Advancing decadal-scale climate prediction in the North Atlantic sector

Abstract

The climate of the North Atlantic region exhibits fluctuations on decadal timescales that have large societal consequences. Prominent examples include hurricane activity in the Atlantic, and surface-temperature and rainfall variations over North America, Europe and northern Africa. Although these multidecadal variations are potentially predictable if the current state of the ocean is known, the lack of subsurface ocean observations that constrain this state has been a limiting factor for realizing the full skill potential of such predictions. Here we apply a simple approach-that uses only sea surface temperature (SST) observations-to partly overcome this difficulty and perform retrospective decadal predictions with a climate model. Skill is improved significantly relative to predictions made with incomplete knowledge of the ocean state, particularly in the North Atlantic and tropical Pacific oceans. Thus these results point towards the possibility of routine decadal climate predictions. Using this method, and by considering both internal natural climate variations and projected future anthropogenic forcing, we make the following forecast: over the next decade, the current Atlantic meridional overturning circulation will weaken to its long-term mean; moreover, North Atlantic SST and European and North American surface temperatures will cool slightly, whereas tropical Pacific SST will remain almost unchanged. Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.

Evaluation of short‐term climate change prediction in multi‐model CMIP5 decadal hindcasts

“…For 6-9 years, the predictive skill does not change much compared to 2-5 years ( Figure S2 in Text S1). The relatively long prediction skill appears over the region where the externally forced component and low-frequency climate variability is dominant [Keenlyside et al, 2008;Meehl et al, 2009;Pohlmann et al, 2009;Chikamoto et al, 2012, Mochizuki et al, 2012Oldenborgh et al, 2012]. High prediction skill also occurs in the tropical Atlantic SST which is an important factor in climate variability in that region and beyond [Keenlyside et al, 2008].…”

“…The AMO and PDO are the dominant decadal oscillations over the North Atlantic Ocean [Schlesinger and Ramankutty 1994;Enfield et al, 2001] and North Pacific Ocean [Mantua et al, 1997], respectively, and are the most predictable components of internal climate variability [e.g., Keenlyside et al, 2008;Mochizuki et al, 2010]. The AMO index is defined as the area averaged annual mean sea surface temperature (SST) anomaly averaged over the North Atlantic from 80 W to 20 W and from 0 to 70 N for both the simulations and observation.…”

“…Not only does natural variability have a large-amplitude influence over broad regions of the globe, it is an integral component of climate variability that modulates low-frequency climate phenomena as well as extreme climate events such as tropical cyclone activity. On decadal timescales, some aspects of internal climate variability may be predictable [Collins and Allen, 2002;Smith et al, 2007;Keenlyside et al, 2008;Meehl et al, 2009Meehl et al, , 2010Pohlmann et al, 2009;Mochizuki et al, 2012]. However, the actual prediction skill of natural climate variability on decadal timescales using various current climate models has received little attention [van Oldenborgh et al, 2012].…”

Mechanisms Determining the Winter Atmospheric Response to the Atlantic Overturning Circulation

“…A deeper understanding of the AMOC climate impacts, and the processes involved are of great interest, as the AMOC has a large persistence and is potentially predicable up to a decade in advance (Keenlyside et al 2008;Msadek et al 2010;Matei et al 2012). Unfortunately, observations of the AMOC only began in 2005 (Smeed et al 2014), so that the observational record is too limited to clearly establish the AMOC climate impacts.…”

On the credibility of climate predictions

“…However, we think that the following passage from Kerr (2008) is indicative of the state of the art in GCMs. Kerr's article refers to the study by Keenlyside et al (2008), who explained the observed constancy (or slight decrease) of the global temperature (instead of the projected global warming) in the last decade, using real sea-surface temperatures as initial conditions (and with this they predict that in the next decade European and North American surface temperatures will decrease slightly): "To take account of such ocean-driven natural variability, Keenlyside and This reveals a culture in the climatological community that is very different from that in the hydrological community. In hydrology and water resources engineering, in real-time simulations that are used for future projections in transient systems (in contrast to steady-state simulations), it is inconceivable to neglect the initial conditions; likewise, it is inconceivable to claim that a model has good prediction skill for half a century ahead but not for a decade ahead.…”