James Lovelock, renegade Earth scientist and creator of the Gaia hypothesis, has written a gloomy new book called “Revenge of Gaia”, in which he argues that we should be stashing survival manuals, printed on good old-fashioned paper, in the Arctic where the last few breeding pairs of humans will likely be found after a coming climate catastrophe. The book is not published in the U.S. yet, but it is available from amazon.co.uk. Lovelock has never been one to shrink from a bold vision. What is it he sees now?
Gaia In the first biogeochemistry class I took, I was assigned to read the first few chapters of Lovelock’s 1978 book, “Gaia: A new look at life on earth”. Since then, I have assigned those same chapters to every biogeochemistry class I have ever taught. Lovelock wrote very eloquently about the eerie stability of the earth system. The sun has been warming throughout its lifetime, and yet the climate of the earth has remained stable between the relatively narrow range of the boiling and freezing points of water. This observation was labeled the “faint young sun” paradox by Carl Sagan , and now has at least a partial explanation in terms of the weathering of silicate rocks, the silicate weathering thermostat [Walker et al., 1981]. Lovelock also points out that the oxygen concentration of the atmosphere has been remarkably stable over the half-billion years since multicellular life appeared in the fossil record, never high enough to explode (doubled atmospheric oxygen would lead to unstoppable continent-scale forest fires), nor low enough to wipe out the animals. Nitrogen, Lovelock points out, ought thermodynamically to exist as nitrate dissolved in the oceans; the reason that most of Earth’s nitrogen exists as nitrogen gas in the atmosphere is because of life.
Lovelock’s bold leap was to envision life on Earth as a single unified organism, capable of regulating the environment on Earth for its own well-being, analogous to the way that you or I regulate the temperature and chemistry of our bodies. A weak version of the Gaia hypothesis would state that the geochemistry of the biosphere is regulated by negative feedback mechanisms, many of which include the effects of life on Earth as integral components. This statement is no longer controversial among Earth scientists. A stronger version of the Gaia hypothesis might conclude, as Lovelock did, that methane is produced by bacteria because Gaia requires a flux of hydrogen to the stratosphere and hence to space, as a long-term balance of her oxidation state. A new idea in “Revenge of Gaia” is that we animals dispose of excess nitrogen in a bioavailable form as urine, rather than saving water and energy by exhaling it as the biologically less available nitrogen gas, because Gaia prefers for us to keep the nitrogen available for plants.
The strong Gaia hypothesis raises issues of altruism and cooperation among different components of Earth’s biota. I personally don’t understand how a Gaian biota would be stable, in the face of competition between organisms. If an organism spent metabolic energy for the common good, would it not be out-competed by another more selfish organism? The evolution of Gaia is another difficulty. Darwinian evolution is essentially a process of trial and error. Evolving a Gaia leaves very little room for error.
The closest I ever came to believing the strong Gaia hypothesis was during a talk I heard by Lynn Margulis, coauthor with Lovelock on the first Gaia paper in the scientific literature [Lovelock and Margulis, 1974]. Margulis’ claim to fame is that she championed the idea that organelles in eukaryotic cells might have originated as symbiotic relationships between multiple cells sharing the same external cell walls. This idea was ridiculed but is now settled as being probably correct. In her talk, she said something like, “The more we look, the more we see symbiosis in life. Gaia is simply symbiosis as seen from space”. For an instant there, I saw the vision.
Gloom So what does visionary Lovelock see now? There is no specific, mechanistic scenario for the downfall of civilized man, but rather a gut feeling of approaching catastrophe. Lovelock’s foreboding arises in part from his impression that Gaia is healthiest in the glacial climate state, such as Earth was in 20,000 years ago. The interglacial climate states, such as we inhabit now, he describes as fevers that Gaia must overcome. The origin of this seemingly peculiar perspective is twofold. First, the sun has been warming over geologic time, so the challenge facing Gaia at present is to stay cool. The glacial Gaia is more in control of this challenge than is the interglacial Gaia, so the glacial Gaia must have been the healthier. Second, the CO2 concentration was lower in the glacial atmosphere, which Lovelock interprets as a product of a healthier, more robust biosphere. (I feel compelled to point out here that the carbon isotopic composition of the deep ocean tells us that there was less organic and biosphere carbon during glacial time than there is now. Plants must have struggled to grow in the lower-CO2 atmosphere. It’s not clear to me how the glacial biota was happier than today. Forgive me, I’m small minded, I nitpick.)
Lovelock argues that a cooler land surface retains water better; a warm land surface is either desert or it could be rain forest, which has learned tricks to recycle water efficiently but is very fragile and would collapse with any further warming. A cool surface ocean is biologically productive, while a warm surface ocean is nutrient-limited and therefore a biological desert. Lovelock argues that a robust thriving biosphere is essential for Gaian regulation. (Small-minded me again. The regulation of CO2 by silicate weathering, alluded to above, in theory doesn’t really require trees or life as a central component. The terrestrial biosphere apparently is taking up carbon from the atmosphere, but the real heavy-hitting mechanisms for regulating CO2 on the long term involve dissolution of rocks, chemical reactions that can be influenced by life but do not really require it. A stronger case can be made for life as a necessary part of atmospheric O2 regulation, but it would take millions of years to change O2, so we are not really concerned about asphyxiating in the next century. The critical process is burial of organic matter in ocean sediments, however, not some process associated with forests on land. Despite what you may have read, the rain forests are not actually the lungs of the planet.)
The argument for approaching doom is made by analogy. (Again I feel compelled to editorialize. Argument by analogy is a powerful rhetorical tool, at which Lovelock is a master. Reasoning by analogy however is not a reliable divining rod for scientific discovery. “As above, so below” was a central tenet of the alchemists. We don’t do that anymore.) The analogy is to the failure of natural regulation of a human body, requiring artificial intervention. If the kidneys fail, a doctor has to take over regulation of blood chemistry using dialysis. If the pancreas fails, the patient requires manual regulation of sugar metabolism by insulin injection. It is generally bad news when the doctor tells you that your body’s natural regulation mechanisms are failing, because artificial, technological fixes are typically not as reliable as the natural ones. There is no doubt that mankind is taking over the reins of global geochemical balance. Industrial production of fixed nitrogen for fertilizer now matches the natural rate of nitrogen fixation on the planet. Rates of fossil-fuel CO2 emission dwarf the natural rate of CO2 release in volcanic gases. Lovelock’s conclusion, by analogy, is that the biosphere of the Earth will soon be beset by all manner of unanticipated complications.
This does not seem to me an unreasonable conclusion, I must admit. Consider Biosphere II. This was a sealed greenhouse in the Arizona desert, an attempt to create a managed, self-contained biosphere. A very humbling effort it turned out to be, all in all. Biological control proved to be completely out of reach. Several species of birds were introduced into the system, based on rational design of ecological balance, and all of them went extinct. The only birds that flourished in BII were a local species that invaded the structure while it was under construction that they never managed to eradicate. Ants and cockroaches became so abundant in BII that the biospherians took to sucking them up into vacuum cleaners and feeding them to their domesticated chickens. Geochemically, the oxygen concentration plummeted and nitrous oxide rose, until the structure became uninhabitable.
At this point in the book, about half-way through, Lovelock diverts from the question of our impending doom into various other, much smaller issues like whether nitrates in food are really bad for you. It felt surreal, like the serving staff on the Titanic arguing about whether a time card had been properly punched or not. Lovelock uses this material to make the point that people worry about all the wrong stuff. OK, that’s a legitimate point, but I was left wishing for some discussion of what shape the catastrophe might take.
Based on the experiences of the Biospherians, I would imagine that the wildest instabilities might be biological. We can cope with bacteria, at least better than humankind could back in the days of the Black Death in Europe, but bacteria are adept at evolving defenses to our chemical weapons, and viruses are much more difficult to attack. A new plague would spread globally, much faster than it did in the middle ages. A biological collapse might be attributable to human overpopulation, or monoculture agriculture, perhaps more so than to climate change.
Geochemically, I could imagine the chemistry of the atmosphere shifting to a new equilibrium, in which (say) carbon monoxide could suddenly rise up to harmful levels. The oxidation chemistry of the atmosphere has been altered in all different directions by human emissions of organic compounds, nitrogen compounds, and methane. No one understands why the lifetime of methane in the atmosphere is as stable as it appears to been over the past decades. Surprises could lurk here.
Methane hydrates seem dangerous, because there is so much methane. If all of the hydrates were to melt within a few years, we would have a methane spike in the atmosphere that would be catastrophic, because methane is such a powerful greenhouse gas. But it seems more likely that the hydrates would melt slowly, over centuries and millennia. If that is the case, the climate impact might be comparable to fossil fuel CO2 combustion. It could double the human climate impact, but probably not make it 10 times worse or anything like that.
Physically, there have been abrupt climate changes in the past, which we are just beginning to figure out. Transitions between stable climate states may be sudden. Some transitions are driven by sharp changes in physical properties of substances like water. There is a sharp boundary between a stable and a runaway greenhouse effect, because of the sharp phase boundary between water vapor and liquid. Abrupt climate changes in the glacial North Atlantic may have been amplified by freezing of sea ice. Dynamical systems may also change states quickly. Ocean circulation seems to have multiple configurations, also apparently generating abrupt glacial North Atlantic climate changes. The dynamical balance in hurricanes on earth is between latent heat and wind friction with the ground, but if the pressure dropped low enough, ground friction fails as a regulator and a new beast, called a “hypercane”, could arise [Emanuel et al., 1995]. No one is suggesting that hypercanes will arise on Earth, but this is an example of a sharp transition in a dynamical system. It would be extremely difficult to forecast abrupt climate changes such as this for the future.
The Earth has existed in hot-house configuration before, and contrary to Lovelock’s vision, I don’t know of anything intrinsic to the hot-house Earth which would preclude human life. The transition from present-day climate to a radically new climate could be catastrophic from the point of view of human civilization however, especially given that Earth is loaded with so many people already. Past climate transitions often drove extinctions and eventually new speciation. Past societies, such as the Classic Mayans, apparently vanished from the face of the earth, leaving behind mute relics of past social structure. These societal collapses were regional, often triggered by regional climate changes. The world today is globalized to an extent that was never a factor in the past, and climate is poised to change in a global way such as civilized humanity has not before witnessed.
We should be very clear. No one, not Lovelock or anyone else, has proposed a specific, quantitative scenario for a climate-driven, all out, blow the doors off, civilization ending catastrophe. Mr. Lovelock has a feeling in his gut that something terrible is going to happen. He could be right, but for what it’s worth, there aren’t any models that explode as catastrophically as this. We can never say that it’s impossible that something might fall out of balance, something we haven’t thought of. But I think in general the consensus gut feeling among small-minded working scientists like me is that the odds of such a catastrophe are low.
Low odds of catastrophe does not imply negligible. Nordhaus  considered the possibility of catastrophe in his analysis of the economics of climate change. He defined catastrophe as comparable to the Great Depression, a 25% decrease in global economic activity that lasts for a long time. The probability of such an event he estimated by polling the gut instincts of a group of climate scientists; for what it’s worth, they came up with probabilities of a few percent. Economically, Nordhaus found that this possibility imposed the largest cost of adapting to climate change, greater than the costs of sea level rise, potential change in storminess, and so on. My own belief is that economics is a flawed tool for managing global climate, because it neglects issues of fairness, and reduces the value of the natural world to units of money. The point is that, within this framework, a small possibility of a large catastrophe looms large as a practical issue.
Emanuel, K.A., K. Speer, R. Rotunno, R. Srivastava, and M. Molina, Hypercanes: A possible link in global extinction scenarios, J. Geophysical Res., 100 (D7), 13755-13765, 1995.
Lovelock, J.E., and L. Margulis, Atmospheric homeostasis by and for the biosphere: the gaia hypothesis, Tellus, 26, 2-9, 1974.
Nordhaus, W.D., Climate change – Global warming economics, Science, 294 (5545), 1283-1284, 2001.
Sagan, C., and G. Mullen, Earth and Mars: Evolution of atmospheres and surface temperatures, Science, 177, 52-56, 1972.
Walker, J.C.G., P.B. Hays, and J.F. Kasting, A negative feedback mechanism for the long-term stabilization of Earth’s surface temperature, J. Geophys. Res., 86, 9776-9782, 1981.