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Other Direct Greenhouse Gases - Stratospheric water

Water vapour in our stratosphere can act as a very powerful greenhouse gas. The amounts of water vapour in our stratosphere are mainly controlled by the earths overall climate. However, some other significant sources exist.

As described in the methane section, water is a by-product of methane breakdown in the atmosphere. Additionally, the water vapour arising from high flying aircraft may be an important source of stratospheric water, particularly in the future with increased global air travel.

The exact global budget for stratospheric water vapour is poorly understood and no reliable projections on how concentrations may change in the future are currently available.

Human Impact

Through both increased methane emissions and high altitude aircraft man may increase stratospheric water concentrations. However, our greatest impact may be brought about via changes in global climate, with a warmer planet leading to larger amounts of water vapour in our stratosphere.

Potential for control

Reducing methane emissions should be a greenhouse gas reduction strategy even without the added impacts methane has in our atmosphere. An area which needs increased research is that of the impact of high altitude flights on stratospheric water vapour, if this source is important then this must be recognised before the number of such flights grows too much.

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