HEALING THE RIFT

Since the 1970s, scientists have been divided over the Gaia hypothesis - the idea that the Earth is a self-healing, self-regulating organism. Now, new evidence is convincing even the sceptics

"Now, Mr Jones, having obtained your promise of inviolable secrecy, I come down to the essential point. It is this - that the world upon which we live is itself a living organism, endowed, as I believe, with a circulation, a respiration and a nervous system of its own." Clearly the man was a lunatic.

(The Day the Earth Screamed, Sir Arthur Conan Doyle)

GAIA, Earth Goddess of the ancient Greeks, may feel her name is being taken in vain. For, 24 years after appropriating Gaia as the icon of the self-regulating biosphere, independent scientist Jim Lovelock is preparing to abandon her.

The Gaia hypothesis was hatched 30 years ago when Lovelock saw the first photographs of the Earth from space. He sensed it had to be a tightly regulated system, able to maintain long-term stability over a range of parameters such as temperature, humidity and concentration in the atmosphere of key gases.

It was in 1972, writing in Atmospheric Environment, that Lovelock first put the his hypothesis forward: that the biosphere was somehow regulating the Earth's climate in such a way as to keep things comfortable for itself. Following a suggestion by author William Golding, he named the regulatory system Gaia.

The concept won enormous popularity among environmentalists, religious devotees and those grasping for elusive holistic visions of Life, the Universe and Everything. But it failed to win over a sceptical scientific community, insistent that organisms regulate only themselves, and anything more was pie-in-the-sky.

And so it was that Lovelock, at a recent seminar at Green College, Oxford, finally came to agree with those sceptics. "It was easy but wrong to propose that organisms did the regulating and in their own interests," he said. But his recantation was only partial. In his new understanding, the Earth's self-regulation was rather "a property of the whole planet involving organisms, rocks, air and oceans, not life alone."

In other words, the entire Earth is alive, or at least has life-like properties. Lovelock can even lay claim to a "respectable scientific history" for the idea, going back over two centuries to the great geologist James Hutton, who stated in 1788: "I think the Earth is a super-organism, and its proper study is physiology".

Lovelock is establishing a new science for the study of the Earth's self- regulation: geophysiology. "I am a hard scientist and my agenda is to establish Gaian ideas in mainstream science. Scientists hate the word Gaia and its New Age associations. By calling it geophysiology, I thought they would be kept happy."

And happy they appear to be. "I took very strong exception to Gaia," says former critic Dick Holland, professor of geochemistry at Harvard University. "To me it was quite unreasonable. Gaia has been overlain by mysticism and religious feelings - they should not be mixed up with scientific endeavour."

Yet he is a founder member of the newly-formed Geophysiological Society. "The modern view is that the Earth and the biosphere have evolved together and have strong interactions," says Holland. "Organisms do have an effect on climate, but other aspects of it have nothing to do with biology."

Under its respectable new banner, Gaian science is now entering its second age. A growing number of multi-disciplinary scientists are at work unravelling the complex feedback cycles that permeate the geosphere, hydrosphere, atmosphere and biosphere, and have - so far at least - maintained life on Earth.

Take, for example, Holland's own research into how the concentration of oxygen in the atmosphere has remained stable at around 20 per cent for the last 300 million years. It has long been presumed that this was the result of biotic processes such as photosynthesis and decay. But Holland believes this is not enough.

Oxygen is released to the atmosphere for the long term, he explains, when carbon is locked up for the long term. This happens when the remains of dead marine organisms are deposited in deep ocean sediments. And the growth of those organisms is limited by the availability of phosphate, a vital plant nutrient.

Enter ferric hydroxide, a "powerful scavenger of phosphate" formed in the oceans when their abundant dissolved iron meets free oxygen. More oxygen means more ferric hydroxide, which means less phosphate, thus less photosynthesis, which means less carbon deposition in marine sediments, which means less oxygen in the ocean, and ultimately in the atmosphere too - completing the loop to make a self-regulating negative feedback cycle.

An even more striking example of geosphere-hydrosphere- biosphere synergy comes from Nick Petford, a geologist at Kingston University, Surrey. We know that limestone and chalk are formed from accumulations of sea-shells, and are thus biotic in origin. But what rock could be more lifeless than granite?

"Pick up a piece of granite and it doesn't inspire any sense of connection with living organisms," Petford concedes. "But it contains many of the essential elements that living things need, like calcium, sodium, potassium." Upwellings of molten granite from deep within the Earth's crust, he adds, recycle other vital nutrients from the deep such as sulphur, zinc and molybdenum. Not only that, but the continents on which terrestial life has evolved are principally made out of granite. "Without granite we would have a Kevin Costner waterworld with just a few basaltic volcanoes breaking the surface," he says.

Granite is formed when basalt is heated in the presence of water. Raw basalt has a very high melting point of around 1250C, far too high to melt in the Earth's crust. But when fluxed with water into granite it melts at a mere 650-700C, a commonly reached temperature. Without water, therefore, continents could not have formed. And water is itself a product of life: it is due to life that we have free oxygen in our atmosphere, which oxidises any free hydrogen to make water. No life, no water. No water, no granite. No granite, no recycling of deep nutrients and no continents, and far worse conditions for life.

"When we look to other planets around the solar system we can see basalt everywhere," says Petford. "Then we look to the Earth and we see water, we see granite and we see life. Clearly granite is pretty important in the scheme of things."

Another example of multi-sphere interaction comes from Bob Charlson, professor of atmospheric science at the University of Seattle, who argues that tiny marine animals called coccolithosporids are responsible for cloud-formation. The tiny droplets of water that make up clouds need particles on which to condense. And Charlson has found that above remote ocean areas, "hard" condensation nuclei of dust and sea salt are outnumbered 100 to one by droplets of sulphate and other oxidation products of dimethyl sulphide (DMS), a volatile gas emitted by coccolithosporids. "Without them," says Charlson, "clouds would have fewer, larger droplets and they would be transparent, making the Earth 10-15 degrees hotter than it is now. Rain would be frequent, localised and sporadic, like fine Cornish drizzle."

As the world got hotter, he surmises, additional water would evaporate from the oceans and saturate the atmosphere with water vapour - a significant greenhouse gas. "Then we could end up with a super-greenhouse effect and life as we know it would be impossible. There is no avoiding the fact that the heat balance of the planet is controlled at least in part by biota."

Other developments are also building on the established foundations of Gaian science. The Gaia hypothesis gained its first scientific credibility in the early 1980s, after Jim Lovelock devised a computer experiment to show that the selfish behaviour of individual organisms can bring about the wider benefit of the biosphere. This involved the imaginary planet Daisyworld, where the ground is covered with white daisies, which cool the environment by reflecting sunshine, and black daisies, which warm it by absorbing sunshine. Both kinds of daisy grow best within a limited temperature range. When Lovelock ran his model and varied the intensity of solar irradiation, he found the daisies automatically modulated their numbers to maintain an even temperature. "It dawned on me that it was not the organisms doing the regulating, but the whole system," he says.

According to Brian Goodwin of the Open University, this spontaneous development of order is analogous to the ordering of the behaviour of ants. Ants' nests do not have any central manager and the behaviour of individual ants is often chaotic. The order that emerges among ants is the result of mutual stimulation arising from random interactions between individuals.

It is this unplanned order that makes it possible to speak of an ants' nest as a superorganism. "My suggestion is that a superorganism is a state of order that emerges from complex interactions between its components," says Goodwin. "That superorganism will manifest a boundary and its own dynamics, but still reflect the chaos from which it arises." The definition, he argues, can be applied to the Gaian complex of regulatory feedbacks.

Lovelock shares this view of the decentralised, distributed Gaia. "We now define Gaia as an evolutionary system in which organisms and their material environment are tightly coupled together, and self-regulation emerges from this process."

Now Stephan Harding, resident ecologist at Schumacher College in Devon, is putting the concept to the test in a new version of Daisyworld, its complement of species expanded to make it more like the real world. His latest version contains 23 kinds of daisy, three kinds of herbivore, and a carnivore. He found that Daisyworld regulated itself better when it contained more species. However the carnivore was vital to its stability. Without it a single species of herbivore would dominate, with knock-on effects on the daisies and their ability to regulate temperature.

"The carnivore helps the herbivores to co-exist amicably, leading to greater stability," says Harding. His main conclusion is that the greater the diversity and complexity of the system, the better it will regulate itself - a notion he will test as he adds in new, more specialised organisms.

But Lee Klinger of the National Center for Atmospheric Research in Boulder, Colorado, argues that we must develop a bigger picture. "Gaia theory has in the past concentrated on organisms," says Klinger, "but that is like trying to understand animals by looking at cells and ignoring the functions of systems and organs. At a global scale, we need to look at the role of communities, landscapes and biomes in Gaian regulation."

His own pet biome is the peat bog, which he sees as a powerful Earth- cooling engine. Bogs lay carbon down as peat for long-term storage, reducing atmospheric carbon dioxide - a major "greenhouse" gas. Bogs also reflect more solar heat back into outer space than forests they replace - high latitude bogs in particular. In summer they transpire more water than forests, stimulating the formation of reflective clouds. In winter, they are covered in snow and reflect far more heat than trees or shrubs capable of trapping any low-angle sunshine. "These are potential mechanisms that could initiate ice ages," says Klinger.

He is scornful of the standard General Circulation Models (GCMs) used to predict climate change. "Most have simplified the biosphere to a cycling of carbon and nitrogen with no ecology and no succession, missing out all the most important things," he complains. Other models represent the biosphere as a giant leaf. "All very well for vascular plants, but no good for mosses with no vascular tissues. These models are going to get it all wrong."

But now Paul Valdes, a meteorologist at Reading University, is refining standard GCMs by including more realistic vegetation feedbacks. First, he tested his model against our knowledge of past climates, derived by examining rocks, ice cores, lake bed sediments and other palaeo-records. "We are very pleased with our results but have thrown up some anomalies," says Valdes. "For example we are finding rainforest in tropical regions previously supposed to have been arid. The question is, is it our model that is wrong or the conventional geological interpretation?"

Even more intriguing is his finding that the model is highly sensitive to original conditions. "For example, if we put forest on the Sahara, it appears to encourage rain by storing and recirculating water - allowing the forest to persist." And his model can pinpoint now-vegetated areas that could easily become deserts.

Many of Valdes's findings are different from the those of the Inter-governmental Panel on Climate Change, as derived from conventional GCMs. "The IPCC's global average figures are probably good but their regional figures are unreliable," he says. "I am worried about this because it is the regional figures we need to get right, and the global climate is after all just the average of all the regions." Notwithstanding the uncertainty, he says the greenhouse gases we are pumping into the atmosphere will definitely make the world hotter - palaeoclimate records leave no doubt of that. "But the warming will in no way be evenly distributed. There are a lot of surprises in store."

Lovelock adds his own warning. "Sadly, what mostly shows up when we include Gaian feedbacks is that the system will amplify the damage we are causing, rather than opposing it."

One example, he believes, is that vital coccolithosporids may be emitting less DMS due to global warming, leading to less cloud cover and yet higher temperatures. "If we were in the usual glacial state things would not be so serious, but the Earth has a fever, and what we are doing now is like shining a lamp on a feverish patient. It's not the right thing to do."