One of the great insights of modern science has been that the ecosystem of the Earth as a whole might be self-regulating, that is, it regulates its systems (temperature, geology, atmospheric chemistry, biology) the way a body regulates itself. It adds a new dimension to the meaning of Mother Earth. This is an insight usually attributed to James Lovelock, who called the Earth Gaia, and extended by the late, great biologist Lynn Margulis. Neither one of them intended to imply that the Earth was a goddess; Lynn Margulis particularly told me so. Gaia is a self-regulating systems, not a goddess.
In this series of essays (Gaia Save Us! Not So Fast), I wish to explain that Earth has a regulatory system, which you can call Gaia if you like. But this system is very unresponsive except on the largest scales of time and space. Don’t trust Gaia to solve any of our current ecological problems.
This essay is the first of the series: about global warming, which is nothing new in the history of the planet.
On an overall scale, the idea of Gaia seems to be correct. Currently, the Earth’s temperature remains relatively stable, because the atmosphere has just the right amount of carbon dioxide, which holds in the heat. That is, when there is too much carbon dioxide, Earth processes remove it from the atmosphere. Over a very long scale, the silicates in the minerals of the crust react with carbon dioxide, removing it from the air. This takes millions of years. On a shorter time scale, the photosynthesis of plants and the respiration of all organisms regulates carbon dioxide. These processes can react to changes in carbon dioxide, therefore global warming, in just a few centuries. If there is too much carbon dioxide, photosynthesis uses it up; if there is not enough, photosynthesis declines and respiration of all cells produces more carbon dioxide. Photosynthesis reduces global warming, respiration increases it, thus stabilizing the temperature, over the course of centuries.
Not only that, but billions of years ago when the Earth had atmospheric carbon dioxide levels thousands of times higher than at present, the sun just happened to be dimmer. The sun is the only source of warmth on our planet. In some way I do not understand, the sun grew brighter just as chemical and biological processes started removing carbon dioxide. Or perhaps the timing was just due to chance.
So far so good. Given enough centuries, photosynthesis will remove the excess carbon dioxide from the atmosphere. But we don’t have centuries. Global warming is already developing into a disaster (I originally wrote this during a French vague de chaleur, heat wave, which is becoming the new normal in the French summer). Whole areas of the Earth, currently home to millions of people, might become so hot as to be uninhabitable in a few decades. Meanwhile, Gaia seems to be still snoring, and is just waking up. It won’t get hot enough to kill the Earth—you can trust Gaia on this—but the Earth might get hot enough that human societies will not survive.
Still, it is conceivable that global warming might occur fast enough that the plants would not have time to recover, photosynthesize, and save us. Could the Earth become hot, forever, like Venus? When somebody in the audience mentioned this possibility to me, during a public lecture, I dismissed the idea right away. But maybe the guy had a point.
Another example of the failure of Gaia to save the Earth from temperature change is the exact opposite of global warming. During the middle of the Precambrian time, the Earth was covered with ice, apparently on three separate occasions. This has been called Snowball Earth. There was apparently more than one cause, but one of the causes was that the photosynthesis of single-celled algae in the oceans (there was not yet any life on land; there wasn’t yet even very much land) scrubbed carbon dioxide from the air so much that it led to global cooling. The Earth might have looked like an ice planet at those times. No one is sure if all of the tropical oceans froze over, but some of them did. Photosynthesis also filled the air with huge amounts of oxygen gas, regarding which there is also some evidence.
The reason the Earth did not slip into a permanently frozen state was because the crust of the Earth fractured into plates. Some of the plates started moving away from, and others toward, one another. At these plate junctures, known as fault lines, volcanoes frequently erupted, putting carbon dioxide back into the air and melting at least the nearby ice.
But it is conceivable that this might not have happened. Just a few fewer volcanoes along the fault lines, and the trajectory of the Earth toward being an eternal snowball might have been unstoppable.
I am thankful for Gaia, but it might not have saved us from unstoppable global warming or cooling. It was mainly luck.
But maybe, we think, Gaia might help us on shorter time scales. Gaia might not have prevented Snowball Earth, but it might be the reason that the Earth’s climate has been stable since life exploded in the oceans and later on land. Can we trust Gaia to maintain this kind of stability? I wouldn’t bet on it, as I explain in a later essay.
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