It’s not every day that a decades-old record gets shattered. Scientists announced this week that in nearly 60 years of monitoring Earth’s climate, never had the amount of carbon dioxide in Earth’s atmosphere been higher than in March 2015.

The latest research from the National Oceanic and Atmospheric Administration says that the average amount of CO2 -- a leading greenhouse gas and the primary driver of global warming -- in the air for that month surpassed 400 parts per million, a benchmark that scientists said they weren’t surprised to reach in the age of climate change.

“It was only a matter of time that we would average 400 parts per million globally,” Pieter Tans, lead scientist of NOAA’s Global Greenhouse Gas Reference Network, said in a statement. “This marks the fact that humans burning fossil fuels have caused global carbon dioxide concentrations to rise more than 120 parts per million since pre-industrial times. Half of that rise has occurred since 1980.”

The air samples were taken from 40 sites around the world, the climate agency says. Previous air measurements have exceeded 400 ppm of CO2, but they were short-lived. In May 2013, scientists announced that global CO2 levels had surpassed the 400-ppm mark for a full 24 hours -- the first time in human history that such a concentration had been reached.

“The last time there has been this much carbon dioxide in the air was 3 million years ago, and the Earth was not a fun place to be,” Fast Company reported that year.

The symbolic milestone is a sign of humans’ continued overuse of fossil fuels, which release huge amounts of C02 into the atmosphere faster than the planet’s carbon sinks -- its oceans and forests -- can handle.