Planet-warming gas levels rose more than ever in 2024

Scientists have stated that the concentration of the most important greenhouse gas in the atmosphere rose at an unprecedented rate last year, jeopardizing key global climate goals. Carbon dioxide (CO2) concentrations are now more than 50% higher than before humans began burning large amounts of fossil fuels.

Last year, fossil fuel emissions reached a record high, while the ability of nature to absorb carbon dioxide declined due to factors such as wildfires and droughts, leading to more carbon dioxide accumulating in the atmosphere. The UK Met Office stated that the rapid increase in carbon dioxide is "incompatible" with the international commitment to limit global warming to 1.5 degrees Celsius above pre-industrial levels.

This is an ambitious target agreed upon by nearly 200 countries at the landmark UN meeting in Paris in 2015, with the hope of avoiding some of the most severe impacts of climate change. Last week, 2024 was confirmed as the hottest year on record, and the first calendar year with average annual temperatures more than 1.5 degrees Celsius above pre-industrial levels. However, this does not break the Paris Agreement's target, which refers to long-term averages over decades, but the continued increase of carbon dioxide in the atmosphere effectively dooms the world to surpass this goal.

Richard Betts of the UK Met Office stated, "Limiting global warming to 1.5 degrees Celsius requires the rate of increase in carbon dioxide to slow down, but in reality, the opposite is happening." The long-term increase in carbon dioxide is undoubtedly caused by human activities, mainly through the burning of coal, oil, and gas, as well as deforestation. The UN stated that climate records of the Earth's distant past obtained from ice cores and ocean sediments show that current carbon dioxide levels are at least the highest in two million years. However, the annual increase varies due to differences in how nature absorbs carbon and fluctuations in human emissions.

Preliminary data from the Global Carbon Project team shows that fossil fuel carbon dioxide emissions reached a new high last year. In addition, the natural El Niño phenomenon—an abnormal warming of surface waters in the tropical eastern Pacific that affects weather patterns—also had an impact. Nature has already absorbed about half of human carbon dioxide emissions, for example through additional plant growth and more gas dissolving in the ocean. However, the additional heat brought by El Niño in the context of climate change meant that natural carbon sinks on land did not absorb as much carbon dioxide last year as usual. Rampant wildfires, including in areas not typically affected by El Niño, also released additional carbon dioxide.

Professor Betts said, "Even without the boost from last year's El Niño, the rate of increase in carbon dioxide driven by fossil fuel burning and deforestation would now exceed the IPCC's [UN climate body] 1.5 degree Celsius scenarios." These factors meant that between 2023 and 2024, carbon dioxide levels increased by nearly 3.6 parts per million (ppm), reaching a new high of over 424 ppm. This is the highest annual increase on record since atmospheric measurements were first taken at the remote Mauna Loa research station in Hawaii in 1958. The station is located on the side of a Pacific volcano, and its remote location away from major pollution sources makes it ideal for monitoring global carbon dioxide levels.

Professor Ralph Keeling, head of the measurement project at the Scripps Institution of Oceanography in the United States, said, "These latest results further confirm that we are entering uncharted territory at an unprecedented rate as the rate of increase continues to accelerate." This record increase has heightened concerns that, in the long term, nature's ability to absorb greenhouse gases may decline. The US scientific organization NOAA stated that the Arctic tundra is turning into an overall source of carbon dioxide due to warming and frequent fires. The ability of the Amazon rainforest to absorb carbon dioxide is also affected by droughts, wildfires, and deliberate deforestation.

Professor Betts told the BBC, "This is an open question, but we need to pay close attention and study it carefully." The UK Met Office predicts that the increase in carbon dioxide concentration in 2025 will not be as extreme as in 2024, but it is still far from the 1.5 degree Celsius target. The La Niña phenomenon—where surface water temperatures in the tropical eastern Pacific are below normal—has replaced El Niño, which tends to allow nature to absorb more carbon dioxide. Professor Betts said, "While temperatures may temporarily ease, warming will continue as carbon dioxide continues to accumulate in the atmosphere."