They knew. They lied. And the planet and its people are now paying the ultimate price.

It's no secret that the fossil fuel industry—the set of companies and corporate interests which profit most from the burning of coal, oil, and gas—have been the largest purveyors and funders of climate change denialism in the world.

Now, a new set of documents and a report released by the Union of Concerned Scientists (UCS) answers the age-old question always asked when it comes to crimes of corruption, cover-up, and moral defiance: What did they know and when did they know it?

As it turns out, "The Climate Deception Dossiers" shows that leading oil giants such as ExxonMobil, BP, and Shell—just like tobacco companies who buried and denied the threat of cancer for smokers—knew about the dangers of global warming and the role of carbon and other greenhouse gas emissions long before the public received warning from the broader scientific community. And what's worse, of course, is not only that they knew—but how they have spent the last nearly thirty years actively denying the damage they were causing to the planet and its inhabitants.

The new report, explains UCS president Ken Kimmell, "is a sobering exposé of how major fossil fuel companies have ... neither been honest about, nor taken responsibility for, the harms they have caused by extracting and putting into commerce the fossil fuels that now place our climate in grave danger. Instead, either directly or indirectly, through trade and industry groups, they have sown doubt about the science of climate change and repeatedly fought efforts to cut the emissions of dangerous heat-trapping gases."

And as this video shows:

The new report reviews internal documents from some of the world's largest fossil fuel companies—including BP, Chevron, Conoco, ExxonMobil, Peabody Energy, Phillips, and Shell—spanning the course of 27 years. UCS obtained and reviewed memos that have either been leaked to the public, come to light through lawsuits, or been disclosed through Freedom of Information Act (FOIA) requests.

The documents show that:

Companies have directly or indirectly spread climate disinformation for decades;

Corporate leaders knew the realities of climate science—that their products were harmful to people and the planet—but still actively deceived the public and denied this harm;

The campaign of deception continues, with some of the documents having surfaced as recently as in 2014 and 2015.

UCS has made the complete collection of 85 internal memos—totaling more than 330 pages—available online.

As part of its research, UCS discovered that as early as 1981—nearly seven years before NASA scientist James Hansen made his famous testimony before Congress about the dangers of human-caused global warming—internal discussions about the reality of the threat were already occurring inside the corporate offices of ExxonMobil and others.

In the case of Exxon, an email by one of the companies key scientists explains that, "Exxon first got interested in climate change in 1981 because it was seeking to develop the Natuna gas field off Indonesia." The email explains that the company knew the field was rich in carbon dioxide and that it could become the "largest point source of CO2 in the world," accounting for 1 percent of projected global CO2 emissions.

The email in question was written in response to an inquiry on business ethics from the Institute for Applied and Professional Ethics at Ohio University.

Speaking with the Guardian newspaper, director of the Institute Alyssa Bernstein said the email makes it clear "that Exxon knew years earlier than James Hansen’s testimony to Congress that climate change was a reality; that it accepted the reality, instead of denying the reality as they have done publicly, and to such an extent that it took it into account in their decision making, in making their economic calculation."

Though stating she did not want to appear "melodramatic," Bernstein told the Guardian that Exxon's behavior amounts to a supremely larger moral offense than even the tobacco industry's obfuscations on smoking "because what is at stake is the fate of the planet, humanity, and the future of civilization."

Given the scale of their crime, UCS says the "time is ripe to hold these companies accountable for their actions and responsible for the harm they have caused."

Offering recommendations for what the industry should be doing, the group said companies must:

Stop disseminating misinformation about climate change. It is unacceptable for fossil fuel companies to deny established climate science. It is also unacceptable for companies to publicly accept the science while funding climate contrarian scientists or front groups that distort or deny the science.

It is unacceptable for fossil fuel companies to deny established climate science. It is also unacceptable for companies to publicly accept the science while funding climate contrarian scientists or front groups that distort or deny the science. Support fair and cost-effective policies to reduce global warming emissions. It is time for the industry to identify and publicly support policies that will lead to the reduction of emissions at a scale needed to reduce the worst effects of global warming.

It is time for the industry to identify and publicly support policies that will lead to the reduction of emissions at a scale needed to reduce the worst effects of global warming. Reduce emissions from current operations and update their business models to prepare for future global limits on emissions. Companies should take immediate action to cut emissions from their current operations, update their business models to reflect the risks of unabated burning of fossil fuels, and map out the pathway they plan to take in the next 20 years to ensure we achieve a low-carbon energy future.

Companies should take immediate action to cut emissions from their current operations, update their business models to reflect the risks of unabated burning of fossil fuels, and map out the pathway they plan to take in the next 20 years to ensure we achieve a low-carbon energy future. Pay for their share of the costs of climate damages and preparedness. Communities around the world are already facing and paying for damages from rising seas, extreme heat, more frequent droughts, and other climate-related impacts. Today and in the future, fossil fuel companies should pay a fair share of the costs.

Communities around the world are already facing and paying for damages from rising seas, extreme heat, more frequent droughts, and other climate-related impacts. Today and in the future, fossil fuel companies should pay a fair share of the costs. Fully disclose the financial and physical risks of climate change to their business operations. As is required by law, fossil fuel companies are required to discuss risks—including climate change—that might materially affect their business in their annual SEC filings. Today, compliance with this requirement is not consistent.

"These companies aren’t just trying to block new polices, they’re trying to roll back clean energy and climate laws that are working and are widely supported by the public,” said Nancy Cole, a report author and UCS’s campaign director for climate and energy. "Climate change is already underway – and many communities are struggling to protect their residents and prepare for future changes. The deception simply must stop. It’s time for major carbon companies to become part of the solution."