1. The ultimate aim must be absolute zero, but net zero means that the carbon that cannot be removed by 2040 can be sequestered. Importantly only internationally validated amounts of sequestered carbon can be considered in net calculations.
2. The necessary actions to meet these commitments are arrived at from the concept of ‘Contraction and Convergence’, which, as with the UNFCCC and the UK Climate Act, is based on principles of precaution and equity. This means that to reach net zero global emissions by 2040 all countries first converge to the average global per capita emissions, then reduce to zero by 2040.
Those countries with high carbon emissions have to make large reductions, whilst most countries with low emissions will have entitlements of increased per capita emissions initially, with all countries reaching net zero by 2040. The implication for a high emitting country like Britain (present average per capita emission 5.6 tonnes of carbon dioxide) is each person rapidly converging to the global average (4.8 tonnes/capita), and then reducing to zero by 2040. This further reduction has to be extremely rapid as the global share of carbon for each Briton is about 0.5 tonnes for each year between 2020 and 2040. The average British home emits 2.7 tonnes of carbon dioxide a year from domestic heating, and a return flight from London to New York emits 1.0 tonne of carbon dioxide.
These examples illustrate the dramatic changes we need to make in how we live, eat, travel, and work to keep below a global temperature increase of 1.5°C.