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Articles by Andrew Dessler

Andrew Dessler is an associate professor in the Department of Atmospheric Sciences at Texas A&M University; his research focuses on the physics of climate change, climate feedbacks in particular.

Featured Article

Over on DotEarth, Andy Revkin has an interesting post about the “burning embers” diagram from the latest IPCC. The upshot of the story is that several countries well-known for their desire to do nothing about climate change were able to remove an alarming figure from the 2007 report:

The diagram, known as “burning embers,” is an updated version of one that was a central feature of the panel’s preceding climate report in 2001. The main opposition to including the diagram in 2007, they say, came from officials representing the United States, China, Russia and Saudi Arabia.

People who argue that the IPCC is an “alarmist” body forget that virtually all of the world’s governments belong to it. Thus, governments that don’t want to do anything about climate change have just as much input to the report as countries that do.

This tension between the ideological factions of the IPCC actually gives the reports credibility. Only statements that everyone agrees to make it into the report. A few countries that object to some result can keep it out of the report. This is, in fact, why the IPCC process was designed... Read more

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  • The problem with climate-model criticism

    I have a paper [PDF] in this week's Science discussing the water vapor feedback. It is a Perspective, meaning that it is a summary of the existing literature rather than new scientific results. In it, my co-author Steve Sherwood and I discuss the mountain of evidence in support of a strong and positive water vapor feedback.

    Interestingly, it seems that just about everybody now agrees water vapor provides a robustly strong and positive feedback. Roy Spencer even sent me email saying that he agrees.

    What I want to focus on here is model verification. If you read the blogs, you'll often see people say things like "the models are completely unvalidated." What they mean is that no one has produced a 100-year climate run with a model, then waited a hundred years, and evaluated how the model did. There are many practical problems with doing this, but the biggest is that by the time you determine if your model was right or not, it would be too late to take any meaningful action to head off the problem.

  • Attack of the zombies: global cooling!

    John Fleck comments on George Will's latest zombie attack: in the 1970s, scientists said the Earth was cooling!

    What's amazing is not that George Will is selectively quoting to mislead the reader, but that he continues to do so after John sent him a copy of the article in question:

    When George Will last wrote about this subject, last May, I sent him a copy of the Science News article he misleadingly quoted in the example I used above. I got a nice note back from him thanking me for sharing it.

    I'll leave it to the reader to decide what this reveals about George Will's journalistic integrity.

    I can sense some frustration from Fleck that this argument lives on despite the publication of his nice BAMS article that lays out the actual history of the argument, and which clearly shows it to be false.

    All I can say is: Welcome to the club, John.

  • Online climate chat: Tuesday, Feb. 10, at 12:45 pm CST

    This Tuesday (Feb. 10, 2009) I'll be doing an online chat over on Eric Berger's SciGuy website. We'll be talking about climate, climate change, and everything else climate related. It will be at 12:45 pm CST. If you can't make it, the transcript will be posted (I'll put a link to it in the comments).

  • There is no negative feedback in the climate system

    The small number of credible skeptics out there (e.g., Spencer, Lindzen) have spent much of the last decade searching for a negative feedback in our climate system. If a sufficiently big one is found, then it would suggest that warming over the next century may well be small.

    Most climate scientists, however, are reasonably certain that a negative feedback big enough to overwhelm the well-known positive feedbacks in the climate system, such as the water vapor feedback [PDF], does not exist. Why?

    Negative feedbacks tend to dampen out climate change. If you add greenhouse gases to the atmosphere or the sun brightens, then the hypothetical negative feedback will counteract the warming, leaving the climate nearly unchanged. While it may be comforting to believe that a negative feedback exists, it is extremely difficult to reconcile the existence of a big negative feedback with our past observations of climate variability.

    For example, the ice ages rely on a carbon dioxide feedback to provide their large amplitude. If there were a big negative feedback in the system, then how do you explain the large swings in to and out of ice ages? No way that I know of.

    Similarly, the Paleocene Eocene Thermal Maximum is also thought to be the result of a huge release of greenhouse gases. With a large negative feedback in the system, how do you explain the rapid temperature rise during that event?