Biodiversity regulates climate - Part I: Adventures in Daisyworld

The idea that biology is affecting climate, a key concept that should be more widely spread for our climate’s sake, is already considered slightly radical. The idea that biodiversity is regulating the climate to benefit life, is even more radical. If true, it has a lot of implications for the climate movement.

This idea, fleshed out more, would look at how microorganisms, fungi, insects, plants, herbivores, carnivores can self-organize in a multiplicity of complex functioning feedback loops with the atmosphere to regulate the temperature, rain, and wind, so that they fall into a range of values that better suits life on earth. Its an idea about how life and atmosphere couple through the exchange of carbon, water, heat, and bioaerosols (microorganisms that seed rain) to guide the climate to stability.

We know that various organisms can alter their environment, intentionally or non-intentionally, to better suit themselves. Examples include constructing nests, building hives, damming streams, and increasing fertility of the soil. This behavior is called niche construction in ecology. Could life forms on earth somehow be enacting niche construction with the whole climate? Could life be doing so without a coordinated plan - self-organizing in a decentralized way?

Is evolution evoIving not just organisms, but also the climate? Should we think of evolution being described not just by the slogan ‘the fittest organisms survive’, but also by the slogan ‘the fittest environment/climate survives’?

One of the first scientists to bring up the idea that life could regulate the climate, was the Soviet geologist and geochemist, Vladimir Vernadsky. He wrote a book “Biosphere” in 1926 in which he discusses how life affected the atmosphere of the planet in a way that was beneficial for itself. For instance life produced oxygen, which then could form ozone in the atmosphere. That ozone then blocked harmful ultraviolet solar radiation. So life created a way to protect itself through regulating the atmosphere. Vernadsky’s way of seeing the world was met with a lot of resistance from scientists.

In 1965, James Lovelock, working as a consultant for NASA, was tasked with figuring out which planets might have life on it. He figured that the if a planet had gases that were in a nonequilibrium state then that would be a signature of life. On our earth, nitrogen, oxygen and methane are not in equilibrium, our gases require life to be producing them.

To Lovelock, the climate was a participatory arena, a co-evolutionary place that involved life. He noted ‘the climate and chemical properties of the earth, now and throughout history seem to have been optimal for life', and explained that this was because organisms were creating those optimal conditions. To him Earth was a self-organizing superorganism. He called his idea Gaia.

It was an idea all together too much for the biologists and ecologists of the day. What is the mechanism for this self-regulation they asked?

Lovelock searched for a biologist to work with him to figure out the mechanisms of this bio-climate self-regulation. In 1971, he starting collaborating with Lynn Margulis, a biologist who had already initiated a revolution in evolution which posited the idea of symbiosis as a mechanism other than competition as a key force in evolution. Now a symbiosis of Lovelock and Margulis worked to create a revolution in climate evolution.

Together they proposed numerous possible mechanisms of environmental and climate regulation. One was that bacteria and microbes in tidal flats could regulate the salinity of oceans and by the way they processed minerals in their bodies. Another mechanism explained how phytoplankton could regulate the climate. When it got hot, more blooms of phytoplankton would form. The phytoplankton emit a molecule DMS. The DMS gets decomposed by the sun into smaller molecules, molecules which help water vapor nucleate into clouds. Those clouds then cool the planet. In this way the phytoplankton amount and clouds adjust themselves until they come into temperature homeostasis.

Daisyworld

In 1983 Lovelock teamed up with the atmospheric scientist Andrew Watson, from the University of Exeter, to come up a simple model called Daisyworld that they used to illustrate how life could regulate the climate. In this simple simulated world there were white daisies and black daisies with a sun shining on it. The hotness of the sun was varied by Lovelock and Watson to see how the Daisyworld would respond. [Watson 1983]

When the sun luminosity was low, black daisies would survive and replicate more because they absorbed more heat. This raised the temperature of Daisyworld. As the sun’s got hotter white daisies would replicate more because they reflected more heat. This cooled Daisyworld. In this way the black and white daisies would adjust their numbers to keep the temperature constant in Daisyworld even as the sun got hotter. It might be surprising to some, that changing the hotness of the sun doesn’t change the hotness of Daisyworld; its not something one might expect if one holds a more linear ‘climate-driver → climate-response’ paradigm.

[In the above figure on the left is what conventionally we might think would happen in Daisyworld. On the right is what actually happens. You can see the temperature does not increase within a regime of solar luminosity values. Outside that regime the planet rapidly cools down or heats up.]

Next Lovelock introduced more biodiversity into his model by including 18 new types of daisies of various amounts of grey in addition to the black and white daisies. He found that for each different value of the sun’s hotness a different gradient of grey daisies would flourish. This helped to regulate the temperature into a homeostasis even better. The importance of having a biodiversity of daisies to choose from is that different daisies are useful for different heat perturbations to the system. As Lovelock said “What seems important for sustenance is not so much biodiversity as such, but potential biodiversity”. He talked about the implications of Daisyworld learnings - “In the Amazon and other regions under threat, destroying biodiversity will reduce the reservoir of apparently redundant of rare species. Among these may be those able to flourish and sustain the ecosystem when the next perturbation occurs.” [Lovelock 1992]

Next, lets introduce herbivores that eat daisies into Daisyworld. What impact would the herbivores have? At first glance, they might seem detrimental to the ability of Daisyworld to regulate itself to a constant temperature. But this turns out not to be the case. When Alberto Erlwein, from the Universidad Austral de Chile, did this simulation, he found that the temperature was even better regulated with herbivores present. With just daisies the temperature on Daisyworld ranged from 23.71 and 25.98 °C. With herbivores and daisies the temperature range narrowed to 25.28 and 25.52 °C. [Erlwein 2022]

What is going on here? Why should herbivores help with regulation? The reasoning is that it is beneficial to have some daisies get eaten, because then when the daisies grow back they can grow back in a gradients of grey that are even better optimized. The disturbance of the herbivores allows the system to adjust for better fit. As an analogy, imagine you throw a bunch of objects into a box in a random manner. The objects won’t fit very well. But if you shake the box a bit, the objects can settle to a bit lower, creating a better fit. The act of herbivores eating daisies is like the shaking of the box.

The herbivore-daisy relationship is an example of a predator-prey relationship, and these relationships are known to oscillate in population quite a bit. As the predator eat a lot of the prey, they increase in number while the prey numbers go down. Then when there are not enough prey to feed all the predators, the predator number goes down too. With less predators the prey numbers to go up. As prey numbers goes up, predator numbers can go up again. If you write these population dynamics in the form of whats called the Lotka-Volterra equations, you can see the oscillation in the variables. What is curious here is that the oscillation in population doesn’t translate into more oscillation of the climate, instead it can translate into more stability of the climate.

Next lets introduce another trophic level, another level of complexity to Daisyworld, by adding carnivores. Carnivores eat the herbivores that eat the daisies. With even more nonlinearity in the system it might seem that the climate would be destabilized. But curiously, again, the introduction of another trophic level helps with stabilization of the temperature.

Here is a plot that Lovelock made of Daisyworld as the sun’s hotness was varied. At each hotness level, different daisies, herbivores (rabbits), and carnivores (foxes) would become dominant. [Lovelock 1992]

Andrew Wood, from the University of Exeter, in a review of these results wrote “Many daisy, rabbit, and fox types were first brought together by Lovelock to create a numerical model for biodiversity. In the real world, biological systems are continually being perturbed by the cycles of day and night, the turn of the seasons, changes in the climate, and innumerable other factors. When a Daisy-world in equilibrium is perturbed by the introduction of a herbivore or a sudden change in solar input, a transient burst of different daisy types appears until the system restabilizes, with new types dominant. [editor note: What happened as the solar luminosity was varied was that many types of daisy would at first appear, before Daisyworld settled to a smaller number of species]. The greater the rate of change of the perturbation, the greater the resultant biodiversity. These results suggested that potential biodiversity is an essential resource for the response to perturbation, while expressed biodiversity is the sign of a perturbed system; hence the primary value of biodiversity may be its potential to regulate against environmental perturbations” [Wood 2007]

Daisyworld with clouds

The Russian astrophysicists Victor Gorshkov and Anastasia Makarieva are proponents of the idea that the biosphere is able to regulate the climate. Their website Biotic Regulation explores this concept. They write “Is there a concept that ecology could offer to put at the core of a global climate model, to adequately represent the biosphere? From our perspective, it is the concept of environmental homeostasis, which is the capacity of natural ecosystems to compensate for environmental disturbances and stabilize a favorable for life environment and climate.” To them “evolution proceeds in the direction of enhancing the regulatory potential of the ecological community.” They propose a number of mechanisms for this biotic regulation. One mechanism is that forests can regulate the amount of rainfall, by the timing of when they evapotranspire in order to attract more rain, which then brings the onset of wet season. Makarieva also posits that there exist some mechanism by which the ecosystem will create high clouds when it wants to warm up (high clouds trap more heat underneath than the solar energy it reflects), and low clouds when it wants to cool down (low clouds reflect more solar energy than the heat it traps underneath).

Lets illustrate a possible mechanism for this in Daisyworld. Lets add clouds to Daisyworld. We create different daisies that transpire different amounts of water. When there is less water vapor in the atmosphere, the water vapor has to rise to higher altitudes to get to colder temperatures before it forms a higher cloud. When there is more water vapor, it can condense at lower altitudes with warmer temperatures, where it forms lower clouds. The ground in Daisyworld can be simulated by a grid of squares, each of which can each host a daisy. Above each ground square we have two levels. The lower level is for low clouds. And the higher level is for high clouds.

As we vary the sun’s hotness, different daisies will create different height clouds. The daisies that evapotranspire more will create low clouds that lead to more coolness, while the daisies that evapotranspire less will create high clouds that lead to more warmth. When the sun is not very hot the daisies creating high clouds will dominate. When the sun gets got the daisies creating low clouds will dominate. In this way Daisyworld can regulate its own temperature through transpiration. There is a range of the sun’s hotness levels for which the system stays in homeostasis.

We can introduce herbivores and carnivores to this world. The herbivores will disturb the population of the daisies in a way that will actually help the ecosystem fine-tune the average height of all the clouds to regulate the temperature even better than if Daisyworld has just daisies. This is because when daisies get eaten, new daisies with different transpiration rates will grow that are better at helping regulate the temperature for that particular solar luminosity.

This regulatory ability will happen only within a range of parameters though. If the herbivore population gets out of hand, it can end up killing too many daisies, and Daisyworld will no longer be able to regulate its own temperature. One of the roles of the carnivore is to help keep the herbivore numbers in check. This role illuminates why biodiversity, why a multiplicity of trophic levels, is important for climate stability.

That changing the suns hotness doesn’t change Daisyworld’s hotness is an intriguing emergent phenomena. We are used to thinking in more linear terms for climate effects. We shift an external factor, technically called a climate driver, and we get a linear climate response. So for example we change carbon emissions and we get a linear climate response of a temperature rise. But what if the earths eco-climate is more nonlinear? What if it is the case that when the earth has enough biodiversity it can handle an increase in carbon emissions by self-organizing itself to keep its own temperature constant, and that the problem is that we have destroyed so much biodiversity that the earth is no longer able to do this. If so the way out of our climate crisis is not only through carbon emission reduction, but also through biodiversity increase.

Anastasia Makarieva writes “The concept of the biotic regulation of the environment provides a very clear scientific base to the necessity of biodiversity conservation. Natural species of the biosphere … are indispensable parts of the working mechanism of maintenance of environment on both local and global scale. Each species inside the community performs strictly specified work on stabilisation of the environment. The programme of this work is determined by the species genome. And due to the unique nature of species genomes this work cannot be done by any other species.”

We currently have a climate movement and a biodiversity movement. These are for the most part, two separate movements. As our understandings grow and spread of how important biodiversity is to climate, these two movements can merge and synergize.

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For more real world examples of biodiversity regulating climate, see my previous article Web of Water

For part II of this ‘Biodiversity regulates climate’ series, “Unifying ecology and climate with the fourth law of thermodynamics” I describe how the fourth law, which is that systems approach states of maximal power, applies to both ecology and climate. It also applies to the earth as a whole, which means that climate integrates its function with ecology to maximize power. In so doing we can see how ecology affects climate. Here is the link to the article.

https://climatewaterproject.substack.com/p/unifying-ecology-and-climate-with

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This is a reader supported publication.

References

Baldocchi, Dennis D., Theresa Krebs, and Monique Y. Leclerc. "“Wet/dry Daisyworld”: a conceptual tool for quantifying the spatial scaling of heterogeneous landscapes and its impact on the subgrid variability of energy fluxes." Tellus B: Chemical and Physical Meteorology 57, no. 3 (2005): 175-188

Erlwein, A. "Exploring Ecosystems Health: Effects of Increments of Biodiversity and Trophic Complexity on the Stability of a Simple Gaian Ecosystem Model." Agro sur 50, no. 2 (2022): 13-24

Lovelock, James E. "A numerical model for biodiversity." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 338

Lovelock, James E. "Geophysiology." Earth and Environmental Science Transactions of The Royal Society of Edinburgh 80, no. 3-4 (1989): 169-175

Muñoz, Estefanía, and Jorge Carneiro. "Plant–microbe symbiosis widens the habitability range of the Daisyworld." Journal of Theoretical Biology 554 (2022): 111275.

Watson, Andrew J., and James E. Lovelock. "Biological homeostasis of the global environment: the parable of Daisyworld." Tellus B: Chemical and Physical Meteorology 35, no. 4 (1983): 284-289

Wood, Andrew J., Graeme J. Ackland, James G. Dyke, Hywel TP Williams, and Timothy M. Lenton. "Daisyworld: A review." Reviews of Geophysics 46, no. 1 (2008)