The greater number of people who use a resource, the faster it is depleted. Global population—symbol P—is rising, and so too is affluence, which we will write as gross domestic product (GDP) per capita, GDP/P. Then material consumption grows as
The last term is the material intensity of GDP. Energy consumption can be expanded in a similar way:
Here the last term is the energy intensity of GDP. Finally, if we want to focus on carbon emissions rather than energy, we have:
GDP Energy Carbon
Carbon emissions = P x x x (11.3)
P GDP Energy
This time the last term is the carbon intensity of energy.
Any move toward sustainability must stabilize and ultimately reduce all three of the quantities on the left of these equations. That means reducing at least one of the terms on the right. Population forecasts indicate continued growth at least in the near term, and to imagine that the world’s population P will not continue to strive for increased affluence GDP/P is, well, unimaginable. You could ask: how much GDP is enough? Figure 11.5 is a plot of one measure of human fulfilment, the U. N. Human Development Index (HDI), as a function of GDP per capita in 2008. There is clearly a plateau. The plot suggests that a GDP per capita between $30,000 and $40,000 is more than enough to achieve it; any further increase buys no
and on the way it is governed. But Figure 11.6 provides some perspective: if all the countries plotted here could achieve the performance shown by France, global carbon emissions and energy consumption would fall by a factor of 2 straight away.