The pollutants can also become the core for cloud droplets.

Smaller drops are called cloud droplets, and their shape is spherical.

"It takes a million cloud droplets to form a raindrop," he said.

As the water molecules slowly collect and condense on the particles, cloud droplets form.

The pollutants can also become nuclei for cloud droplets.

If there was no air in the way, gravity would make a cloud droplet and a lump of lead fall at the same speed.

Individual cloud droplets are falling down, but very very slowly.

The particles, according to the new hypothesis, serve as seeds for cloud droplets, which then reflect the sun's radiation back out to space.

An explanation could be the evaporation of the cloud droplets when precipitation drops are formed.

Later, when the water vapor condenses to form cloud droplets and rain, the heat is released into the atmosphere.