Ten years ago, on June 23, 1988, NASA scientist James Hansen testified before the House of Representatives that there was a strong "cause and effect relationship" between observed temperatures and human emissions into the atmosphere. ...

At that time, Hansen also produced a model of the future behavior of the globe's temperature, which he had turned into a video movie that was heavily shopped in Congress. That model was one of many similar calculations that were used in the First Scientific Assessment of the United Nations Intergovernmental Panel on Climate Change ("IPCC", 1990), which stated that "when the latest atmospheric models are run with the present concentrations of greenhouse gases, their simulation of climate is generally realistic on large scales."

That model predicted that global temperature between 1988 and 1997 would rise by 0.45°C (Figure 1). Figure 2 compares this to the observed temperature changes from three independent sources. Ground-based temperatures from the IPCC show a rise of 0.11°C, or more than four times less than Hansen predicted. ...

The forecast made in 1988 was an astounding failure, and IPCC's 1990 statement about the realistic nature of these projections was simply wrong.

Hansen et al's paper is not available online, but I've posted some extracts so you can check that I haven't taken anything out of context. If you move your mouse over Michaels' Figure 1, you can see the corresponding figure from Hansens's paper. Michaels has erased scenarios B and C from his version of the graph. What did Hansen write about the scenarios?

These scenarios are designed to yield sensitivity experiments for a broad range of future greenhouse forcings. Scenario A, since it is exponential, must eventually be on the high side of reality in view of finite resource constraints and environmental concerns ... Scenario C is a more drastic curtailment of emissions than has generally been imagined ... Scenario B is perhaps the most plausible of the three cases.

So Scenario A was the worst case and Scenario C was the best case and Hansen felt that both of these were unlikely and Scenario B was the most plausible. Hansen's prediction was that the temperature would be between A and C. He wrote:

The model predicts, however, that within the next several years the global temperature will reach and maintain a 3σ level of global warming, which is obviously significant.

The 3σ level is 0.4 degrees above base line in the figure above. In the model this happened in 1998. In reality this happened in ... 1998. OK, maybe he got lucky, but it is wrong to call it an "astounding failure", and erasing B and C from the graph and presenting Hansen's worst case scenario as his prediction really is "fraud, pure and simple."

Michaels also cheated on his presentation of the results of Scenario A. First, he seems to have made a mistake when he measured the temperature rise under scenario A -- it was 0.41, not 0.45. He also calculated the change from 1988 to 1997 but the last year of the observed data was 1987; so he should have started then. 1988 was 0.07 warmer than 1987 so the increase in observed temperatures should have been 0.18. Scenario A increased by 0.44 over that time. So scenario A was too high by 150%, not the 300% that Michaels claimed.

So what does Michaels come up with in his defence?

Krugman was incensed with my July 27, 1998, testimony before the House Committee on Small Business. In it, my purpose was to demonstrate that commonly held assumptions about climate change can be violated in a very few short years.

One of those is that greenhouse gas concentrations, mainly carbon dioxide, would continue on a constant exponential growth curve. NASA scientist James Hansen had a model that did just this, published in 1988, and referred to in his June 23, 1988 Senate testimony as a "Business as Usual" (BAU) scenario.

BAU generally assumes no significant legislation and no major technological changes. It's pretty safe to say that this was what happened in the succeeding ten years.

He had two other scenarios that were different, one that gradually reduced emissions, and one that stopped the growth of atmospheric carbon dioxide in 2000. But those weren't germane to my discussion. Somehow, Krugman labeled my not referring to them as "fraud."

The trick Michaels is using here is to use BAU to mean something different to what Hansen meant. Hansen did not use the term in his paper, but he did use it in his testimony:

The other curves in this figure [besides the observations] are the results of global climate model calculations for three scenarios of atmospheric trace gas growth. We have considered several scenarios because there are uncertainties in the exact trace gas growth in the past and especially in the future. We have considered cases ranging from business as usual, which is scenario A, to draconian emission cuts, scenario C, which would totally eliminate net trace gas growth by year 2000.

In his paper (which was attached to his testimony) Hansen said that scenario A was "continued exponential trace gas growth". So by "business as usual" Hansen meant "continued exponential trace gas growth." All he did was use simpler language to describe scenario A in his testimony. Nor is it accurate for Michaels to pretend that Hansen assumed that greenhouse gas concentrations would continue to grow exponentially since he stated that scenario A was on the "high side of reality" and that B was the "most plausible". Even under his own interpretation of BAU Michaels is wrong since scenario A included exponential growth in CFC emissions, when in fact they fell dramatically as a result of significant legislation (because of the Montreal protocol).

Furthermore, if you go back and look at what Michaels said in his testimony, he wasn't using scenario A to show that BAU increases in emissions hadn't happened. He used it to argue that Hansen's climate model was wrong, that is, that even if given the correct numbers for emissions, it would overestimate (by 300%!) the amount of warming. The fact is, and Michaels knew it the time, that scenarios B and C were close to actual emissions and produced results close to the actual warming.

Michaels continues:

There's also the nagging possibility that we haven't yet figured out the true "sensitivity" of surface temperature to changes in carbon dioxide. Scientifically, that's a chilling possibility.

But somehow, Hansen's model came up with a good prediction. How does Michaels address this? He just ignores it.

On May 30, Roger Pielke, Jr., a highly esteemed researcher [in fact, he is a political scientist] at University of Colorado's Center for Science and Technology Policy Research, examined Hansen's scenarios. Of the two "lower" ones, he concluded, "Neither is particularly accurate or realistic. Any conclusion that Hansen's 1988 prediction got things right, necessarily must conclude that it got things right for the wrong reason." (italics in original)

Pielke's criticism of Hansen's scenarios is badly misconceived. The important input to Hansen's model was the total forcing from greenhouse gasses, but Pielke ignores this to focus on the growth rate of emissions of each gas. For instance, he claims that scenario B was off by a factor of 2 on CO2. This sounds like a lot until you discover that means that emissions grew by 0.5% per year instead of 1% a year. And that works out to scenario B having the concentration of CO2 in the atmosphere within 1% of what has actually happened. Pielke is being much more than a little unfair by calling a prediction that got within 1% of the correct answer as not being "particularly accurate or realistic."

And none of this excuses Michaels' fraudulent testimony.

For more on Hansen's scenarios, see Eli Rabett here and here.