Originally published in GreenSWord June 2005

Contraction & Convergence is a “buzz phrase” which you need to understand as part of the debate about possible responses to climate change.

The idea came out of an organisation called The Global Commons Institute (GCI) which was founded in 1990 in response to climate change becoming a global political issue.

They started by showing the worsening asymmetry, or “Expansion and Divergence” of global economic development. In essence the global majority most (likely to be) damaged by climate change are the same majority who are already impoverished by the economic structures of the minority who are causing most damage to the climate.

In response to this GCI developed a model for future emissions which would be both sustainable, and resolve the inequality inherent in the current situation. This model is known as the contraction and convergence (C&C) model.

It is based on a sound scientific analysis of the causes of climate change. You need to understand two key measurements that it uses.

The first is the concentration of greenhouse gases (GHG) in the atmosphere – this is expressed in ‘parts per million by volume [ppmv] of CO2 equivalent’. In  other words in a million litres of air, how many litres of GHG are there.

In 1900 the level was around 300ppmv. Currently (2004) there are roughly 365ppmv CO2 equivalent in the atmosphere, and this is rising at around 100ppmv every 45  years – and the rate of increase is increasing.

So the first question to be answered is what level of GHG is sustainable globally? Or to put it another way how much climate change can we actually live with before the planet becomes uninhabitable to humans?

The consensus is that anything over 450ppmv CO2 equivalent is “not safe” (a nice euphemism for climate change catastrophic to human life on the planet). There seems to be no-one who is suggesting any level above this is sustainable in the mid-long term. Many scientists are arguing that 350ppmv would be a better long-term bet, and some want to see a return to 300ppmv as more sustainable.

If we continue with the current rate of GHG emission we hit the 450ppmv level around 2025 – in 20 years. But in fact the rate is still INCREASING. To put it another way the government that is elected in three elections time (2017 - the same timescale as when Major was PM) will be having to cope with the effects of catastrophic climate change.

Globally the rate at which we are producing GHGs must be reduced to stabilise the atmosphere at less than 450ppmv. Currently we put about 7.5billion tonnes (7.5GT) of carbon into the atmosphere each year.

The model shows that to stabilise at 450ppmv this needs to reduce to less than 2GT by 2100, and less than 1GT early next century.

This is the Contraction part of C&C.

The second key measurement is the number of tonnes of carbon produced per person per year.

Underlying the Global Commons approach is a principle of “equality and survival” which states that in the long term everyone on the planet should participate equally in the stewardship of the planet.
So if we know how much GHG we can put into the atmosphere “safely” and sustainably, and we know the population; then we can calculate how much each one of us can be allowed to produce – measured in tonnes of carbon per capita per year.

Currently one third of the world’s human population have 94% of global purchasing power and cause 90% of GHG pollution – and that one third includes the UK.

This is the Convergence part of C&C, where over an agreed timescale (eg by 2050) we all converge on a common level of emissions. This throws the onus on those who currently pollute most to make the biggest changes, and allows China, India, Africa and Latin America a very slight increase before we all reduce emissions further together over the following 50 years.

In order to stabilise at 450ppmv with a world population of around 6 billion (the current level with no net increase) then the tonnes of carbon produced per person globally needs to fall to less than one third of a tonne within 50 years.

For us in the west this Convergence part of the equation has extremely dramatic implications. Currently in this country we each are responsible for around 6 tonnes of GHG per year ^*  – so we have to reduce that by at least a factor of 20 as we converge on a safe global steady state.

The Global Commons Institute has done a lot more work on the economic impacts and scenarios which you can access through their website; slideshows, spreadsheets, graphs and loads of further links are all there.

In conclusion the CGI states “Presently the global community continues to generate dangerous climate change faster than it organises to avoid it. The international diplomatic challenge is to reverse this. The purpose of C&C is to make this possible. It enables scenarios for safe climate change to be calculated and shared by negotiation so that policies and measures can be internationally organised at rates that avoid dangerous global climate change”

For us in the Green Party the message is clear – here is a model that the international community is increasingly recognising as a viable way through the challenges that face us (even the USA stated in 1997 that “C&C contains elements for the next (post Kyoto) agreement that we may ultimately all seek to engage in”).

We need to be lobbying and informing our MPs and the wider public about the need for the UK to sign-up to C&C, and we need to be vigorously developing and pursing policies which can help us reduce our own personal emissions below the third-tonne level.

C&C is already enshrined in MfSS (CC243…) and there is a useful policy brief on the GP website which you can download and print as a leaflet.

^{* estimates seem to vary between 9 & 3 tonnes per person for UK}