entists reckon it’s more likely than not that global temperatures will rise
by more than 2°C. The sort of cuts we need to aim for are shown in fig-
ure 1.8. This figure shows two possibly-safe emissions scenarios presented
by Baer and Mastrandrea (2006) in a report from the Institute for Pub-
lic Policy Research. The lower curve assumes that a decline in emissions
started in 2007, with total global emissions falling at roughly 5% per year.
The upper curve assumes a brief delay in the start of the decline, and a 4%
drop per year in global emissions. Both scenarios are believed to offer a
modest chance of avoiding a 2°C temperature rise above the pre-industrial
level. In the lower scenario, the chance that the temperature rise will ex-
ceed 2°C is estimated to be 9–26%. In the upper scenario, the chance of
exceeding 2°C is estimated to be 16–43%. These possibly-safe emissions
trajectories, by the way, involve significantly sharper reductions in emis-
sions than any of the scenarios presented by the Intergovernmental Panel
on Climate Change (IPCC), or by the Stern Review (2007).
These possibly-safe trajectories require global emissions to fall by 70%
or 85% by 2050. What would this mean for a country like Britain? If
we subscribe to the idea of “contraction and convergence,” which means
that all countries aim eventually to have equal per-capita emissions, then
Britain needs to aim for cuts greater than 85%: it should get down from its
current 11 tons of CO2e per year per person to roughly 1 ton per year per