Study: Breaching ‘Carbon Threshold’ Could Trigger Mass Extinction in Oceans

July 25, 2019

MIT scientist Daniel Rothman explains that the earth's oceans may be at the 'precipice of excitation,' due to carbon in the oceans, which would unleash a mass extinction of life

MIT scientist Daniel Rothman explains that the earth's oceans may be at the 'precipice of excitation,' due to carbon in the oceans, which would unleash a mass extinction of life


Study: Breaching “Carbon Threshold” Could Trigger Mass Extinction in Oceans

Story Transcript

DIMITRI LASCARIS This is Dimitri Lascaris reporting for The Real News Network from Montreal, Canada.

According to a new study published this month in the Proceedings of the National Academy of Sciences, the continuous accumulation of carbon dioxide in the planet’s oceans is likely to trigger a chemical reaction in Earth’s carbon cycles similar to those which happened just before past mass extinction events. Daniel Rothman, Professor of Geophysics and Co-Director of the Lorenz Center in MIT’s Department of Earth, Atmospheric and Planetary Sciences, has found that when the rate at which carbon dioxide enters the oceans exceeds a certain threshold, the earth may respond with a runaway cascade of chemical feedbacks. Now here to discuss this study with us is Dr. Rothman himself. He joins us today from Cambridge, Massachusetts. Thank you for coming onto The Real News, Dr. Rothman.

DR. DANIEL ROTHMAN Thanks for inviting me on the program.

DIMITRI LASCARIS So Dr. Rothman, for the laypersons in our audience, could you please break down for us the conclusions you’ve reached? And please talk to us as well about the methodology by which you reached those conclusions.

DR. DANIEL ROTHMAN Sure. The study essentially exists in two parts. The most recent part being published in the PNAS article that you referred to. It began with a purely empirical study of studying all of the past disruptions of the carbon cycle that we can see in the last 540 million years. And from that, a pattern emerged in that there seemed to be on the one hand a, sort of, characteristic disruption. And on the other hand, special disruptions that were exhibiting a faster rate of change— would probably be the best way to put it— and those were associated with mass extinctions. And so, in the present study, in the new study I tried to understand how one might explain that and I was particularly drawn at first to the existence of the characteristic events. Those which are exhibiting serious climate change, but not really mass extinctions.

And the reason I concentrated on those at first was because they comprise about half the database and I’m wondering what makes these special. And something of particular interest became evident and that’s that many of these events exhibit a characteristic rate of change. And that was a bit curious because in looking at the events with a characteristic rate of change, it’s interesting to compare that to the prevailing theories as to what causes these events. There are many, many ideas. I think people think of the mobilization of methane in the atmosphere, changes in carbon burial, volcanism— all sorts of mechanisms have been discussed. And if there is a characteristic rate of change, you would think why would there be, if you have all these multiple possible mechanisms, why would there simply be a characteristic way in which things change?

And so, I decided to look at this from a viewpoint of mathematics, and in particular what’s called dynamical systems theory. And what arises from that kind of study is that it’s possible for the carbon cycle to undergo its own kind of runaway instability. And when it enters into this runaway process, it exhibits a characteristic rate of change because it’s always the carbon cycle which is doing this. It doesn’t really depend on what’s coming from outside. And having reached that level of understanding, I then tried to understand what makes mass extinctions special. And what makes mass extinction special appears to be that these events are not only instigated by some type of runaway process, which I might add is dependent on the exceedance of a threshold in terms of the rate at which carbon is input into the atmosphere and oceans. But it seems to be that there’s even more carbon put into it.

So if you wish, I’ll try to summarize this. There’s a kind of characteristic event which takes place when a sufficient amount of carbon dioxide is put into the atmosphere and oceans at a sufficiently fast rate. And if you put in even more, then you see mass extinctions.

DIMITRI LASCARIS Now I understand that today’s oceans are absorbing carbon far more quickly than they did before the Permian-Triassic extinction in which 90% of life on Earth died out. MIT News quoted you as stating that the planet may now be at the precipice of excitation. In your estimation, if we continue emitting CO2 at current rates, within what timeframe are we likely to exceed that threshold?

DR. DANIEL ROTHMAN So the immediate answer to your question is that there’s a timeframe of on the order of a century, but that there’s something more, something else to discuss here. And you pointed out I think with lot of reason, that the rate at which carbon is entering the oceans today is much faster than we’ve seen before. In fact, it greatly exceeds even the worst-case extinction. However, the carbon is entering the atmosphere today on a century timescale— 200 years if you wish— whereas the carbon entered the atmosphere in past events on timescales of tens of thousands of years. And so, a significant contribution of my study is the ability now to compare what happens at timescales of tens of thousands of years to the processes that occur at timescales of hundreds of years. And the upshot of all this is that for the fast timescales— that is, the short timescales— what matters is how much carbon is put into the system, not how fast it’s occurring. But for the long period events, it’s the rate at which it occurs.

And so, with this insight in hand, we can then address your immediate question that are we going to surpass the threshold. And we can identify the threshold from the historical record. And in doing that, we can then identify what— that is, the slow threshold if you wish— then we can identify what the equivalent fast threshold is. And when we do that, we see that after a certain amount of carbon is added, which is on the order of several hundred gigatons of carbon, three to four hundred gigatons, then we’ll pass that threshold. Now, that will probably occur sometime this century, in the 21st century. And the question is, what happens after that? And the best understanding we have at this point is that it’s a slow process. It’s 10,000-year process because it’s a marine carbon cycle process in which changes occur and it takes a long time to dampen out, but they get bigger and bigger over time, over a long time.

DIMITRI LASCARIS And if we do breach that threshold, what if anything could humanity do to bring the situation under control and restrain temperature increases to manageable levels?

DR. DANIEL ROTHMAN So the threshold is only about the ocean carbon cycle, and effectively what we call ocean acidification. It’s not about temperature changes. On the other hand, temperature changes play a role and they should be studied too. And the short answer to your question, I would say, is we simply need to put less CO2 into the atmosphere, and then therefore less CO2 will go into the oceans. The question of how would we identify whether the threshold is indeed reached, what kinds of problems are occurring— for that, one would need to be monitoring the situation carefully. I can’t stress enough, however, that after the threshold is reached, what happens is that there is a runaway process that’s initiated. But it plays out at a 10,000-year timescale. Whether it can be halted or not is going to depend on how well we understand it. And the first problem at hand is to understand what would happen. And so the paper I just published is our first attempt at trying to do that, but it’s really just a first attempt and there’s a whole lot more work that remains to be done.

DIMITRI LASCARIS We’ve been speaking to Dr. Daniel Rothman of MIT, regarding a new study relating to ocean acidification and the possibility of us reaching an important threshold in CO2 absorption by the oceans. Thank you very much for speaking to us today, Dr. Rothman.

DR. DANIEL ROTHMAN Okay. Thank you for inviting me.

DIMITRI LASCARIS And this is Dimitri Lascaris reporting for The Real News Network.