Sunday 4 April 2010

Biosphere in transition. 1. Carrying capacity

I thought it might be useful to place the transition we’re in into the wider context of life on planet Earth. Over the next four days I would like to talk about the negative impact that we as a species have on the biosphere, as seen by e.g. global warming, loss of soils, pollution, and loss of biodiversity. I will use the formula I=C-PAW* to look at four main factors that influence our impact (I): carrying capacity, population, affluence, and waste. The first one sets the limits, and we’re in transition because of a recognition that the product of the latter three factors is too high. None of these factors by itself is “bad”. It’s natural to have children, to prefer a comfortable over a degrading life, and to produce entropy or waste. The whole of the problem is that the biosphere has a limited capacity to absorb this impact, which in ecology is called the carrying capacity. One of the important things to realise is that if the product PAW exceeds carrying capacity, carrying capacity decreases. That is, impact that isn’t absorbed by the biosphere stays around to do damage. Hence the negative impacts.

Today I will look at carrying capacity. Carrying capacity is the number of organisms that can survive on a given area. Carrying capacity is not absolutely fixed. For instance, if food is grown in a polyculture rather than a monoculture, yields go up and thus the carrying capacity increases. For a given population size and technological efficiency, increasing carrying capacity allows for more affluence. However, carrying capacity is not a panacea. For instance, health care consumes resources without producing food, so the carrying capacity with health care is lower (fewer people with a life expectancy of 80) than without (more people with a life expectancy of, say, 50). I find this a useful yardstick on which to base policies for technology. If it gives us more affluence with the same amount of waste it is good, and if its negative impacts give us a bigger decrease in long-term carrying capacity than any short-term increase in affluence then it is a bad idea, and one has a rational basis for calculating the cost of the negative impacts that can be balanced by a pollution added tax that functions to limit the implementation of this technology until it fits within the carrying capacity.

* I arrived at this formula by combining the formula I=PAT from Ehrlich & Ehrlich (1990) with the concept of the ecological footprint (e.g. Ewing et al. 2008).

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