Some 420 Climate Facts to Consider on 4/20

We finally did it—we’ve hit 420!

Parts per million, that is. Not to harsh your mellow on today of all days, but there’s more carbon dioxide in the atmosphere now than in any other point in recorded history.

Earlier this month, scientists at Mauna Loa Observatory in Hawaii took a measurement of more than 421.21 ppm of atmospheric carbon—the first time researchers have captured a reading over 420 ppm since record-keeping began. This new record is just the latest in a startlingly steep uptick of atmospheric carbon dioxide over the past several decades. When record-keeping started in the 1950s, measurements averaged around 315 ppm. This month’s record means that we’re halfway to doubling our preindustrial levels of carbon dioxide. Bummer.

On this auspicious day, we’d like for our readers to take a beat to think about what the world was like the last time we hit 420 ppm—it’s pretty wild, dude. Atmospheric carbon was this high more than 3 million years ago, during what is known as the Pliocene epoch, where natural processes led to higher concentrations of carbon dioxide in the atmosphere. Studying this time period could give us hints as to what we’re in store for if we keep pumping carbon dioxide levels up at the rate we’re at.

Research using ice cores suggests that the last time carbon dioxide levels were this high, temperatures around the world were around 12.4 degrees Fahrenheit (8 degrees Celsius) warmer than they are now. The Arctic was almost certainly ice-free in the summers; pollen and plant fossils found in ice core samples suggest that it was lush and forested. I highly recommend Googling some animals of the Pliocene if you’re celebrating 4/20 today. It was an era marked by the existence of megafauna, including wooly mammoths, saber-toothed tigers, giant sloths, and armadillos. Hell yeah.

Because there was less land ice at the poles, scientists think that the oceans could have been as much as 98 feet (30 meters) higher than they are now—which means that most of the major U.S. coastal cities and large chunks of Florida, California, and the Gulf Coast would have been underwater.

The current spike in carbon dioxide doesn’t mean big sloths will emerge in Greenland come this summer. The climate system takes awhile to recalibrate to new carbon dioxide levels. Consider it like eating an edible where the onset takes an hour or two. In Earth time, that hour or two could last decades or even centuries, but make no mistake that the planet is certainly going to be different once the carbon dioxide hits.

If the world keeps warming at this rate, some scientists say that we should look at the Eocene epoch for clues as to what could come, a period when carbon dioxide topped out between 1,000 and 2,000 ppm due to volcanic activity. That era—in much more distant history than the Pliocene, between 55 and 40 million years ago—was marked by even more balmier temperatures and some truly wild imagery. Among the wonders of the Eocene were palm trees growing in Canada, alligators and big-ass turtles swimming around the coast of Greenland, and giant 200-pound (91-kilogram) penguins in Australia. Like I said, when the carbon dioxide hits, it hits.

The Eocene was much warmer than today, and warmer than the Pliocene as well. Temperatures were between 12.2 to 25.2 degrees Fahrenheit (9 to 14 degrees Celsius) higher than they are today. It’s not likely we’ll see those types of conditions in our lifetimes or our grandchildren’s lifetimes. And a lot of bad things would have to happen for carbon dioxide to reach those levels. Still, the fact that we’re even bringing the Eocene into the discussion here speaks to just how much and how quickly we’re pushing the Earth’s limits. It took the Earth literal millions of years to go through these types of climatic shifts; in just a couple of centuries, we seem to be accelerating the car off the cliff.

Anyway, happy 4/20, everyone. Celebrate responsibly (and legally, if you can), remember that the cannabis industry needs a lot of environmental reforms, and don’t think too much about this depressing climate change stuff—that’s for Earth Day.