Articles by Andrew Dessler

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?

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.

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 TalkingAboutTheWeather.com, 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.

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?