The big picture

This week in the “Green Room” on the BBC News website the opinion article discusses the role of population and the environment. Not surprisingly a furious debate on the issue follows. I am not going to enter into that affray, but it is useful looking at this issue in the context of CO2 emissions.

The discussion on population and growth is best described by the Kaya Identity which can be written as follows:

CO2 emissions = Population * Wealth/person * Energy/GDP * CO2/Energy

The four parts of this simple equation show the key elements that contribute to overall energy related CO2 emissions. Apart from population, there is a factor for development (i.e. wealth per person), a factor for the energy we use to generate a unit of wealth (or Gross Domestic Product – GDP) which can also be called “efficiency” and finally a factor that represents the type of energy we use to generate that wealth, but expressed in terms of CO2 emissions.  This final factor will be effectively zero for wind, but quite high for coal, for example.

Arguably, all four of these factors should be in play when it comes to managing CO2 emissions. In reality, we are limiting our efforts to just two of them. We don’t really want to talk about population and we seem to have even less desire to talk about wealth limitation. The latter is also problematic given the large wealth disparity that exists in the world today.

That leaves us with efficiency and the type of energy we use. This is where the big focus of policy development sits – encouraging energy efficiency and using tools such as emissions trading to shift the type of energy we use to lower CO2 options or to eliminate the CO2 emissions using technologies such as carbon capture and storage.

The question that the Kaya Identity poses for us is a simple one. Can we reduce CO2 emissions by nearly two thirds in just 40 years (i.e. a 50% reduction from 1990 levels by 2050) whilst population and GDP inexorably rise (by ~50% and ~300% respectively), relying only on energy efficiency and a shift in the type of energy we use (or the massive application of carbon capture and storage) ?