US scientists are working on what could one day become a controversial weapon to fight global warming: clouds.
Misting ocean clouds with saltwater, the theory goes, could make them reflect more sunlight away from the earth.
"If you can reflect away some of that radiation and not allow it to be absorbed, you will cool the planet," says University of Washington atmospheric scientist Tom Ackerman.
The phenomenon has been observed over cargo ships, as microscopic particles in smokestack effluent collect water droplets, leaving trails of "brightened" clouds in their wake.
Ackerman's team believes the effect could be recreated using tiny saalt particles to reduce solar radiation absorbed by the ocean.
Initial computer models have shown promise.
But Ackerman says no funder is willing to back field tests and environmental activists have threatened to disrupt them.
Other researchers in the US, United Kingdom and Germany working on high-tech climate hacks from dimming the sun's rays with stratospheric aerosols to growing phytoplankton to suck carbon dioxide from the seas have hit similar roadblocks.
The point of contention isn't whether humanity could one day use so-called geoengineering to cool the earth - but whether we should.
"People have this sort of innate response that somehow we're tinkering with Mother Nature, and we shouldn't be," Ackerman told DPA - even though, he points out, by burning fossil fuels "we are already adding carbon dioxide to the atmosphere".
Earth's temperature is currently on course to rise at least 4C this century as a result of increasing carbon dioxide and other greenhouse gas levels in the atmosphere.
Starting November 30, representatives of nearly 200 countries intend making the final push in Paris for a new climate agreement that for the first time will include carbon emission reductions by developing countries.
The goal is to stop temperatures rising more than 2C over pre-industrial times, to avoid catastrophic loss of human life from rising sea levels and severe weather.
Many observers fear even the whisper of a Plan B to confront climate change could weaken political will for the hard work of Plan A.
