There are numerous uncertainties concerning aviation's contribution to climate change including:

• The degree to which reduced ozone from aircraft water and sulphur emissions offset  the increased ozone as a  result of NOx emissions

• Uncertainties as to the sources and sinks of methane

• The contribution to warming of water vapour at cruising altitudes as a result of contrails and cirrus clouds – the radiative effect of contrails depends on their optical properties (as well as global cover) which depends on particles emitted or formed. There is scientific uncertainty on these issues

Useful sources of information:

IPCC Special Report - Aviation and the Global Atmosphere - Summary for Policymakers, 1999
http://www.ipcc.ch/pub/av(E).pdf

An Introductory overview of aviation emissions by the FAA
"Aviation & Emissions: A primer", FAA Office of Environment and Energy. Jan 2005
www.faa.gov/regulations_policies/policy_guidance/envir_policy/media/AEPRIMER.pdf