Global atmospheric carbon dioxide levels unfortunately hit a new milestone last month, having surpassed 430 parts per million (ppm), the highest levels on record since records began 67 years ago, and nearly 54 percent higher than the 280 ppm above the pre-industrial average.

The monthly average CO2 levels recorded for May 2025 at Hawaii’s Mauna Loa Observatory come in at 430.51 ppm, a jump of 3.61 ppm over the 426.90 ppm recorded for May of the previous year. This is a little over 30 percent higher than the 330 ppm when direct measurements of the greenhouse gas were first made at the observatory and 53.75 percent over the pre-industrial average.

These levels far exceed any level of CO2 present in the atmosphere over the past 800,000 years, as directly measured from samples preserved in bubbles trapped in the ice sheets of Antarctica and Greenland, with the previous highest levels spiking to only roughly 300 ppm 330,000 years ago. Today’s levels haven’t been seen in 30 million years, according to Ralph Keeling, a professor of climate sciences at UC San Diego’s Scripps Institution of Oceanography.

“It’s changing so fast,” Keeling remarked in an interview with NBC News. “If humans had evolved in such a high-CO2 world, there would probably be places where we wouldn’t be living now. We probably could have adapted to such a world, but we built our society and a civilization around yesterday’s climate.

“This problem is not going away, and we’re moving further and further into uncharted territory, and almost certainly, very dangerous territory,” Keeling added.

“We know why it’s rising faster than ever, it’s because we’re burning more fossil fuels each year.”

“If we want to actually stabilize CO2 levels in the atmosphere, we would need to cut global emissions by more than 50 percent, and we’re nowhere near doing that,” according to Damon Matthews, a climate scientist at Quebec’s Concordia University.

The month of May typically marks the peak of the seasonal fluctuation of atmospheric CO2 levels, as CO2 absorbing vegetation in the northern hemisphere becomes active after being dormant for the winter.

“Every May, we’re going to see a new record of atmospheric CO2, until we actually make a lot more progress on climate mitigation than we have today,” Matthews added.