Connecticut Attorney General William Tong announced Monday that the state is suing ExxonMobil for deceptions that led to climate change.

"This morning, I sued ExxonMobil for lying to Connecticut, and to the American people," he says. "They knew as far back as the 1950s that the planet was warming."

The lawsuit says in 1978, ExxonMobil began researching global warming. By 1982, company scientists concluded that "significant changes in the earth's climate" were possible, but not certain.

Six years later, an internal memo laid out a strategy emphasizing that "uncertainty" to "resist sensationalization which could lead to non-fossil fuel resources."

ExxonMobil says the statements are "cherry picked" from "a small number of employees" and "taken out of context."

"ExxonMobil knew, and it's wonderful that they're going to be held accountable," says DEEP Deputy Commissioner Betsey Wingfield.

In New Haven, officials are spending $200 million on flood protection projects.

"We're spending it on infrastructure to prepare for something that we could have avoided," says Mayor Justin Elicker.

Connecticut is not alone. More than a dozen states and cities are already suing oil and gas companies, although a judge threw out New York's lawsuit.

"This is an existential crisis to Connecticut. I'm not going to wait for somebody in another state to take action and protect us. This is my job," says Tong.

He says the state is seeking however much it will cost to protect it from climate change.

"Allegations about the company’s climate research are inaccurate and deliberately misleading," says Casey Norton, of ExxonMobil "For more than 40 years, we have supported development of climate science in partnership with governments and academic institutions. That work continues today in an open and transparent way. Deliberately cherry-picked statements attributed to a small number of employees wrongly suggest definitive conclusions were reached decades ago. Those statements are taken out of context and ignore other readily available statements that demonstrate our researchers recognized the developing nature of climate science at the time, which mirrored global understanding. When presented with the proper context - more than 4 million pages of documents and 200 hours of interviews - the New York Attorney General abandoned claims about what the company knew about climate science and when. Instead, he pursued accounting claims related to the risks of climate change and ExxonMobil was vindicated."