Forecast: How will the Global Atmospheric Concentration of Carbon Dioxide Evolve in 2024?

The forecast generated by the Met Office indicates that in 2024 the concentration of CO2 will continue to rise. This year, the El Niño effect will make an additional contribution since natural CO2 sinks will not be able to efficiently capture what is emitted.

CO2 2024
The concentration of CO2 in the atmosphere has already comfortably exceeded the 420 ppm barrier. Every year, Met Office makes an estimate of what can happen with this important greenhouse gas.

The Met Office, the weather service of the United Kingdom, makes an estimate every year of the expected behavior of carbon dioxide (CO2) concentration in the atmosphere. Their forecasts in previous years have always been very adjusted to what is finally measured, so they are very taken into account by the global meteorological community.

The current increase in CO2 is mainly due to the burning of fossil fuels and the change in land use, with an additional impact this year from El Niño, which has caused a temporary weakening of the carbon sinks of tropical lands.

It must be remembered that CO2 is the main greenhouse gas in the atmosphere. Between 65% and 80% of CO2 released into the atmosphere dissolves in the ocean and remains there for a period of between 20 and 200 years. The remaining percentage is slowly eliminated, thanks to processes that can last hundreds of thousands of years, processes such as chemical weathering or rock formation. Methane is another greenhouse gas with a greater power than CO2, but with a much lower persistence rate.

In the case of methane, its persistence in the atmosphere is approximately a decade. The third in importance, nitrous oxide, reaches 120 years. That said, to understand the context, Met Office warns that it predicts that the increase in atmospheric CO2 between 2023 and 2024 will be faster than what is necessary to meet the scenarios of the Intergovernmental Panel on Climate Change (IPCC) that limit global warming to 1.5 °C.

The effect of El Niño on CO2

The reference point for CO2 concentration is Mount Mauna Loa, Hawaii. That's where the daily concentration measurements of this gas are made with the longest series globally.

The current increase in CO2 is mainly due to the burning of fossil fuels and the change in land use. However, there is currently an additional impact, since El Niño causes a temporary weakening of the carbon sinks of tropical lands. Areas that would normally absorb some of the released carbon will have a reduced capacity due to the effects of El Niño.

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Professor Richard Betts is the author of the work done by Met Office, and indicates that "the estimated increase for this year in the atmospheric concentration of carbon dioxide is well above the three scenarios compatible with 1.5 ºC indicated in the report of the Intergovernmental Panel on Climate Change (IPCC). Even when we compensate for the temporary effects of El Niño, we found that human-borne emissions would continue to cause the increase in CO2 in 2024 to be within the absolute limits of compliance with the 1.5 °C trajectories."

Met Office predicts that the average annual concentration of CO2 in Mauna Loa, Hawaii, will be 2.84 ± 0.54 parts per million (ppm) higher in 2024 than in 2023. As a result, the forecast suggests that the average annual concentration of CO2 in 2024 in Mauna Loa will be 423.6 ± 0.5 ppm. Beyond everything, the truth is that the scenario points to a sustained increase in the concentration of CO2 in the atmosphere.

Uncertain future

Richard Betts also adds that "the increase in atmospheric CO2 has accelerated in the last six decades. In order for global warming to remain below 1.5 °C, the rate of CO2 accumulation in the atmosphere would have to slow down substantially in the coming years and stop completely before the middle of the century. The forecast for 2024 does not show such a slowdown."

CO2 Met Office
Average annual change in the concentration of CO2 in the atmosphere. Image: Met Office

If the annual changes are observed, the fastest increase in the CO2 concentration expected for this year (red line) is well above the annual change necessary to follow the three key illustrative scenarios compatible with 1.5 °C of the previous graph. The fastest increase in 2024 is associated with the weakening of carbon sinks due to El Niño, which dries out tropical forests and affects their ability to absorb carbon dioxide, so it is expected to be temporary.

However, if this effect is excluded (as shown by the dark green line and the green spot in the previous graph), human-borne emissions would continue to cause an increase in CO2 in 2024 well above the rate necessary to follow the 1.5 ºC scenario of "low energy demand", and at the upper end of the uncertainty interval of the other two 1.5 ºC scenarios. The current level of global warming is approximately 1.3 ºC. Although the global temperature in 2023 was almost 1.5 °C higher than that of the pre-industrial era, which made it the hottest year ever recorded, the natural cycle of El Niño temporarily added to the man-induced warming. Therefore, the record temperatures of 2023 do not represent an exceeding 1.5 °C of human global warming, according to Met Office.