# IPAT and the End of Growth

2013/11/06 at 23:09

In the early 1970s Ehrlich and Holdren devised a simple equation in dialogue with Commoner identifying three factors that created environmental impact. Thus, impact (I) was expressed as the product of (1) population, (P); (2) affluence (A); and (3) technology, (T):

I = P * A * T

Population is the number of people on the planet, affluence is measured in GDP per capita, and technology is environmental impact per GDP. When looking at the growth rates of each I, P, A, and T the formula changes towards this form:

dI = dP + dA + dT

In order to see how the impact changes from one year to the next one, you just have to sum up the changes in population increase, affluence, and technological progress. Technological progress can best be understood here as a change in intensity. So if the environmental impact of choice is CO2 emissions, the T you are looking for is carbon intensity: “Carbon intensity is a measure of how much carbon economies emit for every dollar of GDP they produce.” Improvement here means lower carbon intensity and the change rate is the decrease in carbon intensity dT.

When we average the population increase to the median level of 9 billion people at 2050, we can assume dP to be around 0.5% each year until the middle of this century. The desired dA, the growth in GDP per capita, is 3% each year. The average improvement (decrease) in carbon intesity globally was around 1.9% each year. If we ignore any possible changes to all these numbers in the future we can calculate the annual change in carbon emissions (dI) as

dI = 0.5 + 3 – 1.9 = 1.6% more carbon emissions each year

So in order to not increase carbon emissions, we would have to decrease carbon intensity – via new engine technologies, new forms of energy creation, maybe carbon capture and storage – at least by 3.5% each year. That implies almost an instant doubling of our technological efficiency as regards CO2 emissions. There is no immediate technological solution that could produce this result. The later we do it, the higher the reductions in carbon intensity would need to be. And we are not talking about reducing emissions in total, just to keep the emissions at the same level as today. In order to reduce emissions we need more than 3.5% decrease in carbon intensity. If we want to stick to the 2C-guardrail in temperature increase until 2100, the global economy would need to be emission-free from 2050 onwards. The math is simple: it requires a six-times increase in carbon efficiency each year to reach zero by the middle of the 21st century. Tomorrow. Not in 10, not in 20 years.

From the very simple IPAT equation it is clear, that with a fixed increase in affluence, no environmental goal can be met. Of course there is no consensus up until this day to reduce affluence increase i.e. reduce global growth of GDP per capita. If dA would be below 1% each year, the task would however look much more doable. Of course 1% as a global aggregate would imply degrowth in the global North with, say -0.5 to -1.0%, a steady state development in countries like China and Brazil, and a positive growth rate in the rest of the global South between 4 and 5% maybe. Such a policy would alleviate poverty by 2050 largely and allow the World economy to stay within planetary ecological boundaries.

This policy will not be enforced now. But it will be enforced in a couple of years. The reasons for this are pretty easy regarding the maths of a finite planet. We are overshooting planetary limits by about 50% today, meaning that we would need half of another Earth to satisfy our present consumption levels. So the numbers in the IPAT equation above will not unfold in reality, the development will hit the walls. Paul Gilding calls this the “Great Disruption“. Decrease in crop yields and fishery, increase in food and resource prices will send shockwaves through the global economy, producing even greater financial collapses as we seen in 2008 and 2009. And this will also have geopolitical consequences. There is no “away”. There is no second Earth. We will have to deal with this here and now. At one moment in time, the IPAT equation has to and will change its numbers. The sooner we do it voluntarily with political and economic measures, the easier the transition will be. And with less misery, tears, and blodshed. But regardless, the era of economic growth as we knew it is over. It is simple as math and the numbers add up quite badly.