El Niños, La Niñas and Atmospheric CO2

How much do El Niño and La Niña events affect the rate at which the level of carbon dioxide in the Earth’s atmosphere changes?

Before we answer that, it would help to know how El Niño and La Niña events affect the Earth’s weather. Accuweather provides the following description of how both kinds of events start:

El Niño is a part of a routine climate pattern that occurs when sea surface temperatures in the tropical Pacific Ocean rise to above-normal levels for an extended period of time.

The opposite of El Niño, La Niña, is when sea surface temperatures in the central Pacific drop to lower-than-normal levels.

These warm and cool phases are part of a recurring climate pattern that occurs across this section of the Pacific, known as the El Nino-Southern Oscillation (ENSO), according to the National Oceanic and Atmospheric Administration (NOAA).

Changes in equatorial water temperatures can then affect wind and water currents, which is how something that starts as a local weather condition transforms into something that has a global weather impact. NASA explains what happens when an El Niño event gets underway:

During an El Niño event, the surface waters in the central and eastern Pacific Ocean become significantly warmer than usual. That change is intimately tied to the atmosphere and to the winds blowing over the vast Pacific. Easterly trade winds (which blow from the Americas toward Asia) falter and can even turn around into westerlies. This allows great masses of warm water to slosh from the western Pacific toward the Americas. It also reduces the upwelling of cooler, nutrient-rich waters from the deep—shutting down or reversing ocean currents along the equator and along the west coast of South and Central America.

The circulation of the air above the tropical Pacific Ocean responds to this tremendous redistribution of ocean heat. The typically strong high-pressure systems of the eastern Pacific weaken, thus changing the balance of atmospheric pressure across the eastern, central, and western Pacific. While easterly winds tend to be dry and steady, Pacific westerlies tend to come in bursts of warmer, moister air.

Because of the vastness of the Pacific basin—covering one-third of the planet—these wind and humidity changes get transmitted around the world, disrupting circulation patterns such as jet streams (strong upper-level winds). We know these large-scale shifts in Pacific winds and waters initiate El Niño. What we don’t know is what triggers the shift. This remains a scientific mystery.

The large-scale shifts associated with El Niño events matter where atmospheric carbon dioxide levels are concerned because these events contribute to widespread hot and dry conditions that limit the ability of natural carbon sinks, such as tropical forests and plants, to absorb carbon dioxide from the Earth’s atmosphere.

The opposite situation occurs during La Niña, when these same natural carbon sinks in the tropics are less distressed and are able to pull substantially more carbon dioxide out of the air.

You can actually see the difference in the seasonal variation for changes in the level of atmospheric carbon dioxide. The following animated chart presents sixty years of that data from October 1958 through September 2018, where we’ve color coded El Niño years in red, La Niña years in blue, and neutral years in gray, where we’ve also indicated the intensity of the events with lighter shading for weak years and darker shading for strong years. The chart will cycle from all years, to El Niño years, to La Niña years, and then to neutral years every five seconds before restarting its loop. If you’re accessing this article on a site that republishes our RSS news feed where the animation doesn’t play, you can either click through to our site to see the animation, or just simply follow the links in the previous sentence to access the individual charts used to make the animation.

From the animation (or the individual charts), you can see that El Niños are associated with higher-than-average levels of change in the seasonal variation of atmospheric carbon dioxide, La Niña events are associated with lower-than-average levels of change, while neutral years tend to see seasonal variation in carbon dioxide levels that are pretty closely grouped about the average.

We haven’t seen anyone else put together a similar presentation, where we’re taking the opportunity to do it ourselves! The Mauna Loa Observatory is the source for the atmospheric carbon dioxide data, while the intensity levels for the various El Niño and La Niña events from 1958 through 2018 is taken from Golden Gate Weather Service’s summary for the Oceanic Niño Index.