At the UN Environment Assembly in Nairobi on Wednesday, delegates from the United States, Saudi Arabia, and Brazil blocked a sweeping plan for investigating geoengineering, one of the most controversial tools in the fight against climate change.

The proposal was a Swiss resolution to “prepare an assessment of the status of geoengineering technologies.” Specifically, it called for the study of carbon dioxide removal (CDR) and solar radiation management (SRM)—two techniques that currently dominate the nascent field of geoengineering, which is the manipulation of Earth’s natural processes as a means to stymie climate change.

The final version was withdrawn on Thursday by Switzerland after nations were unable to find consensus, but would have tasked the UN Environment Programme with conducting the assessment.

To observers it seemed as though the United States and Saudi Arabia, both heavy consumers and producers of fossil fuels, had opposed the plan to keep research and development of CDR as open as possible—seeing it as a substitute for some emissions reduction.

“I think there was clear evidence of the fossil link, in that Saudi Arabia at least sees carbon removal forms of geoengineering as a means of sustaining fossil fuel use, while the United States argued that carbon removal is an alternative to emissions reduction,” one source present for the meeting who requested that they remain anonymous told Motherboard.

According to the source, the US objected to language that suggested “geoengineering techniques should not be treated as a substitute for mitigation, or emissions cuts.”

The United States also gave the impression of wanting to reject the plan out of concern that it may hamper development of carbon dioxide removal techniques, ostensibly through increased policies and regulations, according to this source.

“It was clear throughout that [these countries] feared it constraining geoengineering research and development far more than other countries feared that it could enable geoengineering,” the source added.

The US successfully pushed for the matter to be punted to the Intergovernmental Panel on Climate Change (IPCC), according to a source who was at the meeting but chose to speak anonymously due to professional concerns. The IPCC will examine geoengineering in its Sixth Assessment Report due in two years.

The United States’ deferral to the IPCC is “laughable,” said Ted Parson, an environmental law professor at the University of California Los Angeles. Under the Trump administration especially, he pointed out, the country has diminished the IPCC’s climate change recommendations.

But dialogue around geoengineering is nevertheless ramping up, attracting both support and criticism from many stakeholders, ultimately generating more public attention than perhaps ever before.

CDR is a broad term for what is essentially sucking the heat-trapping gas directly out of Earth’s atmosphere. It refers to a host of techniques, some relying on natural sinks such as forests and soil; others on powerful machinery capable of capturing carbon dioxide straight from the air. To make a dent in emissions, CDR would need to be implemented at an extremely large scale.

Solar radiation management is an arguably more stigmatized, and theoretical, geoengineering feat. This approach aims to reflect sunlight back into space, staving off warming, either by using spraying a sheath of reflective aerosol particles into the atmosphere or selectively brightening marine clouds to bounce back Earthbound rays.

But before that can happen, “we need the research to make an informed decision, as to whether it would be riskier to implement it or to not implement it and live with trying to adapt to the impacts of global warming,” said Alan Robock, a professor of environmental sciences at Rutgers University.

Academics not present at the UN meeting postulated that opponents had other motivations, too—namely torpedoing the resolution’s statement that climate change is “one of the greatest challenges of our time,” mandating first and foremost a radical reduction in emissions.

Fossil fuel interests may assume that “taking geoengineering seriously will convey the immense gravity and stakes of the issue, and they’re still fighting the battle [of climate change denial],” Parson said.

“If a government's position is that human-caused climate change is not a problem, it doesn't make sense to advocate for research on extreme approaches to address the risks posed by human-caused climate change,” said Kate Ricke, an assistant professor and climate change scientist at the University of California San Diego.

The plan’s derailment isn’t the end of geoengineering research, even at the UN, though advocates hoped it would be a more global assessment of these technologies. Switzerland and the other countries backing it wanted the UN Environment Assembly to become the preeminent UN body on geoengineering, E&E News reported on Friday.

Other groups, such as the UK’s Royal Society and the US National Academies of Sciences, Engineering, and Medicine, have produced their own geoengineering studies, Nature reported earlier this month.

“It’s actually really good that governments are seriously talking about these issues, finally,” said Janos Pasztor, head of the Carnegie Climate Geoengineering Governance Initiative. “Even though they did not agree to a resolution, there has been a serious negotiation and that’s what’s needed.”