The data originates from a mesocosm experiment with salt marsh plants from the Wadden Sea (Hamburger Hallig: 54°36 06N, 8°49'08E), investigating the impact of increased temperature and CO₂ on salt marsh vegetation. The investigation was conducted over 100days from May to August 2021 using 12 largescale mesocosms (1900L) in a full factorial design with an enhancement of temperature to +3C above ambient temperature and CO2 enrichment of 800ppm. The ambient water temperature was identical to the temperature of the coastal water pumped into mesocosms ranging from 11-22°C over the 100 days of incubation. In the increased temperature treatments, the temperature was kept at 3°C above the ambient temperature, regulated via a system of heaters and coolers. In the ambient CO₂ treatments, atmospheric air was pumped into the systems and reached an air concentration of 380ppm, whereas in the enriched CO2 treatment, atmospheric air was enriched with CO₂ to a concentration of 800ppm and pumped into the systems. CO2 measured in the mesocosms air compartment was 50-150ppm above the ambient concentration, as some CO2 was lost to water and vegetation.