Atmospheric CO2 Hits 420 ppm, Rises 11% in Just Two Decades

Atmospheric carbon dioxide (CO2) concentrations increased to 420 parts per million (ppm) last year, the 12th year in a row when climate pollution rose by at least 2 ppm, the World Meteorological Organization reports in the latest edition of its annual Greenhouse Gas Bulletin.

The WMO report landed just days after the United Nations Environment Programme’s Emissions Gap Report warned that global greenhouse gas emissions in 2023 had put the Earth on track for 2.6° to 3.1°C average global warming.

The analysis shows CO2 levels rising 11.4% in just 20 years, “committing the planet to rising temperatures for many years to come,” the Geneva-based UN agency says in a release. The Earth last experienced comparable CO2 levels in the atmosphere three to five million years ago, “when the temperature was 2° to 3°C warmer and sea level was 10 to 20 metres higher than now.”

Methane concentrations grew to 1,934 parts per billion last year, and nitrous oxide to 336.9 ppb. Methane is about 84 times more potent a greenhouse gas than CO2 over a 20-year span, while nitrous packs 285 times the warming potential.

“Another year. Another record. This should set alarm bells ringing among decision-makers,” said WMO Secretary-General Celeste Saulo. “These are more than just statistics. Every part per million and every fraction of a degree temperature increase has a real impact on our lives and our planet.”

The WMO says CO2 emissions grew faster last year than in 2022, though more slowly than in the three previous years. Just under half of those emissions remain in the atmosphere, with just over 25% absorbed by the oceans and nearly 30% by land ecosystems.

“We face a potential vicious cycle,” explained WMO Deputy Secretary-General Ko Barrett. “In the near future, climate change itself could cause ecosystems to become larger sources of greenhouse gases. Wildfires could release more carbon emissions into the atmosphere, whilst the warmer ocean might absorb less CO2. Consequently, more CO2 could stay in the atmosphere to accelerate global warming. These climate feedbacks are critical concerns to human society.”

Just days before the WMO release, the latest edition of UNEP’s annual Emissions Gap Report said global greenhouse gas emissions hit another new record last year at 57.1 billion tonnes of carbon dioxide equivalent (CO2e), a 1.3% increase from 2022. On a global scale, the power sector was the biggest climate polluter, at 15.1 gigatonnes, followed by transport at 8.4 Gt, and agriculture and industry at 6.5 Gt each. G20 countries accounted for 77% of global emissions, compared to 5% from Africa and 3% from the world’s 47 least developed countries.

“Every fraction of a degree avoided counts in terms of lives saved, economies protected, damages avoided, biodiversity conserved, and the ability to rapidly bring down any temperature overshoot,” UNEP wrote in a key messaging document that accompanied the release.

But while “it remains technically possible to cut emissions in line with a 1.5°C pathway,” the document added, delivering on that potential “would require immediate global mobilization on a scale and pace only ever seen following a global conflict.”

Cover photo: Maxpixels