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.
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.