One of the most significant contributors to climate change shows no signs of slowing down.

On Tuesday, Hawaii’s Mauna Loa Observatory found that there is now more planet-warming carbon dioxide in the atmosphere than ever previously recorded in human history — more than 410 parts per million. And as the atmosphere continues to trap more heat, Earth’s climate is quickly approaching numbers unseen in the past 50 million years.

This number is likely to increase, since carbon dioxide emissions — a major contributor to climate change, as they block heat from leaving the atmosphere — can take anywhere between 20 and several hundred thousands years to disappear from the planet. So even though global carbon emissions have remained flat for the past three years, those emissions remain extremely difficult to eradicate.

Before the industrial age, carbon dioxide levelled off at about 280 parts per million. But in 2013, the Mauna Loa Observatory found that carbon dioxide levels had permanently surpassed the 400 parts per million mark. Even at the time, that measurement was extraordinary, because the atmosphere hadn’t contained that much carbon dioxide in the past 10 to 15 million years.

More than 195 countries pledged to cut down on their greenhouse gas emissions as part of the Paris climate accords, which aimed to help keep the global temperature from increasing two degrees Celsius — the temperature rise that scientists have long cited as an irreversible tipping point that could potentially leave the planet too hot for human habitation. This new carbon dioxide measurement is not good news for people hoping that effort is working.