A sustainable development talk yesterday made the point that we have to be careful not to focus purely on carbon emissions to the atmosphere, since if we do this we may make other environmental problems worse. The examples of acidification and eutrophication (elevated levels of nutrients e.g. nitrogen) were mentioned, but I’d certainly add water availability to the list.
At first sight, different problems of sustainability may seem to be incommensurable. But I suggest they can be related in various ways. For example, we could set up tradable quotas of all different emissions to the atmosphere allowed in a given geography – e.g. globally or in South Cambridgeshire – and establish financial markets for all resources, in particular water and land, and allow the market to sort the problem out for us. Having a Carbon Budget alongside the fiscal Budget, as our friend Alistair Darling has announced the UK will do from 2009, in fact represents a reinvention in a limited form of that clever tool we call “money”. The wrong approach, IMHO. What’s needed is political courage, not a new currency. If it is indeed necessary to postpone from April to August a 2p/litre rise in fuel duty, then we’re only pretending to solve the problem. You can’t make meringue without breaking eggs, Chancellor.
Until and unless we monetise all environmental resources, we can nevertheless make ad hoc analyses to try to work out whether we are doing the Right Thing. The use of biofuels is a case in point. Here, the crucial resource is land, because land (that we humans have deemed is not required for food production or other uses) can be used either to grow biofuels or left alone to sequester carbon. There may be other reasons for using land to grow biofuels, but here we are only concerned about global warming. We therefore consider growing biofuels to be a way of employing land to try to alleviate global warming, using a resource (the land) to (supposedly) reduce a liability (carbon emissions in the atmosphere). Since land stores carbon naturally (go for a walk in the woods!) there is an opportunity cost in terms of carbon emissions of the land we use to grow biofuels. The crucial question is how long we have to grow a given biofuel for on land with a given carbon carrying capacity (dependent on climate conditions etc.) in order to produce a net carbon saving.
A few years ago we were all talking about our “ecological footprints”, i.e. how much land we need to support our lifestyles. If we switch from fossil fuels to biofuels we obviously increase our footprint. Land use therefore seems to me the obvious measure of whether biofuels are indeed sustainable. Growing biofuels saves (if we’re lucky) an amount of carbon each year. This amount is small relative to the amount of carbon stored in a natural ecosystem on the same land. I therefore suggest that the critical measure of sustainability is the payback period, the number of years for which biofuels would have to be grown in order to justify the decision to farm the land rather than allow it to support a natural ecosystem, such as a forest. This idea is developed in this paper:
Biofuel Payback Periods (pdf).
Once again, for a little more discussion around the issue, please see my original essay on this topic, Biofuels Are Not the Answer (pdf).
Note that my argument is not particular to biofuels. It can also be applied to other land uses. We need to take the opportunity cost of the land required into account when, for example, deciding what food to eat or how to produce energy. In the case of renewable energy, my method is really no different to taking into account the carbon emissions (and/or energy) “embedded” in the hardware. PVs, I’m reliability informed, take about 1 year to pay back the energy cost of their manufacture. If the purpose is to “displace” carbon emissions, and we start to cover fields with the things (as apparently is being done in Germany), then we also need to consider the payback period for the land being used – a PV “farm” is no longer able to support an ecosystem, such as a forest. Obviously, the best place to put PVs is in the desert, where there’s also more sun per square metre and less cloud, and not artificially divert the world’s limited supply of solar panels to Northern Europe.