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Global Dimming II

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Translations: (Français)

Guest commentary on BBC documentary on “Global Dimming” aired on January 13th 2005 by Beate Liepert, LDEO, Columbia University

I haven’t yet seen the documentary. I have only read the transcript and hence was spared the pictures of the potential apocalypse and the invocation of biblical-scale famines. However, as one of the lead scientists on the topic [and who was interviewed by the BBC for the Horizon documentary (transcript, previous post)], I feel I should explain a few things about it without using religious analogies and stoking unnecessary fear.

First though, this is a nice example of the power of words: Gerry Stanhill coined the observed reduction in solar energy reaching the ground “global dimming”. He called it “global” dimming because the technical term for the radiative energy is called “global solar radiation” and it contrasts nicely with the more common “global warming”.

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The global cooling myth

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Translations: (Français)

Every now and again, the myth that “we shouldn’t believe global warming predictions now, because in the 1970’s they were predicting an ice age and/or cooling” surfaces. Recently, George Will mentioned it in his column (see Will-full ignorance) and the egregious Crichton manages to say “in the 1970’s all the climate scientists believed an ice age was coming” (see Michael Crichton’s State of Confusion ). You can find it in various other places too [here, mildly here, etc]. But its not an argument used by respectable and knowledgeable skeptics, because it crumbles under analysis. That doesn’t stop it repeatedly cropping up in newsgroups though.

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Senator Inhofe on Climate Change

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by Michael Mann, Stefan Rahmstorf, Gavin Schmidt, Eric Steig, and William Connolley

Senator James Inhofe (R) of Oklahoma recently provided us with an update of his views on the issue of climate change in a speech given on the opening senate session, January 4, 2005. His speech opened with the statement:

As I said on the Senate floor on July 28, 2003, “much of the debate over global warming is predicated on fear, rather than science.” I called the threat of catastrophic global warming the “greatest hoax ever perpetrated on the American people,” a statement that, to put it mildly, was not viewed kindly by environmental extremists and their elitist organizations.

Cutting through much of his polemic, Inhofe’s speech contains three lines of scientific argument which, according to him, provide “compelling new scientific evidence” that anthropogenic global warming is not threatening. We here submit his statements to scrutiny.
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Just what is this Consensus anyway?

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Translations: (Français)

We’ve used the term “consensus” here a bit recently (see our earlier post on the subject), without ever really defining what we mean by it. In normal practice, there is no great need to define it – no science depends on it. But it’s useful to record the core that most scientists agree on, for public presentation. The consensus that exists is that of the IPCC reports, in particular the working group I report (there are three WG’s. By “IPCC”, people tend to mean WG I). Fortunately that report is available online for all to read at http://www.grida.no/climate/ipcc_tar/wg1/. It’s a good idea to realise that though the IPCC report contains the consensus, it didn’t form it. The IPCC process was supposed to be – and is – a summary of the science (as available at the time). Because they did their job well, it really is a good review/summary/synthesis.

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Aerosol

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Translations: (Français)

A collection of airborne solid or liquid particles, with a typical size between 0.01 and 10 µm and residing in the atmosphere for at least several hours. Aerosols may be of either natural or anthropogenic origin. Aerosols may influence climate in two ways: directly through scattering and absorbing radiation, and indirectly through acting as condensation nuclei for cloud formation or modifying the optical properties and lifetime of clouds (from the always useful IPCC glossary).

See-also: wiki:Aerosol.

Welcome to RealClimate

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Translations: (Français)

Climate science is one of those fields where anyone, regardless of their lack of expertise or understanding, feels qualified to comment on new papers and ongoing controversies. This can be frustrating for scientists like ourselves who see agenda-driven ‘commentary’ on the Internet and in the opinion columns of newspapers crowding out careful analysis.

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Comment policy

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  1. Comments are moderated. Comments are periodically reviewed, but especially at weekends, evenings and holidays, there may be some delay in approving otherwise non-contentious posts. Please be patient.
  2. Questions, clarifications and serious rebuttals and discussions are welcomed.
  3. Only comments that are germane to the post will be approved. Comments that are “off-topic” should be made on an open thread (usually entitled “Unforced Variations”), and we may move OT comments to those threads.
  4. Comments that contain links to inappropriate, irrelevant or commercial sites may be deleted.
  5. Discussion of non-scientific subjects is discouraged.
  6. No flames, profanity, ad hominem comments are allowed. This includes comments that (explicitly or implicitly) impugn the motives of others, or which otherwise try to personalize matters under discussion.
  7. We reserve the right to make spelling corrections, correct text format problems, etc.
  8. We use moderation to improve the “signal to noise” in the discussion. For this reason, we may choose to screen out comments that simply repeat points made in previous comments, make claims that have already been dealt with or that “muddy the water” by introducing erroneous, specious, or otherwise misleading assertions. These comments may be sent to “The Bore Hole“.
  9. We reserve the right to either reject comments that do not meet the above criteria, or in certain cases to edit them in a manner that brings them into accordance with our comments policy (e.g. by simply deleting inflammatory or ad hominem language from an otherwise worthy comment). In cases where we do this, it will be noted by an [edit].
  10. Given that RealClimate represents a volunteer effort by about 10 different contributors, each of whom are free to participate in queue moderation, the items indicated above only constitute the basic ground rules. We cannot insure uniform application of the various considerations listed above from one individual comment to the next.
  11. Quick responses to questions that don’t merit a full post will be placed in-line (with credits).
  12. All comments are assumed to be released into the public domain.
  13. Comments generally close after a month.
  14. Repeat violators of our comments policy (in particular, individuals demonstrating a pattern of “trolling”) may be barred from future access to the blog.

revised 01/06/11

The Surface Temperature Record and the Urban Heat Island

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There are quite a few reasons to believe that the surface temperature record – which shows a warming of approximately 0.6°-0.8°C over the last century (depending on precisely how the warming trend is defined) – is essentially uncontaminated by the effects of urban growth and the Urban Heat Island (UHI) effect. These include that the land, borehole and marine records substantially agree; and the fact that there is little difference between the long-term (1880 to 1998) rural (0.70°C/century) and full set of station temperature trends (actually less at 0.65°C/century). This and other information lead the IPCC to conclude that the UHI effect makes at most a contribution of 0.05°C to the warming observed over the past century.

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Contributors

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The current contributors to content on this site are:

William Connolley was a contributor, but has now left academia; Ray Bradley, David Archer, and Ray Pierrehumbert are no longer active; Jim Bouldin was a contributor from 2009 and Caspar Ammann and Thibault de Garidel were early supporters of the site. Group posts can be assumed to be the from the whole set of current contributers, or will be individually signed.