Besides ABIR, insurers dropping support for Heartland include State Farm, XL Group, and Allied World Assurance.

ABIR represents 22 Bermuda-based insurers and reinsurers,

Forecast the Facts says it is an organization “dedicated to ensuring that Americans are accurately informed about climate change.”

The group says it has mobilized more than 20,000 people to call on corporations to pull support from Heartland. GM was the first to respond, ending its 20-year relationship with Heartland on March 28. GM was followed by AT&T, ABIR, beverage maker Diageo, and now State Farm and other insurers.

ABIR withdrew in a letter to Heartland May 4.

In the letter, ABIR President Bradley Kading says, “We write to disavow any future relationship with your organization. Recent revelations of the Heartland Institute's radical position on climate change as portrayed on the new billboard featuring Ted Kaczynski made our association with other parts of your organization untenable.”

State Farm also cited Heartland's recent billboard campaign as its reason for dropping out, according to Forecast the Facts officials.

ABIR has enlisted Heartland in its efforts to expand market-based solutions to catastrophe issues, including providing a role for reinsurers in funding the National Flood Insurance Program.

On its website, Heartland claims that “the most prominent advocates of global warming aren't scientists. They are murderers, tyrants, and madmen” who are “willing to break the law and the rules of ethics to shut down scientific debate and implement their left-wing agendas.”

In 2010, ABIR provided $50,000 in funding to the think tank, followed by $75,000 in 2011, according to Heartland's leaked 2012 fundraising plan.

State Farm Mutual Automobile Insurance Company contributed $120,000 to Heartland between 2010-2011, and ABIR-member XL Group gave $35,000 in 2011.

Editor's Note: This version removes projected 2012 donors from the last paragraph that appears in a previous version of the story, since those entities were included in Heartland's forecast, but did not officially pledge funds for the year.