In the year 1800, only about 10 million tonnes of coal were consumed globally, about 5% of total energy use. By 2011, fossil fuel consumption had risen to the energy equivalent of over 15 billion tonnes of coal, and accounted for about 87% of global energy. Atmospheric carbon dioxide (CO2) levels have risen similarly, from 280 ppm in 1800 to nearly 400 ppm by 2013. For much of the two centuries of fossil fuel use, the main concern was local air pollution, but in recent decades two new problems have come to the fore: global fossil fuel depletion (along with attendant concerns about national energy security) and global climate change, with CO2 derived from fossil fuel combustion the chief culprit. This chapter examines two proposed solutions for the second problem, global climate change. The first method discussed, sequestering CO2, can be done naturally, in vegetation and soils, or mechanically, by separating CO2 from power station smokestacks, and then burying it. In either case, atmospheric CO2 growth is slowed or even stopped. The second approach, geoengineering, merely attempts to counter the climate change effects of rising atmospheric greenhouse gas (GHG) levels, with increasing planetary albedo the most-discussed method. Carbon sequestration in vegetation and soils is already occurring naturally on a large scale, and could be augmented by reforestation, especially in the tropics. Mechanical sequestration would be very expensive in both energy and monetary terms, and the permanence of CO2 burial could be compromised by seismicity and other problems, or its extent limited by citizen opposition. Geoengineering by aerosol placement in thestratosphere appears to have very low costs, could be rapidly implemented with present-day technology, and rapidly discontinued. On the other hand, given the longevity of CO2 in the atmosphere, aerosol injection costs will be incurred each year for centuries. Future generations would have to pay most of the costs for our emissions. Further, oceans would continue to acidify, ozone hole recovery would be delayed, and global precipitation patterns would change, making it difficult to reach international agreement on geoengineering in a water-stressed world. We thus conclude that biotic carbon sequestration is the only feasible approach, and even then cannot be expected to prevent further rise in atmospheric CO2 levels. For effective climate mitigation, large reductions in fossil fuel use will therefore be needed.