The root cause of global warming is that more and more of the energy supplied by the sun is captured by the atmosphere because of increased amounts of CO2 and other climate gases. One way of fixing this is to make sure that more of that energy is reflected and never even penetrates the lower atmosphere. Solar geoengineering proposes to put particles into the upper atmosphere to increase its reflectivity and thereby reduce the temperature. In the episode I talk with Harvard's David Keith about some of the technical aspects, which role this technique can play in the overall fight against climate change, some of the political challenges as well as current avenues of research.