Saturday, December 21, 2013

Gaia: the missing bride

Toby Tyrrel's book "On Gaia" is an interesting book in many respects, but it misses some fundamental features of the self-regulating planetary system that we call "Gaia". (image from Alternative Energy Action Now)

Imagine that a friend of yours invites you to his marriage. You go there and you see everything you expect to see: the church, the flowers, the priest, the groom, and so on. But, as the ceremony goes on, you notice that your friend has overlooked something important: the bride is missing.

With the book by Toby Tyrrel, "On Gaia", you get a similar impression. It is well done in many respects and plenty of details are at the right place: evolution, life, climate, and more. But, as you keep reading it, you notice that the author seems to have overlooked something important: Gaia herself is missing. 

It is said that marriages fail because of excessive expectations of spouses. The same problem seems to be plaguing more than one study on Gaia, including this one. Some people seem to expect really too much from the poor lady and then they end up concluding that she doesn't even exist - as Tyrrell does with this book. His conclusion is wholly negative: there is no such think as a stabilizing feedback system called Gaia and the fact that the Earth has maintained conditions favorable to life for some four billion years is due mainly to "hazard and happenstance" (p 206 of the book).

The problem of excessive expectations appeared early in the history of studies of the stability of the Earth's ecosystem. James Lovelock, the originator of the idea of Gaia (together with Lynn Margulis), proposed that Gaia could "optimize" the ecosystem for the benefit of life. That was too much. The Earth's ecosystem is a complex system of interacting biological and geophysical loops - some tend to stabilize the system, some to destabilize it. The final result is the typical one of all complex system: the tendency of the system to oppose perturbations. That's not the same as optimization - it is homeostasis; something that tends to maintain the system's parameters within certain limits - not necessarily the optimal ones but, at least, in a range that maintains the cycles going.

There are many examples of this behavior; for instance your body is a complex system and it does exactly that: it seeks homeostasis. If the temperature of your body becomes too high, your internal thermostat will bring it down by sweating. But you can't expect the thermostat to be perfect and all powerful: if you fall into a vat of boiling oil, sweating won't help you much. The same is true for Gaia, which is - mainly - a planetary thermostat that tends to keep the planetary temperature within the limits needed for liquid water (and hence life) to exist. You don't have to expect the thermostat to be perfect and all powerful and, indeed, the Earth's history has seen all sorts of catastrophes occurring; when the planet became very hot or very cold, nearly destroying all life on it. But the system has always recovered and has countered all sorts of perturbations. That includes the gradually increasing solar irradiation over the eons that should have had a deleterious effect on life on Earth, had it not been balanced by a decrease in the concentration of greenhouse gases in the atmosphere.

Curiously, however, Tyrrell just can't see the thermostat in action. One reason is that it is very difficult to understand the Earth's feedback system without taking into account geology and, here, the author clearly has troubles in integrating geology in the discussion. Geology, indeed, is the true "missing bride" of the book. Not that geological phenomena are not mentioned in Tyrrell's book, but often in a cursory and insufficient manner. For instance, there is no real discussion of the cycles of the Earth's ecosystem which involve continuous exchanges of matter from the surface to the mantle and back. These cycles renew the atmospheric composition and provide the chemical elements necessary for life. Without a hot core that provides energy for these exchanges, the Earth couldn't be a live planet - it would be dead like Mars.

The problem appears in particular for the main mechanism of the Earth's thermostat: silicate weathering. It is part of the planet-wide carbon cycle, a chemical reaction that removes carbon dioxide from the atmosphere. Its rate depends on temperature, so it has temperature regulating capabilities. (see this post of mine for an introduction and ref. (1) for an in-depth discussion). Tyrrell mentions silicate weathering for the first time only at page 141, quickly arriving to the conclusion that it is only a negative factor for life because of its cooling effect (2)). You need to arrive almost to the end of the main text (p. 191-192) to find a brief discussion of whether silicate weathering can be part of a temperature stabilizing mechanism. Here, too, Tyrrell's conclusion is negative, apparently on no other basis than generic skepticism.

Now, of course one may disagree on all current scientific interpretations, but considering that silicate weathering is a core element of the whole thermostat question, it would surely deserve more discussion before arriving to dismiss Gaia as non existent. This is not the only problem related to geology in the book. Other factors, for instance the effect of the sun's increasing luminosity, are missing or barely mentioned. So, it is really disappointing that the book misses so badly its avowed target - Gaia - especially considering that there are several sections of it that are well done and worth reading, such as the discussion about the temperature effects on biological productivity.

In the end, I think that there is a basic problem in Tyrrell's approach. In the "Conclusions" section, he states that accepting or rejecting the Gaia hypothesis has a strong effect on "how we decide to manage the Earth System" and that "Gaia, by the very nature of the hypothesis, inculcates a predisposition to suspect natural feedbacks to be stabilizing." In other words, Tyrrell emphasizes that Gaia could generate a dangerous feeling of complacency on people and hamper their efforts of fighting climate change.

I beg to differ on this point. Not that I don't share Tyrrell's worries about global warming but in my personal experience the concept of Gaia as a stabilizing factor on climate is alien to the mind of typical science deniers. Rather, most of them seem to use the exactly opposite meme: "climate has always been changing," normally without showing the slightest interest in what exactly causes climate to change - they just don't care. Of course, the internet is so wide that you can find just about anything in it and, as proof of his position, Tyrrell cites a specific site that goes under the name of "The Resilient Earth". However, apart for the title that indeed reminds the concept of Gaia, the contents of the site seem to be the usual mishmash of denialist memes: from "no warming during the past 15 years" to "Al Gore is fat". The general opinion that can be read in deniers' sites about Gaia is that the concept is not just ridiculous but, rather, living proof that climate change is not science but a religion - intended as a derogatory term. (see the figure below as an example of Gaia-bashing. From

So, I think the least thing we should be worried about is that the concept of Gaia could engender a dangerous "lasseiz faire" attitude. On the contrary, understanding the factors that determine the Earth's temperature can only generate a healthy dose of respect for the delicate balance that has kept climate stable during the past ten thousand years or so. Homeostasis is no guarantee of absolute stability; that holds for an entire planet, just as it does for bicycles (and the latter is something that everyone understands).

In the end, Gaia is not a Goddess, (and surely not a benevolent one). She is not all powerful, she has no ability of optimizing the Earth's environment for life, and she is no guarantee whatsoever that we can keep behaving as planetary hooligans without suffering the consequences of our actions. Gaia is a huge and complex system; a gigantic tangle of geological and biological feedbacks. We are just starting to understand how this system generates its overall tendency to homeostasis and how it has evolved over the billion years of its existence (3). It will continue to evolve until, hundreds of millions of years from now, it will "die" when the Sun becomes too hot for the homeostatic mechanisms to continue operating. In the meantime, we have to keep living on this planet (if we can). Gaia may not be the perfect bride; but we can't keep behaving as if she didn't exist. 


1. For a review of the climate effects of silicate weathering, see Lee R. Kump, Susan L. Brantley, and Michael A. Arthur, Chemical Weathering, Atmospheric CO2, and Climate Annual Review of Earth and Planetary Sciences Vol. 28: 611-667 (Volume publication date May 2000) DOI: 10.1146/

2. This point illustrates the problems that this book has with geology. At page 142, Tyrrel attributes one of the "big five" mass extinctions, the Late Devonian one, to excessive cooling caused by silicate weathering. But he doesn't say anything about the generally held opinion that mass extinctions appear to be caused by excessive warming (including the Devonian one). See, eg. David L. Kidder, Thomas R. Worsley "Phanerozoic Large Igneous Provinces (LIPs), HEATT (Haline Euxinic Acidic Thermal Transgression) episodes, and mass extinctions"  Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 295, Issues 1-2, 1 September 2010, Pages 162-191

3. For a thorough description of the feedbacks cycles of the Earth's system, you'll do well in reading the book by Tim Lenton and Andrew Watson "Revolutions that Made the Earth". Beware: it is not an easy book to read, but it is surely worth the effort.

About Gaia, see also these posts by yours truly, Ugo Bardi,  

"The Great Chemical Reaction: life and death of Gaia"
"Man Vs. Gaia"
"The Next ten billion years"



Ugo Bardi is a member of the Club of Rome, faculty member of the University of Florence, and the author of "Extracted" (Chelsea Green 2014), "The Seneca Effect" (Springer 2017), and Before the Collapse (Springer 2019)