Hansen sees a crime against future generations, and so he keeps speaking out.
He will be the keynote lecturer Thursday at West Chester University's Research Day, an annual event highlighting projects ranging through the sciences and the arts.
Hansen, 73, brought a broader awareness to climate change with his congressional testimony in the 1980s. In 2006, Time named him one of the world's 100 most influential people.
As time has passed - and those who deny human-induced climate change have continued their criticism - his advocacy has grown more staunch. He has been arrested five times during protests over mountaintop coal mining and the Keystone XL pipeline, which he called "a big spigot that will hitch our country to one of the dirtiest fuels on Earth for 40 years or more."
A year ago, Hansen retired as director of the NASA Goddard Institute for Space Studies, in part to step up his activism and pursue legal action to limit greenhouse gas pollution.
"The one thing different is that I can now testify in court against the government," said Hansen, now an adjunct professor of earth and environmental sciences at Columbia University's Earth Institute. He lives on a farm in Kintnersville, in upper Bucks County.
He's been called an alarmist. Unrealistic. Flat-out wrong. And worse.
The emotional cost "only makes me feel more determined," he said.
Praise abounds, too. Environmental activist Robert F. Kennedy Jr. pronounced him "a modern-day hero." Former Vice President Al Gore said Hansen will be seen as "the scientist with the most powerful and consistent voice calling for intelligent action to preserve our planet's environment."
While some have said they wish Hansen would stick to science and leave policy to the policymakers, Pennsylvania State University climate-change researcher Michael Mann said he sees "no problem in scientists' views on matters of policy being informed by their understanding of the science. . . . I think we would be derelict in our duty, as a community, if we were unwilling to speak to the implications of the science and the risks of inaction."
Hansen sees no vindication in the succession of reports from the Intergovernmental Panel on Climate Change. In March, it released its most dire prediction yet, saying that without reductions in emissions of heat-trapping gases, the deleterious effects could spiral out of control.
"I have not looked" at the report, Hansen said. "By their nature, they are very conservative, so their conclusions tend to be a decade or so behind."
In March, he testified about climate and energy before the U.S. Senate Committee on Foreign Relations. "The exact limit is debatable," he told the lawmakers, "but there is no scientific debate about the fact that we cannot burn all of the fossil fuels without unacceptable destruction of life and property."
Nevertheless, "the situation does not call for hand-wringing and despair," he said. "We have the potential to meet the challenge."
Hansen does see positive change. He said he is encouraged by the growth of the Citizens Climate Lobby, whose members write op-eds, visit legislators, and otherwise try to persuade the government to tax fossil fuel companies and distribute the money equally to households - in effect, rewarding those who consume less energy.
"This rising carbon fee will spur innovations in carbon-free energy and energy efficiency, and it will allow the market to make decisions," he said. "Not one dime to make the government bigger."
Hansen is hard on himself as not making a convincing-enough pitch for action on climate change.
Last summer, while he gave an informal talk at a friend's house, his wife noticed tears streaming down a child's face. Don't worry, she said, grown-ups are working to solve the problem.
That statement "is gut-wrenching," Hansen later wrote to Sophie, now 15. "It gnaws on me because I am one of the adults who should have been fixing the problem."
If You Go
James E. Hansen's talk, "Tenant Farming the White House Arrests: A Scientific Perspective on the Unfolding Climate Crisis," begins at 7:30 p.m. Thursday in the Emilie Asplundh Concert Hall, South High Street, West Chester. Tickets are $5, available at the door, by phone at 610-436-2266, or at http://tickets.wcupa.edu/