2005 Expedition Blog - Day 5
Thursday, 10 March 2005, 7:21am
Daily Log March 10th 2005
Today you will have almost certainly inhaled an atom of carbon exhaled by Julius Caesar, when he uttered the question 'Et tu Brute?' to his treacherous aide. Now multiply your breathing by the respiration of every plant, fungus, bacteria, human being and other animals. You do not need a calculator to conclude that organisms have, by their very existence, exerted a powerful influence over the global climate. While walking in the snow today it struck me that it is exactly forty years since the British chemist and inventor James Lovelock published a paper in the journal Nature that built on this observation laid a foundation of our current understanding of climate change.
Lovelock had been working for NASA on methods by which life could be detected on other planets. Long before the first landing on our own moon, most space scientists had discounted the possibility that life existed there. They were more hopeful about Mars. Lovelock's ability to transcend the ordinary boundaries of scientific disciplines has allowed him to provide science with some extraordinary insights. In 1962 he decided, to other NASA scientists disappointment and scepticism, that there was no life on Mars. The data he had gathered whilst addressing this question had also started him thinking about the ability life might regulate the atmosphere over millions of years.
The planets either side of Earth, Mars and Venus, have virtually no oxygen in their atmosphere. Yet Earth, the only planet with life, has maintained a fifth of its atmosphere as this highly reactive gas for hundreds of millions of years. The Earth, reasoned Lovelock, must have regulated its atmosphere - just as the human body regulates the concentration of oxygen in its blood supply - via a process called homeostasis.
Even after he had, together with his collaborator Lynn Margulis, developed his idea into a rigorously argued hypothesis, many of their fellow scientists dismissed the idea out of hand. Whatever they thought of the science, many were put off the theory's name. In a marriage of science and art reminiscent of Cape Farewell, Lovelock took the advice of the novelist William Golding and named his idea after the ancient Greek goddess of the Earth, Gaia.
Working with his then student Andrew Watson, Lovelock explained the mechanism behind his theory with his Daisyworld model. Using a simple computer program, it described an imaginary world that was only made up of two kinds of daisy. It demonstrated how homeostasis on a planetary scale could arise by pure Darwinian natural selection. The late Bill Hamilton, an evolutionary biologist, proposed a mechanism whereby the regulatory impact of life on the Earth system could occur not just inside a computer, but in nature.
Hamilton was initially struck that microbes found in the tropical ocean contained anti-freeze. Microbes are masters of eliminating unnecessary components of their metabolism. In seas where freezing is very rare, synthesising anti-freeze is a waste of valuable energy. The more he found out about the marine system from his chemist collaborator, Tim Lenton, the more he began to suspect that microbes were unconsciously orchestrating the elements for their own perpetuation. He proposed that the survival of these microbes were linked to their ability to control the climate. These specks of life were, he suggested, using clouds, wind and rain to carry themselves around the planet, like a global taxi. The anti-freeze was needed not in the sea, but for the sub-zero temperatures the microbes had to survive at altitude. If he was right, this would be the most biologically credible mechanism for Gaia ever discovered.
Twenty years ago, a group of scientists led by Lovelock had proposed that marine microbes were part of a global regulatory system that kept the climate stable. Most of these microbes produce a gas called dimethyl sulphide, which reacts with oxygen in the air above the sea and forms tiny solid particles. These particles then form a surface on which water vapour could condense to form clouds. Clouds keep the planet cool by reflecting solar radiation back into space. Lovelock argued that this process could create a self-regulating global thermostat. Warmer weather would increase microbial photosynthesis and therefore DMS output, seeding more clouds, which would block out the sun. Then, as the climate cooled, microbial activity and DMS levels would decrease. But to be evolutionarily as well as meteorologically stable, DMS production must enhance the survival prospects of individual microbes.
Hamilton's ground-breaking idea was that the microbes were releasing DMS, not as an act of selflessness for the good of the climate, but to get themselves into the air. He had already devised a computer model suggesting that dispersal was a high priority for all organisms, their third objective after survival and reproduction. He also knew that microbes, like fungal spores, had been recorded as making intercontinental journeys at heights of up to 50 kilometres. He suggested that, as DMS causes water to condense around the sulphate particle, it releases energy in the form of heat. This warms the surrounding air, which then starts to rise, taking the microbes with it. Hamilton and Lenton think that a simultaneously-produced chemical DMSP, would act as an antifreeze, stopping the cells dying in the upper atmosphere. Once there, the tiny sulphate particles trigger cloud condensation, which eventually causes rain, allowing the microbes final fall back to Earth.
Biologists such as Hamilton are one of a growing number of scientists that have strayed out of their original discipline to provide valuable insights to climate studies. In an era where climate degradation seems an increasingly dangerous threat, understanding the biological dimensions of our climate is an urgent issue.
Hamilton's theory also has implications for more than just marine microbes. Dispersal is just as important for organisms on land as it is in the sea. Among those species both small enough to, and living in a position from which they can, become airborne, are microbial leaf-surface pathogens such as Fusarium and lichens such as Cladonia. Though much more research is needed, preliminary findings seem to suggest that both marine and terrestrial microbes of this sort are found high in the atmosphere. Hamilton even proposed that they may perform their meteorological magic by working in teams.
As large numbers of scientists have started to study Gaian phenomena, different versions of the theory, and experiments to test which interpretation is correct, have emerged. David Schwatzman, a biologist at Howard University, Washington D.C. suggests that microbes may have allowed life to continue on Earth by simply cooling what would have otherwise been an unbearably hot Earth. The energy the Earth receives from the sun has increased dramatically since the origin of life. Life on land, argues Schwartzman, has intensified the chemical weathering of rocks such that carbon dioxide has been removed from the atmosphere and the surface temperature of the Earth has remained cooler than if life had not been present - a kind of inverted global warming.
Schwartzman argues that the emergence of the major groups of life such as blue-green bacteria, eukaryotes, and plants may have been facilitated by this global cooling. In a subtly different interpretation than Lovelock, Schwartzman sees Gaia as more of a co-evolution of organisms and atmosphere rather than regulation by the biota. Whereas Lovelock sees global temperature as regulated to the extent that conditions have been comfortable for life's evolution, Schwartzman sees the evolution of most life-forms as repeatedly constrained by their inability to tolerate high temperatures.
As the triumph of bacteria over antibiotics has shown, many of the inventions meant to be magic bullet solutions to wipe out a disease have turned out to be more like boomerangs - they've come back to haunt us. Others may become so over time, as microbes catch up with those who would tame them. Gaia's message is similar. We are all ecologically bound up into a larger biological whole. This whole, dubbed Gaia, may or may not regulate the parameters of the Earth that are crucial for life to continue. Even if the regulation occurs, humanity isneither in control of this regulation or necessary for its continuation. We continue to destroy our soils with industrial agriculture and burn up the atmosphere with our cars (and arctic snowmobiles). If we buck this living global system too much, it could move to a state which is no longer hospitable to survival, first for more vulnerable communities, and eventually all of us.