Climate change resulting from CO2 and other greenhouse gas emissions poses a huge threat to human welfare. To contain that threat, the world needs to cut emissions by about 50 per cent by 2050, and to start cutting emissions now. A global agreement to take action is vital. A fair global deal will require the UK to cut emissions by at least 80 per cent below 1990 levels by 2050. In this report, the Committee on Climate Change explains why the UK should aim for an 80 per cent reduction by 2050 and how that is attainable, and then recommends the first three budgets that will define the path to 2022. But the path is attainable at manageable cost, and following it is essential if the UK is to play its fair part in avoiding the far higher costs of harmful climate change. Part 1 of the report addresses the 2050 target. The 80 per cent target should apply to the sum of all sectors of the UK economy, including international aviation and shipping. The costs to the UK from this level of emissions reduction can be made affordable - estimated at between 1-2 per cent of GDP in 2050. In part 2, the Committee sets out the first three carbon budgets covering the period 2008-22, and examines the feasible reductions possible in various sectors: decarbonising the power sector; energy use in buildings and industry; reducing domestic transport emissions; reducing emissions of non-CO2 greenhouse gases; economy wide emissions reductions to meet budgets. The third part of the report examines wider economic and social impacts from budgets including competitiveness, fuel poverty, security of supply, and differences in circumstances between the regions of the UK.