There is more carbon dioxide in Earth’s atmosphere than at any time in the past four million years, as the world’s continued dependence on fossil fuels keeps humanity hurtling toward a “global catastrophe,” officials at the National Oceanic and Atmospheric Administration warned on Friday.

NOAA reports its Mauna Loa Atmospheric Baseline Observatory in Hawaii measured CO2 levels averaging 420.99 parts per million (ppm) in May, an increase of 1.8 ppm over levels at this time last year, while scientists at the San Diego-based Scripps Institute of Oceanography, which also tracks atmospheric CO2, calculated a monthly average of 420.78 ppm.

“The science is irrefutable: humans are altering our climate in ways that our economy and our infrastructure must adapt to,” NOAA Administrator Rick Spinrad said in a statement. “We can see the impacts of climate change around us every day.”

“The relentless increase of carbon dioxide measured at Mauna Loa is a stark reminder that we need to take urgent, serious steps” toward climate resiliency and action, he added.