A Land-Sea Contrast Pattern in Surface Temperature and Atmospheric Circulation Trends in Recent Decades

Abstract

Spatial patterns in observed climate trends remain poorly understood. Here we argue that a warming of land relative to ocean has shaped observed surface temperature and atmospheric circulation trends, including the negative Inter-Decadal Pacific Oscillation (IPO)-like tendency across the Pacific basin. Observed and modeled trends display an overall decline in sea level pressure over the faster-warming land relative to ocean, with a spatial pattern that resembles the seasonal cycle and the response to land heating in idealized climate model experiments. Coupled climate model simulations with historical forcing underestimate the land-sea warming ratio. It is only in the early response of abrupt CO2 quadrupling climate model simulations that climate models are able to recreate the observed land-sea warming ratio, in which case a strengthening of oceanic surface highs and a negative IPO-like surface warming pattern over the Pacific comparable to observed trends are seen. We propose that discrepancies between modeled and observed trends in many climate variables may be explained by the underestimation of the land-sea warming ratio by climate models. Determining the cause of this discrepancy has the potential to constrain projections of future climate change as the underlying mechanism causing climate models to underestimate the land-sea warming ratio discrepancy will set the persistence of this problem.