May 01, 2003

Finiteness of Earth

One of the major changes that has occurred in the relationship between humans and our planet is the realization that Earth is finite. I placed a scale on Earth’s size a few days ago – the radius of a sphere of equal volume. With a radius of about 6000km, that sphere has finite volume. Now that volume is large and for most of human history it was so large as to be essentially infinite. Resources could be extracted and wastes disposed of at no apparent cost to the present or future. This was true because the rates of extraction and disposal were small compared to the overall size of our planet.

As our numbers and capacities have increased, the fluxes of material through our societies have increased to the point that we can now “feel the edges” of Earth’s capacity. Assumptions of infinite sources and sinks must now be replaced with boundary conditions on capacity.

If we assume that there are 5 billion (5e9) people (I know there are more than 6 billion, but 5 is such a nicer number to work with) and that Earth has 1e14 square meters of ice-free land, then everyone gets about 2e4 square meters of land (about 4 American football fields) to produce and absorb all of the inputs and outputs that they need to survive.

Water is another resource that is limiting for humans (actually all life on Earth). Earth has a lot of water, but 97% of it is in the oceans. Of the remaining 3%, 70% is tied up in glaciers and permanent snow. This leaves about 1% of the total water on Earth for all of human needs. Indeed a significant proportion of Earth’s inhabitants do not have access to adequate water resources.

Nitrogen provides an example of human capacity to rival that of natural systems. I don’t have the exact numbers at hand at the moment, but very roughly, human activities are responsible for a doubling of the magnitude of the nitrogen cycle. In the case of nitrogen, humans have overwhelmed the natural system and we do not yet know what the effects of this impact will be.

Finally consider food. I sometimes start a discussion of environmental policy with our cheery friend Malthus. He certainly was concerned about issues of finiteness and rooted his policy recommendations in the assumption that our ability to reproduce would soon outstrip our ability to produce food. The doom and gloom that he expected has, for the most part, not developed because he did not consider the impact of technological innovation on the productivity of farmers. Ignoring infrastructural issues related to the distribution of food, we have the capacity to produce enough food for Earth’s current population.

This leads to the question of whether there is a largest number of humans Earth can support. Certainly there is an upper limit related to the physical space that each person must occupy, but well before that limit, is there a limit based on the ability of Earth systems. Joel Cohen addressed this topic in his book How Many People can the Earth Support? His answer is that it depends on how well you want those people to live. Thus while there are certainly physical limits, there will be cases there our values and desires establish the upper limits of our activities.

The case of Malthus brings up and interesting counter argument to what I have written so far. There are those who will argue that Earth is in fact not finite. There argument is rooted in the idea that technological will always advance faster that resources are depleted and provide substitutions etc. I find these arguments to be hopeful by ultimately not helpful. It is true that the Malthusian disaster has been steady pushed into the future by technological innovation, I think it is overly optimistic to believe that we have nothing to worry about because technologists will always save the day.