The long-term consequences of climate change have received relatively little attention. Models of future climate change typically focus on what will happen by the year 2100 or effects of a doubling of CO2 from pre-industrial levels. This is a serious shortcoming, since integrated carbon-climate models project that if CO2 from current in situ fossil fuel resources continues to be released into the atmosphere, the concentration of atmospheric CO2 could exceed 1400 ppm by the year 2300 and the Earth could be 8 °C or more warmer. Even if atmospheric CO2 remained at current levels, over the next few hundred years, sea levels would rise by tens of meters. If a significant fraction of currently recoverable fossil fuels is burned, the consequences will certainly be dire. Extreme heat and increased weather volatility will destabilize agricultural production. Large-scale population migrations will cause political and social instability. Heavily populated areas of the world will become uninhabitable. This chapter discusses the role of climate change on past human biological and social evolution, looks at various long-run scenarios for future CO2 and temperature increases, and discusses long-run climate change policies in the context of the sustainability debate.