An authoritative French study revises upward the forecasts for global warming in 2100. In the worst-case scenario, temperatures could rise by 7 degrees.
The climate crisis could be far worse than previously imagined. Based on the current trajectory, if the worst-case scenario were to materialise – that is, in the event of strong economic growth fuelled by fossil energy – the rise in the global average temperature by the end of the century could reach as much as 7 degrees Celsius.
What is more, of all the possible scenarios, only one – the most optimistic – would allow the targets of the Paris Agreement to be met, that is, remaining at a maximum of 2 degrees Celsius above pre-industrial levels by 2100. And this «only if enormous efforts to mitigate climate change are made».
This is explained by an authoritative French study, carried out by around a hundred researchers (climatologists, oceanographers, glaciologists, specialists in atmosphere, vegetation and soil, as well as experts in intensive computing) from the National Centre for Scientific Research (Cnrs), the Alternative Energies and Atomic Energy Commission (Cea) and the meteorological service Météo France.
To obtain the data, it was necessary to process an impressive volume of data, amounting to 20 petabytes (millions of gigabytes). These were processed by supercomputers that worked without pause, night and day, for 500 million hours. The report – the results of which will be incorporated into the sixth report of the Intergovernmental Panel on Climate Change (Ipcc), scheduled for 2021–2022 – therefore represents a further warning signal for the international community.
"To date," explains Sergio Castellari, an expert at Ingv seconded to the European Environment Agency, to Lifegate.it, "climate models have highlighted an increase in global average temperature by the end of the century compared to values from the 1986–2005 period of between 0.3 and 1.7 degrees Celsius for the mitigation scenario with very high reductions in greenhouse gas emissions, and between 2.6 and 4.8 degrees for the high-emissions scenario, the so-called 'business as usual'. This new study raises the upper end of the global average temperature increase range to 6–7 degrees under the worst-case scenario. Only with the best-case scenario (characterised by strong international cooperation and prioritising sustainable development) does the analysis state that it is possible to remain below the 2-degree global warming target relative to pre-industrial levels».
This, the scientist continues, «confirms that only through a rapid and drastic reduction in global greenhouse gas emissions, as highlighted in the latest special report of the Ipcc published in 2018, is it possible to remain below 2 degrees (better still would be to stop at 1.5), again relative to pre-industrial levels. And to avoid devastating effects on our society and on ecosystem services and biodiversity".
«The differences,» the researchers explain, «could be explained by an increase in the presence of greenhouse gases of anthropogenic origin in the atmosphere, compared with the data that were analysed during previous simulations». But the worsening of the estimates also depended «on an improvement made to climate models compared with the exercise carried out some years ago. The spatial resolution is finer, while the modelling of the different sectors (oceans, atmosphere, continental surfaces, ice...) is more precise».
French scientists also underline that episodes of extreme heat will become increasingly frequent in the coming decades. Based on the year 2003, during whose summer an exceptionally prolonged heatwave occurred, the experts indicate that there will be a 40 per cent chance of experiencing waves worse than that one. This figure will rise to 70 per cent by the end of the 1950s and to 90 per cent from the 1970s onwards.
Finally, the study highlights the dramatic consequences that could arise for Arctic ice. Under the most negative assumptions, it cannot be ruled out that the Arctic could completely lose its ice cap during summers. And this could happen as early as 2080.
