Scientists are slamming the brakes on deliberately interfering with the climate to temporarily counteract global warming until the pros and cons are more fully known.

What's happening: In the meantime, they're advocating for a comprehensive research campaign that studies the field — known as geoengineering — and its potential.

• This is occurring just as commercial ventures are starting to plow forward with geoengineering plans of their own, with a profit-seeking motive.

Why it matters: Who sets the rules of the road and what they contain, particularly on the type of geoengineering known as solar radiation modification (SRM), may alter the course of global warming itself and affect billions of people.

• SRM would involve injecting particles into the atmosphere to deflect incoming solar radiation, cooling the planet temporarily.

Zoom in: In a new report released Monday, an expert panel convened by the UN Environment Program (UNEP) pours cold water on the notion that SRM is anywhere near ready.

• “Even as a temporary response option, large-scale SRM deployment is fraught with scientific uncertainties and ethical issues. The evidence base is simply not there to make informed decisions," wrote UNEP head Inger Andersen, in a cover letter accompanying the document.
• Andersen notes that SRM may be needed since the world is currently off course from meeting its Paris temperature targets.

The panel called for more research. But until then, it seeks to shut the door to deploying SRM.

• "This expert panel considers that the scientific, technical, social and environmental aspects of a large-scale deployment of SRM have not been fully assessed and deployment is not warranted at present," it states.

The intrigue: The UN panel notes that the direct costs of deploying it without considering all the possible adverse consequences may be in the tens of billions of dollars annually per 1°C (1.8°F) of cooling.

• And to be effective, SRM would need to be maintained for several decades to centuries, depending on emissions cuts and carbon removal rates, the report finds.

The big picture: Also on Monday, more than 60 scientists from three continents signed onto a new letter supporting comprehensive investigations into SRM.

• This is significant because there are some in the scientific community who are against researching SRM at all.
• Like UNEP, the researchers advocate examining scientific, technological, legal and ethical issues involved in SRM.

Between the lines: Recent plans by a geoengineering startup, Make Sunsets, to test SRM and eventually profit from climate credits have spooked but not surprised many scientists who work on this issue.

What they're saying: Veteran climate scientist and diplomat Janos Pasztor, who is heading up the Carnegie Climate Governance Initiative and consulting global governments about their views on geoengineering, told Axios both the UNEP report and the scientists' letter are major developments.

• "Much of the community working on or against SRM is highly critical of [Make Sunsets], but the fact remains that they exist, and they are doing things in a governance vacuum," Pasztor said. "In part they are provoking, precisely because of the governance vacuum."