The truth is, when I was born, atmospheric CO2 levels were around 300 ppm. Today — maybe even this week — will be the last time anyone alive experiences a level below 400 ppm, and no one born in the coming century or even longer will ever see less than 400 ppm again. That is a deep, deep observation, with ramifications for our children and for every future generation. — Peter Gleick during November of 2015

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(NASA model visualization of CO2 in the Earth’s atmosphere. Image source: NASA.)

I just want to take a moment to tell you something that’s pretty important. You are now an alien. You’ve been made an alien by fossil fuel burning. And you’re now living in, breathing, a heat-trapping atmosphere that’s entirely alien to your species. Sometimes races of creatures suffering such habitat changes are capable of surviving the environmental shifts that inevitably occur as a result. Sometimes they are not. But you’ve been placed in this situation now and it’s getting steadily worse.

Big August CO2 Jump Locking 400 ppm In

The August preliminary data are in. And it’s pretty grim. For with a big year-on-year CO2 jump in August, it looks like September of 2016 will be unable to achieve monthly CO2 averages below 400 parts per million. What that means is that the last month below the 400 level was probably October of 2015. So, for almost a year now, we’ve been living in the climate age of 400+, likely never to return to monthly atmospheric CO2 levels in the 300s again during the lifetimes of any of us humans now inhabiting this Earth.

According to NOAA, August CO2 measurements at the Mauna Loa Observatory averaged 402.25 parts per million, which is a big 3.32 parts per million jump over 2015 August readings. Adding this number to previous months, we find that 2016, so far, has seen an average rate of rise of 3.495 parts per million during its first 8 months — significantly ahead of previous annual record rates of rise during 2015 and 1998 (3.05 and 2.93 ppm respectively).

(Two year Keeling Curve trend seems to indicate that it’s unlikely monthly values will fall below 400 parts per million during 2016 and, for all practical purposes, ever again unless some kind of unprecedented change is made to global carbon emissions policies. Image source: The Keeling Curve.)

Such a big August jump makes it highly unlikely that September will average below 400 parts per million due to the fact that monthly drops leading into September typically average around 1.8 ppm CO2. If this trend holds true for 2016, then September will average around 400.5 ppm CO2. And since September typically sees the lowest atmospheric CO2 levels during any given year, the current month is basically the world’s last chance to see a 30 day period that averages below 400 ppm.

Conditions Not Seen in Millions of Years

Atmospheric CO2 levels are now so high that you have to go back about 3 million years into the Pliocene to find similar ranges. During that time, the world was between 2 and 3 degrees Celsius warmer than 1880s temperatures. Oceans were 25 to 75 feet higher and the world was a dramatically different place.

(The age of 400 parts per million CO2 is here. It’s something not seen in about 3 million years. In other words, you’re breathing air right now composed of properties that no homo sapiens sapiens has ever breathed before. Image source: Climate Central.)

But adding in all greenhouse gasses like Nitrogen compounds and Methane resulting from fossil fuel burning (and other human activities) and you end up with a CO2 equivalent in the atmosphere close to 490 parts per million. Such a level of forcing correlates more closely to an even more ancient climate period called the Middle Miocene of about 15 million years ago when global temperatures were between 3 and 4 C warmer than they are today.

As such, crossing the 400 ppm CO2 threshold is not merely symbolic. It is a sign of the increasing likelihood of climate harms to come. And it appears now that we crossed that pass back during October of 2015 — unaware that we’d already entered a tough new climate age.

Links:

NOAA CO2 Trends

The Keeling Curve

Pliocene Climate

Miocene Climate

What Passing Key CO2 Mark Means to Climate Scientists

A Year in the Life of CO2