(Part of the How to Talk to a Global Warming Skeptic guide)

Objection: In 1988, Hansen predicted dire warming over the next decade — and he was off by 300%. Why in the world should we listen to the same doom and gloom from him today?

Answer: While in some instances it is ignorant repetition of misinformation, at its source this story is a plain lie.

In 1988, James Hansen testified before the U.S. Senate on the danger of anthropogenic global warming. During that testimony he presented a graph — part of a paper published soon after. This graph had three lines on it, representing three scenarios based on three projections of future emissions and volcanism.

Hansen graph

Line A was a temperature trend prediction based on rapid emissions growth and no large volcanic event; it was a steep climb through the year 2000 and beyond.

Line B was based on modest emissions growth and one large volcanic eruption in the mid 1990s.

Line C began along the same trajectory as Line B, and included the same volcanic eruption, but showed reductions in the growth of CO2 emission by the turn of the century — the result of hypothetical government controls.

As it happens, since Hansen’s testimony, emissions have grown at a modest rate and Mt. Pinatubo did in fact erupt, though in the early 1990s, not the middle. In other words, the Line B forcings scenario came remarkably close to predicting what actually came to pass.

Not coincidentally, the observed temperature trend has tracked closely with the Line B prediction as well.

Hansen was right on the money, and the models he used proved successful.

Unfortunately, when Patrick Michaels made his testimony before Congress in 1998, ten years later, he saw fit to erase the two lower lines, B and C, and show the Senators only Line A. He did so to make his testimony that Hansen’s predictions had been off by 300% believable. He lied by omission. This lie was picked up by Michael Crichton in his novel State of Fear (one of many omissions, confusions, and falsehood in that book — see here).

To my knowledge, Patrick Michaels has never owned up to his deception, either with an apology and retraction or with an explanation, and consequently the urban myth lives on to this day.

RabettRun has some more detail and illustrations here.