Strong El Niño events linked to short-term spikes in atmospheric CO2, new study reveals

New research suggests that strong El Niño events may be responsible for short-term increases in atmospheric CO2 levels, challenging previous assumptions about the relationship between CO2 and tropical temperatures.

Extreme weather events play a crucial role in the short-term fluctuations of carbon dioxide in the atmosphere.

Study finds that El Niño events, not long-term climate changes, cause short-term CO2 fluctuations, highlighting uncertainties in climate projections.

El Niño, CO2 levels, climate change, carbon cycle, atmospheric CO2, climate models

Strong El Niño events may be responsible for short-term fluctuations in atmospheric CO2 levels, according to a new study that challenges previous assumptions about the link between CO2 and tropical temperatures. The research, conducted by scientists from the Max Planck Institute for Biogeochemistry and the University of Leipzig, suggests that these extreme weather phenomena could explain observed CO2 sensitivity in recent decades.

Between 1959 and 2011, the atmospheric CO2 content responded twice as strongly to tropical temperatures as it had in previous years. While this increase was often attributed to rising droughts in the tropics and changes in the carbon cycle due to climate change, the new study proposes a different explanation. The research points to strong El Niño events as a significant factor in this increased sensitivity.

Published in the journal Science Advances, the findings question prior assumptions about the relationship between atmospheric CO2 and tropical temperature. The study highlights the importance of El Niño events, which occur in irregular intervals, leading to significant changes in global climate patterns.

Both tropical and non-tropical ecosystems absorb large amounts of carbon, which would otherwise be released into the atmosphere through human CO2 emissions. Globally, terrestrial ecosystems act as a carbon sink, absorbing roughly one-third of human-generated CO2 emissions. These ecosystems thus play a vital role as a natural buffer against climate change.

In the 1980s and 1990s, researchers noticed an increase in the fluctuations of global carbon storage on land. The growth rate of atmospheric CO2 appeared to be particularly sensitive to tropical temperatures. Researchers from Jena and Leipzig found that this "doubling" of sensitivity was due to the increased occurrence of El Niño events during the 1980s and 1990s compared to the period from 1960 to 1979.

Vegetation Releases Large Amounts of CO2

This includes the extreme El Niño events of 1982/83 and 1997/98, which caused severe droughts and heatwaves in the tropics. These conditions negatively affected plant growth, reducing carbon absorption. During El Niño periods, vegetation can even release significant amounts of carbon that would otherwise remain sequestered in soil or forests, leading to a rise in atmospheric CO2.

The study’s authors emphasize that this increase in CO2 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 an indication of a fundamental change in the carbon cycle's response to climate change," explains Na Li, from the Max Planck Institute for Biogeochemistry and lead author of the study. Instead, it is caused by the combination of extreme El Niño events and their global impact.

Professor Ana Bastos of the University of Leipzig, the study's principal investigator, adds, "Thanks to our work, we were also able to demonstrate that this phenomenon is related to the 'slow-in, fast-out' dynamics of the carbon cycle. This means that carbon is absorbed slowly by ecosystems but can be released suddenly and rapidly during extreme weather events like strong El Niño events."

Implications for Climate Projections

The study's findings are important because they highlight uncertainties in future climate projections. Until now, it was assumed that greater sensitivity of CO2 increases to tropical temperatures was due to long-term, climate-related changes in the carbon cycle and the global climate system. However, this research shows that extreme events can cause short-term fluctuations that do not necessarily indicate permanent changes in the carbon cycle.

"These new findings could help develop more accurate climate models and reduce uncertainties in predicting future climate scenarios," states Professor Sebastian Sippel from the University of Leipzig. He further asserts the need to better understand how extreme climate events, such as El Niño, affect carbon dynamics to make more reliable forecasts for the future.