Module 08: Future Climate Change

The IPCC 6th Assessment provides a striking range of potential futures, depending primarily on the choices people make over the coming decades with respect to CO2 emissions. In the lowest emission scenarios (SSP1-1.9 and SSP1-2.6), emissions fall immediately and rapidly, CO2 stabilizes, and climate remains relatively constant in the future with warming of less than 2 C above preindustrial levels. We might call this the “new normal.” On the other hand, at high levels of emissions (SSP3-7.0 and SSP4-8.5), CO2 and warming continue to increase, and simulated impacts are severe. Warming is most severe on land, in continental interiors, and in the Arctic with average temperatures 5 C warmer than preindustrial by 2100. Large parts of the subtropical continents become very dry both through reduced rainfall and the increased evaporative demand of warmer air. Depletion of soil moisture is especially severe over the Mediterranean region, the Amazon Basin, and the southwestern USA. Both extremely hot days and extremely heavy rainfall become dramatically more frequent. In high CO2 emission scenarios, carbon sinks on land and in the ocean absorb a smaller fraction of emissions due to extreme warming. Arctic summer sea ice is lost completely by late century in all but the lowest emission scenarios. Sea levels continue to rise in all scenarios and accelerate in later centuries under high emissions.