Climate scenarios and projections

Projections of CO2 emissions according to the five IPCC scenarios

Note: the last numbers (1.9, 2.6, 4.5, 7.0 and 8.5) naming each trajectory correspond to the radiative forcing induced by 2100 compared to the pre-industrial era, expressed in W/m2.
Source: IPCC, 1st working group, 2021

The IPCC published its first report (First Assessment Report) in 1990. The first volume of its sixth report (AR6) was released in August 2021. With each publication, the IPCC communicates climate projections based on GHG concentration assumptions and presents the state of scientific knowledge on climate change.

A core set of five scenarios based on Shared Socioeconomic Pathways (SSPs) is used consistently in the IPCC 6th Assessment Report (AR6). These scenarios range from low GHG emission trajectories with climate change mitigation to high. For example, the SSP1-2.6 scenario would correspond to a sustainable development that would limit the temperature rise to 1.8°C at the end of the century. The worst case scenario (SSP5-8.5) would lead to a rise of 4.4°C.

Methane ( CH4 ), the second major component of greenhouse gases
The atmospheric concentration of methane since 1983

Note: monthly averages of air samples over global marine surfaces.
Source: National Oceanic and Atmospheric Administration (NOAA), USA, 2022

The atmospheric concentration of methane in May 2022 is 1 909 ppm (NOAA preliminary estimate), about 200 times less than that of CO2 . However, its global warming potential (GWP, see glossary) is 84 times greater than that of CO2 during the first 20 years after its emission. More than a quarter of the global warming since pre-industrial times could be attributed to methane. The increase in methane emissions has been accelerating in recent years, including during the Covid-19 pandemic.

Projections of CH4 emissions according to the five IPCC scenarios

Source: IPCC, 1st Working Group, 2021

Temperature and sea level evolution according to the five IPCC scenarios
Projection of the global average temperature variation compared to the period 1850-1900

Source: IPCC, 1st Working Group, 2021

Projection of average sea level rise relative to 1900

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

The main drivers of sea level rise (see p. 14) are thermal expansion of the oceans and melting of land-based ice reservoirs (glaciers, polar ice caps, etc.). By 2100, mean sea level would rise relative to the 1995-2014 average by 0.28-0.55 m under the sustainable development scenario (SSP1-2.6) and by 0.63-1.02 m under the worst-case scenario (SSP5-8.5). Rising sea levels are likely to cause significant population migration, as more than 1 billion people live in coastal lowlands (below 10 m elevation).

Carbon budgets and rising temperatures

The remaining carbon budget corresponds to a maximum amount of CO2 emissions for which there is a reasonable probability of avoiding the average temperature increase above a certain level. Only the most ambitious trajectories for climate change mitigation efforts (SSP1-1.9 and SSP1-2.6) could limit the temperature increase to 1.5°C and 2°C respectively by 2100. In 2021, the UN assessed that the commitments made by the parties to the Paris Agreement place the world on SSP2-4.5; this is associated with a temperature increase by 2100 of between 2 and 2.9 °C compared to the period 1850-1900.

Remaining carbon budget to limit the average temperature increase to 1.5°C and 2°C

Note: Values are expressed as a percentage of the total carbon budget since pre-industrial times, obtained by comparing cumulative emissions between 1850 and 2021 (Friedlingstein et al., 2022) with the remaining carbon budget from 2019 (IPCC, 2021). Carbon budgets are given with a 67% probability of meeting the associated climate target (1.5°C or 2°C). The uncertainty ranges for the carbon budgets are high, in the order of ± 3.7 Gt CO2 . These include uncertainties about the evolution and impact of non-CO2 greenhouse gases, the responses of the climate system to increasing cumulative emissions and radiative forcing, and the responses of the Earth system to increasing temperatures.
Sources: I4CE, based on Friedlingstein et al, Global Carbon Budget 2021, 2022; IPCC, 1st Working Group, 2021

To limit the average temperature increase to 2°C compared to the pre-industrial era with a 67% probability, the remaining carbon budget from 2021 is 1075 Gt CO2, and only 325 Gt CO2 to limit the increase to 1.5°C (IPCC, 2021). If CO2 emissions continue to grow at this rate, the remaining carbon budget that would allow with two chances out of three to limit the temperature increase to 2°C will be exhausted before 2050. To limit the rise to 1.5°C, it will be exhausted within the next ten years only (IPCC, 2022).

Consequences for the world
Observed impacts of climate change on ecosystems

Note: degree of confidence in the role of climate change on observed changes in ecosystems based on a review of the scientific literature.
Source: IPCC, 6th report, 2022

Climate change has altered marine, terrestrial and freshwater ecosystems around the world. It has caused local species extinction, increased disease, and mass die-offs of plants and animals. Extreme weather events generate conditions beyond which many species are no longer adapted. They are occurring on all continents, with severe impacts. The most severe impacts are found among the most climate-sensitive species and ecosystems. The effects of climate on ecosystems have also resulted in measurable economic and livelihood losses, and altered cultural practices and recreational activities around the world.

Consequences for France
Annual soil moisture cycle

Source: Climat HD, Météo-France

Comparison of the annual soil moisture cycle in France between the 1961-1990 climate reference period and the near (2021-2050) or distant (2071-2100) time horizons of the 21st century (according to a scenario corresponding to the current trajectory) indicates a significant drying out in all seasons.

In terms of potential impact on vegetation and non-irrigated crops, this evolution translates into an average lengthening of the dry soil period by about 2 to 4 months, while the wet period is reduced in the same proportions. The average soil moisture at the end of the century could thus correspond to today's extreme dry situations.