Global-Scale Multidecadal Variability Missing in State-of-the-Art Climate Models

Abstract

Reliability of future global warming projections depends on how well climate models reproduce the observed climate change over the twentieth century. In this regard, deviations of the model-simulated climate change from observations, such as a recent “pause” in global warming, have received considerable attention. Such decadal mismatches between model-simulated and observed climate trends are common throughout the twentieth century, and their causes are still poorly understood. Here we show that the discrepancies between the observed and simulated climate variability on decadal and longer timescale have a coherent structure suggestive of a pronounced Global Multidecadal Oscillation. Surface temperature anomalies associated with this variability originate in the North Atlantic and spread out to the Pacific and Southern oceans and Antarctica, with Arctic following suit in about 25–35 years. While climate models exhibit various levels of decadal climate variability and some regional similarities to observations, none of the model simulations considered match the observed signal in terms of its magnitude, spatial patterns and their sequential time development. These results highlight a substantial degree of uncertainty in our interpretation of the observed climate change using current generation of climate models. Climate models are in universal agreement that ongoing emissions of greenhouse gasses will lead to global warming. However, models often struggle to simulate realistic patterns of decadal climate variability, raising questions about their representation of key climate physics. Here, Sergey Kravtsov and colleagues show that a previously unknown pattern of climate variability can account for up to 0.3 °C of warming or cooling over the course of several decades. The climate signal originates in the North Atlantic and propagates throughout the world over the course of two to three decades. While numerous patterns of decadal variability are known to exist within the climate system, Kravtsov and colleagues suggest that global — rather than regional — climate variability is influenced by the North Atlantic. State-of-the-art climate models do not simulate the observed climate cycles, suggesting that key mechanisms remain to be discovered.