marcelo Gleiser
18/04/2012 - 13,7 Blog
An intense debate has been raging on The New York Review of Books the past few weeks on the issue of global warming and its skeptics. Even though Adam wrote about global warming yesterday, this is so important and powerful that it shouldn't pass unnoticed here on 13.7.
In one corner stands William D. Nordhaus, the Sterling professor of economics at Yale University. In the other corner stand three of the 16 scientists behind an op-ed published in The Wall Street Journal on January 27, 2012, "No Need to Panic About Global Warming." The piece spells out their basic objections to global warming.
As Nordhaus explains, "The basic message of the article is that the globe is not warming, that dissident voices are being suppressed, and that delaying policies to slow climate change for fifty years will have no serious economic or environment consequences." He goes on to identify the six chief objections to global warming brought up by the group:
• Is the planet in fact warming?
• Are human influences an important contributor to warming?
• Is carbon dioxide a pollutant?
• Are we seeing a regime of fear for skeptical climate scientists?
• Are the views of mainstream climate scientists driven primarily by the desire for financial gain?
• Is it true that more carbon dioxide and additional warming will be beneficial?

Nordhaus then proceeds to argue against each one of them. Of all the issues, the second seems to be the one of greatest import. Are we contributing to warming the planet, or is it happening due to natural causes (volcanism, solar output, etc.)?
Usually, models of climate change run two options, with and without the forcing due to humans, mostly through the output of the warming gas CO2 and of cooling due to particulate aerosols. The conclusion, as Nordhaus notes, is that the results are only consistent with the recorded temperature data if human-induced changes are included.
In their detailed response, Roger W. Cohen, a Fellow of the American Physical Society, William Happer, a professor of physics at Princeton and Richard Lindzen, a professor of atmospheric sciences at MIT, argue that the models aren't as good as Nordhaus and the International Panel on Climate Change (IPCC) claim: "Such a procedure absolutely requires that the model include correctly all other sources of variability."
I disagree with this claim. Models can never be perfect and all-inclusive, or they wouldn't be models. Every model has limitations, precisely due to the fact that we usually don't know all there is to know. An efficient model is such that it can, albeit incompletely, reproduce the observed behavior of a given system. It works because many of the potential contributions are irrelevant or mostly so. Models are our best effort to cope with our limited knowledge of the natural world. So, the test of a model is to see if it matches observations without artificial tweaking of its parameters.
It is the nature of scientific modeling to have discord and debate. Thus, it's no surprise that scientists will argue about the merits and limitations of their models. If we had a perfect model, it wouldn't be called a model. So, what matters most in the end is that although specific models may disagree in the specifics, the general trend is clear: the rapid industrialization of the planet has affected the constitution of the atmosphere in ways that tend to increase the long-term average temperature.
Still, it is also the nature of statistical analysis not to give a firm answer, but probabilities of different outcomes. Thus, one can always gamble in the face of statistical evidence, hoping his chosen odds are the winners. When the consequences can be so dire, gambling is a risky undertaking.
Nordhaus, of course, responds to his critics. I invite the reader to see for him/herself how the debate unfolds, but close quoting from his response, since I wholeheartedly agree with it:
"It is possible that the world will not warm over the coming years. It is possible that the impacts will be small. It is possiblethat a miraculous technology will be invented that can suck CO2 out of the atmosphere at low cost. But in view of the evidence we now have, it would be foolish to bet on these outcomes just because they are possible."

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super carrinho. faça as idéias rodarem aqui também.
obrigada pela participação no debate.