Communication Breakdown: The Impacts of Climate Change on Tropical–Extratropical Teleconnections

WTG balance is used to examine how changes in the moist thermodynamic structure of the tropics affect the MJO in two simulations of the Superparamtereized Community Earth System Model (SP-CESM), one at pre-industrial (PI) levels of CO2 and one where CO2 levels have been quadrupled (4xCO2). While MJO convective variability increases considerably in the 4xCO2 simulation, the dynamical response to this convective variability decreases. The decreased dynamical response to MJO convective variability is shown to be a consequence of increased static stability, which allows weaker variations in large-scale vertical velocity to produce sufficient adiabatic cooling to balance variations in MJO convective heating. This weakened dynamical response results in a considerable reduction of the MJO's ability to influence the extratropics, which is closely tied to the strength of its associated divergence. The ability of MJO convective heating to force the extratropics is reduced by ~40% in the 4xCO2 simulation relative to the PI simulation. Results of this study suggest that, while MJO convective variability may increase in a warming climate, the MJO's role in "bridging weather and climate" in the extratropics may not. As these same physical mechanisms act across the broad range subseasonal-to-seasonal timescales, these results suggest a broader tropical-extratropical communication breakdown, including ENSO teleconnections.