For the layman paleoclimatology is ‘proof’ that any climate change is natural. For educated thinkers the lessons from the long ago contain the biggest warnings for the current artificially created state of our planet.
Yesterday Nature Geoscience brought us another big oops moment. That one climate event that happened really-really fast in geological terms, was still nothing compared to today. And that’s just become twice as clear. We now know the historic mass extinction* happened thanks to not 6 degrees warming over 10.000 years, but 6 degrees warming over 20.000 years.
And the current rise of atmospheric carbon concentrations happens 10 times faster, which means ecosystems, now already under numerous other environmental strains, will have to adapt much faster than they could in prehistoric times, when Earth was lush and green by nature, as things like farmland, highways and business parks still had to be designed, together with CFKs, trawling nets, palm oil plantations and transporting exotic invasive species with tankers and 747 jumbo jets from continent to continent, day in and day out.
But let’s not linger in the present.
[*) The PETM mass extinction shows itself mainly in the marine fossil record, where up to 50% of carbonate-producing benthic foramifera disappeared. Terrestrial life did not suffer an equal blow – like the one that happened at the Cretaceous–Tertiary extinction event, 10 million years earlier – let’s just say dinosaurs can only die out once. Something must have happened on land too though, as the PETM broke an evolutionary deadlock – indeed much like the end of Snowball Earth we reported on last week. This time life on land was again scaled down in size – and that brought a new wave of tiny mini-mammals to lose their shyness and eventually turn in to more recognisable creatures like horses and primates.]
PETM phase one: volcanism? asteroid? – CO2 route likely
Paleoclimatologists are still nor sure what was the initial cause of the Paleocene-Eocene Thermal Maximum, or PETM, some 55.8 million years ago. It may have been immense flood basalts or other fierce volcanism hitting carbon-rich sediments. We do know it wasn’t the Deccan Traps in India though, as these are at least 5 million years too old. It also wasn’t the onset of the Himalayan orogenesis, with the Indian subcontinent sliding under Eurasia, as that happened at least 5 million years later.
We do know something caused the Earth’s atmosphere to warm – and that that something was likely CO2 at first.
PETM phase two: clathrates release lots of methane
As warming set in, the most-feared positive climate feedback system Earth has at its disposal took over: methane clathrates -or gas hydrates- from the ocean floors. It led to enormous amounts of C13-depleted carbon entering the biosphere.
Measuring the isotope ratio of the carbon in fossil sediments dating back to the PETM can tell us something about the speed with which the concentration of greenhouse gases rose.
Older research used deep sea calcium carbonate sediments for this. The marine carbonate environment however changes dramatically and simultaneously with rising CO2 levels – as of course we know because it is also happening right under our noses, today, with ocean acidification. We are now at the level where carbonate formation is being hindered. We may enter a next level, as pH values drop further, where existing carbonate deposits start dissolving in the ocean waters [almost ironically] releasing further CO2 to the water and atmosphere.
It is what happened during the PETM and it is why deep see marine sediments may not present an accurate record of the actual rise in carbon concentrations all these millions of years ago.
New PETM research
That’s why geoscientists of Pennsylvania State University and colleagues from other US and UK universities decided to take a better look at a newly discovered PETM site. Although these rocks are also marine, they were formed in a shallow environment (of the prehistoric Arctic Ocean) were sedimentation happened many times faster, so much more of the carbon was simply locked away – and stored for science.
With help of American, British, Dutch and Norwegian graduate geoscience students, the team drilled for the PETM cores on the island of Spitsbergen, of the Svalbard Archipelago, and closely examined the rock samples.
From this they conclude CO2 levels during the PETM rose over 20,000 years. [On such timescales CO2 is also a direct indication of methane, as methane oxidises to CO2 in the atmosphere – within years usually.]
Lee Kump, one of the authors of the study, warns ecosystems that may have survived PETM-like climate change may not do so now, as the current CO2 rise happens so much faster, as does the current warming – much faster* indeed than the fastest warm-state analogue paleoscience can provide.
[*) The actual current warming may be a staggering 100-200 times as fast as during the PETM. Because we are currently on a path of temperature rise to anywhere from 3 to <insert Mark Lynas' book title> within this century.]
© Rolf Schuttenhelm | www.bitsofscience.org