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

World greenhouse gas emissions
Global emissions scenarios
Figure 1.8. Global emissions for two scenarios considered by Baer and Mastrandrea, expressed in tons of CO2 per year per person, using a world population of six billion. Both scenarios are believed to offer a modest chance of avoiding a 2°C temperature rise above the pre-industrial level.
Figure 1.9. Breakdown of world greenhouse-gas emissions (2000) by cause and by gas. “Energy” includes power stations, industrial processes, transport, fossil fuel processing, and energy-use in buildings. “Land use, biomass burning” means changes in land use, deforestation, and the burning of un-renewed biomass such as peat. “Waste” includes waste disposal and treatment. The sizes indicate the 100-year global warming potential of each source. Source: Emission Database for Global Atmospheric Research.