A contingent of powerful U.S. representatives are pressing the chief executives of six of the country's largest fossil fuel companies, including ExxonMobil, Chevron and Shell, to answer questions about when the companies first understood that burning fossil fuels drives climate change and whether they became active partners in an effort to downplay the harm that could result.

The inquiry was prompted by recent disclosures that ExxonMobil scientists were aware of the potential harm of global warming as far back as the late 1970s.

"We are alarmed by reports stating that Exxon (becoming ExxonMobil in 1999) hid the truth about the role of fossil fuels in influencing climate change and intentionally spread disinformation about climate science," according to the letter signed by 45 Democratic representatives.

In the Dec. 7 letter, representatives ask a pivotal question of the fossil fuel companies: what did they know about the risks of global warming and when did they know it.

The inquiry by the House Democrats is spearheaded by Reps. Ted Lieu of California and Peter Welch of Vermont, and includes senior representatives who sit on the Health Subcommittee on Ways and Means, the Natural Resources Committee, Permanent Select Committee on Intelligence, and the Energy and Commerce Committee.

"When you have the potential of multiple companies knowing of climate change and go to lengths to cover that up—not only is that morally wrong in many cases it could be illegal," Lieu said in an interview with InsideClimate News.

"We need answers and we need this to send a message that these companies have an obligation to act responsibly when it means protecting the future of our children and grandchildren."

Lieu said that getting answers to key questions, such as when and what the companies knew about the fossil fuel-global warming connection, would expand the world's scientific understanding. It could also raise additional "red flags" that could necessitate a deeper, more formal probe before Congress.

He said he is optimistic that the six companies will cooperate.

"I believe if the companies did nothing wrong they will answer," Lieu said. "So for the companies that don't answer it sends a red flag that they have something to hide."

The letter suggests the representatives are seeking a deep dive into the fossil fuel companies' climate change history and policy positions, asking if the CEOs would release past scientific data and findings regarding climate change, and what state or federal legislation to mitigate climate change each company has supported.

In addition to ExxonMobil, Chevron and Shell, the representatives also sent their inquiry to ConocoPhillips, Peabody Energy and BP.

Exxon has recently come under intense scrutiny following the publication of an investigative series of stories by InsideClimate News that revealed the company participated in cutting-edge climate change science for nearly a decade beginning in the late 1970s, which showed the dangers posed by increasing levels of atmospheric CO2 caused primarily by the burning of fossil fuels. Although Exxon was aware of the potentially catastrophic consequences, the company elected a course that placed it at the forefront of climate denial.

Similar, independent findings were later published by a team based at the Columbia Journalism School in partnership with the Los Angeles Times.

The letter also cites an investigation by the Union of Concerned Scientists that concluded ExxonMobil was not alone in developing early knowledge of climate change and later spreading disinformation about climate science. The organization said there was a "coordinated campaign of deception" on climate science by ExxonMobil, Chevron, ConocoPhillips, BP, Shell, Peabody Energy and other members of the fossil fuel industry.

Following the publication of the ICN series, dozens of activist groups and politicians have been calling for a U.S Justice Department probe into what Exxon knew about climate change and when, including the Democratic presidential field, Hillary Clinton, Bernie Sanders and Martin O'Malley. New York State Attorney General Eric Schneiderman subpoenaed ExxonMobil last month seeking documents related to its climate science research and communications to shareholders.

Along with asking the companies when they became aware that burning fossil fuels could result in climate change and what the companies did with that information, the representatives are asking:

Did the company fund organizations that denied climate change or sought to spread uncertainty about climate change?

What state and federal legislation to mitigate climate change have the companies opposed?

Did the company, or organizations funded by the company, forge letters to Congress regarding climate change?

Did the company, or organizations funded by the company, secretly finance an independent scientist or scientists to deny or spread uncertainty about climate change?

Does the company support the science-based 2 degree Celsius temperature target to limit dangerous climate change?

What each company's business plan is for reducing emissions consistent with that safe climate target?

Read the full letter: