A climate change signal in the tropical Pacific emerges from decadal variability (Invited Presentation)

Recent debates have centered around whether the La Niña-like sea surface temperature (SST) trend pattern in the tropical Pacific in the past several decades is a response to anthropogenic forcings or internal variability, particularly the Interdecadal Pacific Oscillation (IPO). A definitive anthropogenic link would allow us to reliably predict a cooler tropical Pacific, hinting at a broader, naturally mitigating effect on global warming at least for the near future due to the tropical Pacific's climatic pacemaker effects. Alternatively, if the cyclic IPO is dominantly driving the recent cooling, we may be approaching a strong warming regime when it reverses that would dramatically reshape our climate anticipations. Here, in support of the first possibility, we identify an emerging SST warming pattern in the tropical Pacific featuring a narrow equatorial cooling band alongside warming elsewhere, in stark contrast to the meridionally broad SST trend pattern shaped by the IPO. The emerging SST trend pattern is associated with changes in subsurface temperature structure and sea level height that are distinct from those related to the recurrent IPO. The differences are primarily driven by their different surface wind stress patterns. The emerging wind stress pattern, characterized by a strengthening of trade winds in the central-to-western Pacific and a weakening in the eastern Pacific, drives distinctive ocean dynamical processes fostering the unique eastern Pacific cooling. While none of the state-of-the-art climate models perfectly capture the observed trend patterns in the tropical Pacific, we find that those simulating a similar emerging wind stress pattern are best able to reproduce the historical surface and subsurface temperature trend patterns in observations. These findings set a path to distinguish the often-tangled tropical Pacific climate change signals from internal variability through the underlying dynamics of each, which is crucial for setting a benchmark against which to assess the ability of climate models to reproduce the observed forced response in the presence of strong internal variability, thereby ensuring more dependable future climate projections.