The world is getting warmer, globally averaged surface temperatures have increased substantially over the past 100 years and much of this can be associated with an increased greenhouse effect. The increased greenhouse effect is caused by accelerating concentrations of greenhouse gases in the atmosphere, in particular carbon dioxide resulting from man made burning of fossil fuels. In the future we can expect further increases of carbon dioxide concentrations, compared to pre-industrial times the concentration is likely to increase by 100% or more within the coming century. The implications for global climate are quite dramatic. Using basic laws of physics we can construct climate models that can be used to estimate future climate change. The estimates are associated with a large uncertainty, but nevertheless we may conclude that a continued global warming is very likely to occur. The magnitude depends on how successful we will be in decreasing future emissions of carbon dioxide.