Atmospheric CO2 Hits 431 ppm in April 2026, Setting a New Monthly Record, as the Observatory That Measures It Faces Defunding

Overview

Atmospheric carbon dioxide reached 431.12 parts per million at Mauna Loa Observatory in April 2026, according to NOAA’s Global Monitoring Laboratory, setting a new monthly record and extending a decades-long rise that has pushed concentrations to levels not seen in more than two million years, per the UK Met Office’s 2026 CO2 forecast. At the same time, the very station responsible for this record faces possible closure: a White House budget proposal would eliminate all federal funding for NOAA climate research, threatening the continuity of a measurement series that began in 1958.

The Record and What It Means

April 2026’s reading of 431.12 ppm is up 1.48 ppm from April 2025’s monthly average of 429.64 ppm, according to NOAA’s Global Monitoring Laboratory. The seasonal CO2 peak, which typically arrives in April or May as decaying plant matter releases gases across the Northern Hemisphere before the growing season draws concentrations back down, crossed 430 ppm for the first time in May 2025—when Scripps Institution of Oceanography measured a monthly average of 430.2 ppm and NOAA recorded 430.5 ppm. The May 2025 reading represented an increase of 3.5 ppm over May 2024’s 426.7 ppm, according to Scripps.

To put the current level in context: when Charles David Keeling began measurements at Mauna Loa in 1958, the observatory recorded approximately 315 ppm, according to Mongabay. Pre-industrial concentrations stood at 280 ppm or below, according to Scientific American. The UK Met Office forecasts the May 2026 seasonal peak will reach 432.2 ± 0.6 ppm—which, if it occurs, would represent the highest atmospheric CO2 concentration for over 2 million years.

The rate of increase has itself accelerated. The growth rate of atmospheric CO2 averaged 0.86 ppm per year in the 1960s and 2.41 ppm per year in the 2010s, according to the UK Met Office. The actual rate through 2025 was 2.61 ppm per year—well above the 1.33 to 1.79 ppm per year that IPCC scenarios compatible with limiting warming to 1.5°C would require, according to the UK Met Office.

“It’s just another sign that carbon dioxide continues to increase in our atmosphere as our planet continues to warm,” said Zachary Labe, a scientist at Climate Central, as quoted by Scientific American. “For many climate scientists, this is just ‘here it is again, [another record] in the wrong direction,’” Labe added.

Ralph Keeling, director of the Scripps CO2 Program and son of Charles David Keeling who established the measurement series, offered a terse assessment when the May 2025 milestone was recorded: “Another year, another record. It’s sad,” as quoted by Scripps Institution of Oceanography.

Elevated CO2 concentrations trap heat in the atmosphere, altering weather patterns and intensifying extreme events including heat waves, droughts, wildfires, and flooding. Rising concentrations also drive ocean acidification, hindering shell and skeleton formation in marine organisms, according to Scripps Institution of Oceanography.

The Threat to the Observatory

The Trump administration’s fiscal year 2027 budget proposal, presented to Congress in April 2026, would eliminate federal funding for climate research at NOAA entirely. The budget explicitly allocates $0 for climate research, according to Eos, and would terminate the Office of Oceanic and Atmospheric Research—the unit that oversees the Global Monitoring Laboratory and Mauna Loa operations—for the second consecutive year. The proposal would cut more than $1 billion from NOAA programs, a reduction of 26%, and terminate 35 projects and institutes, including the Global Monitoring Laboratory network and 14 climate labs, according to Medill News Service. Over 2,000 full-time NOAA positions would be eliminated, according to Eos.

The operational threat is concrete and near-term. The lease on the supporting laboratory in Hilo, Hawai’i, expires at the end of August 2026, with no funds allocated for renewal or relocation, according to Climate Fact Checks. Staff reductions have already affected greenhouse gas monitoring programs, the same outlet reports.

Mauna Loa Observatory sits at 11,135 feet elevation on Hawai’i’s Big Island, a location chosen because its altitude and distance from major population centers allow it to record baseline atmospheric CO2 with minimal interference from local emission sources, according to Mongabay. The site has produced 70 years of continuous CO2 data since Charles David Keeling’s first systematic measurements in 1958, when the global average stood near 315 ppm, according to Mongabay.

Ralph Keeling has warned that “even short gaps in the record could hinder climate research” and described the situation as “deeply worrying,” according to Climate Fact Checks. He has also stated: “We need to do everything we can do make sure these stations don’t close,” as quoted by Mongabay.

Dan Powers of CO-LABS, a coalition of federally funded laboratories, called the potential closure “surreal and dangerous,” according to Eos. Climate scientist Daniel Swain said it “would involve a wholesale dismantling of entities relevant to weather, climate, & ocean research,” according to Eos.

At a budget hearing on April 29, 2026, NOAA Administrator Neil Jacobs defended the proposal by saying the agency would “transfer a lot of the internal research to the operational offices,” and that “it’s really the extramural research that’s going to be cut,” according to Medill News Service.

Opposition to the cuts crosses party lines. Representative Zoe Lofgren (D-CA) argued that “the mission that you’ve said today is to protect lives and property, and that requires research as well as operational capacity,” according to Medill News Service. Representative Brian Babin (R-TX) opposed eliminating extreme weather warning grants, citing 135 deaths from Texas flooding in July 2025, according to the same outlet. The budget proposal requires Congressional approval to become law, according to Eos.

What We Don’t Know

The May 2026 monthly average for Mauna Loa has not yet been published, as the current month is still in progress. The UK Met Office forecast of 432.2 ppm is a projection with a margin of error of ± 0.6 ppm, not a confirmed measurement. The fate of NOAA’s monitoring network depends on Congressional budget negotiations that remain ongoing. It is not yet clear whether alternative funding mechanisms—from universities, international partners, or private sources—could sustain Mauna Loa operations if federal funding lapses.