Either the entire world is set to experience dramatic additional warming once we stabilise at the current (400+ ppm) CO2 concentration – or we are still dramatically underestimating the local climate sensitivity of the Arctic – a region that might in that case not warm 2 or 3 times as fast as the global average, but rather about 6 to 8 times. (Perhaps most likely it’s something in between.)

In any case, it’s bad news that’s being dredged up from the bottom of Lake El’gygytgyn.

Lake El’gygytgyn and additional Arctic Pleistocene and Pliocene drilling sites. The results of these sediment cores are worrying: the last time the atmosphere had CO2 concentrations around 400ppm, temperatures in the Arctic were about 8 degrees higher. Does this imply there is still a huge amount of global average warming in the pipelines?

Just listen to us. Don’t go hiking in the Siberian Arctic 3.6 million years ago

If you’re the adventurous type and you like the company of sizeable wolf packs for some proper permafrost hiking, we would definitely recommend Chukotka Autonomous Okrug. But we would not advice to go there 3.6 million years ago.

That’s when a huge meteorite blasted an 18 kilometre wide crater in this part of the Siberian Arctic – creating the (in today’s world) ice-covered Lake El’gygytgyn.

Lake El’gygytgyn is special. Although it is close to the Arctic, there are no (high-precipitation) mountain ranges anywhere near, so its surroundings were never covered by an ice sheet. Therefore throughout the 3.6 million years that passed, the lake has been able to very steadily pile up sediment layers at its bottom – establishing a very nice paleoclimate record, that scientists are now drilling for.

The sediments that filled this crater tell us something about the Arctic climate in the times before the onset of the (Pleistocene) ice ages – the warmer Pliocene.

The Pliocene climate analogue. Useful – and worrying

The Pliocene is very interesting for paleoclimate comparisons, because it is recent enough for Earth to have had a very similar appearance, geographically, as today’s world. That means the oceans, the continents and the mountain ranges were about where they are now. That cannot be said of the ice sheets (none on Greenland, none on West Antarctica) – nor the sea levels, that were up to 32 meters higher than they are today.

What was also at a similar levels though, worryingly, was the Pliocene’s CO2 concentration – about as high as it is today (400 ppm, or just over).

So you would expect temperatures in the Pliocene were also as high as they are today?

But they were not. And that’s bad news. We may still be looking way too much at short-term climatic responses – and therefore underestimate the magnitude of the ‘real’ thermal climate inertia, the warming you get once the atmospheric CO2 concentration is stabilised.

We learned from Hansen in Science in 2005 that on a time scale of a couple of decades this ‘warming in the pipeline’ is now likely in the order of 0.6 degrees. That’s bad enough – but something continued ocean CO2 absorption (another inert climate process) could still compensate for – essentially saving us from a runaway warming scenario.

Three Science publications in a row telling us at current CO2 levels there’s more warming to come – if at least there’s truth in paleoclimate

But then there’s this research, performed by a large group of paleoclimatologists led by Julie Brigham-Grette of the University of Massachusetts and Martin Melles of the University of Cologne – that managed to get their findings published twice in Science (2012 and 2013).

Their first publication (that looked at the El’gygytgyn sediment record up to 2.8 million years ago) showed super interglacials in the Pleistocene that were much warmer than thought – with Arctic maximum summer temperatures 4 to 5 degrees higher than today.

Their second publication (that looked at the oldest part of the El’gygytgyn sediment record – between 2.8 and 3.6 million years ago) showed that at current CO2 concentration levels, the Pliocene climate was a lot warmer.

The researchers write the following:

“Evidence from Lake El’gygytgyn, in northeast (NE) Arctic Russia, shows that 3.6 to 3.4 million years ago, summer temperatures were ~8°C warmer than today, when the partial pressure of CO2 was ~400 parts per million.”

Now perhaps most interesting to look at is the question at the top of this article. Do their findings tell us something about (higher than thought) Arctic climate sensitivity – or about (higher than thought) global average climate sensitivity?

In other words: is this paleoclimate lesson a prediction for increased expected Arctic warming – or can we expect a huge additional rise in global temperatures, even if we manage to stabilise atmospheric CO2 concentrations at the current level (404 ppm – so ‘close to’ 400 ppm)?

Paleoclimate research. Let’s just acknowledge it’s work for specialists.

The answer may be provided by yet another Science study, one that was performed by a research group led by the University of Cambridge and published in 2009. That one looked at the middle Miocene – the predecessor of the Pliocene epoch (boundary is at 5.3 million years ago).

These authors write the following:

“The carbon dioxide (CO2) content of the atmosphere has varied cyclically between ~180 and ~280 parts per million by volume over the past 800,000 years, closely coupled with temperature and sea level. For earlier periods in Earth’s history, the partial pressure of CO2 (pCO2) is much less certain, and the relation between pCO2 and climate remains poorly constrained. We use boron/calcium ratios in foraminifera to estimate pCO2 during major climate transitions of the past 20 million years. During the Middle Miocene, when [global average] temperatures were ~3° to 6°C warmer and sea level was 25 to 40 meters higher than at present, pCO2appears to have been similar to modern levels.”

Bad news.

Another important lesson: climate sensitivity increases with warming (skip those Last Glacial Maximum ECS estimates)

We may extent this even further back in Earth’s history, to the Paleocene-Eocene. At the border of these two geological epochs a rapid warming occurred that we wrote about more often here at Bits of Science. It’s called the Paleocene-Eocene Thermal Maximum, and often simply referred to as PETM. PETM is interesting because it was a CO2 and methane-induced warming spike that was in geological terms really rapid (therefore leading to a minor extinction event) – but one that still happened about 10 times slower than the current rise in carbon concentrations.

Now new research, led by Gary Shaffer of the University of Copenhagen, published in Geophysical Research Letters, shows evidence that the CO2 sensitivity of Earth’s climate system may in fact increase with warming.

During the PETM, when temperatures rose by 5-8 degrees in about 10,000 years Earth’s CO2 climate sensitivity rose from 3.3–5.6 to 3.7–6.5 – values that are much higher than today’s most cited numbers (IPCC’s range = 1.5/2-4.5 degrees – most experts say ‘close to or just over 3 degrees’)

This new understanding is important because it implies we may need to look for climate comparisons that are close to today’s average global temperatures – to find the best paleoclimate assessments of climate sensitivity. Ice age estimates, like the much-used Last Glacial Maximum climate sensitivity estimates (ranging between 2 and 3 degrees Celsius) could lead to underestimation of today’s world’s climate sensitivity.

© Rolf Schuttenhelm | www.bitsofscience.org