Geoscience Reference
In-Depth Information
(see Figure 2.4). Thus, trajectory RCP8.5 corresponds to the strongest
radiative forcing. It reaches 8.5 W/m
2
in 2100 and then increases. It
corresponds to scenario SRESA2 and is considered the upper limit of
the range for emissions; scenario RCP4.5, which approximately
follows the trajectory of SRESB1, reaches a radiative forcing of
4.5 W/m
2
in 2100 and then stabilizes around this level. Scenario
RCP2.6, after an
excess
predicted
around 2030-2040, seeks to impose
measures for mitigation that will enable the reduction of emissions to
meet the policy objective not to exceed 2°C of global warming. The
choice of these trajectories, expressed in radiative forcing, is directly
usable by coupled models in their external forcing; the coherence of the
RCP trajectories with the SRES enables the comparison of new results
with old simulations; the RCP trajectories permit us to take account of
policies for mitigation, without being prescriptive, and of socio-
economic models for picturing measures to take in order to follow a
given trajectory.
Year
Figure 2.4.
Evolution of the Earth's radiative budget or “radiative forcing”, in Wm
-2
for the period 1850-2250. From 2006, the continuous lines represent new scenarios
called Representative Concentration Pathways; the dotted lines represent the old
scenarios (IPCC, 2007 and 2001) (© Stéphane Senesi (CNRM-GAME, Météo-
France/CNRS)) (see color section)
