Climate scenarios and projections

The IPCC's five shared socio-economic pathways

The IPCC published its first Assessment Report (AR) in 1990. The first volume of its sixth report (AR6) was published in 2021. In these publications, the IPCC presents the state of scientific knowledge on climate change and communicates climate projections based in particular on GHG concentration assumptions.

A set of five socio-economic scenarios (SSP - Shared Socioeconomic Pathways) is used in AR6. These scenarios correspond to possible evolutions towards different models of society, which are broken down into several GHG emission trajectories:

• scenario SSP1 corresponds to an evolution towards sustainable development;
• scenario SSP2 considers a continuation of current socio-economic and technological trajectories;
• in scenario SSP3, policies focus on national and regional security issues;
• scenario SSP4 corresponds to an exacerbation of global inequalities;
• finally, scenario SSP5 illustrates development based on fossil fuels.

Projections of CO₂ emissions according to IPCC scenarios

SSP = shared socio-economic pathway.
Note: the numbers associated with each SSP (1.9, 2.6, 4.5, 7.0 and 8.5) correspond to the radiative forcing induced by 2100 compared with the pre-industrial era, expressed in W/m².
Source: IPCC, 1^st working group, 2021

Projections of CH₄ emissions according to IPCC scenarios

Source: IPCC, 1^st working group, 2021

Temperature change according to IPCC scenarios

Projected global mean temperature change compared with the period 1850-1900

Source: IPCC, 1^st working group, 2021

Scenarios SSP1-1.9 and SSP1-2.6 correspond to development patterns that will limit global temperature rise to well below 2°C compared with the pre-industrial era. Scenario SSP2-4.5 is an intermediate scenario. It corresponds to a global temperature rise of 2.7°C by 2100. The most pessimistic scenarios (SSP3-7.0 and SSP5-8.5) would respectively lead to a temperature rise of 3.6°C and 4.4°C by 2100.

Sea-level evolution according to IPCC scenarios

Projected mean sea level rise relative to 1900

Note: solid lines show median projections. Shaded areas show probable ranges for SSP1-2.6 and SSP3-7.0. The dotted line (83rd percentile) indicates a maximum, albeit low-probability, impact of the SSP5-8.5 scenario on sea levels.
Source: IPCC, 1^st Working Group, 2021

The main drivers of sea-level rise (see p. 17) are thermal expansion of the oceans and melting of terrestrial ice reservoirs (glaciers, polar ice caps, etc.).

At 2100, mean sea levels would rise by 0.28 to 0.55 m compared with the 1995-2014 average under the sustainable development scenario (SSP1-2.6), and by 0.63 to 1.02 m under the worst-case scenario (SSP5-8.5).

Rising sea levels are likely to cause major population migrations, as more than a billion people live in coastal lowlands (below 10 m elevation).

Remaining carbon budgets to limit temperature rise to 1.5°C and 2°C

Note: values are expressed as a percentage of the total carbon budget since the pre-industrial era, obtained by comparing cumulative emissions between 1850 and 2023 with the carbon budget remaining from 2024. Carbon budgets are given with a 67% probability of meeting climate targets (1.5°C or 2°C).
Sources: Global Carbon Budget, 2025; Climate Change Tracker, 2025

The carbon budget corresponds to the maximum amount of CO₂ emissions for which there is a reasonable probability of avoiding average temperatures rising above a certain level.

To limit the average temperature rise to 2°C compared with the pre-industrial era, with a probability of 67%, the carbon budget remaining from 2024 is 870 Gt CO₂. This budget falls to 80 Gt CO₂ if we wish to sustainably limit the average increase to 1.5°C, out of a total budget of 3,520 and 2,730 Gt CO₂ respectively since 1850. Uncertainties concerning carbon budgets are very high, particularly in relation to the evolution and impact of greenhouse gases other than CO₂ and the reactions of the climate system to the increase in cumulative emissions.

If CO₂ emissions continue to grow at the current rate, the remaining carbon budget, which would with two chances out of three enable us to limit the rise in temperatures to 2°C compared with the pre-industrial era, will be exhausted in 2046. In an attempt to limit the rise to 1.5°C, it will be exhausted as early as 2027.