Contraction and Convergence - The C&C Proposal

The C&C Proposal

The "contraction" part of Contraction and Convergence model calculates the total amount of carbon being put into the atmosphere as a 'path-integral' or a total 'contraction-event'. Future global emissions will shrink over time and the shape and extent of this will depend on the final level of atmospheric carbon considered safe, subject to the changing source-sink relationship in future as future atmospheric GHG accumulation continues.

The "convergence" part structures how the entitlements to emit carbon are shared between the countries or regions of the world. Initially entitlements would reflect current emissions, however subject to a negotiation of 'the rate of convergence' these initial entitlements will converge towards equal per capita entitlements across the planet. An early date of convergence will mean that countries with currently low per capita emissions (which as a rule are poorer countries) will see their entitlements rise while a late date for full convergence would risk curtailing poorer countries' chances of development.

Once convergence is reached then all countries entitlements would continue to fall, subject to the contraction-event required to be UNFCCC-compliant.

Some argue that the per capita focus risks giving an incentive to countries to increase their population to "earn" more entitlements. To answer this, the GCI put a 'population base-year' function in the model for users to choose and specify any date between 2000 and 2050 beyond which no further entitlements would result from population growth.