Controversial geoengineering projects that may be used to cool the planet must be approved by world governments to reduce the danger of catastrophic accidents, British scientists said.
Met Office researchers have called for global oversight of the radical schemes after studies showed they could have huge and unintended impacts on some of the world's most vulnerable people.
The dangers arose in projects that cooled the planet unevenly. In some cases these caused devastating droughts across Africa; in others they increased rainfall in the region but left huge areas of Brazil parched.
"The massive complexities associated with geoengineering, and the potential for winners and losers, means that some form of global governance is essential," said Jim Haywood at the Met Office's Hadley Center in Exeter.
The warning builds on work by scientists and engineers to agree to a regulatory framework that would ban full-scale geoengineering projects, at least temporarily, but allow smaller research projects to go ahead.