Abstract: The 2007 Intergovernmental Panel on Climate Change (IPCC) report showed that to limit global temperature rise since the industrial revolution to 2 ºC (thought by the European Union to represent a prudent limit to avoid dangerous climatic change) CO2 emissions may have to be cut by the year 2050 to as little as 15 % of the year 2000 value, with the peak emission year in 2000-2015. Since about 77 % of the climatic radiative forcing of anthropogenic greenhouse gas emissions from all sources comes from carbon dioxide, (with most of this in turn coming from fossil fuel use) this chapter mainly considers these emissions. Geoengineering is the only mitigation approach that does not require emission reductions, but carries serious risks—in attempting to solve one problem it creates others. Mitigating climate change will thus require that large emission reductions be made rapidly. The three most commonly discussed measures, carbon sequestration, use of non-carbon fuels and energy efficiency, can do little to reduce emissions in the time frame required, a point tacitly acknowledged by the IPCC and other authorities. Heavy emphasis will therefore need to be placed on a very different approach. Particularly in countries with high-energy per capita use, we argue emission cuts will also require reductions in the use of energy-using devices—including cars, airplanes and domestic appliances. Although this approach can be implemented quickly, it evidently requires profound changes in the global economy.