Atmospheric levels of carbon registered 415 parts per million over the weekend at one of the world’s key measuring stations, a concentration level researchers say has not existed in more than 3 million years—before the dawn of human history.

Taken at the Mauno Loa Observatory in Hawaii by the Scripps Institution of Oceanography, the measure continues the upward trend of atmospheric carbon concentration that lies at the heart of the global warming and climate crisis:.

Meteorologist Eric Holthaus, a journalist who covers the climate crisis for Grist, contextualized the latest readings in a tweet that was shared widely on Sunday:

This is the first time in human history our planet’s atmosphere has had more than 415ppm CO2. Not just in recorded history, not just since the invention of agriculture 10,000 years ago. Since before modern humans existed millions of years ago. We don’t know a planet like this.

One person responded to the Holthaus tweet by asking, “How is this not breaking news on all channels all over the world?”

Rich Pancost, head of the School of Earth Sciences at the University of Bristol in the U.K., said that the best guess of the scientific community is that global atmospheric carbon levels have not been this high for “about 3 millions years . . . maybe more.”

Writing on his Informed Comment blog Monday, historian Juan Cole said that life on Earth in that pre-historic era, known as the Pliocene Period, is not a place humans would recognize:

In the Pliocene, it was much hotter. In the Pliocene, oceans were much higher, maybe 90 feet higher.

That is our fate, folks. That is what 415ppm produces. It is only a matter of time, and some of the sea level rise will come quickly. Amsterdam, New Orleans, Lisbon, Miami – the list of cities that will be submerged is enormous.

Elsewhere online, reaction to the unsettling milestone was met with a mix of frustration, alarm, and fresh demands for urgent action to address the crisis.

Despite the new measurement, it is not as if humanity has not been endlessly warned that this is the path it’s on.

“If the threshold seems unremarkable (it shouldn’t),” wrote Jonathan Shieber at TechCrunch, “it’s yet another indication of the unprecedented territory humanity is now charting as it blazes new trails toward environmental catastrophe.”

While scientists have stated that much of the future warming is already “locked in,” Cole points out that humanity’s main focus must be to make sure all efforts are made to reverse the emissions trend in order to limit the scale of the destruction.

“What can be stopped is its getting any worse,” Cole concluded. “But that would require moving with blinding speed to wind and solar power and electric cars.”

And the message from the global climate justice movement has been crystal clear: It’s an emergency. Act like it.