How Climate Change Affects El Niño

11/17/20223 min read

An El Niño (“EN”) event describes the phenomenon in which prevailing trade winds, which would usually blow warm air from the east to the west of the Pacific, become weaker or even reverse, resulting in more warm water being retained in the central and eastern Pacific. Consequently, “sea surface temperatures in the central and eastern tropical Pacific Ocean become substantially warmer than average, and this causes a shift in atmospheric circulation,” creating conditions which are “more favourable for tropical rainfall and cloud development” (BOM, 2014).

During an EN event, “areas in the northern U.S. and Canada are dryer and warmer than usual,” while “in the U.S. Gulf Coast and Southeast, these periods are wetter than usual and have increased flooding” (NOAA). Australia, Indonesia, Brazil, India, and Africa “could experience drought conditions because moisture-bearing storms are shifted away” while “Argentina, South China, Brazil and Japan can receive an increase in moisture-bearing storms that cause long periods of heavy rains and flooding” (Priddy, 1997).

Extreme EN events are expected to increase in both frequency and intensity.

This is because “the equatorial western Pacific has experienced a significant warming trend coincident with global warming,” which turn creates conditions conducive for EN events in the central equatorial Pacific (Wang et al, 2019).

Additionally, warming in the western Pacific facilitates the westward movement of events within the Madden-Julian Oscillation (Wang et al, 2019), which is “an eastward moving ‘pulse’ of cloud and rainfall” (BOM), thereby increasing the frequency of westerly wind bursts and the probability of the occurrence of strong basin-wide (“SBW”) EN events (Wang et al, 2019).

Historical changes in El Niño properties tell us that climate change, and the associated rise in average global sea surface temperatures, is contributing to more extreme weather events. We are learning that the warming of the surface of the ocean, coupled with the circulation of heat through ocean currents, is exacerbating certain natural weather events such as El Niño and causing them to manifest in more extreme and less manageable ways.

Recent rapid global warming has had a direct impact on the El Niño changes observed by Wang et al (2019).

All moderate EN events in the eastern Pacific (“MEP EN events”) took place prior to the late 1970s; all moderate El Niño events in the central Pacific (“MCP EN events”) after the late 1970s (Wang et al, 2019). In other words, we can visualise EN events moving in a westward direction from the east to central Pacific over the years. Further, not only did the 3 most extreme SBW El Niño events to date happen after the late 1970s, they all took place adjacent to MCP EN events.

These changes in EN events correspond to the sudden rate of increase of Earth's average surface temperature, which has more than doubled since 1981, most likely due to (amongst others) population peaking at 2.1% per year between 1965 and 1970 (WEF, 2021).

We already know that human-derived emissions are the primary contributor to the enhanced greenhouse gas effect which has caused extreme changes in the climate.

If these trends continue, we can expect even more frequent, intense, and extreme weather events including El Niño.

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