United States scientists documented the highest level of carbon dioxide in the atmosphere in millions of years, at the same time as record wildfires blazed through Canada, lacing the air from the Midwest to the East Coast in a blanket of smoke with enough disease-causing particles to make venturing outside unsafe for people with breathing problems.

Carbon dioxide levels measured at the federal governments Mauna Loa Atmospheric Baseline Observatory in Hawaii reached concentrations of 424 parts per million in May, the month when the heat-trapping gas typically peaks in the Northern Hemisphere.

Thats more than 50% higher than before the industrial era began roughly 250 years ago and 3 parts per million higher than what federal scientists counted in May 2022. It represents the fourth-largest annual increase since the National Oceanic and Atmospheric Administration started its tally 65 years ago. In a separate analysis, the Scripps Institution of Oceanography at the University of California San Diego announced almost identical findings.

The eruption of Mauna Loa volcano on Nov. 29, 2022, buried over a mile of access road and destroyed transmission lines delivering electricity to the observatory campus for 10 days. But NOAA restored its measuring operation with temporary equipment installed on the deck of the University of Hawaiis observatory, located near the summit of the Mauna Kea volcano. Scripps began collecting air samples at Mauna Kea six days later, and resumed sampling at Mauna Loa on March 9.

The University of California researchers collected samples from both Mauna Loa and Mauna Kea every day during May and found nearly identical results: Mauna Loa showed 423.78 parts per million carbon dioxide, Mauna Kea indicated 423.83 parts per million.

While NOAAs satellites monitor wildfire smoke , the carbon concentrations recorded in Hawaii represent centuries of emissions into the atmosphere which have increased dramatically in total annual volume in recent decades. Increasingly catastrophic blazes like those in North America are one of many symptoms of global temperatures rising as increased carbon dioxide traps more of the suns heat within the Earths atmosphere.

The result announced Monday amounts to what the federal research agency called a broken record, an apparent reference to both its unprecedented new height and the routineness with which each passing year brings higher carbon dioxide levels than the previous.

Every year we see carbon dioxide levels in our atmosphere increase as a direct result of human activity, NOAA Administrator Rick Spinrad, a veteran oceanographer whose research received awards from presidents from both parties, said in a statement.