Around the same time NASA was planning its moon missions, US oil companies were working on technologies that could have reduced greenhouse gas emissions.

Scientists and engineers had submitted patents for techniques to peel carbon dioxide out of fossil fuel exhaust, boost engine efficiencies, and produce electricity from fuel cells, according to industry documents released Thursday. They also pondered ways of offsetting the expected effects of increased carbon dioxide levels by pouring sulfur particles into the air to reflect solar energy back into space, or manipulating the weather to control smog.

But the industry ultimately settled on raising doubts about whether any effort to rein in carbon emissions was needed to head off the threat of global warming, according to the researchers who have collected those records.

"Faced with the knowledge of climate change and climate risks, particularly by the latter part of the 1960s, the oil companies had a choice," said Carroll Muffett, president of the Washington-based Center for International Environmental Law (CIEL). "They could invest in responding to and reducing that risk, or they could invest and continue to exploit oil and to look for ways to explain away climate change and explain away climate risk. Our research strongly suggests they chose that second path."

'They could have chosen to invest in it and really pursue it and bring it to life decades earlier than they ultimately did.'

The trove of papers released Thursday is the second wave of documents released by CIEL. The records, amassed over four years of research, have outlined how much American petroleum companies knew about the dangers of carbon emissions from fossil fuels long before global warming became the hot-button issue it is today.

Some of the documents have echoes in today's arguments over what to do about climate change. For instance, oil and coal producers have argued in recent years for increased work on carbon-capture technology, which would allow them to keep selling their products while offsetting the resulting emissions. Petro-kingdom Saudi Arabia is betting heavily on the technology, pledging to build the world's largest carbon-capture plant as its part of the recently signed Paris climate pact.

"We have an array of patents that demonstrate that the oil industry spent decades developing and refining technology to pull CO2 out of gaseous streams," Muffett said. The methods were developed to purify natural gas or to pull carbon dioxide out as a product in itself. But they weren't cheap — and the industry decided "from a pure profit motive" not to use it to reduce emissions, he said.

"When you're staring down the barrel of potentially real and meaningful regulation, suddenly the industry has a solution, and it's carbon capture and sequestration," Muffett said. He added that the technology has its problems and risks — "And yet, had we begun exploring that as an option 40 years ago, when we had more time and pollution burdens were lower, might that conversation have been completely different?"

Another document recounts opposition from the American Petroleum Institute (API) to federal funding of fuel cell-powered vehicle research in the late 1960s. The industry's leading trade association argued it wasn't necessary because the research was already under way, Muffett said. Several oil companies had patented various fuel cell technologies by that time, but the first commercially produced fuel vehicles have only recently hit the market.

"The companies had this technology," Muffett said. "They could have chosen to invest in it and really pursue it and bring it to life decades earlier than they ultimately did."

API did not respond to requests for comment.

Other companies, as well as NASA, were investigating fuel cell technology at the same time, and Muffett said he couldn't say whether the oil companies deliberately suppressed their patented designs.

"But it does raise the question of what they were doing with those technologies, particularly in light of their opposing research into similar technologies before Congress," he added.

Similar reports by InsideClimate News and the Los Angeles Times last year have led to investigations of ExxonMobil in 17 states. Prosecutors are looking into whether the company misled investors by making misleading statements about climate change and its potential impact on the company's bottom line.

The CIEL documents could spell trouble for other companies, said Tom Sanzillo, finance director at the Cleveland-based Institute for Energy Economics and Financial Analysis (IEEFA).

"There is a clear potential — I would say a high likelihood — of multiple levels of litigation against oil companies," said Sanzillo, the former chief of the New York state pension fund. Those could include private lawsuits as well as government actions; there's also the prospect of a revolt by stockholders who find the company facing unexpected liabilities or a congressional investigation.

"This looks like it's pretty serious, and it just seems to get worse," he said.

CIEL's previous release revealed industry studies from the 1950s and '60s that identified the burning of fossil fuels as a contributor to the rise of carbon dioxide concentrations in the atmosphere. A 1968 study produced for the API warned that rising carbon dioxide concentrations in the atmosphere "may be the cause of serious world-wide environmental changes."

But around the same time, oil companies began promoting alternative theories for climate change that scientists had discounted, such as changes in the sun's intensity or the orbit of the Earth. A 1968 paper co-sponsored by Gulf Oil declared that cyclical changes in the Earth's axis "must be recognized as the number-one contender in the climatic sweepstakes."

"They resurrected the theory of astronomical or solar-driven climate change that had been moribund for years," Muffett said. "Industry-funded research resurrected it, and it's become a go-to argument for climate denialists even to this day."

Sanzillo said the oil companies had "the best scientists and the best minds," and may have been far more aware of the risks than the nascent environmental movement in the 1960s and '70s. But that means they "bear a certain responsibility," he added.

"It's a shame that many of the technological innovations that they were developing didn't come to fruition," he said. "The oil companies, as a research entity, are probably some of the best minds in the world on energy, and it's unfortunate that they've not helped to develop real solutions over the decades. That's what society was looking to them for."