Worldwatch Institute is partnering with Grist to bring you this three-part series commemorating the 20-year anniversary of NASA scientist James Hansen’s groundbreaking testimony on global climate change next week. Part two of three follows. Part one is here; part three is here.


An unprecedented heat wave gripped the United States in the summer of 1988. Droughts destroyed crops. Forests were in flames. The Mississippi River was so dry that barges could not pass. Nearly half the nation was declared a disaster area.

The record-high temperatures led growing numbers of people to wonder whether the climate was being unnaturally altered.

Meanwhile, NASA scientist James Hansen was wrapping up a study finding that climate change, caused by the burning of fossil fuels, appeared inevitable even with dramatic reductions in greenhouse-gases. After a decade of studying the so-called greenhouse effect on global climate, Hansen was prepared to make a bold statement.

Hansen found his opportunity through former Sen. Tim Wirth (D-Colo.), who chose to showcase the scientist at a Congressional hearing. Twenty years later, the hearing is regarded as a turning point in climate science history.

To build upon Hansen’s announcement, Wirth used the summer’s record heat to his advantage. “We did agree that we should figure out when it’d be really hot in Washington,” says David Harwood, a legislative aide for Wirth. “People might be thinking of things like what’s the climate like.”

They agreed upon June 28. When the day of the hearing arrived, the temperature in the nation’s capital peaked at 101 degrees Fahrenheit (38 degrees Celsius). The stage was set.

Seated before the Senate Committee on Energy and Natural Resources, 15 television cameras, and a roomful of reporters, Hansen wiped the sweat from his brow and presented his findings. The charts of global climate all pointed upward. “The Earth is warmer in 1988 than at any time in the history of instrumental measurements,” he said. “There is only a 1 percent chance of an accidental warming of this magnitude…. The greenhouse effect has been detected, and it is changing our climate now.”

Hotter-than-usual summers in cities like Washington, D.C., or Omaha, Neb., were becoming more frequent each year, Hansen told the committee. Between 1950 and 1980, the likelihood of such heat waves was 33 percent. In the late 1980s, the probability was somewhere between 40 and 60 percent. By the 1990s, it was as much as 70 percent.

Hansen also presented maps of estimated global temperatures for years between 1986 and 2029. “In any given month, there is almost as much area that is cooler than normal as there is area warmer than normal,” he said, pointing to maps of the 1980s. “A few decades in the future, as shown on the right, it is warm almost everywhere.”

Until Hansen’s testimony, the science of climate change was considered tentative at best. But, “the scientific evidence is compelling,” Wirth announced at the hearing. “The global climate is changing as the Earth’s atmosphere gets warmer.”

Other senators also reacted with calls for action. Senator Dale Bumpers of Arkansas said there was an “obligation to take very dramatic action.” The committee chairman, Louisiana Senator Bennett Johnston, recalls that he was struck by Hansen’s confidence. “There was a real kindling of curiosity and desire to learn more about this issue,” Bennett says.

The next day, The New York Times published a story about Hansen’s statements on its front page. “Global Warming Has Begun,” the headline read.

Climate change awareness had shifted. Surveys conducted in the months after Hansen’s testimony found that 68 percent of respondents had heard about the greenhouse effect, a big jump from the 38 percent who said the same in 1981. Politicians reacted, too. By the end of 1988, 32 climate-related bills had been introduced in Congress.

But Hansen was not the only predictor of the future that day. Sen. Pete Domenici (R-N.M.) entered the hearing late and admitted he had not read the testimonies. Yet as the meeting wrapped up, he forecasted the future of climate change politics with eerie accuracy. “It seems that we as a people, and probably peoples all over the world, are very skeptical to move in areas such as this until we either have a disaster or we have absolute concrete proof,” he said.

All the climate bills introduced that year went nowhere. In the coming decades, an unprecedented industry-led campaign to smear climate science would confuse much of the public and stall a U.S. climate solution.

While Hansen would later find more — and stronger — proof that his testimony’s predictions were true, attempts from the White House to silence his results would also intensify.

Hansen refused to remain silent.