El Niño events are commonly thought of as important drivers of abnormally warm conditions along the U.S. West Coast. Such conditions can be disruptive and sometimes disastrous to marine ecosystems, so it’s critical for scientists to be able to predict them. According to a recent study in Nature Scientific Reports, however, El Niño may not always be the one to blame.
Funded in part by NOAA’s Modeling, Analysis, Predictions, and Projections Program, the study identifies patterns not identical to El Niño that have a stronger influence on unusual West Coast warming, and could help improve predictability.
The 2013 - 15 warming event
From the winter of 2013/14 to 2014/15, the Northeast Pacific experienced extreme and persistent warming that had substantial impacts on the ecosystem and the economy. During this time, the region saw mass strandings of marine mammals and seabirds, an outbreak of toxic algae, and dramatic shifts in the range of species. The economy also took a hit from the closure of commercial fisheries, resulting in the loss of millions of dollars.
Dungeness crab fisheries in California experienced a crash due to the marine heatwave. (Photo credit: Benjamin Drummond)
Despite being a typical suspect, the anticipated strong El Niño event never appeared in 2014, causing scientists to question its role.
“While El Niño events do exert an influence on the U.S. West Coast, this influence varies from event to event and is not necessarily stronger during strong events. Thus, our study asked which tropical Pacific conditions are actually most likely to cause warm conditions along the coast,” explained Antonietta Capotondi, lead scientist on this research from NOAA’s Earth System Research Laboratory (ESRL) and Cooperative Institute for Research in Environmental Sciences (CIRES).
Capotondi and co-authors from ESRL, CIRES, Georgia Institute of Technology, University of Colorado, and Scripps Institute of Oceanography identified the optimal spatial patterns of tropical sea surface temperature and sea surface height conditions, or “sensitivity patterns”, that are most influential to warming along the U.S. West Coast.
The important finding of this study is that the central and western Pacific is a key area for U.S. West Coast warming, rather than eastern Pacific where many El Niño events peak. In addition, they found that a distinctive evolution of North Pacific atmospheric and oceanic fields prior to the El Niño peak phase was also conducive to the warming on the West Coast.
USWC warming v no USWC warming during an El Nino event in February-April (first panel), June-August (second panel), and October-December (third panel)
“An important message from this is that El Niño is a diverse and complex phenomenon, which cannot simply be described by any single index. The details of its evolution and spatial pattern can have important worldwide consequences,” explained Capotondi.
With this research, the group has identified regions of the tropical Pacific that can be expected to be more influential on US West Coast marine conditions. This helps provide a better assessment of the predictability of the conditions which could lead to better advanced warning for planning and managing marine resources and ecosystem services.
The Modeling, Analysis, Predictions, and Projections (MAPP) Program is a competitive research program in NOAA Research's Climate Program Office. MAPP's mission is to enhance the Nation's and NOAA's capability to understand, predict, and project variability and long-term changes in Earth's system and mitigate human and economic impacts. To achieve its mission, MAPP supports foundational research, transition of research to applications, and engagement across other parts of NOAA, among partner agencies, and with the external research community. MAPP plays a crucial role in enabling national preparedness for extreme events like drought and longer-term climate changes.
For more information, please visit www.cpo.noaa.gov/MAPP.