Even these figures are likely to be an understatement of the full climate impact of UK related transportation. As noted in section 5, while the scientific evidence remains complex, there are strong grounds for considering that the full climate impact of aviation emissions at high altitudes is greater than that attributable to carbon dioxide emissions alone. Additionally, as discussed in more detail in section 7, rough estimates of UK carbon emissions from international shipping based on the UK's share of global GDP or international trade would suggest figures around 3-4 MtC higher than those based on sales of marine fuels in the UK - reflecting the fact that the UK is not a major refuelling hub for international cargo ships. In summary, carbon emissions from transport represent a significant proportion of total UK carbon emissions which, depending upon the method of calculation, are between around a quarter and a third of total UK emissions. 2.6 2.7 2.8 Carbon emissions from transport are also rising - over the last decade transport has been the fastest growing source of carbon emissions, both in the UK and many other countries. This reflects the impact of increased personal mobility and a growing economy on the demand for goods and services. While forward projections, which are inevitably uncertain, suggest that carbon emissions from domestic transport may begin to plateau out in the following decades, if emissions from international aviation and shipping are included then the overall trend on a business as usual basis remains upwards. The Government has not set individual carbon reduction targets for different sectors of the economy - as we consider that emissions reduction efforts should be first focussed on the areas in which they are most cost effective. Nonetheless transport policies in the Government's existing climate change programme are expected to deliver around 6.8MtC of savings in 2010 compared to a business as usual scenario. The Stern Review suggested that in the short term many transport abatement policies may not be cost-effective, but that action is nevertheless required to contain emissions and to bring forward technologies which can deliver more cost-effective carbon reduction in the future. In the longer run, if lower carbon technologies can be effectively commercialised and their costs reduced, modelling analysis suggests that in a carbon constrained world by 2050 it may be cost effective for domestic transport to abate carbon emissions by around 40-60% relative to 1990 though