The amount of carbon dioxide (CO2) entering Earth’s atmosphere increased by a record amount in 2024, locking in further global warming, according to a new report.
CO2 levels increased by 3.5 parts per million (ppm) from 2023 to 2024, marking the largest one-year increase since modern records began in 1957. Researchers attributed the record rise to humanity’s continued use of fossil fuels, a surge in wildfires, and less absorption from Earth’s carbon sinks (such as oceans and forests) that naturally take CO2 out of the atmosphere.
“The heat trapped by CO2 and other greenhouse gases is turbo-charging our climate and leading to more extreme weather,” Ko Barrett, the deputy secretary general at WMO, said in a statement. “Reducing emissions is therefore essential not just for our climate but also for our economic security and community well-being.”
CO2 and other greenhouse gases trap heat by absorbing radiation. As greenhouse gas concentrations increase, so do global average temperatures. The effects of global warming are shifting weather patterns, raising sea levels, compromising our ability to grow food and are having a variety of other expensive impacts that ultimately threaten the lives of billions of people.
Climate scientists consider CO2 to be the most significant climate-impacting greenhouse gas. It has been responsible for about 80% of the total greenhouse gas heating influence on our atmosphere since 1990, according to the National Oceanic and Atmospheric Administration (NOAA).
Atmospheric CO2 levels have steadily climbed for decades. The 3.5 ppm increase in 2024 was up from a 2.4 ppm rise in 2023 and higher than the average annual growth rate of 2.57 ppm established over the past decade. The total atmospheric CO2 concentration was about 423.9 ppm in 2024, up 152% compared to the pre-industrial level — the estimated concentration before 1750.
Concentrations of methane (CH4) and nitrous oxide (N2O), the second and third most important greenhouse gases, also increased by record amounts in 2024, up 166% and 25% from their respective preindustrial levels, the report found.
The biggest emitters
China, the U.S. and India were the three biggest emitting countries in 2024, according to the Emissions Database for Global Atmospheric Research. China was responsible for about 29.2% of all human greenhouse gas emissions, while the U.S. contributed 11.1% and India contributed 8.2%. Furthermore, China and India increased their emissions compared to 2023, while U.S. emissions remained largely unchanged.
China emits a staggering amount of CO2, but has also recently set targets to cut its greenhouse gas emissions. In the U.S., President Donald Trump has signed an executive order to withdraw the U.S. from the 2015 Paris Agreement (for the second time), which is an international treaty that aims to limit global warming. The president has also pledged to “drill, baby, drill” as part of a strategy to expand oil and gas exploration.
Neither the U.S. nor China is doing enough to combat emissions, according to Climate Action Tracker, an independent scientific project monitoring climate action efforts against the previously agreed Paris Agreement targets. Climate Action Tracker currently rates China’s efforts as “highly insufficient” and the U.S.’s efforts as “critically insufficient,” the second-worst and worst ratings, respectively.
Carbon sink feedback
Humans can directly reduce the amount of greenhouse gas in Earth’s atmosphere by burning less fossil fuels, such as oil and natural gas, and limiting other activities that produce emissions. The planet does some of that work for us through carbon sinks, which absorb about half of the total CO2 emitted each year while the rest stays in the atmosphere.
However, these carbon sinks may now be compromised according to the report. As the planet gets hotter, scientists expect sinks like the ocean to absorb less CO2 because gases don’t dissolve as well in warmer waters. This process is known as a positive feedback loop, where warming leads to more warming.
“There is concern that terrestrial and ocean CO2 sinks are becoming less effective, which will increase the amount of CO2 that stays in the atmosphere, thereby accelerating global warming,” Oksana Tarasova, a senior scientific officer at WMO, said in the statement. “Sustained and strengthened greenhouse gas monitoring is critical to understanding these loops.”