More than 50 nations are using various modifying techniques to adapt their own weather, the World Meteorological Organisation says.
Tracy Raczek, former climate adviser to the UN Secretary General, said techniques to adapt weather should be brought under a long-ratified UN convention.
She wants to see the Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques, or Enmod, modified to help accommodate new technology.
Enmod could also be used to prevent one country’s weather plans if it was detrimental to a second nation, Ms Raczek said.
“In the face of climate change, countries need first and foremost to reduce emissions and support climate adaptation,” she said.
“Simultaneously, however, they need to attend to the security implications of geoengineering and weather modification.”
Under Enmod, countries are banned from “environmental modification techniques having widespread, long-lasting or severe effects” for military reasons.
Peaceful efforts are legal but there are ambiguities in the convention. Ms Raczek said it was time for Enmod to be updated to reflect a common and contemporary understanding of "peaceful" and "hostile" intent.
There are questions over the main weather-changing technology and potential ripple effects in efforts to curb climate change, she said.
Cloud-brightening is a technique to reflect more sunlight back into space and thus reduce local warming. But there is uncertainty over how it might adversely affect ecological systems and climate change, as well as depleting the ozone layer.
The most common technology involves injecting aerosols into the stratosphere to increase rainfall or snow, or to modify a storm.
Another modification to fertilise the ocean involves adding nutrients to the sea to increase its uptake of carbon.