Scenarios

The Intergovernmental Panel on Climate Change (IPCC)

Created by the United Nations, this intergovernmental body evaluates scientific, technical and socio-economic information published in scientific journals related to the issue of climate change.

Its goal is to consider adaptation and mitigation strategies, based on an understanding of the scientific underpinnings of man-made climate change.

The IPCC has issued several assessment reports, and the 5th is a reference for climate change. The three volumes that make it up

  • Scientific elements
  • Impacts, vulnerabilities and adaptation
  • Mitigation of climate change

The RCP and SSP scenarios

In its last report, the IPCC has defined four reference scenarios, the RCPs (for Representative Concentration Pathways), representing each of the possible evolution profiles of greenhouse gas (or GHG) concentrations. Socio-economic development scenarios and various adaptation and mitigation strategies are associated with them, the Shared Socioeconomic Pathways (SSPs). This approach allows coherent work between climatologists and economists.

The graph below shows the temperature rise in degrees Celsius as a function of time for the four SPCs.

The models used allow a regionalization of the projections, passing from a resolution of 100 to 300 km for the global models to a resolution of 10 to 50 km for the regional models. These are then local adaptation models that take over with a resolution of the order of one kilometer and give us a more detailed idea of the impacts at the scale of our territories and even a forest plot !

In parallel with the work of climatologists, sociologists and economists assess the costs of adaptation and mitigation related to climate change, according to possible developments in our society.

This graph represents the challenge of adapting societies to climate change in relation to the challenge of mitigating GHG emissions.

The SSPs then define five types of evolution of societies :

  • SSP1: strong international cooperation giving priority to sustainable development;
  • SSP2: continuation of current trends;
  • SSP3: Fragmented world affected by competition between countries, slow economic growth, and policies oriented towards safety and industrial production and little concern for the environment;
  • SSP4: large inequalities between countries and within countries; a minority will be responsible for the bulk of GHGs and the majority of the population will remain poor and vulnerable to climate change;
  • SSP5: traditional and rapid development of developing countries with high energy consumption; the rise in living standards will increase the capacity to adapt thanks to the decline of extreme poverty.

According to T. Kram, the SSP3 and SSP5 families do not allow to limit GHG emissions to a low level, and are therefore not compatible with the RCP 2.6 scenario. Only the SSP3 family would allow the realization of the scenario RCP 8.5, the most alarming RCP.