What Will Happen in the Future If We Do Nothing or If We Try Very Hard to Aggressively Reduce GHG Emissions: Projected Change Under Different Emission Scenarios - The Changing Arctic Environment: The Arctic Messenger - page 369

The A2 storyline and family explore a future with pronounced differences in regional
economic development, lower per capita economic growth and a continuously growing
global population.
The B1 storyline and scenario family portray a similar future as the A1 storyline but
with rapid changes towards less energy-dependent economies and intensification of clean
and resource-efficient technologies and environmental sustainability.
The B2 storyline and scenario family portray a future characterized by local solutions
to economic, social and environmental sustainability. Economic development and techno-
logical change are less rapid and more diverse than in the B1 and A1 storylines, while the
global population continues to increase but at a rate lower than in A2.
Altogether, 40 scenarios were developed under the SRES framework. The GHG emis-
sions anticipated from these scenarios have been fed into the atmosphere-ocean global cli-
mate models (AOGCMs) we met earlier when looking at why climate scientists are able to
confidently attribute present global warming to the increase in anthropogenic GHG emis-
sions. The model runs usually begin in preindustrial times using observed natural forcing
agents (such as solar activity) and observed values for GHG and aerosol concentrations.
They then proceed into the future, “feeding” on the GHG and aerosol atmospheric concen-
trations computed for whichever of the SRES scenarios is under study (such as A1FI). At
least 20 different climate models have been used to examine these scenarios.
The SRES scenarios do not consider the possibility of active global mitigation by
world governments to reduce their GHG emissions. A new approach has been used in the
fifth IPCC assessment. This consists of the development of a set of four scenarios con-
taining emission, concentration and land-use trajectories referred to as representative con-
centration pathways (RCPs) for the main forcing agents of climate change. Four emission
trajectories have been selected based on how much forcing they would produce at the end
of the century: 2.6, 4.5, 6 and 8.5 watts per square metre. Integrated assessment models
(IAMs) can then be used to look at different technological, socioeconomic and policy op-
tions for the present and the future that could lead to a particular magnitude of climate
change. This approach holds promise for the evaluation of the costs and benefits of long-