technologies, A1T for non-fossil energy technologies, and A1B for an equilibrated
forecast encompassing all the renewable and non-renewable sources.
Scenario B1 describes a world with the same global population as A1, converging fast toward a service and information economy, with rapid changes in
economic structures.
The B2 scenario relates to a world with a medium-level population and economic growth, with emphasis on local policies for economic, social, and environmental sustainability.
The A2 scenario described a very heterogeneous world with high population
growth, slow economic development, and slow technological change. No likelihood
has been attached to any of these scenarios.
The AR5 Report assumed that anthropogenic GHG emissions are mainly driven
by population size, economic activity, lifestyles, energy use, land-use patterns,
technology, and climate policy. AR5 used improved knowledge to change the
nomenclature of AR4, establishing for the twenty-first century a set of four Representative Concentration Pathways (RCPs) profiling for GHG emissions and
atmospheric concentrations, air pollution emissions, and land use. The four RCPs
are as follows: (i) RCP2.6, representative of a profile with likely global warming
below 2 °C above pre-industrial temperatures that can be achieved through a
package of rigorous mitigations policies; (ii) RCP4.5 and RCP6.0 are intermediate
profiles; and (iii) RCP8.5 a profile with very high GHG emissions. Most models
indicate that scenarios that meet forcing levels, like RCP2.6, are characterized by
substantial net negative emissions by 2100 averaging about 2 Gt CO 2 yr
−1 .
RCP2.6 is the only climate profile where projections consider unlikely that
global surface temperatures, in the period 2081–2100, exceed the average temperatures in the periods 1850–1900 and 1986–2005, by 2 °C and 0.3 °C to 1.7 °C,
respectively. The baseline profiles corresponding to scenarios where no effort is
made to control CGH emissions fall into the RCP6.0 and RCP8.5 classes.
Over the period 2010–2100, the RCP2.6 profile is within a predicted range, from
430 to 480 ppm ranges of atmospheric CO 2 -eq. For the twenty-first century, the
RCP4.5 profile corresponds to ranges from 430 to 480 ppm in the period 2010–
2040, and from 530 to 580 ppm in the remaining decades. RCP6.0 falls in predicted ranges 480–530 ppm and 530 to 580 ppm over the periods 2010–2030 and
2030–2050, and over a predicted range of 720–1000 ppm from 2050 onwards.
Finally, RCP8.5 corresponds to a predicted atmospheric CO 2 -eq. concentration
higher than 1000 ppm.
Overall, the main differences in the climate systems are expected to occur by the
end of the twenty-first century over the period 2081–2100. For the period 2016–
2035, the increase in global mean surface temperature is similar for the four RCP
profiles and is expected to be in the range of 0.3–1.7 °C, relative to the period
1986–2005. This statement assumes that there are no drastic outliers such as major
volcanic eruptions, dramatic changes in some natural sources, for example, CH 4
and N 2 O, and big changes in total solar irradiance.
8.3 Alternative Scenarios for Climate …
279
forecast encompassing all the renewable and non-renewable sources.
Scenario B1 describes a world with the same global population as A1, converging fast toward a service and information economy, with rapid changes in
economic structures.
The B2 scenario relates to a world with a medium-level population and economic growth, with emphasis on local policies for economic, social, and environmental sustainability.
The A2 scenario described a very heterogeneous world with high population
growth, slow economic development, and slow technological change. No likelihood
has been attached to any of these scenarios.
The AR5 Report assumed that anthropogenic GHG emissions are mainly driven
by population size, economic activity, lifestyles, energy use, land-use patterns,
technology, and climate policy. AR5 used improved knowledge to change the
nomenclature of AR4, establishing for the twenty-first century a set of four Representative Concentration Pathways (RCPs) profiling for GHG emissions and
atmospheric concentrations, air pollution emissions, and land use. The four RCPs
are as follows: (i) RCP2.6, representative of a profile with likely global warming
below 2 °C above pre-industrial temperatures that can be achieved through a
package of rigorous mitigations policies; (ii) RCP4.5 and RCP6.0 are intermediate
profiles; and (iii) RCP8.5 a profile with very high GHG emissions. Most models
indicate that scenarios that meet forcing levels, like RCP2.6, are characterized by
substantial net negative emissions by 2100 averaging about 2 Gt CO 2 yr
−1 .
RCP2.6 is the only climate profile where projections consider unlikely that
global surface temperatures, in the period 2081–2100, exceed the average temperatures in the periods 1850–1900 and 1986–2005, by 2 °C and 0.3 °C to 1.7 °C,
respectively. The baseline profiles corresponding to scenarios where no effort is
made to control CGH emissions fall into the RCP6.0 and RCP8.5 classes.
Over the period 2010–2100, the RCP2.6 profile is within a predicted range, from
430 to 480 ppm ranges of atmospheric CO 2 -eq. For the twenty-first century, the
RCP4.5 profile corresponds to ranges from 430 to 480 ppm in the period 2010–
2040, and from 530 to 580 ppm in the remaining decades. RCP6.0 falls in predicted ranges 480–530 ppm and 530 to 580 ppm over the periods 2010–2030 and
2030–2050, and over a predicted range of 720–1000 ppm from 2050 onwards.
Finally, RCP8.5 corresponds to a predicted atmospheric CO 2 -eq. concentration
higher than 1000 ppm.
Overall, the main differences in the climate systems are expected to occur by the
end of the twenty-first century over the period 2081–2100. For the period 2016–
2035, the increase in global mean surface temperature is similar for the four RCP
profiles and is expected to be in the range of 0.3–1.7 °C, relative to the period
1986–2005. This statement assumes that there are no drastic outliers such as major
volcanic eruptions, dramatic changes in some natural sources, for example, CH 4
and N 2 O, and big changes in total solar irradiance.
8.3 Alternative Scenarios for Climate …
279