Should we accept the Gaia Hypothesis?

In 1965, physiologist James Lovelock and microbiologist Lyn Margulis proposed an intriguing theory known as the Gaia Hypothesis. They turned the traditional assumption that living (biotic) and non-living (abiotic) processes operate pretty much independently of each other on its head. Their theory was that life on earth evolved with physical processes instead of as a result of them, and explains the relatively constant climatic conditions on earth (as opposed to say Mars) not as a ‘happy oxygen accident’ but as a direct consequence of the ability of biological organisms to regulate their physical and chemical surroundings. It proposes that in this way the earth (termed ‘Gaia’ after the earth goddess in Greek mythology) functions as an organism in homeostasis. Just as in the human body, negative feedback* regulates internal temperature and fluid balance, so the earth’s ‘organs’ (the oceans, atmosphere, soil) maintain a chemical and physical environment that is suitable for life.

As an Ecologist I study the interplay between biotic factors (e.g. behaviour, physiology and genetics) and abiotic factors (e.g. chemistry, geology and hydrology) and so the concept of Gaia makes sense to me. But is it true?! Or, in more scientific terms, can we accept the hypothesis based on evidence?

The best evidence comes from the sea. It has been demonstrated that cloud formation over the ocean is almost entirely dependent on the metabolism of marine algae (seaweed), a waste product of which, dimethyl sulphide (DMS), is oxidised to form aerosols on which water droplets condense[1]. Cloud formation is an important part of the hydrological cycle, which affects climate. Lovelock and Margulis also theorise that the reason we have atmospheric oxygen optimal for life (21% of total air composition) is related to the activity of bacteria that produce methane from dead organic matter.

The problem is that there are other examples of organisms not self-regulating at all, or where positive feedback** occurs. Under Gaia, the increase of atmospheric CO2 over the last 50 years should have been balanced by an increase in rates of carbon uptake by ecosystems, but carbon uptake has only increased by 2% in response to the 35% rise in atmospheric CO2[2].  This could be because the timescale is too short, or that the process of Gaia is just not enough to compensate.

At the end of the day, it seems that the Gaia hypothesis, like so many theories in the complex subject of environmental science, can neither be rejected nor accepted using current knowledge. There is evidence for and against it. The jury is out. I believe, however, that it raises important issues about the effects of human activity on the environment. After all, the human species, widespread burner of fossil fuels and agent of deforestation, is the most obvious organism influencing global climate of all.

* e.g. if it’s too hot, it gets colder, if it’s too cold it gets hotter.

** e.g. if it’s hot it just gets hotter! If it’s cold it just gets colder!