Clouds trap solar energy, which helps to warm the atmosphere. A warmer atmosphere can hold more moisture and could build up even more clouds. These clouds would then trap more heat and…well, you get the idea. This is called a positive feedback mechanism. There are many positive feedback mechanisms in climate change. Another is albedo. As temperatures warm, snow and ice melt. This reduces albedo, which causes temperatures to warm and more snow and ice to melt.

Clouds also reflect energy and shade the land. This would help to reduce global temperatures. So scientists are not sure what the net effect of clouds on global temperatures is. Clouds are the second biggest uncertainty in climate models. The biggest is in how people’s behavior will change, to change human impacts on the atmosphere.

^{Courtesy of Rob Simmon and NASA. earthobservatory.nasa.gov/IOTD/view.php?id=44250. Public Domain.}