Climate change has been viewed as a national security threat multiplier. To offset its damage, scientists in the United States and other countries are working on technology to manipulate the climate. Most of this technology is still in its infancy, but its strategic importance is evident. As countries face climate security threats beyond anything seen before, they might consider geoengineering as the new form of defensive technology to manipulate the environment in their favor. Yet some of this technology holds the potential to disrupt the earth and mount a coercive threat with implications as serious as those in wartime.