The pace at which carbon dioxide accumulates in the Earth's air continues to rise. Through September 2024, that pace is nearing the record for the modern era recorded in January 2017.

That increase has taken place as China, the world's largest source of CO₂ emissions, has seen its factory output slow as the nation's industrial output has weakened. Even so, China's carbon dioxide emissions more than double those of the United States, which means a sluggish Chinese economy still cranks out more CO₂ than any other nation by a very wide margin.

The following NASA animation illustrates that output, showing how emissions originating from various locations around the world diffuse through the Earth's atmosphere. Check out the CO₂ 'smoke cloud' erupting from eastern China....

With Chinese factories slowing, the continued increase in the accumulation rate of CO₂ during the last few months may be a consequence of the strong El Niño event, which ran from May 2023 through April 2024. While not as strong as the 2015-16 El Niño event that was accompanied by extensive wildfires in Indonesia, it appears to be having a similar lingering impact, as seen in the following chart tracking the rate at which the trailing year average of the year-over-year change in the concentration of carbon dioxide in the Earth's atmosphere is changing.

New published research by Leipzig University researchers points to the role of strong El Niño events behind that observation. Here's a summary of their findings from the university's press office:

A recent study challenges previous assumptions about the connection between CO₂ in the atmosphere and temperatures in the tropics. Between 1959 and 2011, the CO₂ content in the atmosphere responded twice as strongly to temperatures in the tropics than before. This has often been attributed to increasing droughts in the tropics and to changes in carbon cycle responses caused by climate change. However, the current study conducted by researchers from the Max Planck Institute for Biogeochemistry and Leipzig University suggests that a small number of particularly strong El Niño events could be responsible for this.

Both tropical and non-tropical ecosystems absorb large amounts of carbon that were previously released into the atmosphere through human CO₂ emissions. Globally, land surface ecosystems act as a carbon sink and absorb on average around a third of human CO₂ emissions. These ecosystems are therefore a natural buffer for climate change. In the 1980s and 1990s, however, researchers observed an increased fluctuation in global carbon storage on land, and it appeared that the CO₂ growth rate was particularly sensitive to temperatures in the tropics. In a recent study, researchers from Jena and Leipzig found that this “doubling” of sensitivity was caused by the increased occurrence of El Niño events in the 1980s and 1990s compared to 1960–1979. This also includes the extreme El Niño events of 1982/83 and 1997/98. El Niño events cause severe droughts and heat waves in the tropics, which affect plant growth and thus reduce carbon uptake. In times of El Niño, vegetation even releases large amounts of carbon that would otherwise be sequestered in the soil or forests. This causes the CO₂ content in the atmosphere to increase.

The authors of the study emphasise that this CO₂ increase is due to internal climate variability rather than a systematic change in the carbon cycle caused by climate change. “Our results show that this doubling of sensitivity is not necessarily a sign of a fundamental change in the response of the carbon cycle to climate change,” says Na Li from the Max Planck Institute for Biogeochemistry, first author of the study. Instead, it is caused by the combination of extreme El Niño events and their global impact.

Tropical droughts associated with strong El Niño events contribute to a faster pace of CO₂ accumulation in the atmosphere by reducing its absorption by plant life until the affected regions have had sufficient time to recover, which can be aggravated by related wildfire events. Our chart showing the strong El Niño events of 2015-16 and 2023-24 suggests that effect continues for many months after the El Niño events themselves have ended. Through this point of 2024, that effect would seem to be more than offseting the slowing output from China's economy.

The big question for the months ahead is whether the Chinese government's new efforts to stimulute China's economy will offset the natural recovery from the 2023-24 El Niño event and cause the rate of CO₂ accumulation to continue increasing rather than diminishing.

References

National Oceanographic and Atmospheric Administration. Earth System Research Laboratory. Mauna Loa Observatory CO2 Data. [Online Data]. Updated 5 October 2024. Accessed 11 October 2024.