A sign is seen in front of the Exxon Mobil Baton Rouge Refinery. (Lee Celano/Reuters)

EXXON DESERVES criticism for playing down the danger of climate change. But was its behavior criminal? We’re not convinced.

Investigations at InsideClimate News and the Los Angeles Times found that the oil giant conducted serious climate research a few decades ago but subsequently poured cold water on the idea of responding to the sorts of scientific conclusions it helped generate. While the company studied the potential impact of global warming on its operations, it dismissed climate warnings as “sheer speculation.”

The stories depict a company that once aimed to lead the way toward renewable energy but then turned from one of the greatest challenges facing the planet, in the process exerting a negative influence on the debate about climate change. This is a discouraging example of corporate irresponsibility.

Late last month, environmental groups asked Attorney General Loretta E. Lynch to launch an investigation into Exxon Mobil. Then New York Attorney General Eric Schneiderman announced he would do so on his own, using securities and consumer fraud laws. Exxon’s misdeeds, the environmentalists’ letter states, “are reminiscent — though potentially much greater in scale — than similar revelations about the tobacco industry.”

That’s quite an accusation. A federal judge found in 2006 that tobacco companies “consistently, repeatedly, and with enormous skill and sophistication, denied [facts about smoking’s risks] to the public, to the Government, and to the public health community.” Moreover, the judge found, these companies “marketed and sold their lethal products with zeal, with deception, with a single-minded focus on their financial success, and without regard for the human tragedy or social costs that success exacted.” The history includes secret research, hiding documents and a shocking congressional hearing at which tobacco company executives insisted that nicotine isn’t addictive — in 1994, after decades of conclusive, if not always publicized, research linking tobacco to illness.

Exxon’s story is more mixed. Starting in the late 1970s, the company invested in climate research, including the creation of the sorts of climate models that serve as a partial basis for the current scientific consensus on global warming. The firm changed course in the late 1980s, pushing back against the emerging scientific consensus rather than advancing it. Even so, the company released much of the research it helped conduct, it currently acknowledges climate change is a environmental risk and it favors taxing carbon dioxide emissions as a remedy. Moreover, emphasizing that predictive climate models are uncertain may be misleading, but it is not demonstrably false as is denying that smoking causes lung cancer.

Perhaps Mr. Schneiderman’s investigation will turn up something damning. But there’s also a risk whenever law enforcement holds the prospect of criminal penalties over those involved in a scientific debate. Legitimate scientific inquiry depends on allowing strong, even unfair, criticism of the claims that scientists make. As the Exxon investigations show, respecting that principle will not lead to positive outcomes in all cases. But it nevertheless demands that the government leave a sizable buffer zone between irresponsible claims and claims it believes may be criminally fraudulent.