Atmospheric carbon dioxide measurements from Mauna Loa Observatory last week topped 410 parts per million for the first time in modern history.

That’s up from 280 ppm when measurements began in 1958.

On Tuesday, the reading at Mauna Loa was 410.28 ppm, Climate Central reported. It took 55 years — until 2013 — for the measurement to reach 400 ppm.

“It’s pretty depressing that it’s only a couple of years since the 400 ppm milestone was toppled,” said Gavin Foster, a paleoclimate researcher at the University of Southampton in England. “These milestones are just numbers, but they give us an opportunity to pause and take stock and act as useful yardsticks for comparisons to the geological record.”

CO2 levels fluctuate by season, but the average has risen to form what is known as the Keeling Curve, after the late Charles D. “Dave” Keeling, an atmospheric scientist at Scripps Institution of Oceanography in La Jolla, Calif.

Average carbon dioxide concentrations have skyrocketed over the past two years due in part to natural factors such as El Nino causing more of it to end up in the atmosphere. But it’s mostly driven by the record amounts of carbon dioxide humans are creating by burning fossil fuels, scientists say.

“The rate of increase will go down when emissions decrease,” said Pieter Tans, an atmospheric scientist at the National Oceanic and Atmospheric Administration. “But carbon dioxide will still be going up, albeit more slowly. Only when emissions are cut in half will atmospheric carbon dioxide level off initially.”

The planet has warmed 1.8 degrees Fahrenheit from pre-industrial levels, including a run of 627 months in a row of above-normal heat.