Historical Changes in Wind‐Driven Ocean Circulation Can Accelerate Global Warming

Abstract

Mitigation and adaptation strategies for climate change depend on accurate climate projections for the coming decades. While changes in radiative heat fluxes are known to contribute to surface warming, changes to ocean circulation can also impact the rate of surface warming. Previous studies suggest that projected changes to ocean circulation reduce the rate of global warming. However, these studies consider large greenhouse gas forcing scenarios, which induce a significant buoyancy‐driven decline of the Atlantic Meridional Overturning Circulation. Here, we use a climate model to quantify the previously unknown impact of changes to wind‐driven ocean circulation on global surface warming. Wind‐driven ocean circulation changes amplify the externally forced warming rate by 17% from 1979 to 2014. Accurately simulating changes to the atmospheric circulation is key to improving near‐term climate projections.

Historical changes in wind-driven ocean circulation drive pattern of Pacific warming

“…Many previous studies have been devoted to understanding the cause of cross-equatorial winds in the EP, mostly related to the local or remote hemispheric asymmetry in warming as we see in our simulations 33 . The proposed mechanisms include asymmetric aerosol forcing 45,46 , tropical North Atlantic warming 47 , Atlantic meridional overturning circulation (AMOC) 48,49 , wind-evaporation-SST feedback (WES) 26,50,51 , and the Southern Ocean heat uptake [52][53][54] .…”

“…To investigate the impact of wind-driven ocean circulation changes, we analyze another set of large ensemble members, mechanically decoupled (MD) historical simulations with CESM2, in which ocean surface wind stress is fixed to its seasonally varying pre-industrial climatological state 33 (see Methods) using the wind stress overriding technique [36][37][38][39][40] . Through this approach, the Bjerknes feedback is cut off, and therefore the effects of ENSO variability and Walker Circulation adjustment on SST trends are both eliminated 41 .…”

“…Wind stress overriding experiments have been demonstrated to be helpful in isolating the influence of wind-driven ocean circulation on the ocean-atmosphere coupled system [36][37][38][39][40] . The second CESM2 ensemble, MD for "Mechanically Decoupled Model", is created by branching 20 members from a pre-industrial MD model run 33 . Each ensemble member is branched from a different pre-industrial control date, making it a macro ensemble.…”

“…To address this question, here we compare two Community Earth System Model version 2 (CESM2) large ensembles, first introduced in ref. 33 that allow us to isolate the impacts of externally forced changes in wind-driven ocean circulations on the tropical Pacific warming pattern over the historical period. As we will show later, this unique experimental set-up and our ocean heat decomposition analysis can lead us to identify a dynamic mechanism critical to the historical tropical Pacific warming pattern that has been overlooked in the existing literature.…”

Climate Changes and Sustainability

“…Oceanic and atmospheric circulation are affected by seasonal fluctuations in the energy that the Sun makes accessible. The flow of energy from atmospheric and oceanic circulation is substantially responsible for the seasonal climatic variations that occur at any point on Earth's surface [52]. Storm tracks and pressure centers change in location and intensity due to variations in surface heating that occur between summer and winter.…”