Ancient Climate Change May Help Us Navigate The Climate Emergency Today

Coral bleaching. Scott Reef, April 2016.

As humans continue to burn fossil fuels, more and more carbon is added to our atmosphere which leads to further destabilization of our planet’s climate and weather and adds to an ever-rising average global temperature. The effects are not limited to the Earth’s surface, however. Our oceans play an integral role in the survival of life both on the surface and in the seas. Human-driven climate change affects the seas in a unique way: ocean acidification. And this isn’t the first time they’ve faced this threat. A new study has peered into the ancient past in the hopes of understanding the oceans’ reaction to sudden warming and acidification.

Ocean Acidification

Ocean Atlas 2017, Petra Böckmann/Heinrich Böll Foundation

You might recall from your school days learning about pH scales. All liquids fall on a scale of acidic, neutral, or basic. Battery acid is a 0, highly acidic. Your blood is nearly neutral at 7.4. Bleach and some oven cleaners fall around 13.5, highly basic. Combining liquids or introducing new chemicals to liquids can change the pH level. Life, even the microscopic life within your body, is adapted to survive and function in liquids of a certain pH level. This is also true for the largest liquid bodies we know of: our own oceans. Anthropogenic climate change has already damaged our oceans. Since 1850, studies tell us that the acidity of the oceans has increased as much as 26%.

Wildlife is dying out due to habitat destruction, overhunting, toxic pollution, invasion by alien species and climate change. But the ultimate cause of all of these factors is “human overpopulation and continued population growth, and overconsumption, especially by the rich”, say the scientists, who include Prof Paul Ehrlich, at Stanford University in the US, whose 1968 book The Population Bomb is a seminal, if controversial, work.

Damian Carrington — The Guardian

Often ecosystems are talked about as chains or webs, in this case, it might be better to visualize it as a Jenga tower. If too many blocks are pulled from the tower, eventually it collapses. Two of the lowest blocks on that tower, a foundation without which the rest of the tower cannot hope to stand, are the coral reefs and shelled invertebrates like snails and bivalves that inhabit our ocean.

Ocean acidification has a direct and measurable impact on both coral reefs and shelled organisms. In particular, higher levels of acidity result in thinner shells and weaker coral skeletons. The natural consequence of this weakening includes lower rates of survival for both of these essential groups of life. Should the oceans’ pH level drop too low and grow too acidic, there is the possibility that some organisms will not be able to produce their shells or skeletons properly at all. Worse, it may even prevent algae, responsible for producing 70% of the Earth’s oxygen, from photosynthesizing.

To top it all off, that’s not the only issue endangering our coral reefs. An ocean that is too acidic for these organisms to survive is not equivalent to removing a block from our Jenga tower. It would be like knocking out the entire base. Potential total ecosystem collapse. More names to add to the list of victims of the extinction event we are presently living through.

How Earth Responds to More Carbon

One of the best ways to understand how our oceans will react to rapid increases in carbon and acidity is to learn from history. This isn’t the first time the Earth has grown warmer, nor the first time the ocean has grown more acidic. While in the short term, sudden increases in carbon dioxide can have catastrophic effects on the seas, historically it has not been a death sentence for Earth. Even in the worst known extinction event, the Great Dying, which eliminated 96% of all marine species, Earth recovered, eventually. Ocean acidification played a significant role in the Great Dying.

“Earth’s greatest extinction event happened in a one-two punch 252 million years ago. Research now suggests that the second pulse of extinction, during which nearly all marine species vanished from the planet, happened in the wake of huge volcanic eruptions that spewed out carbon dioxide and made the oceans more acidic.”

Alexandra Witze — Nature

A recent paper published in Science has delved into the ancient past in search of data that will help us make sense of how the Earth recovers from these events. The article researches the fossil and geological records of Earth during the Paleocene-Eocene Thermal Maximum (PETM), a period of time 55 million years ago in which the Earth’s temperature rose unusually quickly and large amounts of carbon were released for reasons we do not fully understand.

In order to properly explain the contents of the paper, below are definitions for some of the many terms that feature prominently in it.

In this paper, the authors studied δ13C (delta-13-C), the isotopic signature of carbon’s two stable isotopes: C-12 and C-13 (C-14 exists but is unstable). Every element has more than one isotope. When an element is described as having two or more isotopes, it means that atoms of the same element possess the same number of protons but a different number of neutrons with their nuclei. Chemically they react similarly, but the atomic mass of one isotope differs from another.

Measuring δ13C is essential to understanding ancient climates; in the fossil record, it serves as an account of the relative ratio of C-13 to C-12 in the environment at a given time. To explain the use of ‘negative’ in this context, Wikipedia states:

“Use of the PDB standard gives most natural material a negative δ13C.[9] A material with a ratio of 0.010743 for example would have a δ13C value of −44‰ from (0.010743/0.01124—1) X 1000″

δ13C — Wikipedia

Large negative carbon isotope excursions (nCIE) like those discussed in this article are best described as episodes of massive carbon release. Measuring δ13C excursions are key in identifying periods of global warming and ocean acidification, as negative excursions in the δ13C records coincide with rising global temperatures and ocean acidity like we see in the Paleocene-Eocene Thermal Maximum.

This latest paper seeks to understand how the Earth reacted to and recovered from the last nCIE, in which they identify deep-sea mixing as playing a crucial role by analyzing shallow marine carbon isotopes in unprecedented resolution using a “novel laser ablation approach” thanks to Environmental Scientific Lasers’ ESL-193 laser system.

Earth’s ecological response to, and eventual recovery from, the PETM may indicate one possible outcome of the modern anthropogenic extinction event. At present, evidence suggests we are living through a new nCIE that will eventually be recorded in the future fossil record and understanding how Earth recovered before may help us find the path to recovery for future generations.

Deep-Sea Mixing

Ultimately, this research did identify a recovery back to background Paleocene levels in the samples they took. This may illustrate the robust nature of our oceans and the climate’s ability to stabilize and even recover from sudden events on a geologic timescale.

Evidence of a transient precursor carbon release(s) has been identified in a few localities, although it remains equivocal whether there is a global signal. Here, we present foraminiferal δ13C records from a marine continental margin section, which reveal a 1.0 to 1.5‰ negative pre-onset excursion (POE), and concomitant rise in sea surface temperature of at least 2°C and a decline in ocean pH. The recovery of both δ13C and pH before the CIE onset and apparent absence of a POE in deep-sea records suggests a rapid (< ocean mixing time scales) carbon release, followed by recovery driven by deep-sea mixing.

Surface ocean warming and acidification driven by rapid carbon release precedes Paleocene-Eocene Thermal Maximum — Science

Deep-sea mixing is one aspect of thermohaline circulation, the process in which ocean waters with varying salinity and temperature intermingle and mix all around the world. This process is integral in the ocean’s role in climate stability, and also acts as a limited buffer to surface climate change by storing atmospheric carbon dioxide, as some of that carbon dioxide is drawn from the atmosphere down into the deep ocean through this mixing process. While this buffer delays disaster for land-based life, the addition of more carbon dioxide to the seas is the driving force behind ocean acidification.


“The capacity of ocean waters to take up surplus anthropogenic CO2 has been decreasing rapidly. This study suggests that the ocean’s “buffer capacity” could decrease by as much as 34 percent from 2000 to 2100 under the Intergovernmental Panel on Climate Change (IPCC) RCP8.5 scenario, which is the highest “Representative Concentration Pathway” of potential greenhouse gas emissions and atmospheric concentration levels through 2100. The rapid decrease in this “buffer capacity” suggests that while the ocean will likely continue to take up more CO2 in the future due to the increasing atmospheric CO2 concentrations, the proportion of anthropogenic carbon dioxide entering the ocean will decrease. The ocean’s role in buffering global climate change will gradually diminish, and ocean acidification could accelerate.”


What Does It Mean For Us?

In the case of Earth’s ancient past, these nCIEs arose due to natural events with a measurable beginning and end. The trouble with adapting this science to modern events is that we don’t know when global emissions will slow down, let alone stop.

If human-driven carbon emissions do eventually cease without triggering further devastating events, this new data could shed light on a possible, eventual path to recovery for the planet. However, such a recovery would still take place over a long period of time, certainly more than a human lifetime, even if we went carbon neutral today. We know when emissions began to increase, but we have little to no way of predicting when or if we will stop.

Despite slightly slowing in 2020 due to the COVID-19 pandemic, the emissions dip has ended. 2022-2023 emissions are still expected to exceed 55 billion tons. While we are coming up with methods of trapping more carbon and reducing emissions, the outlook for Earth is still grim.

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