The Intergovernmental Panel on Climate Change (IPCC) recently warned that the average global temperatures would breach the two degrees Celsius mark by 2100 compared to pre-industrial times.
To understand how quickly the climate can recover from this warming, an international team studied a global temperature rise that occurred 56 million years ago. Their findings show that it took about 20,000 to 50,000 years for the climate to stabilise after the rise of five to eight degrees Celsius. The results were published recently in the journal Science Advances.
About 56 million years ago, our Earth experienced a natural period of global warming triggered by a volcanic eruption. This period was known as the Paleocene-Eocene Thermal Maximum (PETM) and there were huge amounts of carbon dioxide released into the atmosphere. This caused about 8°C surface ocean warming in the high latitudes. Several studies have shown that during this period ocean acidification caused mass extinctions in the deep ocean and there were changes in the biota in the surface ocean.
How did they study what happened millions of years ago?
The team analysed rocks, single-celled marine organisms, clay minerals, and lithium isotopes to decode what happened during the period.
Due to global warming, there would have been weathering of rocks. These dissolving rocks release lithium into surrounding water bodies and by studying the isotopes of lithium we can understand the amount of erosion. Clay minerals from the bottom of the sea were used to study the lithium isotopes stored in water.
“Lithium has the advantage that it is one of the very few elements that is not used by biology or plants at all. So signals from growing or dying plants don’t affect lithium. Also, Lithium isotopes (Li-6 and Li-7) have their relationship (ratio) to each other changed by the weathering process – Li-6 is preferentially retained in clays that form during weathering. So, basically, Li is a tracer that only is affected by weathering and nothing else, which is a great advantage,” explains lead author Philip Pogge von Strandmann in an email to indianexpress.com. He is a Professor in Sedimentary Geochemistry at the Institute of Geosciences, Johannes Gutenberg University, Mainz, Germany.
They also examined planktonic foraminifera or single-celled organisms with calcareous shells that were formed millions of years ago.
So, will our temperature decrease after thousands of years?
Prof. Philip Pogge von Strandmann explains that in terms of stabilisation timing, the difference between the PETM and the present is that the PETM had more warming (up to 8°C) but was slower, but what we’re seeing at the moment is probably 3-4°C (worst case), but much much quicker than the PETM.
He explains that recovery will probably be broadly similar in timing (plus/minus a few thousand years). The findings will hold true only if there is a significant reduction in CO2 release.
When asked if other greenhouse gases can delay our climate stabilisation, he explained: “Methane and nitrous oxide are big problems in the short term, but they don’t stay in the atmosphere as long as CO2. Also, methane is removed from the atmosphere by weathering…If you’re looking at timescales longer than a few hundred years, CO2 is the main player in warming.”
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Prof. Philip Pogge von Strandmann adds that there is a key interest now in studying whether we can use weathering to artificially remove CO2 from the atmosphere on more useful timescales for us. The process is known as ‘enhanced weathering’. “You speed up weathering by grinding up rock into powder (so it weathers faster) and ploughing it into fields, where it should remove CO2 and act as a fertiliser. This is now at the field experiment stage in several places around the world.”
“It will never remove all the CO2 we’re adding to the atmosphere, but if we manage to significantly reduce emissions, processes such as enhanced weathering could remove the rest, and help us with ‘negative emissions’, that is removing more CO2 than we add, and reducing CO2 concentrations,” he explains.