As CO2 levels hit a new record global high of 405.66 ppm yesterday, I couldn’t help but think that HG Wells could not have imagined a more perilous mechanism for exploring the world’s past.

For when it comes to testing the range of new climate extremes, the present mass burning of fossil fuels is like stepping into a dark time machine. As all that carbon hits the airs and waters, the climate dial spins backward through hundreds of thousands and millions of years. Speeding us on toward the hothouse extinction eras of Earth’s deep history. Now, not only is it driving us on through extreme weather and temperature events not seen in 100, 1,000, 5,000 or even 10,000 years, it is also propelling us toward climate states that haven’t occurred on Earth for ages and ages.

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Ever since 1990, the world has experienced atmospheric CO2 levels in a range that hasn’t been seen since the Pliocene geological epoch. A period of time 2.6 – 5.3 million years ago hosting carbon dioxide levels ranging from 350 to 405 parts per million and global average temperatures that were 2-3 degrees Celsius hotter than 1880s levels. Overall, global sea levels towered about 80 feet higher than those humankind has grown accustomed to.

(Never has the Earth seen a CO2 build-up so rapid as the one produced by the human fossil fuel energy era. Rates of CO2 increase just keep ramping higher ever as the world’s climate sinks appear to be filling up. In this context, 2015 saw the swiftest pace of CO2 rise yet. Warming ocean surface waters can’t absorb as much CO2 as cooler oceans. And a record hot ocean during 2015 contributed to this extreme atmospheric CO2 accumulation. For the whole of the past year, CO2 built up in the atmosphere at a rate of 3.2 parts per million per annum. That’s well above the already raging pace of 2 parts per million average annual accumulation during the decade of the 2000s. Image source: NOAA ESRL.)

If global atmospheric CO2 levels had stabilized in this range, it’s likely that we would have eventually seen climates, temperatures, and sea levels that became more and more like those experienced 2-5 million years ago. A process that would have likely taken centuries to reach a final, far warmer climate state. One in which little to no ice remained upon Greenland or West Antarctica, and one hosting a substantial retreat of coastlines.

From 1990 through 2015, that was our climate context. The new world that was steadily settling into place. One that would eventually assert itself unless atmospheric CO2 levels were somehow drawn down to below 350 parts per million. It was kind of a big deal. Unfortunately, few experts really talked about it.

Exiting the Pliocene

But starting in 2015 and continuing on into 2016 the fossil fuel burning time machine again cranked us back toward hotter, more dangerous times. For during the past two years we began to exceed the maximum CO2 threshold of the Pliocene and we started to enter CO2 ranges that were more typical to those of the Middle Miocene climate epoch of 15 to 17 million years ago.

(Rocketing on past the Pliocene. On February 4 of 2016, a record daily atmospheric CO2 level of 405.66 was recorded at the Mauna Loa Observatory. The Earth hasn’t experienced CO2 levels this high in 15-17 million years. Image source: NOAA ESRL.)

By late April of 2015, as CO2 approached its typical May high point, daily readings had hit a range of 404.9 parts per million — propelling us toward the outside boundary of the Pliocene climate context. For a brief period of 9 months, CO2 retreated back from the Pliocene boundary as spring and summer-time plants in the Northern Hemisphere respired. However, average atmospheric CO2 levels were still ramping higher as a rampant burning of fossil fuels around the world continued. By yesterday, February 4, 2016, daily CO2 levels at the Mauna Loa Observatory had rocketed to 405.66 parts per million. A level well outside the upper range for the Pliocene climate epoch. One more typical for periods seen during the Miocene of 15-17 million years ago.

Entering the Middle Miocene

Unfortunately, this daily Februay peak at 405.66 parts per million is not the end to the current year’s ramp up. Typical atmospheric peaks occur during May. And this year, we are likely to see atmospheric levels hit near a range of 407-409 (estimate revised in March of 2016) parts per million in the weekly and monthly averages over the next few months. Such a range thrusts us solidly out of the Pliocene climate context and well into that of the Miocene.

Though the Middle Miocene was not a hothouse extinction climate, it was one much more foreign to humankind. Back then, only the great apes existed. Our most ancient ancestor, Australopithecus, was still at least 9 million years in the future. It’s fair to say that no human being, or even our closer offshoot relatives, have ever breathed air with the composition that is now entering our lungs. Never lived under the oppressive and intensifying dome of such a great global atmospheric heat forcing.

(We said farewell to the Holocene climate context when CO2 levels rose above 280 parts per million back during the 19th Century. By around 1990, we had begun to enter the Pliocene context, a period occurring 2-5 million years ago. As of 2015, we had begun to exit the Pliocene climate context and enter the Middle Miocene. If current rates of fossil fuel burning or business as usual rates of fossil fuel build-up continue, we will be entering the Ogliocene climate context in about 25 to 50 years. Image source: NOAA ESRL.)

We are now entering a period in which atmospheres are more similar to those seen during the Middle Miocene Climate Optimum — the last time CO2 measures exceeded a threshold of roughly 405 parts per million (see here and here).

The Middle Miocene Climate Optimum of 15-17 million years ago was a radically different world. It hosted an atmosphere in which carbon dioxide levels varied wildly from 300 parts per million to 500 parts per million. Temperatures were between 3 to 5 degrees Celsius hotter than the 19th Century. And sea levels were about 120 to 190 feet higher. During this period, the world was still cooling down from the heat of the Paleocene and Eocene epochs. Carbon was being sequestered. And it was the first time the world broke significantly below a 500 part per million CO2 plateau that had been established during the Oligocene 24 to 33 million years ago.

If CO2 levels remain in this range, these are the temperatures, sea levels, and climate conditions we will transition to and ultimately experience. But time, and fossil fuel burning, is not on our side. For under business as usual fossil fuel burning rates of increase, we could hit the Oligocene threshold within as little as 25-30 years. And even if the current rate of increase were maintained, the Oligocene boundary sits about 5 decades away.

Links:

NOAA ESRL (Please support public, non-special interest based, science like the fantastic and essential work produced by the experts at NOAA.)

The Keeling Curve

Pliocene Climate

Entering the Middle Miocene

Hat tip to Kevin Jones