SRES Scenarios- Climate Change Projections

SRES scenarios are often used in climate modeling and to predict what if scenarios when modeling the implication of some system on climate. SRES stands for Special Report on Emissions Scenarios which was a report produced by the IPCC first published in 2000 in the 3^rd IPCC. The 4^th IPCC in 2007 saw an update of SRES available for scientists to use. They are widely referred to in a wide range of materials such as RAMSAR report and others. Ramsar Convention is an international treaty, which seeks to encourage conservation and sustainable utilization of wetlands. The convention was named after an Iranian city- Ramsar, where it was first signed in 1971. It recognizes the essential ecological function of wetlands and their economic, cultural, scientific and recreational values. They are also widely used by hydrologists and climatologists as well as meteorologists and geologists when trying to predict the future climate or its particular aspects. They are different world scenarios that consider population growth, globalization and world economics, the cleanliness of technologies and world environmental priorities (Ramsar Report, 2002).

I mentioned them in the previous blog post in a study about geology and CCS implications so I thought I’d write a little blog post about SRES scenarios themselves too. Other examples of studies involving the use of these are the example of Nicholls’ 2004 study on how the impact of a particular climate change- sea-level rise in his case, would be affected under SRES and thus what is the climate likely to look like in the future. Nicholls used SRES to improve his original study of sea-level rise and how it would effect coastal wetlands due to increased flooding (Nicholls, 2004).

The scenarios are four scenarios which each has their own GHGs trajectories for the future where A1 and A2 has high GHGs which continue to increase beyond 2100 and B1 and B2 have mid to low levels of GHGs with rates of increase showing signs of slowing by the end of 2100. Figure 1 below summarizes these scenarios.

 Figure 1.

Source: Ramsar Report, 2002 Description of SRES scenarios.

Using full range of SRES scenarios, the atmospheric CO2 concentrations are projected to increase from the 1990 level to 475-1100 ppm by 2100. The mean global temperatures are projected to be 1.4C-5.8C higher by 2100 with variation in the increase in different regions on Earth. Generally temperatures are projected to increase the most in mid to high latitudes of the northern hemisphere. Precipitations changes are also to occur on much smaller scales of only 5-20% and also show regional variation. Although these changes could be enough for serious hydrological, ecological and global climate implications (Ramsar Report,2002). The potential implications of SRES are shown below by figure 2.

Figure 2.

Source: United States EnvironmentalProtection Agency, 2015. Projected changes over the 21^st Century in the atmospheric concentrations of 3 GHGs: CO2, methane and nitrous oxide (N2O).

The 5^th IPCC, published in 2014 updated SRES yet again now renaming them as RCPs (Representative Concentration Pathways). They are four scenarios yet again used for climate modeling and research. They also depend on GHGs emissions into the atmosphere mainly up to 2100 but also give some predictions beyond that into the 22^nd century. We have to think well beyond the 21^st century and at least about the 22^nd century as the potential effects of GHGs on the planet lag due to slow responses of global earth systems such as ocean circulation thus lagging impacts such as sea level rise which in turn also has further ability to create positive feedbacks on climate change. The four RCPs are named RCP2.6, RCP4.5, RCP6, and RCP8.5. RCP2.6 assumes the peak of GHG emissions between 2010 and 2020; RCP4.5 peak around 2040 then decline; RCP6 emissions peak around 2080 and RCP8.5 emissions continue to rise throughout the 21^st century. These are portrayed by Figure 3 below.

Figure 3.

Source. All forcing agents’ atmospheric CO2 equivalent concentrations (in ppmv) according to four RCPs.