Investigating Carbon Cycle Dynamics of Tropical and Boreal Ecosystems with an Improved Land Surface Model (JULES)

The Joint UK Land Environment Simulator (JULES) is the land surface of the next generation UK Earth System Model (UKESM1). Recently, the model was updated with new plant functional types and physiology based on a global plant trait database. These developments improved the simulation of terrestrial gross and net primary productivity on local and global scales, and enabled a more realistic representation of the global distribution of vegetation. In this study, we explore the stability of ecosystem dynamics and carbon storage for the historical period and up to 2100, focusing on tropical and boreal ecosystems. These regions will experience large-scale climate change and pressure from anthropogenic activity, and therefore we expect large responses in ecosystem carbon dynamics. JULES predicts a net increase in carbon stored in high latitude ecosystems resulting from the combined effects of warming and increased CO2 (with the caveat that permafrost carbon is not accounted for in this study). Productivity increases due to northward migration of woody vegetation, a longer growing season, and CO2 fertilization, while carbon stored in soils decrease due to warming. In tropical ecosystems, productivity does not significantly increase, possibly due to changes in dry season characteristics, and carbon residence times decrease, resulting a net loss of carbon from these ecosystems. These results, as well as opportunities for observational constraints on the predicted future changes, will be discussed.