In a report, the United Nations (UN) Intergovernmental Panel on climate change (IPCC) described that between + 1.5 °c and + 2 °c of warming, the impacts will be quite different, according to provisional versions of Report.
Where are we?
If GHG emissions (greenhouse gases) generated by humans keep their current rhythm, average terrestrial warming will exceed + 1.5 °c (relative to pre-industrial level) by about 2040.
If all these emissions ceased immediately, it is likely that the world would remain below this critical threshold of 1.5 °c. However, the gases already emitted would continue to generate certain impacts, particularly in terms of sea level rise.
What are the anticipated impacts?
The risks are reduced to + 1.5 °c, compared to + 2 °c, whether it is the number of extreme events, heat waves around the world, torrential precipitation forecast in most regions, forest fires, invasions or extinction of species, ocean productivity, overall agricultural yield, or more limited loss of permafrost, frozen soils in high latitudes.
These risks will be lower in particular if we avoid exceeding 1.5 ° (instead of exceeding it and then lowering the temperature later in the century). Because getting closer to a warming of + 2 °c would have irreversible impacts on some species (plants and vertebrates).
However, stopping the mercury at 1.5 °c by 2100 may not be enough to halt the destabilization of the Antarctic and Greenland ice caps, promises of significant sea rise in the coming centuries.
What should I do?
Stabilising warming at 1.5 °c requires a neutrality in CO2 emissions (80% of fossil fuel combustion) in the middle of the century: no longer emit in the atmosphere more than we are able to remove. While reducing other GHG, especially the very warming methane. And the chances of success are increased if this is done by 2030.
The provisional summary also suggests, in its graphs, that the maximum of global CO2 emissions is achieved… in 2020.
So how do you do that? There is "no simple answer" to the question of feasibility, stresses the IPCC.
This will require a "fast and vast" transition, these 10 or 20 years to come, in terms of energy systems, urban, industrial…
Most of the scenarios studied by the experts to remain at + 1.5 °c, include procedures for CO2 absorption (e.g. by soils and forests).
But in the current state of knowledge, the capture and storage of CO2 on a very large scale is not controlled by industrialists. The safest remains a very rapid reduction of emissions, note the experts.
The IPCC, on the other hand, does not retain the very "uncertain" option of using solar radiation manipulation techniques (e.g. by sending aerosols into the stratosphere to cool the climate).