Sen. Richard Blumenthal called on the Department of Justice Monday to investigate big oil companies.

After the hottest month on record, state officials are demanding that oil companies, including Shell and ExxonMobil, reveal how much they know about climate change.

Internal documents released this spring show that Shell has known about the dangers of global warming since the 1970s.

"The big oil companies have engaged in the biggest single consumer deception fraud in American history. By covering up clear evidence of climate change that they knew was ongoing, and in fact they've continued this campaign of climate change deception right to the present," said Blumenthal.

Connecticut Attorney General William Tong is suing Exxon Mobil, asking for millions to pay for climate change mitigation.