Climate Links August 2019

Gaia exists! Here is the proof. Ugo Bardi, Cassandra's Legacy. Aug. 4, 2019.

Gaia is neither benevolent nor merciful. She is harsh and ruthless.

Environmentalists are sometimes defined as "Gaia worshippers," a term supposed to be an insult. That's a little strange because most people on this planet openly worship non-existing entities and that doesn't normally make them targets for insults. Maybe it is because there is an important difference, here: Gaia exists. Oh yes, she does exist!

Who or what is Gaia, exactly? The name belongs to an ancient Goddess, but the modern version is something completely different. As you probably know, the term was proposed for the first time by James Lovelock in 1972 and co-developed with Lynn Margulis. As it happens for many innovative ideas, it was the result of a simple observation: if the Sun radiative intensity increases gradually over the eons, how come that the Earth's surface temperature has remained approximately constant over the past 4 billion years or so? There has to be something that keeps it like that and Lovelock proposed that the mechanism was based on regulating the concentration of greenhouse gases, mainly CO2.

So, Gaia is not supposed to be benevolent nor merciful, and not even a Goddess. She is a feedback-driven process: we could say that She is what She is. She is what keeps the biosphere alive. But does She really really exist? Not everyone agrees on this point and entire books have been written to demonstrate that there is no such a thing as "Gaia." Indeed, in the beginning, the idea was mostly qualitative and not proven. Lovelock proposed a clever model called "Daisyworld" that showed how a simple biosphere could control the temperature of a planet. But the Earth's biosphere is not just made out of daisies and something more than that was needed. And, yes, over time proofs have accumulated to show that Gaia is much more than a qualitative hypothesis (or an object of worship by people believing in non-existing beings).

Let me show you some data from a 2017 paper by Foster, Royer, and Lunt that can be seen as the definitive proof of the existence of Gaia, even though they never mention the term. It is not about new discoveries, but it uses available data to look at how CO2 concentrations and sun irradiation varied over the past 400 million years, most of the eon we call the "Phanerozoic." It is somewhat technical, but clearly written and you can follow the argument even if you are not a specialist in atmospheric physics. Here are the main results:

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So, the data are clear: the increasing sun irradiance over the Earth's geological history has been compensated mainly by a declining CO2 concentration that keeps the Earth's temperature nearly constant, although oscillating. And would you believe that this near-perfect compensation occurred by chance? Yes, chance happens, but can it keep happening for 400 million years?

Anyone said "Gaia"? Smile! The Lady is in front of you. She exists and we are lucky that She is what She is. Otherwise, the biosphere would have died long ago, burned or frozen.

At this point, the question is: what mechanism causes the CO2 concentration to decline as solar irradiance increases? And where does the removed CO2 go? Lovelock had proposed that it was just the biosphere that did the job, it seems now that we need a tight coupling of biosphere and geosphere to obtain the effect we see. In part, CO2 is removed from the atmosphere by photosynthesis and then transformed into the inert substance called "kerogen" (the precursor of fossil fuels) that is then buried into the crust. In part, CO2 reacts with silicates in the crust to form solid carbonates. Both reactions are slow and reversible: It is a long story and not everything is known, but things start to make sense.

Now, take a moment to reflect on what you just read. Do you realize the importance of these results? Yes, there are still uncertainties, yes, there are large oscillations. But the data are converging to prove the idea that Lovelock had proposed in 1972: CO2 is the main control of the Earth temperatures. Of course, there are other factors affecting climate: other greenhouse gases, changes of albedo, ocean currents, clouds, atmospheric particulate, orbital and axial oscillations. But they seem to play a minor role at the time scale of an eon.

Now, are events occurring over hundreds of millions of years relevant for us? Absolutely yes. The time scale may change, but the physics remains the same. There is no fiddling, here, with mysterious models. These are experimental data coupled with simple physical principles that have been known and established for at least a century. And we can easily calculate that the forcing that we are creating with our CO2 emissions (at present about 3 W/m2, and rising) is going to have a strong effect on the Earth's temperature.

If we keep going like this, we may well arrive at a total forcing that will propel us to a "hothouse Earth," 10-20 degrees warmer than it is today. It has happened in the remote past, it may well happen again. But it is not the kind of conditions in which humans could survive. Fortunately, we will collapse much before we arrive at emissions sufficient to reach that point and that may limit the damage. Still, what we have done already will cause a remarkable mess.

So, now that we know that Gaia exists, could She come to the rescue? Eventually, She will, but She operates on a time scale that's not the same as for humans. As we saw from the data, Gaia reacts to forcings, but very slowly, She'll fix the damage done by humans, but it will take a few million years. It takes some patience. But plenty of things may happen in the meantime: you never know what an angry Goddess can do.





Breaching a “carbon threshold” could lead to mass extinction. Jennifer Chu, MIT News Office. July 8, 2019.

Carbon dioxide emissions may trigger a reflex in the carbon cycle, with devastating consequences, study finds.

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 pushes past a certain threshold — whether as the result of a sudden burst or a slow, steady influx — the Earth may respond with a runaway cascade of chemical feedbacks, leading to extreme ocean acidification that dramatically amplifies the effects of the original trigger.

This global reflex causes huge changes in the amount of carbon contained in the Earth’s oceans, and geologists can see evidence of these changes in layers of sediments preserved over hundreds of millions of years.

Rothman looked through these geologic records and observed that over the last 540 million years, the ocean’s store of carbon changed abruptly, then recovered, dozens of times in a fashion similar to the abrupt nature of a neuron spike. This “excitation” of the carbon cycle occurred most dramatically near the time of four of the five great mass extinctions in Earth’s history.

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What does this all have to do with our modern-day climate? Today’s oceans are absorbing carbon about an order of magnitude faster than the worst case in the geologic record — the end-Permian extinction. But humans have only been pumping carbon dioxide into the atmosphere for hundreds of years, versus the tens of thousands of years or more that it took for volcanic eruptions or other disturbances to trigger the great environmental disruptions of the past. Might the modern increase of carbon be too brief to excite a major disruption?

According to Rothman, today we are “at the precipice of excitation,” and if it occurs, the resulting spike — as evidenced through ocean acidification, species die-offs, and more — is likely to be similar to past global catastrophes.

“Once we’re over the threshold, how we got there may not matter,” says Rothman, who is publishing his results this week in the Proceedings of the National Academy of Sciences. “Once you get over it, you’re dealing with how the Earth works, and it goes on its own ride.”

Characteristic disruptions of an excitable carbon cycle. Daniel H. Rothman. PNAS. July 23, 2019.

Significance
The great environmental disruptions of the geologic past remain enigmatic. Each one results in a temporary change in the oceans’ store of carbon. Although the causes remain controversial, these changes are typically interpreted as a proportionate response to an external input of carbon. This paper suggests instead that the magnitude of many disruptions is determined not by the strength of external stressors but rather by the carbon cycle’s intrinsic dynamics. Theory and observations indicate that characteristic disruptions are excited by carbon fluxes into the oceans that exceed a threshold. Similar excitations follow influxes that are either intense and brief or weak and long-lived, as long as they exceed the threshold. Mass extinction events are associated with influxes well above the threshold. 

Abstract
The history of the carbon cycle is punctuated by enigmatic transient changes in the ocean’s store of carbon. Mass extinction is always accompanied by such a disruption, but most disruptions are relatively benign. The less calamitous group exhibits a characteristic rate of change whereas greater surges accompany mass extinctions. To better understand these observations, I formulate and analyze a mathematical model that suggests that disruptions are initiated by perturbation of a permanently stable steady state beyond a threshold. The ensuing excitation exhibits the characteristic surge of real disruptions. In this view, the magnitude and timescale of the disruption are properties of the carbon cycle itself rather than its perturbation. Surges associated with mass extinction, however, require additional inputs from external sources such as massive volcanism. Surges are excited when CO2 enters the oceans at a flux that exceeds a threshold. The threshold depends on the duration of the injection. For injections lasting a time ti≳10,000 y in the modern carbon cycle, the threshold flux is constant; for smaller ti, the threshold scales like t−1i. Consequently the unusually strong but geologically brief duration of modern anthropogenic oceanic CO2 uptake is roughly equivalent, in terms of its potential to excite a major disruption, to relatively weak but longer-lived perturbations associated with massive volcanism in the geologic past.