The Relationship Between the East-West Surface Temperature Gradient, Tropical Pacific Ocean Heat Uptake, and Climate Sensitivity

Abstract

The surface temperature (ST) gradient between the eastern and western tropical Pacific Ocean strongly affects the global climate. Take for example the El Nino Southern Oscillation, a mode of inter-annual variability that affects weather patterns around the globe. How this zonal gradient will respond to global warming is debated, and its role in global heat uptake and changes in climate sensitivity is poorly understood. Using previously published model output from low and high-resolution CESM models, we analyze the relationship between the west minus east (zonal) ST gradients, tropical Pacific heat uptake, and climate sensitivity at 2x, 4x, 8x, and 16x pre-industrial carbon dioxide levels. Previous work has shown that increasing carbon dioxide can lead to enhanced east Pacific warming, and therefore a lower zonal temperature gradient as equilibrium is approached. In both models, the zonal ST gradient strengthens in a transient response during the first 50 years, while over the next 150 years, the equilibrium response shows a slight weakening in the high-resolution model, and a substantial weakening in the low-resolution model. We find that correlations between tropical pacific zonal ST gradients and the basin-wide or global surface heat flux (SHF) are dependent on the amount of CO2 forcing. Differences in climate sensitivities between the models present in the first 50 years compared to the climate sensitivities over the next 150 years, and the first 200 years as a whole, and reflect important differences between the transient and equilibrium response, which may be due to the transient strengthening and equilibrium weakening of the zonal gradient.