Salt marshes provide an array of ecosystem services, and are recognized as a significant global carbon store. Climate-induced warming, however, is likely to alter salt-marsh ecosystem functioning, with potential implications for the biogeochemical cycling of climate-relevant compounds. With regards to warming effects on salt marsh ecosystems, there is a dearth of experimental data, particularly for subsurface soils. Established in 2018, the MERIT (Marsh Ecosystem Response to Increased Temperature) in situ salt marsh warming experiment combines both passive aboveground warming with feedback-controlled active belowground and soil surface warming. This setup allows assessment of warming-induced changes to both above- and belowground plant and soil characteristics. Three replicate plots for three temperature scenarios (ambient, 1.5°C, and 3.0°C) were established in each of the three salt marsh zones: pioneer zone, low-marsh, and high marsh (n=27). Mixed models show that the experimental setup is effective at warming the ecosystem. Initial results show earlier plant greening and later senescence, slightly increased seed mortality, and increased rates of organic matter decomposition in experimentally warmed plots.