Background

The 2013 IPCC report estimated that human activity had caused global warming of 1°C compared to pre-industrial levels and that average sea levels had risen 19 (17-21) cm between 1901 and 2010.

At the end of 2015, the 21st Conference of the Parties (or COP21) established the objective of reducing man-made greenhouse gas emissions in order to limit global warming to 2°C or less compared to pre-industrial levels by the end of this century.

Projections for the middle and the end of the 21st century

These projections are based on trajectories of greenhouse gas, ozone and aerosol concentrations: Representative Concentration Pathways (RCP). Climatologists use these trajectories as entry data for models that simulate the future climate, which makes it possible, for example, to simulate global warming and sea levels at the end of the century.

By the middle of the century, it is probable that global warming (average temperature at the earth’s surface) will reach +1.5°C compared to pre-industrial levels (IPCC Special Report on Global Warming of 1.5°C, 2019).

By the end of the century, if we take two ‘extreme’ trajectories – the first pessimistic (RCP 8.5) which represents a high level of emissions and is commonly referred to as ‘business as usual’, and the other (RCP 2.6) involving the reduction in emissions needed to limit global warming to 2°C – we get the following simulations by 2100 (IPCC report 2013):

• global warming of between +2 and +6°C compared to the pre-industrial period (1850-1900) ;
• rising sea levels of between 30 and 80 cm compared to the period 1986-2005.

The latest data

Since the 2013 IPCC report, a study carried out using French models (Climeri-France, 2019) shows that the higher trajectory of 6°C of global warming by the end of the century could be one degree higher (around 7°C).

Regarding sea levels, given recent data on the loss of mass of the Greenland and Antarctic ice sheets (IPCC, Special Report on the Ocean and Cryosphere in a Changing Climate, 2019), sea levels could increase by over a metre (110 cm) by the end of the century compared to the period 1986-2005 if emissions are high (RCP 8.5).

Dominique Raynaud
Emeritus Director of Research at the CNRS
Institute of Environmental Geosciences (IGE), at Grenoble Alpes University
Former member of the Intergovernmental Panel on Climate Change (IPCC) created by the UN in 1988