Homage to Gaia (44 page)

Geologists rejected the Gaia book gently, but biologists ridiculed it. Ford Doolittle was the first to do so. His article ‘Is Nature motherly?’ in the New Age journal,
Co-Evolution
Quarterly,
argued that self-regulation by organisms required them to have foresight and to plan, which was impossible. Then Richard Dawkins argued against it in his book,
The
Extended
Phenotype.
His robust criticism observed that a living Earth could never have evolved by natural selection. How could planets compete with one another? It took me until December 1981 to find the answer to these criticisms and it was in the form of a mathematical model, which I called Daisyworld. I never intended Daisyworld to be more than a caricature, and accept that it may turn out a poor likeness when we finally understand the world. Even so, I still see it as my proudest invention and its main value is as Andrew Watson called it, a parable about Gaia and Earth System Science.

I populated my model world with two species of plant, dark-and light-coloured daisies; their world was well watered and had a simple climate uncomplicated by clouds or greenhouse gases. Daisyworld was in orbit around a star like the Sun, one that increased its flux of heat as it grew older. The model showed that the natural selection of daisy species growing on this planet led to the self-regulation of climate at a temperature near optimal for plant growth, despite large variations in heat from the star. When the star was young and cool, dark daisies covered the planet and, by absorbing sunlight, made it 17° C, warmer than it would have been without them. As the star warmed, the lighter daisies began to grow and compete, and their
reflection of sunlight cooled the planet and kept the temperature optimal as the star increased its output of heat. Eventually, the star became so hot that even a total cover with light daisies was insufficient to prevent overheating and the system failed. It showed definitively that Ford Doolittle’s criticism that teleology would be required was wrong, as was Richard Dawkins’s criticism that planets would have to compete to select for self-regulation.

Daisyworld is much more than an answer to these criticisms; it shows how self-regulation could be a property of a planetary system and result from the tight coupling of biological and physical evolution. Daisyworld also provides a tractable working model of the phenomenon of emergence, and is an illustration of that wonderful state when the whole is more than the sum of its parts. I presented the first account of Daisyworld at a conference in the Netherlands in 1982 hosted by the Dutch scientist, Peter Westbroek. It appeared in the conference proceedings, but this kind of publication only establishes priority in a legal sense. Scientists now accept only peer-reviewed papers. I knew that Daisyworld needed publication in a proper journal. My problem was that I could not write mathematical papers in a way the referees would accept. I therefore asked my friend, Andrew Watson, if he would join with me as co-author. Andrew writes well and, unlike me, in a way that other scientists like. He is also an accomplished mathematician. He agreed and we prepared our Daisyworld paper. We tried
Nature
first, but that journal would not even consider sending it to referees. We then submitted it to
Tellus,
the journal that had published my second paper on Gaia, the one written with Lynn Margulis in 1974.
Tellus
published Daisyworld in 1983.

Daisyworld is a synopsis of Gaia Theory. It shows how organisms evolving under the rules of natural selection are part of a system that is self-regulating. Daisyworld keeps its temperature close to the optimum for daisy growth. There is no teleology or foresight in it. Neither is there, as our critics persist in saying, any built-in prejudice in favour of regulation. The persistence of this inept criticism so irritated me, especially since it came from prejudice, not from thought, that I made a simple variant of Daisyworld where, at the start, the organisms were all grey daisies. Grey daisies have no effect on global temperature. I then allowed them a small chance to mutate at random either to slightly darker than grey or to slightly lighter than grey. This chance mutation is what would happen in nature, and biologists would see it as adaptation. Not surprisingly, when this
new model Daisyworld was cold, the daisies that mutated to slightly darker than grey had a better chance of survival because they were warmer. In a short time, mutation had moved the average daisy colour almost to black. This is similar to the change of skin colour when white-skinned people are exposed to a few thousand years of tropical sun—the cumulative ill effects of sunburn reduces the family size of paler people. As Daisyworld warmed, so the average colour grew lighter, until at the hottest, it was close to white. This model was a better temperature regulator than the original Daisyworld. Tim Lenton has developed and expanded it. He demonstrated that adapting by mutation confers advantages not present in the original black-and-white Daisyworld.

Daisyworld can model the regulation of the chemical environment as well as the climate. In my book,
The
Ages
of
Gaia,
written in the mid-1980s, are described models of bacterial ecosystems that simultaneously regulate climate, greenhouse gases, and oxygen. Daisyworld models are distinguished by their remarkable resilience and stability. Disasters can occur in the models that destroy up to eighty per cent of the organisms, but in spite of them, the system promptly recovers once the disaster is over. Stephan Harding, an ecologist working at the Schumacher College in Devon, has built complex ecosystems involving a wide range of food webs among plants, herbivores, and carnivores. He has taken advantage of Daisyworld’s stability to show how more complex food webs give rise to greater climatic and ecosystem stability, and how this comes about due to tight coupling between organisms and their global climate. Stephan is a biologist who trained in Oxford in the Department of Zoology and had as mentors such luminaries as Richard Dawkins and William Hamilton. Stephan has been instrumental in building bridges between Gaian scientists and the evolutionary biologists. He and his partner, Julia Ponsonby, have become firm friends and we walk and work together regularly.

Daisyworld is the first mathematical model of a world that evolves by Darwinian natural selection, and on which the evolution of the environment, represented by temperature and the evolution of the organisms, is a single coupled process. The self-regulation of global climate emerges as the model evolves. It is both a simple climate model and a population biology model. Peter Saunders, Professor of Mathematics at King’s College London, wrote a fine paper for the
Journal
of
Theoretical
Biology
in 1994 analysing the mathematics of
Daisyworld and confirmed it as a valid evolutionary model. Few biologists seem to agree and some even refer to it as a mere computer game. There are fouls in science, just as in sport, and this foul criticism of Daisyworld is an own goal. No competent computer modeller would make the mistake of denigrating a computer game. However trivial the play, it can take the imagination of an artist and the skill of a wrangler to write the program for a game. A high moment in my quest for Gaia was a visit to Coombe Mill of a talented game programmer, Will Wright, who was at that time with the firm Maxis, and who had developed the popular game SimCity. He asked me if I would collaborate with them to produce a game about the Earth called SimEarth, which would include versions of Daisyworld. It was a thrill and enlightenment for me to work for a while with so competent a computer programmer. Maxis, without my asking, paid royalties from the sales of SimEarth to our charity, Gaia, that sustained our research during a difficult time.

The years between 1979 and 1984 were difficult. No matter how I tried to persuade scientists that they should take Gaia seriously, I rarely succeeded. Through the 1980s, Gaia was treated more as science fiction than science, and it became almost impossible to publish a paper with Gaia in the title or even in the text, unless it was to denounce it. The New Age movement took Gaia to their bosom but, sadly, too many of their good intentions were neutralized by a lack of rigour. The rejection by some New Agers of science itself made my task even harder. It confirmed for many senior scientists that Gaia was not only wrong; it was dangerous. They saw it as a topic like astrology that masqueraded as a science but was nonsense. An outstanding exception to the loose thinking of the New Age was the journal
Co-
Evolution
Quarterly,
under the editorship of Stewart Brand. The journal published several articles from Lynn and from me and from scientists who criticized Gaia. Stewart and Patti, his wife, became good friends, and we have visited and corresponded over the years.

A great comfort during these bad times was the presence of Teddy Goldsmith at Withiel, not far from Coombe Mill. Teddy was much like my Uncle Hugo Leakey—wonderfully erudite, fast on his feet in argument and, like his famous brother Sir James Goldsmith, effective. He was a fine critic and needed to be, because there were many issues of Green politics on which we disagreed, notably my liking for nuclear power. Teddy had more influence on my thinking than I think he knew. His strength and consistency made him for me a touchstone on
Green affairs and his book on Green philosophy,
The
Way,
is a powerful statement of the philosophy behind Green thinking. Teddy and his wife Kathy lived in a manor house where they lived a life consistent with their principles, even to the extent of using earth closets inside the manor house. Few things vex me more than Green hypocrisy, such as the sight of a monstrous four-wheel-drive gas-guzzler with a sticker on the back bearing some trendy Green message.

The disappointment I felt over Gaia’s rejection was intensified by my problems at home; Helen was slowly losing her battle with multiple sclerosis, and I seemed to spend too much of my time in hospital for surgery. The 1980s were a decade of pain and long discomfort. Of course, there were good moments: visits to and from Bob and Cynthia Garrels were joyful events. And looking back, I think I was too depressed by my personal problems to notice that the work I did with Andrew Watson and Michael Whitfield at the Marine Biology Laboratory in Plymouth, was key to the establishment of Gaia theory in science. I had long thought that the observation that CO
₂
in the soil throughout the world was concentrated between ten and thirty times more than in the atmosphere was important evidence for Gaia. Biogeochemists accepted the evidence and agreed that it was due to the metabolism of soil micro-organisms, but they failed to see its significance globally. I saw the high concentration of soil CO
₂
linked with faster rock weathering and a greater rate of removal of CO
₂
from the air, which in turn leads to a cooler global climate. We proposed that the weathering of the rocks by carbon dioxide and rainwater was part of a self-regulating process, which involved the living organisms in the soil. When it was warm, growth was faster, more carbon dioxide was pumped from the air, and any tendency to excessive heat or carbon dioxide was resisted. By this and other means the Earth was kept always at a comfortable level for life. We argued that rock weathering was more than just a geochemical activity, because the rocks were always in contact with organisms ranging from bacteria, through lichens, to plants, and we suggested that weathering took place at least ten times faster as a result. Not only this, but because plant growth is temperature-sensitive, the presence of organisms coupled climate to weathering, and to the rate of removal of carbon dioxide from the air. This long-term geological process has kept the Earth at a favourable temperature as the Sun has warmed up. We published these ideas in two papers in the early 1980s and the American scientists, David Schwartzman and Tyler Volk confirmed
them by experiment in 1989. They are now part of the wisdom of Earth System Science.

I was always seeking possible mechanisms for the self-regulation of climate, and the work of Glenn Shaw, an aeronomist working at the University of Alaska, intrigued me. He proposed that the biological emission of sulphur compounds from ocean sources was the source of the sulphate aerosol in the stratosphere. This aerosol reflects sunlight back to space and makes the earth cooler. It occasionally increases in density when volcanoes inject sulphur dioxide into the stratosphere, and consequently several years of cold weather follow the eruption. Glenn Shaw suggested that the biological emission of sulphur gases from the ocean might be part of a climate-regulating mechanism. It might have been in the Earth’s past, but it seemed that at present the climatic effect of the background stratospheric aerosol was small.

The event that was to lift Gaia theory from its mid-life doldrums came unexpectedly. In 1986 the ocean scientist, Dr Murray, of the University of Washington in Seattle, invited me to be a Walker Ames Visiting Professor. This involved a month’s visit to lecture and to interact with students and scientists of the university. Following a lecture in the Chemistry department, I had a fruitful discussion with Robert Charlson, a distinguished atmospheric scientist interested in clouds. Bob Charlson belied the name of his calling, he was no light ethereal being, but one with feet firmly anchored to the ground. He is a dark-haired sturdy man with the look of a sailor, and he would have fitted naturally on the quayside of my nearest fishing village, Port Isaac. I am proud to have him as a friend.

Bob told me that there was an unanswered question about clouds over the ocean. What is the source of the tiny particles, the nuclei of water-soluble substances, from which clouds form? Without these nuclei, there can be no clouds. When Bob said this, I was surprised. Surely, the water that evaporates from the warm sea will condense into droplets as it rises into the cold air. ‘Yes,’ he said, ‘it will. But the droplets will be large because there are few nuclei for them to condense on. They will not be cloud droplets, which are so small that they almost float in the air. They will be large drops that fall from a clear blue sky.’ He went on to say that over the land there are always particles for clouds to form on, such as the sulphuric droplets of air pollution; over the oceans, apart from a few volcanoes on islands, there are no sources of these nuclei. We used to think that sea-salt crystals blown and dried by the winds from the sea were the
condensation nuclei. We have sampled the air over the Pacific Ocean far from land and we find a few sea salt crystals, but we always find abundant nuclei in the form of droplets of sulphuric acid and ammonium sulphate. Bob finished with the question ‘Where does this sulphuric acid and ammonium sulphate come from?’ It was one of those important moments in science. I had lectured the previous day on the regulation of the sulphur and other chemical cycles through the emission of dimethyl sulphide from ocean algae, and suddenly it occurred to us both that the oxidation of dimethyl sulphide could make the cloud-nucleating sulphuric acid droplets. We went on to wonder if this was part of some large-scale climate self-regulation. By coming to Seattle and talking about Gaia, Bob and I had been able to share two essential pieces of information that solved the puzzle: where do the clouds over the ocean come from? Here perhaps was the most important scientific discovery that either of us had made. Without the clouds over the ocean, life as we know it would not exist. This is because oceans cover seventy per cent of the surface of the Earth, and they are dark, and absorb sunlight strongly, whereas clouds are white and reflect sunlight. Bob told me that without clouds the Earth would be about twenty degrees Celsius hotter and that a cloudless Earth would have a surface temperature near 35° C, which would make the world inhospitable for our kind of life. There are other sources of nuclei for cloud formation, but we did think it reasonable to speculate about the link between climate, clouds, DMS, and algae as part of Gaia’s self-regulation. There was little doubt that the microscopic algae of the oceans were the principal source of DMS.