Twenty-first Century Climate Simulated by HadGEM2-ES under RCP8.5 Modified to Account for the Effects of Thawing Permafrost, Wetlands and Nitrogen Limited Vegetation on CO2 and Methane Concentrations

Abstract:

Emissions of carbon dioxide and methane from thawing permafrost and wetlands, together with reduced uptake of CO₂ by vegetation due to nitrogen limitation, are expected to exert a positive feedback of increasing magnitude on the climate system over the coming century. The current generation of Earth System models is unable to simulate interactively these climate-carbon cycle feedbacks. We have used offline methodologies to estimate a range of CO₂ and methane emissions from permafrost, methane emissions from wetlands, and reduced sequestration of CO₂ by nitrogen-limited vegetation under the high-end representative concentration pathway, RCP8.5. By translating these fluxes into increments to the concentration of each gas we have generated a new range of scenarios, exceeding RCP8.5 by up to 266 ppm of CO₂ and 732 ppb of methane by 2100. We have used these new scenarios to force the Hadley Centre Earth System model, HadGEM2-ES, over the 21st century. We found that accounting for these feedbacks leads to additional global mean warming of up to 1.5 °C relative to the standard RCP8.5.