Investigating the Feedbacks between Land Surface Cover and North Atlantic Climate Variability in the HadCM3 Coupled Climate Model

Abstract:

The North Atlantic displays a number of major modes of decadal variability, namely the North Atlantic Oscillation (NAO) and the Atlantic Meridional Overturning Circulation (AMOC). On decadal to multi-decadal timescales, this unforced climate variability is expected to be more influential on the overall pattern of climate than anthropogenic forcing. Greater understanding of this decadal-scale variability is essential to improve its predictability, which in turn is vital to constrain uncertainty in decadal to centennial climate change predictions.

Numerous studies have investigated how oceanic and atmospheric forcing modulates climate variability. However the feedbacks between the land surface and decadal variability have not been examined to the same degree. The land surface influences climate via biogeophysical and biogeochemical processes which interact and vary across a wide range of spatial and temporal scales. Increasing concentrations of CO₂ are expected to drive a change in the distribution and physiology (i.e. stomatal conductance and leaf area index) of vegetation, which can alter land surface structure and influence biogeophysical processes. It is important to more accurately constrain if/how land surface cover influences decadal variability and the associated feedback mechanisms and how these may change in a warming climate.

This sensitivity study will use the HadCM3 climate model to investigate the impact of a range of vegetation distributions on the strength and variability of the AMOC/NAO at increasing CO₂ concentrations. We aim to elucidate feedbacks between the land surface, ocean and atmosphere in a coupled climate model and potential implications for decadal modelling studies.