Anthropogenic emissions of greenhouse gases (GHGs) like CO2 have been increasing since the pre-industrial era. Based on multiple lines of scientific evidence, there is an overwhelming agreement that the resulting unprecedented atmospheric concentration of GHGs is extremely likely the dominant cause of global surface warming. Consequently, continued emissions of GHGs will likely cause further warming and long-lasting changes in patterns of extreme weather. Because projections of emissions vary depending on both socio-economic development and climate policy, climate modelers considered numeruous scenarios with different plausible trajectories of certain atmospheric and geophysical aspects to better understand the associated uncertainty and ultimately better inform decision making.

According to the IPCC AR5 Synthesys Report (2014), the Representative Concentration Pathways or RCPs (van Vuuren et al., 2011) describe four different 21st century pathways of GHG emissions and atmospheric concentrations, air pollutant emissions, and land use, which include a stringent mitigation scenario (RCP2.6), two intermediate scenarios (RCP4.5 and RCP6.0) and one scenario with very high GHGs emissions (RCP8.5). While RCP2.6 is representative of a scenario that aims to keep global warming likely below 2°C above pre-industrial temperatures, RC8.5 is regarded as a highly unlikely worst-case scenario. For an enlightening discussion about RCPs, take a look at this article by Hausfather & Peters (2011). In our Atlas, you will find maps and data of all four RCPs.

The Shared Socioeconomic Pathways or SSPs (O'Neill et al., 2016; Riahi et al., 2017) are five socio-economic and technological trajectories that the world could follow during the 21st century. Each of the SSPs is associated to one of 5 narratives spanning a range of future challenges in terms of adaptation and mitigation to climate change. While SSP1 describes a future in which adaptation and mitigation challenges are low (Sustainability or "Green Road"), SSP3 supposes high challenges in both mitigation and adaptation aspects (Regional rivalry or "a Rocky Road"). Two asymmetric cases were designed, one of which combines high challenges to mitigation with low challenges to adaptation (SSP5, fossil-fueled development or "Taking the Highway"); the other one is the opposite case (SSP4, inequality or "a Road Divided"). Lastly, SSP2 ("Middle of the Road") describes a world with intermediate challenges for both adaptation and mitigation. All SSPs were first modeled employing baselines in which no climate policies were enacted after 2010. Then, mitigation scenarios (with climate policies) were designed aiming to follow the path of the existing RCPs (i.e., achieving the climate targets of the RCP2.6, RCP4.5, and RCP6.0 scenarios by 2100). In our Atlas, you will find maps and data of the combined SSP-RCP scenarios that are being widely used in climate change adaptation studies as well as in climate risk evaluations.