IPCC scenarios

Intergovernmental Panel on Climate Change (IPCC)

Created by the United Nations, the IPCC is an intergovernmental body which 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. It is made up of four volumes:

RCP and SSP scenarios

In its last report, the IPCC has defined four reference scenarios, the RCPs (for Representative Concentration Pathways), each representing one possible evolution profile of greenhouse gas (or GHG) concentrations. Socio-economic development scenarios and various adaptation and mitigation strategies are associated with them, and they are called 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 RCPs.

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. Then, local adaptation models 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 of 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.

SSPs then define five types of evolution of societies :

  • SSP1: strong international cooperation giving priority to sustainable development;
  • SSP2: middle of the road;
  • SSP3: fragmented world affected by competition between countries, slow economic growth, and policies oriented towards safety and industrial production, little concern for the environment;
  • SSP4: large inequalities between countries and within countries; a minority will be responsible for most of GHG emissions 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.

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