Aviation contrails and their climate impact

Aviation has experienced a very rapid expansion over the last fifty years, with passenger traffic growing by approximately 9% per year, almost 2.5 times the average growth rate of the Gross Domestic Product. The aircraft emissions associated with air traffic have a warming effect on climate that is expected to increase in the years to come due to the continuing expansion of the aviation sector. An important share of this warming effect comes from linear contrails and aviation induced cirrus, but the current best estimates of these effects still have a high level of uncertainty. We developed a contrail parameterization within the UK Met Office Climate Model. Using this new parameterisation, we estimate that for the air traffic of year 2002, the global mean annual linear contrail coverage was approximately 0.11%, a value which in good agreement with several other estimates. We also estimate that the corresponding contrail radiative forcing is approximately 8 mWm-2 in all-sky conditions. The new parameterisation is employed in fifty-year slab-ocean model runs in order to give one of the first insights into contrail effects on daily temperature range and the climate impact of contrails.