Does I = PAT?

The equation I = PAT was invented by Barry Commoner in 1972 and is widely used by the pressure group Population Matters in arguing for population control. It asserts that humanity's environmental impact (I) depends on population (P), affluence (A) and technology (T). The last factor is best understood as a measure of the resource inefficiency of our various industrial, agricultural and other processes.

The terms P and A are easy to understand and relatively easy to measure. GDP per head is a workable measure of A. I and T are much harder since there are many kinds of environmental impact, eg greenhouse gas emissions, deforestation, mineral resource depletion and loss of biodiversity, which are not always strongly correlated. (see, eg, Cole and Neumayer, 2004).  That is, we need a set of IPAT equations, one for each kind of environmental impact. Each will need its own T value which will be defined as I/PA rather than calculated independently.

IPAT, therefore, is not so much a proposed law of nature as a suggestion for relevant factors when considering environmental change. Initially IPAT was useful but it can now be seen to be rather misleading.

The variations between groups
The equation suggests (at least when applied globally) that the affluence of the world's population can be expressed by a single number. Though technically correct it's very misleading. The reality, obviously, is of vast variations in affluence and lifestyle both between countries (contrast Somalia and Switzerland for instance) and within countries (contrast bankers and farm workers).

Single numbers are sensible where everyone is the same or where a characteristic shows a normal distribution (as for human height for instance). Affluence shows a Pareto or, colloquially, 80:20 distribution (20% of the people own 80% of the wealth) and is thus not well represented by a single number.

The interdependence of P and A
The equation suggests that population and affluence are independent variables which in general they are not. During the 19th century the UK's population and prosperity rose together as the agricultural, industrial and scientific revolutions (plus the spread of empire) produced ever more food, manufactured goods and services. In this period the true independent variable was probably 'progress'. This pattern has been repeated many times as other countries have industrialised and in most cases the main growth phase has been followed by a marked reduction in population growth.

Today growth in affluence is greatest where population growth is modest.

The parity of P and A
The equation suggests that population and affluence are of comparable importance in creating environmental impact. In fact that's not true. In recent decades our impact has risen much faster than population and is largely driven by increasing affluence. Some of this is due to the increasing wealth of the mega-rich 1% (or 0.1% globally I suppose) but much is due to the increasing numbers of Koreans, Brazillians, Indians and Chinese who can afford cars, meat and broadband Internet.

The meaningless differential
The equation suggests that its first differential would be
            dI/dP =AT.

That is, that a small (say 1%) increase in population will produce the same proportional increase in environmental impact. That, of course, is unreal. The world's population comprises many subpopulations with very different lifestyles and levels of affluence. One extra Briton will consume much more than one extra Bengali and will have correspondingly more impact.

So this first differential will be accurate only if every subpopulation increases by the same small amount. But that isn't happening. Some countries are still experiencing rapid population growth whilst growth elsewhere is static or even negative.

The first differential also requires an associated growth in the local economy to provide the extra people with goods and services. It is, at least, unclear whether local economies can respond in this way without accelerating impacts on the environment. Two examples may illustrate this:

• As people migrate to London suburbs they will need roads, houses and schools. If they find work and pay taxes they can afford them. But since there can be no more land we may expect more air pollution, less green space, higher house prices and higher population densities.
• As population increases in many East African villages the women must walk further for firewood. That gives them less time for farming and childcare whilst reducing the ground cover.

The complexity of things
The IPAT equation suggests a simplicity that simply does not exist. The complexity of things is not in doubt and its time to stop using this simplistic equation.


Refs

Cole, M. A. and Neumayer, E. "Examining the impact of demographic factors on air pollution," Population Environment 26.1 (2004): 5-21.

Commoner, Barry. 1972:  “The Environmental Cost of Economic Growth.” in Population, Resources and the Environment. Washington, DC: Government Printing Office Pp. 339-63, 1972.

Methane hydrates: Threat or promise?

Methane is a valuable fuel and a potent greenhouse gas. At low temperatures and high pressures it combines with water to make methane hydrates. There's a huge amount of the hydrates - perhaps twice as much as all other fossil fuel deposits - on the seabed - especially in the far north.

The obvious threat is that warming waters - those in the north are warming fastest - will destabilise the hydrates releasing vast amounts of methane and thus accelerating climate change. This is a particularly scary possibility for three reasons:

• It's a positive feedback loop. Once established it will probably overwhelm all the other mechanisms.
• The sea warms slowly and warming lags the relevant gas releases. 
• Hydrate deposits are poorly understood so we can't forecast how much methane will be released how soon. 

It's therefore possible that we have already released enough greenhouse gases to create catastrophic climate change. Most climate scientists think this unlikely; but the IPCC consensus has usually been over-optimistic.

Hydrates also have a promise. Methane is a very clean fuel and its extraction from hydrates will probably be an efficient process. IF we switched from coal and oil to methane and IF we could keep leakage well below 1% then we would reduce the greenhouse effect. It's no panacea but it would help a lot.

Those are big IFs. In practice new energy sources usually add to consumption. The US currently benefits from fracked methane but instead of closing coal mines it is exporting coal - much of it to Europe.

In a sane world hydrates might be an opportunity. In fact they remain a dreadful threat.

Geo-engineering is coming of age

According to New Scientist (12/10/13, p 10) the IPCC now sees geo-engineering as essential if we are to avoid catastrophic climate change. That was the conclusion of the recent Oxford Conference on Negative Emmission Technologies. 

New Scientist's summary shows seven technologies any one of which could, if energetically implemented, remove at least one gigaton of carbon per year from the atmosphere. That's 10% of annual emissions.

The costs, for what are often theoretical technologies, are highly uncertain and fall in the range $10 to $2,000 per ton of CO2 captured. So the cost of removing one gigaton of carbon per year would be on the order of $400 B dollars per year. That's a lot by any ordinary standard. On the other hand it's just a quarter of the world's annual arms bill.

But money isn't the only issue. Some methods require physical resources such as gas-tight strata or land for tree planting and these are needed for other purposes too.

Has aviation seen the light?

New Scientist (12 Oct 13, p 6) reports that the airlines have agreed to participate in an emissions trading scheme. That's a useful point of principle gained but may have no real effect. It will only be worthwhile if the airlines are given significantly LESS permits than their current emissions. (Why give them any? Beats me but that's how it is.)

Experience with the EU ETS and the shipping rules are discouraging but I suppose we have to hope.