We know that global climate change affects large-scale climate events, like monsoons and tropical cyclones, so should the same be true for the frequency and strength of El Niño events?
Why Would El Niño Events Be Tied to Global Warming?
First, the El Niño Southern Oscillation (ENSO) can be summed up as a very large volume of unusually warm water that builds up in the Pacific Ocean off the coast of South America. The heat contained in that water is released in the atmosphere, affecting weather over a large portion of the globe. El Niño conditions appear following complex interactions between tropical air instability, atmospheric pressure, dominant wind pattern shifts, ocean surface currents, and deep water mass movements. Each of these processes can interact with climate change, making predictions about the characteristics of future El Niño events very difficult to do. However, we know that climate change significantly affects both atmospheric and ocean conditions, so changes should be expected.
A Recent Increase in the Frequency of El Niño Events
Since the beginning of the 20th century, the frequency of El Niño events appears to have increased, with a similar trend for the events' intensity. However, wide year-to-year variations lower confidence in the observed trend. Nonetheless, three recent events, 1982-83, 1997-98, and 2015-16 were the strongest on record.
Too Complex a Phenomenon to Forecast?
Over the last two decades, studies have identified mechanisms by which global warming could affect many of the El Niño drivers mentioned above. However, in 2010 a careful analysis was published, where the authors concluded that the system was too complex to draw clear conclusions. In their words: “the physical feedbacks that control the characteristics of ENSO are likely to be affected by climate change but with a delicate balance between amplifying and damping processes meaning that it is not clear at this stage whether ENSO variability will go up or down or be unchanged… ” In other words, feedback loops in climate systems make predictions difficult to make.
What Does the Latest Science Say?
In 2014, a study published in the Journal of Climate found a clearer way to anticipate differences in El Nino events under climate change: instead of the events themselves, they looked at how they interact with other large scale patterns occurring over North America, in a phenomenon called teleconnection. Their results hint at an eastward shift in above-average precipitation during El Niño years over the western half of North America. Other teleconnection-mediated shifts are expected in Central America and northern Columbia (becoming drier) and in Southwest Colombia and Ecuador (getting wetter).
Another important study published in 2014 used more refined climate models to revisit the issue of whether global warming would change the frequency of strong El Niño events. Their findings were clear: intense El Niños (like the 1996-97 and 2015-2016 ones) will double in frequency over the course of the next 100 years, occurring on average once every ten years. This finding is sobering, given the large impacts these events have on lives and infrastructure thanks to droughts, floods, and heat waves.
Cai et al. 2014. Frequency of Extreme El Niños to Double in the 21st Century. Nature Climate Change 4:111-116.
Collins et al. 2010. The Impact of Gobal Warming on the Tropical Pacific Ocean and El Niño. Nature GeoScience 3:391-397.
Steinhoff et al. 2015. Projected Impact of Twenty-First Century ENSO Changes on Rainfall over Central America and Northwest South America. Climate Dynamics 44:1329-1349.
Zhen-Qiang et al. 2014. Global Warming-Induced Changes in El Niño Teleconnections over the North Pacific and North America. Journal of Climate 27:9050-9064.