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.

Why you should believe the IPCC, part 134,992,653

The ideological tensions inside the IPCC gives its reports alarming credibility

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 this way. This is why some people argue that the actual science of climate change is more alarming than that revealed in the IPCC reports. In any event, if you read the IPCC reports and find it alarming, then you can have great confidence that your alarm is warranted.

Looking for validation

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.

Me, on the interwebs

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).

Negative climate feedback is as real as the Easter Bunny

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?

Roy Spencer: Inhofe 650 is bogus!

Marc Morano agrees that only experts in climate feedbacks can make judgments on climate

Tuesday, I received an email from Marc Marano, staffer for Sen. James Inhofe (R-Okla.). Usually, these are vectored straight into my junk folder, but apparently my computer's spam filter has a sense of humor, because this email made it into my inbox. And what I saw astounded me. Marc's email contained a link to a recent post by Roy Spencer. In it, Spencer claims: Obviously, the thermostat (feedback) issue is the most critical one that determines whether manmade global warming will be catastrophic or benign. In this context, it is critical for the public and politicians to understand that the vast majority of climate researchers do not work on feedbacks. In popular political parlance, most climate researchers do not appreciate the nuanced details of how one estimates feedbacks in nature, and therefore they are not qualified to pass judgment on this issue. Therefore, any claims about how many thousands of scientists agree with the IPCC's official position on global warming are meaningless. Did I read that right? The only people qualified to make judgments on the science of climate change are experts in climate feedbacks? I'll ignore the questionable and obviously self-serving nature of this claim for now. The surprising point here is that Roy has clearly disqualified virtually every member of Inhofe's list of 650 "experts" who dismiss the IPCC's view of climate science. Not only are the Inhofe 650 members not experts on climate feedbacks, but also most of them are not experts on any aspect of the climate. (Note, however, that I'm still an expert because I actually do work on climate feedbacks.) And since Marc Moreno sent out a link to this post, he obviously agrees that Inhofe's list is a pile of rubbish. Finally, something Marc and I can agree on.

Huff Po blows it

Skeptic screed on progressive news site recycles familiar myths

This post was co-written with David Roberts. Recently Harold Ambler, climate crank and proprietor of, published an essay on Huffington Post replete with gross factual errors about the science of climate change. Word is that this was an editorial slip-up on HuffPo's part; they don't typically provide a place for this kind of agitprop. The essay is gone from the site's portal pages and rumor has it The Huff herself may address the issue soon. Regardless, the essay is out there getting skeptics all twitterpated (again). These folks can't find a scientific journal with two hands and a flashlight, but nothing escapes their RSS feeds. So lets examine a few of the claims again. After all, the only thing hucksters need is for the rest of us to get tired of repeating the same damn truths over and over again. Right? Right off the bat Mr. Ambler recycles a classic, one of the most durable and thoroughly discredited skeptic chestnuts: Because it turns out that there is an 800-year lag between temperature and carbon dioxide [in the ice age record], unlike the sense conveyed by Mr. Gore's graph. You are probably wondering by now -- and if you are not, you should be -- which rises first, carbon dioxide or temperature. The answer? Temperature. In every case, the ice-core data shows that temperature rises precede rises in carbon dioxide by, on average, 800 years. The basic science of atmospheric carbon dioxide is well explained in the IPCC reports and on numerous web sites, including in Grist's How to Talk to a Skeptic series. It's puzzling that it continues to confuse skeptics.

The third degree

Why large future warming is very likely

A friend of mine from college emailed me the other day and expressed some skepticism about the connection between carbon dioxide emissions and global warming. It occurred to me that it would make a good topic for my next post. So here is the reasoning that has led me to conclude that business-as-usual carbon dioxide emissions will lead to temperature increases over the next century of around 3 degrees C. First, it has been known for over 150 years that adding carbon dioxide to the atmosphere will increase the temperature of the planet. In fact, the very small number of credible skeptics out there, such as Dick Lindzen and Pat Michaels, are on record agreeing that adding greenhouse gases to the atmosphere will warm the planet. What they argue is that the warming will be very small. More on that later. The conclusion that emitting greenhouse gases will result in warming does not rest on the output of climate models, but is a simple physical argument that predates the invention of the computer. And if you don't believe in physics, take a look at Venus. That planet features a thick carbon dioxide atmosphere and consequently a surface temperature hot enough to melt lead. So we know that adding carbon dioxide is going to warm the planet. This leads us to the real question: How much warming are we going to get?

What to do on day one

Memo to the president-elect about NASA

Memo To: PEBO From: Andrew Dessler Re: What to do about NASA on your first day in office Two things: Fire Michael Griffin, NASA’s current …