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30 Years On, Remembering James Hansen’s 1988 Congressional Testimony

Bernie Lewin, Enthusiasm, Scepticism and Science

With the Greenhouse scare turning thirty this summer, we remember the Congressional testimony that launched it in the USA.

James Hansen testifying to the US Senate Committee on Energy and Natural Resources, 23 June 1988

Thirty years ago, on 23 June 1988, James Hansen testified to a Congressional committee that anthropogenic global warming has been detected—he claimed a 99% statistical certainty that greenhouse warming is happening now. Later, surrounded by reporters, Hansen urged an immediate policy response, thereby launching the greenhouse warming scare in the United States.


The committee hearings were called to promote a climate bill introduced by the Democrats and to promote responses to the greenhouse threat in the environmental policy platform of the Dukakis presidential campaign. There had been a number of previous attempts to promote the issue at Congressional hearings—particularly persistent was Al Gore—so it does pay to ask why this one was so spectacularly successful.

Bold claims by a scientist

Undoubtedly important was the strength and confidence of the claims Hansen made under solemn oath. Where previously scientists were guarded and qualified and they avoided policy advice, Hansen made a strong and confident ‘detection’ claim followed by an unreserved call for action.

Hansen backed up his detection claim with startling new evidence. Already in April he had published a new graph of the global temperature trend, which showed how the recent warming had shot past the late-1930s peak.

Click to enlarge and notice how the running 5-year mean climbs through 1987 and then seems to continue steeply up to a point for the first five months of 1988.

In that paper he quoted the 99% confidence level (i.e., that 1987 is abnormally warm at 3 standard deviations from the 1951-80 mean) but rejected any ‘causal connection’ with ‘the greenhouse effect’. In his testimony Hansen extended the graph by including incomplete trend data for 1988 (collected up to the previous month). This suggested that 1988 will be warmer than ever, and its inclusion created a striking visual effect. The 5-year running mean seems to continue on a steep rise into 1988 so that it looked like the line is about to burst through the top of the graph. (See testimony here.)

Extreme weather

Weather also played a part in the success of Hansen’s performance. The hearing followed a warm spring and a widely reported drought, which would continue through that long hot North American summer. In Washington summer opened with a stifling heatwave. The day before the hearing the thermometer topped 100o F and the following day was not much cooler. The 22nd of June 1988 was the warmest 22nd of June on record. The day of the hearing also set the record for the 23rd of June.

False claims of human intervention

Human intervention had accentuated the influence of the weather conditions in the crowded meeting room. At least, that claim was made on the good authority, but it has since been withdrawn.

The senator presiding over the hearing was Tim Wirth. In 2007 he told an interviewer how they had purposefully scheduled the hearing for a date that the Weather Service told them is likely to be the hottest day of summer. Then, the night before, they opened all the windows of the hearing room so that the air-conditioning would not be able to cope. With all the TV lights warming the room, this meant that ‘the wonderful Jim Hansen’, was ‘wiping his brow’ when he gave his ‘remarkable testimony’.

When skeptics first heard this story they were amazed as much at the audacity of  the stratagem as at the boldness of this admission. Nevertheless, the story was accepted and widely repeated on the authority of Senator Wirth. This writer certainly accepted it and repeated it, even while holding reservations on two points. One was that the third day of summer is unlikely to be its statistical peak. The other was that the video footage in the news reports do not show Hansen or anyone else mopping sweat, or, indeed, noticeably uncomfortable with excessive perspiration. A recent fact check by The Washington Post has challenged every part of the story. Wirth himself even withdrew the claim about the opening of the windows and excused himself for repeating a boastful mythology. So, while the hot weather certainly served to fortify Hansen’s message, it now seems this was mostly fortuitous, with no one giving it a helping hand.

The response of the research community

The media and public response to the Hansen testimony is widely known, but not so the response of the research community. The overwhelming reaction was outrage and condemnation of the detection claim.

'Hansen vs. the World on the Greenhouse Threat' by Richard Kerr, Science; 2 June 1989, p. 1041

Tremendous hostility was directed towards James Hansen following his testimony. An article in Science by Richard Kerr reveals the acrimony that persisted one year later [2 June 1989, p. 1041].

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