The Breathing Goddess: What's Happening to Oxygen in our Atmosphere?

The Goddess herself has created the oxygen she breathes (image by Dezgo.com) 

There is a hugely interesting paper that appeared this year on "Annual Reviews of Earth and Planetary Sciences." It deals with the evolution of oxygen during the Phanerozoic.  The story of the ecosphere is all in there. Unbelievably, some 300 million years ago, the Permian fauna and flora lived in a concentration of oxygen of about 35%, nearly double the current one (about 20%). Even the dinosaurs of the Cretaceous breathed air with about 25%-30% oxygen in it. Ever wondered why the diplodocus was so big? That's one possible reason. 

In comparison, we are oxygen-starved. And we are further reducing the oxygen concentration by burning fossil fuels (it can be observed experimentally). All this may have to do with the different breathing architecture of mammals and birds (aka dinosaurs).

But why these oscillations? They may be the result of geophysical factors. The oxygen concentration in the atmosphere is related to the interplay of carbon sedimentation and sedimented carbon oxidation. The former is mainly due to plate tectonics, the latter to large igneous provinces and similar volcanic events. The winding down of oxygen concentration might be explained by a slowdown of plate tectonics and hence of sedimentation at continental edges, but that's far from being certain. 

I tend to think that it is an indirect result of the sun becoming brighter over the Eons. This increase in irradiation forces the system to reduce the CO2 concentration to keep temperatures within the range needed for life. But that will also indirectly reduce the oxygen concentration because oxygen comes from a photochemical reaction that involves CO2 molecules. Less CO2, less oxygen. And that means we are winding down with the ecosystem complexity: it means, basically, that the biosphere doesn't produce as much oxygen as it used to in earlier times. 

If the oxygen concentration goes below certain limits, metazoa will not be able to survive. In a few tens of millions of years, Earth may have reverted to protozoa only (single-celled creatures), as it had been for more than 2 billion years.

Unless someone starts burning a fraction of the sedimented carbon to increase CO2 concentration AND simultaneously manages to reduce the solar irradiation. Maybe good old Gaia has exactly that in mind!!

https://www.annualreviews.org/doi/full/10.1146/annurev-earth-032320-095425

Plenty of Reasons why we Need More Whales!

 

From Cook et al. 2020

2.2.2.1. Enhanced biodiversity and evolutionary potential

The ES (Eecosystem Services) of enhanced biodiversity and evolutionary potential, and enhanced primary production, are interrelated. Via the supporting ecosystem service of nutrient cycling, through abundant releases of iron from whale faeces and nitrogen from urine and faecal plumes, enhanced primary production occurs, including extended phytoplankton blooms (Lavery et al., 2010; Lundsten et al., 2010; Roman and McCarthy, 2010; Roman et al., 2014). In addition to ocean currents meeting and upwelling, the physical movement of animals in the water column, especially larger animals such as whales, contributes to the wider distribution of nutrients and oxygen in the water, leading to greater primary production (James et al., 2017). Areas rich in primary production also tend to be associated with an abundance of prey, and are thus often more biodiverse. In contrast, marine areas which have suffered losses of great whales have been associated with trophic cascades, leading to the associated stock decline of many other species, such as sea otters, kelp forests and birds of prey (Wilmers et al., 2012; Roman et al., 2014). In addition, the sunken carcasses of great whales, of whale falls, provide an important deep-sea habitat for more than 100 species that may be considered whale-fall specialists (Smith et al., 2019). The loss of these habitats as a result of commercial whaling is likely to have had a big impact on the diversity of whale-fall specialists in areas where whales have been hunted for centuries.

2.2.2.2. Climate regulation (carbon sequestration)

Over their lifetime, whales contribute to the removal of carbon from the atmosphere through the accumulation of large amounts of carbon in their bodies (Smith and Baco, 2003; Roman et al., 2014; James et al., 2017). After death, whales sink to the ocean floor. So-called ‘whale falls’ result in the locking in of organic carbon content on the sea floor. Smith and Baco (2003) reported that the carcass of a 40-tonne grey whale can contribute a level of organic carbon content equivalent to around 2000 years of the background flux. In addition, a study by Pershing et al. (2010) reported that restoring baleen whale stocks to pre-whaling levels would remove 1.6 × 105 tons of carbon each year through whale falls.

Is there enough fossil carbon in the atmosphere to create global warming? Lessons from mistakes, misinterpretations, and propaganda

 

The great holobiont called the "biosphere" continuously exchanges carbon with other parts of the Earth system: the hydrosphere and the geosphere. It is a fascinating section of the science of the atmosphere that, just like all other sections, is subjected to misinterpretations, mistakes, and sheer propaganda,   

Earth's climate is one of the most fascinating fields of study nowadays and if you are interest you can learn something new every time you stumble into a new report. Even the so called "debate," biased as it is, may be useful to learn something not just about climate science, but about human psychology as well. Let see an example starting from a comment that recently appeared on twitter,

"Goggle Bob" defines himself as "Engineer that likes technical financial charting (energy, precious metals, commodities, cryptos); as well, a student of the fiat money system." 

First lesson learned: people will think that something they don't understand is "very good science" if it agrees with their personal biases. 

Now, let's go to the paper by Skrable et al that Google Bob cites. It is not an easy paper to digest, but it is an attempt to quantify the fraction of atmospheric CO2 that's the result of the burning of fossil fuels. It is all wrong, as we'll see in a moment, but it is a good occasion to learn something about atmospheric physics and hydrocarbon dating.

It is all about the "Suess Curve;" proposed by Hans Suess in 1967. The curve is about the fraction of the 14C isotope contained in the atmosphere as a function of time. 14C is an unstable isotope, but it is continuously created in the atmosphere by a reaction of carbon nuclei with cosmic rays, and its concentration can be taken as approximately constant, apart from human perturbations. One of these perturbations is the burning of fossil fuels. Since 14C gradually decays with time, those carbon materials which are not continuously exchanged with the atmosphere tend to lose it. So, fossil hydrocarbons contain essentially zero 14C, and burning them is expected to reduce the fraction of 14C. 

Quantifying this amount is not easy, but the final result is that fossil fuels generated about 75% of the extra 145 ppm (from ca. 280 to 425 ppm) of CO2 relative to pre-industrial times. The rest was generated mainly from deforestation and cement production. Another conclusion is that just about 45% of the carbon generated by fossil fuels remains in the atmosphere right now; the rest is stored somewhere in various reservoirs in the ocean and in the biosphere. This is a story I already knew in its main lines, but the discussion about the paper by Skrable et al. led me to go deeper into the matter. 

Second lesson learned: bad science can lead you to learn some good science. 

Now, let's go into the details. At a first read, the paper by Skrable et al. looks legitimate. For someone like me, not an expert in atmospheric radiochemistry, the way the paper is written seems to make sense: there are estimates, equations, and conclusions, all written in the standard jargon of scientific papers. But the  problem, a big one, is their statements that "the quantity of anthropogenic fossil CO2 in the atmosphere in 2018 represents about 23%  of the total amount of anthropogenic fossil-derived CO2 that had been released to the atmosphere since 1750." They also say that ""the atmospheric concentration, <CF(t)>, of anthropogenic fossil derived CO2 in 2018 is 46.84 ppm." And that "the percentage of the total CO2 due to the use of fossil fuels from 1750 to 2018 increased from 0% in 1750 to 12% in 2018, much too low to be the cause of global warming."  (boldface mine)

You only need to know the basic elements of climate science to understand that the final statement is a flag for something badly wrong. Today, we have about 425 ppm of CO2 in the atmosphere, which is about 145 ppm more than the pre-industrial concentration of 280 ppm. Let's assume that the authors are right in their estimate (47 ppm of CO2 resulting from fossil fuels). It means that there are about 100 ppm of extra CO2 in the atmosphere that are NOT the result of fossil fuel burning. And where does this huge amount of carbon come from? 

You would have to think that the total ca. 300 ppm of CO2 emitted by the burning of fossil fuels was almost wholly absorbed by the reservoirs. And not only that: this CO2 must have triggered a huge release of carbon that had been stored in some surface reservoirs for a short time. Otherwise, it would be depleted in 14C and indistinguishable from fossil carbon. Difficult to believe, but even if it were true, the current CO2 excess would still be an indirect result of hydrocarbon burning. No matter how you see it, the statement that "the total CO2 due to the use of fossil fuels ... is much too low to be the cause of global warming." simply makes no sense. It is not a specific isotope of carbon that generates warming; it is the total amount. 

From this, the authors do much worse when they state that "unsupported conclusions of the dominance of the anthropogenic fossil component of CO2 and concerns of its effect on climate change and global warming have severe potential societal implications that press the need for very costly remedial actions that may be misdirected, presently unnecessary, and ineffective in curbing global warming." In Italy we have a way of defining this kind of statements as "peeing outside the pot," and I think you understand what it means. 

Third lesson learned: bad scientific papers can often be identified by their politically-oriented statements.

So, what was actually wrong with Skrab's paper? Examining in detail a scientific paper dense with equations, numbers, and tables is a lot of work (and, in Italian, we have a principle describing how unrewarding it is, but I won't report it here because it uses scatologic terms). In this case, though, there is a crystal clear explanation provided by Andrews and Tans that highlights the trivial mistakes that Skrab et al. made. 

Without going into the details, the main mistake in Skrab's paper was to neglect the effect of nuclear explosions in creating an extra amount 14C, thus giving the impression that the fraction of fossil carbon in the atmosphere is lower than what it actually is. It is more complicated than that, but it is enough to pinpoint the most glaring mistake in the story. 

Fourth lesson learned: a good rebuttal to a bad paper can teach you a lot!

Now, how can it be that a group of scientists with a good reputation in their field choose to deal with a subject they are not familiar with and end up making fools of themselves? It may happen that a scientific revolution comes from newcomers in the field; for instance, when Galileo showed that planets couldn't possibly move because they were pushed by angels, he made a fundamental contribution to a field that wasn't his; theology. But that's rare. Making a fool of oneself is much more common. It could be easily avoided with a minimum of humility: before publishing your paper, why don't you submit it first to the experts in the field? That doesn't mean that the experts are always right, but they can point at the mistakes that you may well make if you are an amateur. Nevertheless, it happens all the time.

Fifth lesson learned: scientists can be blinded by their preconceived ideas just like everyone else. 

To conclude, as you may have imagined, the statement that "the total CO2 due to the use of fossil fuels ... is much too low to be the cause of global warming." is making the rounds on Social Media, being reported by people who made no effort to understand why it was uttered, nor why it is wrong. And so it goes

Sixth (and final) lesson learned: Politics always trumps science in the debate.  

Is Gaia going to die of heat stroke?

 

Figure from the recent paper by Duffy et al. on "Science"

What is the maximum temperature that the Earth's Holobiont (aka "Gaia") can withstand before collapsing? Some data from a recent paper in "Science" indicate that we are not so close to the "Venus scenario" that would sterilize our planet. Nevertheless, the system is under stress

As you see in the figure at the beginning of the post, the optimal average temperature of planet Earth for the standard C3 photosynthesis (that of trees) is around 16 C, not far from the current value of around 18 C. (note that the graph takes into account not just temperature, but CO2 concentrations, supposed to be affecting temperature). Switching to the C4 mechanism (grass and others) moves the maximum to about 28 C;  10 degrees higher than it is now. 

So, we have a comfortable range in terms of plant life, and consider that the "zero" in the curve doesn't mean that all plants die; just that they are less efficient, especially in the hot equatorial zones. Note also how the "respiration" curve keeps growing as a function of temperatures; in the paper, they say that it keeps growing up to 60-70 C. 

Complicated story, but in any case, Gaia is not going to die soon. Note that during the Eocene, some 56 million years ago, the Earth's temperature was indeed some 8-10 degrees higher than it is now, and the planet was covered with lush forests. It is believed that C4 photosynthesis didn't appear on Earth before 35 million years ago. So, even an extra 10 C of warming will not destroy the biosphere: Gaia has a thick skin.

Eventually, the increasing solar irradiation will kill the Great Earth Holobiont but, hopefully, that will take a few hundred million years (at least). About humans, though.... well, it is another story. Do we still have a few decades left? Maybe. 

Flying Rivers, the Biotic pump, and the Consequences of Deforestation

A talk given a few years ago by Anastassia Makarieva where she focuses on the concept of "biotic pump" a fundamental concept of the biotic regulation of the ecosphere, part of the general concept of "Planetary Holobiont." She will update her results in a Webinar to be held on Jan 2nd, 2023. You can register at

https://tum-conf.zoom.us/webinar/register/5016722254879/WN_tDztF8fJSrGWOJLaYv5B2Q

Reality is real no more. Whom to trust in science?

 

The "World Climate Declaration" returns. It is a document that has been around in various forms since 2009 that has all the appearance of "legitimate" science. It is not, but how to judge? We face an unsolvable epistemological problem.

Recently, one of the members of the Holobiont Group posted the link to a document titled "There is No Climate Emergency" on FB. He defined it as "bonkers" -- it was clearly irony. Yet, Facebook's Fact-Checkers don't know irony, and the post was promptly censored and branded "false information."

That highlights, I think, the problem we have with science. Place yourself in the shoes of a person who has no training in science, and knows only what can be read in the media about climate. What should she think about this story? 

We have a document that, at first sight, it looks legitimate. The signatories are bona fide scientists, although one may notice that some of them are a little old (actually, more than a little) (*). But being over 90 does not mean being automatically wrong. And what to say about the anonymous "fact checker" who so peremptorily deemed the document to be "false"? The link provides leads only to a post in Croatian, written by a young lady named Melita Vrsaljiko (https://www.linkedin.com/in/melita-vrsaljko/). She has a degree in journalism awarded by the Faculty of Political Science in Zagreb. Probably she is the "fact checker" hired by Facebook who struck down the post. If this is the case, one could reasonably be a little vary of a fact check based on something written by the fact-checker alone. 

Machine-translated into English, the "fact check" is not much better than the documents it purports to check. Among other things, we are told the document is "false" because it was diffused also by a site that diffuses "anti-vaxxer" information. And also because only a few of the signatories are climatologists. The accusation of the authors not being climatologists is a little perplexing since it comes from someone who has no other qualifications than a degree in journalism. (**)

The problem, here, is that when we deal with climate change, most of us, even scientists competent in our fields, are unable to comprehend the immense complexity of the story. The only way that people can do that is based on the principle of authority. But are 1200 old scientists signing a document titled "There is no Climate Emergency" a sufficient authority? Or you'd rather trust the large number of scientists who adhere to the IPCC (I don't know how many, but surely many). But truth, as we all know, is not based on the majority of believers and from the time when Karl Rove said that "we create our own reality, reality has ceased to be real. So, why should trust FB's fact checkers? Or anyone else?  

This is just not possible. We cannot do science in this way. We need to rethink the whole idea. You may think that I am a little manic (probably I am), but I think we should apply the concept of holobiont to science, too. Maybe we could think of a "horizontal" science, where facts and ideas are shared among peers, that is all of us. That is they do not arrive from the sky, screaming, "trust me, I am Science!!!" They come from our peers, whom we trust. Science cannot come as a revealed trust. It must come from all of us. 

We keep at it. Onward, fellow holobionts!

(*) The Nobel prize at the top of the list is 93. The Italian member of the group (Prof. Zichichi) is 92. About this Italian member, I can tell you that he has made a fool of himself in public so many times that there is an entire popular literature dedicated to his mistakes (for those of you who can read Italian, there is a popular term "Zichicche," not literally translatable, but more or less meaning "Zichichi's gems" -- intended as howlers). On this, though, I can tell you that I have no respect for the people who have made money and a reputation for themselves by selling books that ridicule a scientist who, with all his idiosyncrasies and naivety, has some merits.

(**) I am not criticizing Ms. Vrsaljiko. She did her best, and her article is good in many respects. But the task she was charged with was basically impossible. 

The epidemic of obesity keeps getting worse. What's a good holobiont supposed to do?

 

The obesity epidemic keeps expanding. The above are, I believe, the most recent data available for the US. The COVID-19 lockdowns and isolation measures are reported having made things even worse. This trend is simply horrendous: what the heck is happening to humankind? (Disclaimer: I am not a nutritionist, I am just someone who is fascinated by data and trends. And, of course, we are all interested in our health! Here, I report some data I found, hoping you may find them useful. Don't take them as the last word on the subject. As always, before acting on things that affect your health, do your own search and use your judgement about what works for you.)

The obesity epidemics had a considerable boost by the lockdowns during the Covid-19 pandemic. Coupled with the opposite effect, that obesity is a risk factor for people who contract Covid, you have a remarkable disaster in the making. With several Western countries having percentages of obese people close to or higher than 50%, one wonders what's going to happen in the future. Why are the human holobionts in such a poor shape?

The story is complicated, and I don't pretend to say anything new. I just want to attract your attention to some recent studies that I think shed some light on the mechanism of human obesity (but even our fellow dog holobionts are suffering from obesity). 

First, the work by Raubenheimer and Simpson on the food preference of various animals, summarized in a recent book titled, "Eat like the Animals." (Mariner Books, 2021). Their discovery is easy to summarize: it seems that most living beings have a specific set point in their needs for the main nutrients. They seek for a specific balance among proteins, fats, and carbohydrates. In particular, they aim at a minimum intake of protein. If animals are fed an unbalanced diet, for instance, poor in protein, they will tend to eat more food until they reach the right level. Raubenheimer and Simpson call this the "protein leverage hypothesis:" 

"In a protein-poor but energy-rich food environment, humans will overeat carbs and fats to try to reach their protein target. However, when the only available diet is rich in protein, human will underconsume carbs and fats"

Since excess carbohydrates are stored in the body as fat, we can say that one of the causes of the obesity pandemic is that the human diet in Western countries is overstocked in carbohydrates. 

Here comes Robert Lustig and his book "Metabolical" (Yellow Kite 2021) where he minces no words on how this is not only true but also a profitable strategy for the food industry. They discovered long ago that if they put more and more carbohydrates (sugars) in the food they sell, then people will get fat, they will eat more, and that will increase their profits. Just like sick people are a boon for medical doctors, obese people are a boon for food producers. 

You don't believe that? Let me show you a picture I took a few days ago in an Italian supermarket:

There are four kinds of regular mayonnaise on sale, plus a fancy one with no eggs. Can you guess which is the only one that does not contain added carbohydrates? Let me tell you, it is the most expensive one among the regular ones. All the others contain sugar. Maybe it is not the same for all mayonnaise brands on the market, but I think it is significant. Food companies do add sugar everywhere, even when it is not called for by the traditional recipes. They deny that, but it is written on the list of the ingredients (I have pictures, if you don't believe me!)

Now, it may well be that there is much more to obesity than just carbohydrates, but I think that these results point at an important cause of the problem. There are data showing that what we are seeing may be a delayed effect of "peak sugar" that occurred around the year 2000. From then on, the amount of sugar consumed in the U.S. has been going slightly down. But it remains high. 

The beauty of this is that, if it is true, with obesity we don't have such a wicked problem as others, say, global warming. We know that to avoid global warming, we should stop burning hydrocarbons, but it is also true that we can't just stop: billions of people would die. But we could stop, or at least strongly reduce, the extra carbohydrates added to processed food, and we could do it today. Nobody would die, but the problem would be eased and many people would be healthier! But this is the way things are in the world: no problem can ever be solved when there is somebody making money if it remains unsolved. 

To make you happier, let me show you some data that tell us that a little excess weight (a little!) is not necessarily bad for your organism. Here are some data from Malcolm Kendrick's wonderful book "The Clot Thickens" (Columbus 2021). 

BMI stands for "Body Mass Index" and the overall lowest risk of death is for a BMI of 25-30 that's normally classified as "overweight" (if you want to know, I am at BMI=27). Being underweight is a larger risk than being obese! But obesity has many other problems, not least in terms of self-esteem. 

In the end, remember that you are a holobiont and that for hundreds of millions of years your holobiont ancestors never ate anything that was processed in an industrial plant. You are a fine-tuned machine that includes trillions of friendly viruses and bacteria living in your guts. They want a balanced diet of fats, protein, fiber, and not too much in terms of carbohydrates (but you need them, too!). Try to make them happy, and you'll be happier, too!

When the Ice Will be Gone: The Greatest Change Seen on Earth in 30 Million Years.

 

 

An image from the 2006 movie "The Meltdown," the second of the "Ice Ages" series. These movies attempted to present a picture of Earth during the Pleistocene. Of course, they were not supposed to be paleontology classes, but they did show the megafauna of the time (mammoths, sabertooth tigers, and others) and the persistent ice, as you see in the figure. The plot of "The Meltdown" was based on a real event: the breakdown of the ice dam that kept the Lake Agassiz bonded inside the great glaciers of the Laurentide, in the North American continent. When the dam broke, some 15,000 years ago, the lake flowed into the sea in a giant flood that changed Earth's climate for more than a thousand years. So, the concept of ice ages as related to climate change is penetrating the human memesphere. It is strange that it is happening just when the human activity is pushing the ecosystem back to a pre-glacial period. If it happens, it will be the greatest change seen on Earth in 30 million years

 

We all know that there is permanent ice at Earth's poles: it forms glaciers and it covers huge areas of the sea. But is it there by chance, or is it functional in some way to Earth's ecosphere? 

Perhaps the first to ask this question was James Lovelock, the proposer (together with Lynn Margulis) of the concept of "Gaia" -- the name for the great holobiont that regulates the planetary ecosystem. Lovelock has always been a creative person and in his book "Gaia: A New Look at Life on Earth"  (1979) he reversed the conventional view of ice as a negative entity. Instead, he proposed that the permanent ice at the poles was part of the planetary homeostasis, actually optimizing the functioning of the ecosphere. 

Lovelock was perhaps influenced by the idea that the efficiency of a thermal engine is directly proportional to the temperature differences that a circulating fluid encounters. It may make sense: permanent ice creates large temperature difference between the poles and the equator and, as a consequence, winds and ocean currents are stronger, and the "pumps" that bring nutrients everywhere sustain more life. Unfortunately, this idea is probably wrong, but Lovelock has the merit to have opened the lid on a set of deep questions on the role of permanent ice in the ecosystem. What do we know about this matter?

It took some time for our ancestors to realize that permanent ice existed in large amounts in the high latitude regions. The first who saw the Northern ice sheet was probably Eric the Red, the Norwegian adventurer, when he traveled to Greenland around the year 1000. But he had no way to know the true extent of the inland ice, and he didn't report about them.

The first report I could find on Greenland's ice sheet is the 1820 "History Of Greenland", a translation of an earlier report (1757) in German by David Crantz, where you can find descriptions of the ice-covered inland mountains. By the early 20th century, the maps clearly showed Greenland as fully ice-covered. About Antarctica, by the end of the 19th century, it was known that it was also fully covered with a thick ice sheet. 

Earlier on, in the mid 19th century, Louis Agassiz had proposed a truly revolutionary idea: that of the ice age. According to Agassiz, in ancient times, much of Northern Europe and North America were covered with thick ice sheets. Gradually, it became clear that there had not been just one ice age, but several, coming and going in cycles. In 1930, Milutin Milankovich proposed that these cycles were linked to periodic variations in the insulation of the Northern Hemisphere, in turn caused by cycles in Earth's motion. For nearly a million years, Earth was a sort of giant pendulum in terms of the extent of the ice sheet. 

The 2006 movie "An inconvenient truth" was the first time when these discoveries were presented to the general public. Here we see Al Gore showing the temperature data of the past half million years.

An even more radical idea about ice ages appeared in 1992 when Joseph Kirkschvink proposed the concept of "Snowball Earth." The idea is that Earth was fully covered by ice at some moment around 700-600 million years ago, the period appropriately called "Cryogenian."

This super-ice age is still controversial: it will never be possible to prove that every square kilometer of the planet was under ice and there is some evidence that it was not the case. But, surely, we are dealing with a cooling phase much heavier than anything seen during relatively recent geological times.

While more ice ages were discovered, it was also clear that Earth was ice-free for most of its long existence. Our times, with permanent ice at the poles, are rather exceptional. Let's take a look at the temperatures of the past 65 million years (the "Cenozoic"). See this remarkable image (click to see it in high resolution)

At the beginning of the Cenozoic, Earth was still reeling after the great disaster of the end of the Mesozoic, the one that led to the disappearance of the dinosaurs (by the way, almost certainly not related to an asteroidal impact). But, from 50 million years ago onward, the trend has been constant: cooling. 

The Earth is now some 12 degrees centigrade colder than it was during the "warmhouse" of the Eocene. It was still ice-free up to about 35 million years ago but, gradually, permanent ice started accumulating, first in the Southern hemisphere, then in the Northern one. During the Cenozoic, Earth never was so cold as it is now.

The reasons for the gradual cooling are being debated, but the simplest explanation is that it is due to the gradual decline of CO2 concentrations in the atmosphere over the whole period. That, in turn, may be caused to a slowdown of the outgassing of carbon from Earth's interior. Maybe Earth is just becoming a little older and colder, and so less active in terms of volcanoes and similar phenomena. There are other explanations, including the collision of India with Central Asia and the rise of the Himalaya that caused a drawdown of CO2 generated by the erosion of silicates. But it is a hugely complicated story and let's not go into the details.

Let's go back to our times. Probably you heard how, just a few decades ago, those silly scientists were predicting that we would go back to an ice age. That's an exaggeration -- there never was such a claim in the scientific literature. But it is true that the idea of a new ice age was floating in the memesphere, and for good reasons: if the Earth had seen ice ages in the past, why not a new one? Look at these data:

These are temperatures and CO2 concentrations from the Vostok ice cores, in Antarctica (you may have seen these data in Al Gore's movie). They describe the glacial cycles of the past 400,000 years. Without going into the details of what causes the cycles (solar irradiation cycles trigger them, but do not cause them), you may note how low we went in both temperatures and CO2 concentrations at the coldest moments of the past ice ages. The latest ice age was especially cold and associated with very low CO2 concentrations. 

Was Earth poised to slide down to another "snowball" condition? It cannot be excluded. What we know for sure is that during the past million years or so, the Earth tethered close to the snowball catastrophe every 100,000 years or so. What saved it from sliding all the way into an icy death?

There are several factors that may have stopped the ice from expanding all the way to the equator. For one thing, the sun irradiation is today about 7% larger than it was at the time of the last snowball episode, during the Cryogenian. But that may not have been enough. Another factor was that the cold and the low CO2 concentrations may have led to a weakening -- or even to a stop -- of the biological pump in the oceans and of the biotic pump on land. Both these pumps cycle water and nutrients, keeping the biosphere alive and well. Their near disappearance may have caused a general loss of activity of the biosphere and, hence, the loss of one of the mechanisms that removes CO2 from the atmosphere. So, CO2 concentrations increased as a result of geological emissions. Note how, in the figure, the CO2 concentration and temperatures are perfectly superimposable: the reaction of the temperature to the CO2 increase was instantaneous on a geological time scale. Another factor may have been the desertification of the land that led to an increase in atmospheric dust that landed on the top of the glaciers. That lowered the albedo (the reflected fraction of light) of the system and led to a new warming phase. A very complicated story that is still being unraveled. But how close was the biosphere to total disaster? We will never know.

What we know is that, 20 thousand years ago, the atmosphere contained just 180 parts per million (ppm) of CO2 (today, we are at 410 ppm). That was close to the survival limit of green plants and there is evidence of extensive desertification during these periods. Life was hard for the biosphere during the recent ice ages, although not so bad as in the Cryogenian. Lovelock's idea that permanent ice at the poles is good for life just doesn't seem to be right.

Of course, the idea that we could go back to a new ice age was legitimate in the 1950s, not anymore as we understand the role of human activities on climate. Some people maintain that it was a good thing that humans started burning fossil hydrocarbons since that "saved us from a new ice age." Maybe, but this is a classic case of too much of a good thing. We are pumping so much CO2 into the atmosphere that our problem is now the opposite: we are not facing an "icehouse Earth" but a "warmhouse" or even a "hothouse" Earth. 

A "hothouse Earth" would be a true disaster since it was the main cause of the mass extinctions that took place in the remote past of our planet. Mainly, the hothouse episodes were the result of outbursts of CO2 generated by the enormous volcanic eruptions called "large igneous provinces." In principle, human emissions can't even remotely match these events. According to some calculations, we would need to keep burning fossil fuels for 500 years at the current rates to create a hothouse like the one that killed the dinosaurs (but, there is always that detail that non linear systems always surprise you . . .)

Still, considering feedback effects such as the release of methane buried in the permafrost, it is perfectly possible that human emissions could bring CO2 concentrations in the atmosphere at levels of the order of 600-800 ppm, or even more, comparable to those of the Eocene, when temperatures were 12 degrees higher than they are now. We may reach the condition called, sometimes, "warmhouse Earth."

From the human viewpoint, it would be a disaster. If the change were to occur in a relatively short time, say, of the order of a few centuries, the human civilization is probably toast. We are not equipped to cope with this kind of change. Just think of what happened some 14,500 years ago, when the great Laurentide ice sheet in North America fragmented and collapsed. (image source) (the 2006 movie "Meltdown" was inspired exactly by this event). Earth's climate went through a series of cold and warm spells that is hard to think we could survive. 

 

Human survival concerns are legitimate, but probably irrelevant in the greater scheme of things. If we go back to the Eocene, the ecosystem would take a big hit during the transition, but it would survive and then adapt to the new conditions. In terms of life, the Eocene has been described as "luxuriant." With plenty of CO2 in the atmosphere, forests were thriving and, probably, the biotic pump provided abundant water everywhere inland, even though the temperatures were relatively uniform at different latitudes. A possible mental model for that period is the modern tropical forests of Central Africa or Indonesia. We don't have data that would allow us to compare Earth's productivity today with that of the Eocene, but we can't exclude that the Eocene was more productive in terms of life. Humans might well adapt to this new world, although their survival during the transition is by no means guaranteed. 

Again, it seems that Lovelock was wrong when he said that ice ages optimize the functioning of the biosphere. But maybe there is more to this idea. At least for one thing, ice ages have a good effect on life. Take a look at this image that summarizes the main ice ages of Earth's long history

 (image source)

The interesting point is that ice ages seem to occur just before major transitions in the evolutionary history of Earth. We don't know much about the Huronian ice age, but it occurred just at the boundary of the Archean and the Proterozoic, at the time of the appearance of the Eucaryotes. Then, the Cryogenian preceded the Ediacaran period and the appearance of multicellular life that colonized the land. Finally, even the evolution of the Homo Sapiens species may be related to the most recent ice age cycle. With the cooling of the planet and the reduction of the extent of forested areas, our ancestors were forced to leave the comfortable forests where they had lived up to then and take up a more dangerous lifestyle in the savannas. And you know what it led to!

So, maybe there is something good in ice ages and, after all, James Lovelock's intuition may have hinted at an important insight in how evolution works. Then, there remains the question of how exactly ice ages drive evolution. Maybe they have an active role, or maybe they are simply a parallel effect of the real cause that drives evolution, quite possibly the increasing concentration of atmospheric oxygen that has accompanied the biosphere over the past 2.7 billion years. Oxygen is the magic pill that boosts the metabolism of aerobic creatures -- what makes possible creatures like us. 

In any case, it is likely that ice ages will soon be a thing of the past on planet Earth. The effect of the human perturbation may be moderate and, when humans will stop burning fossil hydrocarbons (they have to, one day or another) the system may reabsorb the excess CO2 and gradually return to the ice age cycles of the past. That may occur in times of the order of at least several thousand years, possibly several tens of thousands. But the climate is a non-linear system and it may react by reinforcing the perturbation -- the results are unknowable. 

What we know for sure is that the cycle of Earth's ecosystem (Gaia) is limited. We still have about 600 million years before the sun's increasing brightness takes Earth to a different condition: that of "wet greenhouse" that will bring the oceans to boil and extinguish all life on the planet. And so it will be what it will have to be. Gaia is long-lived, but not eternal.