David McLees (Letters, 29 July) is wrong in asserting that air travel by clergy is gratuitous.   Air travel contributes 2-3 per cent of carbon dioxide (CO2) emissions. The gas turbine (jet) is the most efficient means yet invented of turning fossil fuel into power. The aviation industry is at the forefront of further increasing efficiency and reducing the production of gases such as oxides of nitrogen (NOx). The largest sources of CO2 are electricity generation (25 per cent) and land use (24 per cent).