Cirrus cloud thinning is a proposed strategy to manage Earth’s energy imbalance and stop global warming. Cirrus clouds are composed of ice crystals at high altitudes and appear as wispy streaks. Compared to clouds at lower altitudes, they are less effective at reflecting incoming sunlight and more effective at blocking outgoing longwave radiation emitted by the Earth. Thus, they have a net heating influence on the climate. The heat trapped by cirrus clouds is greater than that trapped in the atmosphere as a product of human CO2 emissions. Researchers at ETH Zurich, a Swiss university, proposed that drones could inject solid aerosol particles into cirrus clouds, causing the clouds to dissipate more quickly thus there being less time for the cloud to trap heat.  Source: A Cirrus Cloud Climate Dial?