{"id":54373,"date":"2021-09-14T15:32:09","date_gmt":"2021-09-14T13:32:09","guid":{"rendered":"https:\/\/preprod.i4ce.org\/2021\/09\/14\/dou-viennent-les-cinq-nouveaux-scenarios-du-giec\/"},"modified":"2023-03-06T10:54:35","modified_gmt":"2023-03-06T09:54:35","slug":"where-do-the-five-new-ipcc-scenarios-come-from-climate","status":"publish","type":"post","link":"https:\/\/staging.i4ce.org\/en\/where-do-the-five-new-ipcc-scenarios-come-from-climate\/","title":{"rendered":"Where do the five new IPCC scenarios come from?"},"content":{"rendered":"

The IPCC scenarios are constantly cited when we are interested in climate and its evolution, but sometimes wrongly, and often without a clear understanding of what they imply. On the occasion of the release of the\u00a0latest IPCC report<\/a>, in which five new scenarios have appeared,\u00a0Charlotte Vailles<\/a> of I4<\/span>CE<\/strong> explains how they were constructed and what information is available about them.\u00a0<\/strong><\/p>\n

 <\/p>\n

 <\/p>\n

New IPCC scenarios explore a wide range of plausible futures to 2100<\/span><\/h2>\n

In its latest report, the first working group of the IPCC does not only reconstruct past climate changes and observe those that are taking place today. Crucially, it also explores possible futures. The five new scenarios used in this report present possible evolutions of the climate throughout the 21st century as a function of greenhouse gas (GHG) emissions and of the evolution of human societies. The use of scenarios \u2013 which are plausible representations of an uncertain future \u2013 enable to\u00a0explore different possible evolutions of human societies and their implications for the climate<\/strong>. The aim of these scenarios is not to predict the future \u2013 no probability is associated with the different scenarios \u2013 but to take into account the uncertainty linked to future human activities and to\u00a0inform the decisions of States and more widely of societies<\/strong>.<\/p>\n

 <\/p>\n

These five scenarios cover\u00a0a wide range of plausible futures<\/strong>\u00a0for GHG emissions \u2013 from a scenario in which CO2<\/sub>\u00a0emissions decline drastically to carbon neutrality by 2050 and are negative in the second half of the century (SSP1-1.9) to a scenario in which CO2<\/sub>\u00a0emissions continue to rise sharply to twice current levels in 2050 and more than three times current levels in 2100 (SSP5-8.5) (see Figure 1).<\/p>\n

 <\/p>\n

Figure 1: Future CO2\u00a0<\/sub>emissions in the five illustrative scenarios<\/strong><\/p>\n

 <\/p>\n

Click on this button to see the image<\/a><\/p>\n

 <\/p>\n

Source: Sixth Assessment Report of IPCC Working Group I, 2021<\/em><\/p>\n

 <\/p>\n

 <\/p>\n

These scenarios have been constructed from plausible developments in societies over the 21st century<\/span><\/h2>\n

The five scenarios are based on reference socio-economic trajectories \u2013 the\u00a0SSPs (Shared Socioeconomic Pathways)<\/strong>\u00a0\u2013 developed by the scientific community in order to create a common framework for thinking about the issues related to climate change.<\/p>\n

 <\/p>\n

Five narratives describing possible social, economic, political and technological developments by the end of the century were developed<\/strong>\u00a0(see Table 1).\u00a0These five narratives were used to model\u00a0different scenarios of evolutions of the economic, energy and land use systems<\/strong>. Some of these scenarios were constrained by the achievement of a climate objective (these are called \u201ctransition scenarios<\/strong>\u201c), while others were not (\u201creference scenarios<\/strong>\u201c).\u00a0This scenario-building was carried out by the scientific community of the IPCC third working group, which assesses solutions for mitigating climate change.\u00a0Note that the socioeconomic pathway can be more or less favourable to the achievement of climate objectives, as indicated in the two columns on the right: for example, limiting global warming to 1.5\u00b0C or 2\u00b0C may prove very difficult, if not impossible, in a context of regional rivalries and inequalities described by the SSP3.<\/p>\n

 <\/p>\n

Table 1: The SSPs and their narratives<\/strong><\/p>\n

 <\/p>\n

Click on this button to see the image<\/a><\/p>\n

 <\/p>\n

Source: I4<\/span>CE<\/strong>, 2019, based on Riahi et al. (2017), O\u2019Neill et al. (2015), Bauer et al. (2017)<\/em><\/p>\n

 <\/p>\n

The GHG, aerosol, and land use emission trajectories resulting from these scenarios were then processed by the scientific community to harmonize them and supplement them with other datasets -in particular, a geographic grid of emissions.\u00a0In total, nine emission scenarios were obtained \u2013 representing consistent and distinct evolutions of human societies<\/strong>.<\/p>\n

 <\/p>\n

These scenarios are identified by a name of the form SSPx-y, where SSPx is the socioeconomic pathway used to model the scenario and y is the approximate level of\u00a0radiative forcing<\/a>\u00a0resulting from the scenario in 2100.<\/p>\n

 <\/p>\n

Five scenarios demarcated from each other were chosen for further evaluation in this report:<\/p>\n

 <\/p>\n