Although aviation may only contribute approx 3% of the global CO2 emissions, it would also seem important to measure the % contribution to C02 in the upper atmosphere since apparently that is where CO2 and other pollutants have a greater warming effect. The overall contribution to global warming from aviation pollution could be significantly higher than 3%. Although there has been great strides made in reductions of CO2 emissions from jet engines, the modern jet engine has signifcantly increased nitrogen oxide emissions. Nitrogen oxide reacts with other gases in the air to form ozone, another heat trapping gas. At the same time Nitrogen oxide removes methane thus probably cooling to some extent. In any case might it not be sensible to limit growth in some way to the rate at which aviation improves its fuel efficiency?