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Global Dimming and climate models

Filed under: — group @ 17 April 2006

Guest posting from Beate Liepert (LDEO)

On April 18th PBS will air the NOVA documentary “Dimming the Sun” which stirred up lively discussions among scientists and non-scientists when originally shown by BBC in the UK (under the name ‘Global Dimming’ – see our previous posts). [The NOVA version has been thoroughly re-edited and some of the more controversial claims have apparently been excised or better put into context [and we look forward to seeing it! - Ed.].

Global dimming is the phenomena of an observed reduction (about 1-2% per decade since ~1960) of sunlight reaching the surface of the Earth caused by air pollution (aerosols – small particles) and cloud changes. Some of this solar energy is reflected back out to space and this cooling effect is believed to have counteracted part of the greenhouse gas warming. The original version of the film focused mainly on the observational recognition of global dimming, but one aspect did not receive much attention in the film – namely the oft-claimed lack of global dimming in climate models. This led some to assume that climate modelers were ignoring air pollution other than greenhouse gases emissions from fossil fuel burning. Another implication was that climate models are not capable of adequately simulating the transfer of sunlight through the atmosphere and the role of clouds, sunlight extinction of aerosols and aerosol effects on clouds etc, and therefore model projections should not be trusted. The NOVA version will address this issue more prominently by adding an interview with Jim Hansen from NASA Goddard Institute for Space Studies. Along this line, I’d like to elaborate on aerosols in climate models in more detail. More »

Lindzen: point by point

Filed under: — group @ 13 April 2006

Daniel Kirk-Davidoff (U. Maryland and one-time Lindzen co-author) provided a more detailed rebuttal of Lindzen’s argument in the comments to our previous post. It deserves to be more widely seen, so here it is again.

Here’s an effort at a point by point rebuttal. I would say that the central flaw in the op-ed is a logical one: if you’re trying to stifle dissent, then you want less funding for climate research, not more. If you’re trying to stop global warming, then you want more money for carbon sequestration research, and you don’t care how much is spent on climate research. On the other hand if you just love climate research as a really interesting intellectual pursuit, that’s when you’ve got an interest in shedding doubt on the reigning view that CO2-induced climate change is a serious policy program, requiring action. Twenty-five years ago, when global warming wasn’t a big public worry, one might expect climate change researchers to hype the problem. In 2006, when public opinion mostly accepts that there’s a problem, scientists who want research money should be emphasizing uncertainty.
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Open Thread on Lindzen Op-Ed in WSJ

Filed under: — group @ 12 April 2006

We’ve received a large number of requests to respond to this piece by MIT’s Richard Lindzen that appeared as an op-ed in today’s Wall Street Journal. We’ve had lots to say before about the Wall Street Journal (e.g. here and here), and we’ve had plenty to say about Lindzen as well. Specifically, we have previously pointed out that there is no evidence whatsoever that ‘alarmism’ improves anyone’s chances of getting funded – if anything it is continued uncertainty that propels funding decisions, and secondly, the idea that there is a conspiracy against contrarian scientists is laughable. There is indeed a conspiracy against poor science, but there is no need to apologise for that! But rather than repeat ourselves once again, we thought we’d just sit back this time and allow our readers to comment…

Lessons from Venus

Filed under: — rasmus @ 11 April 2006

by Rasmus Benestad and Ray Pierrehumbert

Venus Express will make unprecedented studies of the largely unkown phenomena taking place in the Venusian atmosphere. Credits: ESA - AOES Medialab A special report in The Observer on Sunday (April 9) titled ‘Venus – The Hot Spot’, provides a well-written account on a mission called the Venus Express. The Venus express is an European Space Agency (ESA) mission to probe the the atmosphere of Venus and address questions regarding the differences between the climates on Venus and Earth. According to the plans, the probe will enter the final orbit around Venus in May 2006, i.e. within about a month.

What relevance does a mission to Venus have for a blog like RealClimate? Primarily, Venus offers scientists the chance to see how the same basic physics used to study Earth’s climate operates under a very different set of circumstances. In one sense, Venus is rather similar to Earth: it has nearly the same mass as Earth, and while its orbit is somewhat closer to the Sun, that effect is more than made up for by the sunlight reflected from Venus’ thick cloud cover. Because of the cloud cover, the surface temperature of Venus would be a chilly -42C if were not for the greenhouse effect of its atmosphere. In reality, the surface of Venus, at 740K (467C) is even hotter than the surface of Mercury, which is a (relatively!) pleasant 440K. Per unit of surface area, the atmosphere of Venus has as much mass as about 100 Earth atmospheres, and it is almost pure CO2. This accounts for its very strong greenhouse effect. In contrast, the CO2 in the Earth’s atmosphere accounts for a mere .00056 of the full mass of one Earth atmosphere.
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Getting the balance right…

Filed under: — group @ 10 April 2006

We’ve commented before on the “false objectivity of balance”, i.e. the tendency for many journalists to treat scientific issues–for which differing positions often do not have equal merit– in the same “he said, she said” manner they might treat a story on policy or politics.

This approach can appear balanced, but it leaves it to the reader to figure out on their own which position is most likely correct. However, the reader is rarely as well equipped as the writer to determine the bottom line, and in practice this plays into the hands of those who might seek to confuse the public through clever disinformation campaigns.

Thankfully, some journalists “get it”, and take the time (and effort) to assess where the balance of evidence really lies and report it accordingly. Two recent articles discuss what it takes, the first, an interview with Andy Revkin of the NY Times by Paul Thacker and the second a recent Ideas piece in the Boston Globe by Christopher Shea.

Hopefully this attitude is catching on!


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