After you have picked your location and selected your variable of interest you can choose a greenhouse gas (GHG) emissions scenario. The purpose of the different emissions scenarios is to explore alternative pathways for future changes in climate depending on future human activities, i.e. future GHG emissions. The scenarios are divided into four groups (A1, A2, B1 and B2), where A1 is subdivided into three additional groups, A1B, A1FI, A1T. Of these seven scenarios, the user can choose between three ‘marker scenarios’ (B1, A1B, and A2). The three scenarios belong to the SRES (Special Report on Emissions Scenarios) emissions scenario family and were chosen as they provide the lowest, the medium and the highest concentration of GHGs by the end of the 21st century (see Figure 1). The scenarios are based on different assumptions on population growth, economic structures and technology development, resulting in different future GHG emissions scenarios. The emissions scenarios are described in detail in the IPCC SRES (Nakicenovic and Swart, 2000), but to give the user an idea, here is a brief overview what storyline is behind those chosen emissions scenarios:

Figure 1: Future development of CO2 concentrations for three GHG emissions scenarios.

A1B – medium concentrations of GHGs

The A1 storyline describes a future world of:

The A1 scenario family develops into three groups that describe alternative directions of technological change in the energy system. The three A1 groups are distinguished by their technological emphasis, A1B is a balance across all energy sources.

A2 – High concentrations of GHGs

The A2 storyline and scenario family describes a very heterogeneous world:

B1 – Low concentrations of GHGs

The B1 storyline describes a convergent world with:

RCP Scenarios

The described SRES emissions scenarios, published in 2000, have been used to make projection of future climate change for the IPCC third and fourth Assessment Report. For the fifth IPCC Assessment report, Representative Concentration Pathways (RCPs) that supersedes SRES scenarios have been adopted by the IPCC.

The RCP scenarios are named according to their radiative forcing (the change in the balance between incoming and outgoing radiation to the atmosphere caused primarily by changes in atmospheric composition) values in the year 2100 relative to the pre-industrial values, namely:

RCP 8.5: - Rising radiative forcing pathway leading to 8.5 W/m2 in 2100

RCP 6.0: - Stabilization without overshoot pathway to 6.0 W/m2 at stabilization after 2100

RCP 4.5: - Stabilization without overshoot pathway to 4.5 W/m2 at stabilization after 2100

RCP 3-PD2: - Peak in radiative forcing at ~3 W/m2 before 2100 and decline

Figure 2: Atmospheric CO2 concentrations according to the RCP scenarios (Figure from van Vuuren et al. 2011)