The Global Warming Challenge

Evidence-based forecasting for climate change

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How I Became a Skeptic about Global Warming Forecasts

with 4 comments

April 15, 2008

J. Scott Armstrong

I have been working on a book on persuasion for the past 14 years. Having reviewed the evidence, I concluded that rational arguments are not effective in leading people to change strongly held opinions—especially not in the short term. This intransigence is a problem, because if peoples’ opinions are at odds with the facts, they are likely to act and vote in ways that cause harm to themselves and others.

There is a solution, however, and that is to persuade oneself. In other words, in order to reduce the risk of making bad decisions each of us should identify what information would, if it existed, lead us to change our opinion about important issues—such as whether humanity is faced with a problem of dangerous manmade global warming.

My own self-persuasion journey on the topic of global warming started more than a year ago. Needing a featured talk for the International Symposium on Forecasting in June 2007, I discussed possible topics with Kesten Green. We concluded that global warming was an important issue that hinged on long-term forecasts. As it happened, Kevin Trenberth, an IPCC lead author, was a keynote speaker at the symposium. I sent him a cordial note and asked him if he would share his slides with me prior to the conference. He said “no.” This experience was repeated in my contacts with other people who warn of dangerous global warming. When I have asked for evidence, data, or published papers to support their position (such as the statement that all scientists agree that global warming will occur in the future), I have typically received either no reply or a refusal. Such behavior is strange for scientists. In contrast, global warming skeptics have been anxious to make their papers and the data available.

My review of the evidence led me to become a skeptic. Indeed, we were unable to find a single scientific forecast of global warming despite contacting over one hundred global warming advocates directly, and also issuing our request in talks, on email lists, and on web sites. We kept the global warming advocates informed of our research and asked them for suggestions and peer review. In return we received mostly silence although there were some nasty comments and some people who asked that they be removed from our mailing list.

My conclusion is that the scientific evidence clearly favors the skeptics’ position. In addition, I believe that the global warming advocates have violated many of the tenets of the scientific method; the global warming advocates say that it happens on both sides, but that has not been my observation.

So I have made a decision based on the evidence that I needed to convince me. In addition, in our papers, we have also described the information that would change our minds yet again—in effect, proper forecasts would convince us. We are hoping to do some of this forecasting ourselves, but it is costly and so far we have not obtained funding. Our two papers to date (available at have been written with no funding.

The problem is essentially a forecasting problem. Those who are forecasting global warming have demonstrated little knowledge of how to forecast. This is unfortunate as there have been many useful (and often surprising) findings from the research on forecasting that have been published, especially over the past half century. Moreover, global warming advocates tend to become upset when the research findings are pointed out and they claim that different principles apply to them. We have replied by asking them to tell us which principles differ and to provide the evidence for their assertions. They seldom reply, and when they do, they do not provide evidence; at least, not yet.

Written by climatebet

April 16th, 2008 at 7:58 pm

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