THE Heartland Institute, the world's most prominent think-tank promoting scepticism about man-made climate change, is getting a lot of heat. In recent weeks it has lost an estimated $825,000 in expected donations, a couple of directors and almost its entire branch in Washington, DC. At its annual shindig in Chicago this week, the institute's president, Joseph Bast, said Heartland had “discovered who our real friends are.” The 100-odd guests who failed to show up for the “7th Climate Conference” were not among them.

The institute's problems began in February when an American water scientist, Peter Gleick, published internal Heartland documents that he had obtained under a false name. They provided details of its accounts—including references to an anonymous donor who gave $8.6m between 2007 and 2011—and of a plan to send teaching materials denouncing global warming to American primary schools. (Mr Bast says that far from exposing his institute, the documents exonerated it from charges that it was a front for the fossil-fuel industry.)

Worse ensued early this month after the institute put up a digital billboard in Chicago that linked belief in global warming to madness and terrorism. It depicted the “Unabomber”, a mass-murderer called Ted Kaczynski, with the slogan, “I still believe in Global Warming. Do you?” The offending sign lasted only for a day. But PepsiCo, BB&T bank and Eli Lilly, a pharma company, are among donors that announced the end of their support.

Mr Bast decries double standards: those who accept global warming routinely call their opponents Nazis, he argues. He admits that the billboard was in “poor taste” but says it was designed to get attention, and was good value at $200. The real price is proving rather higher.