Research results

For the past ten years, total CO2 emissions have remained comparatively stable after rising by an average of 2 percent per year from 2004 to 2013. Though this indicates progress on the way to reaching the goals of the Paris Agreement, it’s a far cry from staying well below the 2-degree limit and gradually reducing global emissions toward a net-zero level. To reach net-zero CO2 emissions by 2050, overall emissions would need to be reduced by an average of 1.6 metric gigatons per year. If emissions remain unchanged, we will exhaust the remaining carbon budget for limiting global warming to 1.5 degrees Celsius (with a 50% probability) by or before the end of this decade. The Global Carbon Project (GCP) projects global greenhouse-gas emissions and their causes in its annual report. Experts from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and the Ludwig-Maximilians-Universität München (LMU Munich) are responsible for coordinating the content on the ocean sinks and land use change.

Emissions from fossil sources

The fact that global fossil emissions will likely rise in 2024 can be attributed to increasing oil and gas emissions, e.g. from international air and shipping traffic. These emissions will likely increase by 7.8 percent in 2024 while remaining below the pre-pandemic level from 2019. At the same time, coal emissions, which make up roughly 41 percent of global emissions, will also climb slightly (by 0.2 percent). This year, the United States will likely reduce its emissions by 0.6 percent compared to 2023 (13 percent of global emissions); for the European Union, the reduction will be 3.8 percent (7 percent of global emissions (EU27)). In contrast, emissions are expected to increase by 0.2 percent in China (32 percent of global emissions) and by 4.6 percent in India (8 percent of global emissions). Many countries appear to have successfully reduced their fossil CO2 emissions. In 22 countries responsible for 23 percent of global fossil CO2 emissions, said emissions declined in the decade 2014 – 2023, while their economies grew. However, this marked decarbonisation trend in energy systems alone will not suffice to put total global emissions on a downward path toward net zero.

The ocean as CO2 sink

In 2024, the ocean and land-based plants and soils will once again absorb roughly half of the anthropogenic CO2 that finds its way into the atmosphere. However, climate change is increasingly burdening both sinks. For example, in the past decade, the oceans have absorbed 10.5 metric gigatons per year on average, or 26 percent of overall emissions. “In the last ten years, climate conditions have reduced the oceans’ capacity to absorb CO2 by roughly 6 percent,” says Prof Judith Hauck, an environmental researcher at the AWI. “This is most likely due to changed winds, which disrupt ocean circulation, and to the fact that the oceans continue to warm, which is not conducive to the solubility of CO2.” The report’s preliminary estimate for the oceanic sink is, at 10.8 metric gigatons of CO2 for 2024, slightly above the value for 2023. “We were able to confirm last year’s projection for 2023, namely that, for the first time in three years, the ocean sink absorbed more CO2.” The three-year stagnation period was produced by a rare triple La Niña event, which the GCP had also described in its previous report. “In 2023 came the switch to El Niño conditions, under which the ocean sink is always a bit more effective, since less carbon-rich deep water rises to the surface.” The performance of the ocean sink is estimated on the basis of readings taken on CO2 concentrations in the surface ocean, and on simulations run with global ocean models. In the experts’ view, another troubling trend is the decline in ocean observations, which are now at the same level as in the early 2000s.

Twofold pressure on land-based ecosystems

Climate change is also affecting the land-based CO2 sink: from 2014 to 2023, landmasses absorbed an average of 11.7 metric gigatons – or 29 percent of total CO2 emissions – per year. “However, reduced precipitation and intensifying warming have cut the absorption capacity of terrestrial ecosystems by roughly 27 percent,” says Prof Julia Pongratz, a geographer at the LMU. These ecosystems are also under massive pressure from another source: changing and expanding land use. “Although global CO2 emissions from changed land use, at a projected 4.2 metric gigatons in 2024, remain quite high, over the past few decades we can see a declining trend.” This is chiefly because fewer forests are being cleared and more reforestation is being practiced. That being said, the constant clearing of forests over the past ten years released ca. 3.7 metric gigatons of CO2, approximately half of which was offset by reforestation efforts. “These high emissions underscore once again how important it is to completely stop deforestation in order to reduce emissions.”

Total global emissions and increased atmospheric CO2

Total CO2 emissions are expected to reach 41.6 metric gigatons this year, roughly 2 percent more than in 2023. They’ve remained fairly constant over the past ten years, which points to progress, but it won’t be enough to put global emissions on a downward path, an indispensable aspect of combating climate change.

In the course of 2024, the atmospheric concentration of CO2 is expected to reach 422.5 ppm (parts per million) – 2.8 ppm more than in 2023 and more than twice the preindustrial level. This is chiefly due to increased CO2 emissions, though the actual increase also depends on the reaction of the land-based CO2 sink and to a lesser extent, of the oceanic sink, to climatic conditions. Because of droughts and wildfires, land-based ecosystems absorbed less CO2. Although the ocean absorbed more under El Niño conditions, it wasn’t enough to compensate for the decline on land; as a result, more CO2 remained in the atmosphere.

About the Global Carbon Project

The GCP is an international project on global sustainability coordinated by the research initiative Future Earth. Its goal is to provide a comprehensive representation of the global carbon cycle, one that encompasses biophysical aspects, the human dimension, and interplays and feedbacks between them. Climate researchers from around the globe contribute to the report. The Global Carbon Budget 2024 is the 19th instalment of the annually released update, which began in 2006 and is published in the journal Earth System Science Data. Many researchers from German-speaking countries took part. Hailing from the Alfred Wegener Institute (Bremerhaven), the ETH Zurich, the GEOMAR Helmholtz Centre for Ocean Research in Kiel, the Helmholtz-Zentrum Hereon, the International Institute for Applied Systems Analysis (IIASA), the Karlsruhe Institute of Technology (KIT), the Leibniz Institute for Baltic Sea Research in Warnemünde, the Ludwig-Maximilians-Universität München (LMU Munich), the Max Planck Institute for Meteorology (MPIM) in Hamburg, the Max Planck Institute for Biogeochemistry in Jena, the Potsdam Institute for Climate Impact Research (PIK), and the Universities of Bremen, Bern and Hamburg, these experts contributed ocean observations, model-based simulations of the ocean, land and atmosphere, and a broad range of analyses.

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Wissenschaftlicher Ansprechpartner:
Judith Hauck
Judith.Hauck@awi.de
+49(471)4831-1848

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Originalpublikation:
Friedlingstein et al. (2024) Global Carbon Budget 2024. Earth System Science Data. https://essd.copernicus.org/preprints/essd-2024-519

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Weitere Informationen:
http://drive.google.com/drive/folders/1yJ0hW9nQFih_3mmjAOKtRaMDi2mql1vo Media packet on the Global Carbon Project
http://www.awi.de/en/about-us/service/press.html