Those Pesky Savanna Monkeys: The New Large Igneous Province

 

This is the second part of a short series dedicated to the "Savanna Monkeys," aka "homo sapiens". In the previous post, I described how they evolved and how they changed Earth's ecosystem in the process. Here, we take a peek at the future. The monkeys could really do a lot of damage. 

The giant volcanic eruptions called LIPs tend to appear on our planet at intervals of the order of tens or hundreds of million years. They are huge events that cause the melting of the surface of entire continents. The results are devastating: of course, everything organic on the path of the growing lava mass is destroyed and sterilized, but the planet-wide effect of the eruption is even more destructive. LIPs are believed to warm coal beds at sufficiently high temperatures that they catch fire. These enormous fires draw down oxygen from the atmosphere, turning it into CO2. The result is an intense global warming, accompanied by anoxia. In the case of the largest of these events, the End-Permian extinction of some 250 million years ago, the whole biosphere seriously risked being sterilized. Fortunately, it recovered and we are still here, but it was a close call. 

LIPs are believed to be the result of internal movements of the Earth's core. For some reason, giant lava plumes tend to develop and move toward the surface. It is the same mechanism that generates volcanoes, just on a much larger scale. From what we know, LIPs are unpredictable, although they may be correlated to a "blanketing effect" generated by the dance of the continents on Earth's surface. When the continents are clustered together, they tend to warm the mantle below, and that may be the origin of the plume that creates the LIP

Of course, if a LIP were to take place nowadays, the results would be a little catastrophic -- possibly more catastrophic than the fantasy of Hollywood's movie makers can imagine. They have thrown all sorts of disasters at hapless humans, from tsunamis to entire asteroids. But imagine the whole North American continent becoming a red-hot lava basin, well, that's truly catastrophic!

Fortunately, LIPs are slow geological processes and even if there is one more of these events in our future, it won't happen on the time scale of human lifetimes. But that doesn't mean that humans, those pesky Savanna Monkeys, can't do their best to create something similar. And, yes, they are engaged in the remarkable feat of creating a LIP-equivalent by burning huge amounts of organic ("fossil") carbon that had sedimented underground over tens or hundreds of millions of years of biological activity. 

It is remarkable how rapid the monkey LIP has been. Geological LIPs typically span millions of years. The monkey LIP went through its cycle over a few hundred years: we see it developing right now. It will be over when the concentration of fossil carbon stored in the crust will become too low to self-sustain the combustion with atmospheric oxygen. Just like all fires, the great fire of fossil carbon will end when it runs out of fuel, probably less than a century from now. Even in such a short time, the concentration of CO2 is likely to reach, and perhaps exceed, levels never seen after the Eocene, some 50 million years ago. It is not impossible that it could reach more than 1000 parts per million. 

There is always the possibility that such a high carbon concentration in the atmosphere will push Earth over the edge of stability and kill Gaia by overheating the planet. But that's not a very interesting scenario: we all die and that's it. So, let's examine the possibility that the biosphere will survive the great carbon pulse generated by the savanna monkeys. What's going to happen?

The savanna monkeys themselves are likely to be the first victims of the CO2 pulse that they generated. Without the fossil fuels they have come to rely on, their numbers are going to decline very rapidly. From the incredible number of 8 billion individuals, that they recently reached, they are going to return to levels typical of their early savanna ancestors: maybe just a few tens of thousands. Quite possibly, they'll go extinct. In any case, they will hardly be able to keep their habit of razing down entire forests. Without monkeys engaged in the cutting business and with high concentrations of CO2, forests are advantaged over savannas, and they are likely to recolonize the land, and we are going to see again a lush, forested planet (arboreal monkeys will probably survive and thrive). Nevertheless, savannas will not disappear. They are part of the ecosystem, and new megaherbivores feeding on them will evolve in a few hundred thousand years. 

Over deep time, the great cycle of warming and cooling may restart after the monkey LIP is over, just as it did for the "natural" geological LIPs. In a few million years, Earth may be seeing a new cooling cycle that will lead again to a Pleistocene-like series of ice ages. At that point, new savanna monkeys may evolve. They may restart their habit of exterminating the megafauna, burning forests and building things in stone. But they won't have the same abundance of fossil fuel that the monkeys called "Homo sapiens" found when they emerged into the savannas. So, their impact on the ecosystem will be smaller, and they won't be able to create a new monkey-LIP. 

And then what? In deep time, the destiny of Earth is determined by the slowly increasing solar irradiation that is going, eventually, to eliminate all the oxygen from the atmosphere and sterilize the biosphere, maybe in less than a billion years from now. So, we may be seeing more cycles of warming and cooling before Earth's ecosystem collapses. At that point, there will be no more forests, no more animals, and only single-celled life may persist. It has to be. Gaia, poor lady, is doing what she can to keep the biosphere alive, but she is not all-powerful. And not immortal, either. 

Nevertheless, the future is always full of surprises, and you should never underestimate how clever and resourceful Gaia is. Think of how she reacted to the CO2 starvation of the past few tens of millions of years. She came up with not just one, but two brand-new photosynthesis mechanisms designed to operate at low CO2 concentrations: the C4 mechanism typical of grasses, and another one called crassulacean acid metabolism (CAM). To say nothing about how the fungal-plant symbiosis in the rhizosphere has been evolving with new tricks and new mechanisms. You can't imagine what the old lady may concoct in her garage together with her Elf scientists (those who also work part-time for Santa Claus). 

Now, what if Gaia invents something even more radical in terms of photosynthesis? One possibility would be for trees to adopt the C4 mechanism and create new forests that would be more resilient against low CO2 concentrations. But we may think of even more radical innovations. How about a light fixation pathway that doesn't just work with less CO2, but that doesn't even need CO2? That would be nearly miraculous but, remarkably, that pathway exists. And it has been developed exactly by those savanna monkeys who have been tinkering with -- and mainly ruining -- the ecosphere. 

The new photosynthetic pathway doesn't even use carbon molecules but does the trick with solid silicon (the monkeys call it "photovoltaics"). It stores solar energy as excited electrons that can be kept for a long time in the form of reduced metals or other chemical species. The creatures using this mechanism don't need carbon dioxide in the atmosphere, don't need water, and they may get along even without oxygen. What the new creatures can do is hard to imagine for us (although we may try). 

In any case, Gaia is a tough lady, and she may survive much longer than we may imagine, even to a sun hot enough to torch the biosphere to cinders. Forests are Gaia's creatures, and she is benevolent and merciful (not always, though), so she may keep them with her for a long, long time. (and, who knows, she may even spare the savanna monkeys from her wrath!). 

We may be savanna monkeys, but we remain awed by the majesty of forests. The image of a fantasy forest from Hayao Miyazaki's movie, "Mononoke no Hime" resonates a lot with us.

How Gaia Saved the Earth from a Cold Death

 

The Goddess Gaia in the form of the winter deity Khione, daughter of Boreas, the North Wind, and the Athenian princess Oreithyia (image by "Nobody-Important"). 

Earth is a fragile planet and it might freeze to a snowball if not taken care of. So far, the Goddess has done a good job at that but, at least a couple of times during the past few billion years, the Earth actually froze. Might that happen again? It seems that we were close to that just a few tens of thousands of years ago. Now, the problem doesn't exist anymore, with humans pumping zillions of tons of greenhouse gases into the atmosphere. And, who knows? Humans could be the tool used by the Goddess to avoid another "snowball Earth." But now we may have too much of a good thing and the Earth risks boiling. Hopefully, Gaia can take care of that, too.   

It is always amazing to realize how complex is the system that we call the "Ecosphere". And how the system's complexity keeps its parameters within the limits needed for life to exist and prosper. It is the concept of "Gaia" as it was proposed by James Lovelock and Lynn Margulis. The ecosystem is in homeostasis and tends to maintain relatively constant parameters by means of a tangle of internal feedbacks, as all complex adaptive systems ("CAS") do. 

But homeostasis doesn't mean perfect stability. The system's parameters may oscillate - even wildly - before the internal feedbacks can bring them back to the "good" values. Sometimes the system gets close to its limits and it may well be that, at times in its long history, the ecosystem risked going over the edge and then Gaia could "die." This seems to be a common destiny for extrasolar planets, as recently argued by Chopra and Linewaver.

A recent paper by Galbraith and Eggleston on Nature starts from these concepts, noting how the concentration of CO2 in the atmosphere never went below ca. 190 ppm during the past 800,000 years. That happened in correspondence with the lowest temperatures ever observed during that period: the planet was going through a harsh ice age.

This figure from a recent paper by Galbraith and Eggleston on Nature shows an interesting fact: the concentration of CO2 in the atmosphere never went below ca. 190 ppm over the past million years or so. Possibly, it touched the danger limit for the ecosystem to survive. For lower concentrations, plants wouldn't have been able to perform photosynthesis and the biosphere would have largely disappeared.

About these ice ages, there is an interesting point related to the system's feedback. The more ice there is, the more reflective the planet's surface becomes (more exactly, the planetary albedo increases). But, the more reflective the planet's surface is, the cooler the planet becomes. So, we have an enhancing feedback that may transform the whole planet into a single, frozen ball: "snowball earth". It has happened, although possibly not completely, at least twice in the history of Earth. It was during the period we call, appropriately "Cryogenian," from 720 to 635 million years ago. It was not a real "snowball" -- not all of Earth was covered in ice. But what was not under the ice was a frozen desert. To give you some idea of the fascination of this subject, here is an excerpt from the abstract of a paper by Hoffmann et al. on "Science"

"....the small thermal inertia of a globally frozensurface reverses the annual mean tropical atmospheric circulation, producing an equatorial desert and net snow and frost accumulation elsewhere. Oceanic ice thickens, forming a sea glacier that flows gravitationally toward the equator, sustained by the hydrologic cycle and by basal freezing and melting. Tropical ice sheets flow faster as CO2rises but lose mass and become sensitive to orbital changes. Equatorial dust accumulation engenders supraglacial oligotrophic meltwater ecosystems, favorable for cyanobacteria and certain eukaryotes. Meltwater flushing through cracks enables organic burial and submarine deposition of airborne volcanic ash. The sub-glacial ocean is turbulent and well mixed, in response to geothermal heating and heat loss through the icecover, increasing with latitude. Terminal carbonate deposits, unique to Cryogenian glaciations, are products of intense weathering and ocean stratification. "

Can you imagine the Earth in these conditions? A wasteland of dry deserts and ice sheets. At that time, there were no multicellular creatures and life may have survived in hot pockets, maybe volcanic lakes, where it was still possible to find liquid water. 

We may have been dangerously close to a new snowball Earth episode during the past million years or so. Not a trifling matter because today the ecosphere is much more complex than it was at the time of the Cryogenian. A new snowball Earth would likely cause all vertebrate lifeforms to go extinct. It is not just a question of being too cold: the limit of concentration of CO2 that permits plants to perform photosynthesis at a reasonable rate is considered to be around 150 ppm, at least for the most common kind of plants. Under that value, all multicellular plants die, and with them all animal life. Only single-celled creatures could eke out a precarious existence in those conditions. 

But something prevented the ice sheets to expand all the way to envelop the whole Earth and, at the same time, prevented the CO2 concentration to go below 190 ppm. What was that? Several hypotheses are possible. Galbraith and Eggleston favor a biological one, saying that:

In terrestrial ecosystems, carbon fixation by plants is limited by low ambient CO2 (ref. 31). On this basis, ref. 12 proposed that CO2-limitation had significantly reduced plant-mediated silicate weathering during low-CO2 intervals of the past 24 million years, thereby enforcing a lower bound on the ocean–atmosphere carbon inventory over >10^5 yr timescales. Subsequent experiments have been consistent with this ‘carbon starvation’ mechanism, showing reduced weathering by tree-root-associated fungi under low CO2 (ref. 32). Although the feedback on silicate weathering would appear too slow to play a role on the 104 yr timescale of glacial CO2 minima 30, it may be possible that strongly reduced weathering rates lowered ocean alkalinity (thereby decreasing CO2 solubility) on a millennial timescale. Alternatively, reduced photosynthesis rates during the LGM (last glacial maximum) would have slowed the accumulation of terrestrial biomass14, consistent with estimates for lower terrestrial primary production rates33. By slowing the accumulation of carbon in vegetation and soils, this would have provided a stabilizing feedback via an increase of the ocean–atmosphere carbon pool.

Complicated stuff, right? But, basically, the idea is that CO2 is slowly drawn down from the atmosphere by a reaction with rocks (silicates), forming carbonates. This reaction is called "weathering" and it is favored by plants, whose roots provide a good environment for it to take place. Fewer plants, less CO2 drawdown. At the same time, a smaller global biomass means that the quantity of CO2 stored in it becomes lower and this extra carbon most likely ends up in the atmosphere as CO2. So, there are two feedbacks embedded in the system that tend to stabilize its temperature. But, as you may understand from the text by Galbraith and Eggleston, it is even more complicated than this! In any case, these stabilizing geobiological feedbacks oppose the ice/albedo feedback and tend to slow down the glaciation before the two sides of the ice sheet touch each other at the equator. 

But suppose that the Earth really became the snowball that some studies claim to have observed: how did it recover? If it is frozen, it is frozen. Maybe not completely dead, but poor Gaia was reduced to a minor sprite inhabiting hot springs. How could Earth return to the lush ecosphere we are used to?

There is an explanation: it is because volcanoes do not care whether the Earth's surface is frozen or not. They continue pumping CO2 and other greenhouse gases into the atmosphere. Again from Hofmann et al. 

“If a global glaciation were to occur, the rate of silicate weathering should fall very nearly to zero (due to the cessation of nor-mal processes of precipitation, erosion, and runoff), and carbon dioxideshould accumulate in the atmosphere at whatever rate it is releasedfrom volcanoes. Even the present rate of release would yield 1 bar ofcarbon dioxide in only 20 million years. The resultant large green houseeffect should melt the ice cover in a geologically short period of time”[(69), p. 9781]. Because Snowball Earth surface temperatures are below the freezing point of water everywhere, due to high planetary albedo,there is no rain to scrub CO2(insoluble in snow) from the atmosphere."

Note one subtle detail: if temperatures were to go below the freezing point of CO2 (-78 C) even in small regions at the poles, that would form a nearly infinite CO2 sink. And that would be "snowball forever" -- maybe it would have made the Goddess Khione happy, but it didn't happen. Possibly, that was too cold even for a Winter Goddess!

In any case, it seems that CO2 was pumped into the atmosphere by volcanoes, maybe it was the work of the volcanic form of Gaia, the goddess Pele, known for her habit of taking lava showers. 

When the CO2 concentration arrived at levels hundreds of times those of the present-day atmosphere, the result was a cataclysmic rapid collapse of the glaciers and a rise in temperatures. Not only the Earth's ecosystem was saved from a cold death, but it rebounded spectacularly: it was now the time of the "metazoa," the formal term indicate animals. There came the Cenozoic, in which we are still living, with its incredible variety of lifeforms when plants and animals colonized the continental lands. 

You see how the job of Gaia is not so simple. it involves a delicate balance of many factors. Some tend to stabilize the system, while others tend to destabilize it. During the past 15 million years or so, cooling factors took the lead and slowly pushed Earth to lower and lower CO2 concentrations and, with that, lower temperatures.

 Image from Wikipedia Commons. The x scale is in million years from the present. Note the rapid cooling of the past million years or so.

We do not know exactly what caused the cooling, there are several theories. But one thing is sure, Gaia started feeling that it was too cold for her, even in her form of Khiome, goddess of ice. She could die and, this time, perhaps for good. 

(Image source)

So, it became imperative for Gaia to mobilize some of the geosphere carbon and push it into the atmosphere in the form of a greenhouse gas that would warm the Earth back to comfortable temperatures. The Goddess Pele was too slow for that, maybe she is now a little tired after blowing CO2 into the atmosphere for four billion years. So, maybe Gaia thought of a more creative solution. 

Why not use those clever monkeys which had just evolved in Earth's savannas to dig carbon out of Earth's crust, combine it with oxygen, and then pump it back into the atmosphere?  It worked: in just a few hundred years, the monkeys managed to bring back the CO2 concentration to the levels that were typical of Earth as it was a few tens of millions of years ago. 

It may be that, now, Gaia faces the opposite problem: those monkeys have pumped so much CO2 into the atmosphere that now we risk pushing the planet on the opposite side of a climate collapse, to a "hothouse Earth" that might kill the biosphere. Something like that happened with the great extinctions at the end of the Permian and the Cretaceous. Alas, life is difficult, but Gaia can cope. Does that mean getting rid of those pesky carbon-burning monkeys? Maybe. After all, Gaia is a Goddess, she ought to know what she is doing and she has no qualms when it is time to do what's to be done. She can find ways. 

(Image Source)

Forests: do they cool Earth, or do they warm it? A comment by Anastassia Makarieva

 

Anastassia Makarieva, giving a talk. Together with Viktor Gorshkov, she developed some fundamental concepts on the functioning of the ecosphere: the "biotic regulation of the environment" and the "biotic pump." Here, with her permission, I reproduce a message that she sent to a discussion forum on these matters. If you are interested in joining the forum, write me at "ugo.bardi(thingette)unifi.it"

by Anastassia Makarieva

Dear colleagues,

thank you very much for these fascinating discussions. I am learning so much from this group, just to mention a couple of more recent things, thanks Svet for reminding us of those important mice studies, thanks Mihail for the note about agroecology in North Korea and thank you, Christine, for sharing your experiences as a farmer. It is indeed a very hard job, I am no farmer but I lived in the wild where you have to care about most things that are vital, and this job leaves little time for doing science, especially in a cold climate. (you can find some photos here). And I am overwhelmed with more things discussed in the group, trying to catch up, and will write later.

Here I thought that I would share my understanding of whether the forests cool or warm the Earth, I did discuss it a few times so sorry if it is a repetition.

In the review article recently quoted by Ugo, as Mara rightly noted, there is nothing controversial or revolutionary. Everybody knows that when a certain part of solar energy is captured by evaporation, the surface gets locally cooler than in the absence of this process. Just because, by energy conservation, a certain part of solar energy, instead of heating the surface, is spent to extract water vapor molecules from the liquid phase by overcoming intermolecular attraction.

But, importantly, this energy remains in the biosphere -- unlike the part of solar radiation that is reflected back to space by a bright surface.

So, whether the Earth as a whole will get cooler or warmer in the presence of evaporation, will depend on how the biosphere dispenses this latent energy.

Take a look at this figure, above. It shows how condensation occurs in the rising air. The latent heat is released in the upper atmosphere and can radiate to space from those upper layers without interacting with greenhouse absorbers (that are mostly concentrated below). This will serve to cool the planet, by effectively making the planetary greenhouse effect smaller. Once again: a certain share of solar energy will leave the Earth with less interaction with the greenhouse absorbers. It is a cooling effect of evaporation.

Importantly, this effect will be stronger if the warm air spends more time in the upper atmosphere. If it descends shortly after condensation, all latent heat becomes sensible and just warms the surface. But if there is a large-scale circulation pattern with the air traveling thousands of kilometers, the effect will be more pronounced. So the biotic pump circulation will make this effect stronger (more than in a local shower). (*)

But, besides this cooling effect, there are warming effects. One of them is the mere presence of more water vapor in the atmosphere over moist surfaces. Since water vapor is a greenhouse substance, its presence over land increases the concentration of greenhouse absorbers. The share of energy leaving without interacting with them increases, but the total number of molecules increases as well. Which effect will win?

Furthermore, more water vapor and convection mean more clouds. And some of the cloud types warm the Earth. Others cool the Earth. Which will prevail?

These arguments show why the message about cooling by forests will never spring up from global climate models. They are not suitable to estimate whether it exists and how strong it might be.

My personal position is that focusing on cooling or warming is strategically harmful to the forest protection case. What natural forests definitely do is that they minimize the fluctuations of the water cycle, heat waves, droughts, and floods. While these extremes are currently officially attributed to CO2 emissions, it is well-known that this attribution suffers from many problems. I would recommend this short video by Dr. Sabine Hossenfelder https://www.youtube.com/watch?v=KqNHdY90StU on this topic.

So in fact to argue that a particular (LOCAL) heatwave has to do with forest destruction (which is known to severely change LOCAL temperatures) might be much easier and more productive than to argue about the role of forests in global warming or cooling -- where there is no simple argumentation.

So, think how it works now: we have a heatwave, and people are told it is due to CO2 emissions, to cut emissions people use "biofuel" by cutting more forests. With more natural forest loss, the water cycle is further disturbed and we have more heatwaves, which are again attributed to global warming, etc. It is a complex situation.

Anastassia