Although they cover only 3 percent of Earth’s land surface, peatlands store about 30 percent of the total soil carbon. Despite the uncertainty about their response to climate change, large-scale manipulations simulating climate change have not been conducted until SPRUCE (Spruce and Peatland Responses Under Climatic and Environmental Change Experiment). The SPRUCE experiment is an ambitious ecosystem-level experiment that is testing the response of high-carbon northern peatland ecosystems to increased temperatures and elevated carbon dioxide. Located at the Forest Service’s Marcell Experimental Forest near Grand Rapids, MN, the experiment is a collaboration between the Forest Service and the Department of Energy’s Oak Ridge National Laboratory and many other collaborators. The manipulation is evaluating the response of the existing communities to a range of warming levels from ambient to plus 9 degrees Celsius, with and without elevated carbon dioxide (CO2), provided via large, open-top chambers. Both direct and indirect effects of these perturbations are being analyzed to refine models needed for full Earth system analyses. Belowground heating began in 2014, aboveground heating in 2015, and elevated CO2 treatments commenced in 2016. Responses to warming and interactions with increased atmospheric CO2 concentration will have important feedbacks on the atmosphere and climate.