Has Gaia really been explained?

I was interested in a new paper which claims to be able to explain the Gaia hypothesis, first proposed by James lovelock, that life stabilises the earth’s climate.  The paper is described in an article in the Conversation. The paper itself is here.

Life has existed on Earth for the last 3.7 billion years during which time the sun’s output has increased 30% while the atmospheric content has changed dramatically, determined by life and geology. Lovelock proposed a simple ‘Daisy World’ model of white and black daisies to illustrate how life could regulate temperature by changing surface albedo. This new paper takes this idea much further by generalising to an ensemble of species and environments. Each species is best adapted to a particular set of environmental parameters where they flourish and struggles far outside this optimum. Their interaction with the environment is such as to maintain these ideal set of conditions.  The model assumes a Gaussian like distribution about these optimum conditions. There is then a competition between species, and external astronomy and geology which selects who survives and which species preferred environment wins out over time. They call this model “sequential selection”. It  is illustrated in their Figure 1. below.

The figure shows a hypothetical interaction between 4 species as the environment changes (eg. Solar increases). Life acts to dampen change as 4 species flourish and then die off. Environmental variable E could simply be temperature.

This mechanism can only work if each species interacts with its environment so as to dampen changes from its preferred value, i.e. it has a negative feedback.  If any Species evolves which globally has a positive feedback on an environmental variable, then it will quickly drive itself to extinction. This is where we find a bit of politics creeping into the article, because what is implied is that humans, despite our success, are nevertheless driving temperatures beyond the optimum value for our species.

What is true is that we are releasing a fraction of buried organic carbon back into the atmosphere over a relatively short time span, after which the atmosphere will slowly recover.  The effect on climate and on other species will be negative in some places and perhaps even positive in others. As a result these other species will begin to react to these changes so as to counterbalance this increase in CO2. Plants are an obvious example.

I don’t think “sequential selection” is really a fundamental breakthrough in understanding Gaia. Instead it is more like an ensemble of ‘Daisy’ like species each with a Gaussian value for its optimum ‘environment’, whose populations acts to stabilises each successive optimum. If one fails (goes extinct) another then takes over, until (hopefully never) none are left and the planet dies.

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