U.N. delegates on Thursday withdrew a motion calling for more research into technologies that aim to fight climate change by reflecting the sun’s rays back into space, amid concerns about health and environmental risks.

Some who opposed the draft resolution at the U.N. Environment Assembly were also worried that the use of solar radiation modification (SRM) might let big polluters off the hook, organizations watching the debate said.

Switzerland and Monaco first tabled the resolution on examining the geoengineering technology in December, and it was discussed during this week’s assembly in Nairobi.

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The original version called for the convening of an expert group that would produce a report examining SRM’s possible applications, risks and ethical considerations.

One of the best-known proposals for using it involves blasting sulphur dioxide – a coolant – into the higher reaches of the atmosphere.

There are only a handful of small SRM projects in operation. Some scientists say SRM could be made available when necessary to avert climate tipping points.

Critics are concerned about possible impacts on weather patterns and agriculture, especially in poorer countries. They also worry SRM could serve as an excuse to delay cutbacks on greenhouse gas emissions.

After going through six revisions over the past two weeks, the resolution was withdrawn on Thursday, the website of the United Nations Environment Programme (UNEP) showed.

“There was agreement among many countries on the need for scientific assessment of SRM, but there were also significant concerns about equity, and the delegates ran out of time to resolve their differences,” said Nico Esguerra, Director of International Strategy at SilverLining, a non-profit that promotes research on geoengineering methods.

The various drafts of the resolution showed countries inserting concerns about the safety of the technology.

The Center for International Environmental Law (CIEL) said African nations, the European Union, Pacific Island states, Colombia and Mexico opposed the resolution.

“These technologies cannot tackle the root causes of the climate crisis and would instead enable major polluters to delay the urgent need to phase out fossil fuels,” Mary Church, Senior Geoengineering Campaigner at CIEL, said.

A representative from Switzerland’s Federal Office for the Environment who was listed as the contact person for the draft resolution did not immediately respond to a request for comment.