Cirrus

Cirrus clouds are high level clouds forming at over 6,000 metres. They are made up of ice crystals and often are a sign of the approach of a front. Scientists are still trying to work out the impact of cirrus clouds on climate. It is known that they can have a major impact on global warming as there is less albedo (reflection of incoming solar radiation back into space) than in lower level clouds composed of water droplets. They are also much more effective in trapping outgoing radiation. (See also cumulus, altocumulus and cumulus)