Evidence for multiple drivers of North Atlantic multi‐decadal climate variability

Abstract

Observed North Atlantic Ocean surface temperatures have changed in a non‐monotonic and non‐uniform fashion over the last century. Here we assess the relative roles of greenhouses gases, anthropogenic aerosols, natural forcings and internal variability to the North Atlantic surface temperature decadal fluctuations using multi‐model climate simulations driven by estimates of observed external forcings. While the latter are the main source of decadal variability in the tropics and subtropics, there is a large contribution from the unforced component to subpolar Atlantic variations. Reconstruction of forced response patterns suggests that anthropogenic forcings are the main causes of the accelerated warming of the last three decades while internal variability has a dominant contribution to the early 20th‐century temperature multi‐decadal swings and recent abrupt changes in the subpolar Atlantic. Significant inter‐model spread with regard to the spatial response patterns to anthropogenic forcing leads to substantial uncertainty as to robust attribution statements for the mid‐to‐late 20th century North Atlantic warm and cold periods.