change
At the current rate of atmospheric warming (0.2°C per decade), a warming of 1.5°C is expected by 2050 (IPCC 2014). Under the worst-case scenario and an increase of 8.5 watts per square meter, the temperature could rise by 4°C. The rise in sea level would be between 50 cm and 1 m by 2100 according to the latest IPCC report on cryosphere and oceans (IPCC 2019 and Chapters 2 and 3).
Figure 1.8. (a) Mean change in surface temperature. (b) Mean sea-level rise from 2006 to 2100 (as determined by multi-model simulations). For a color version of this figure, see www.iste.co.uk/mercier/climate.zip
COMMENT ON Figure 1.8.- All changes relate to 1986-2005. Time series of projections and a measure of uncertainty (shading) are presented for the RCP2.6 (blue) and RCP8.5 (red) scenarios4. The average and associated uncertainties averaged over 2081-2100 are given for all RCP scenarios as colored vertical bars on the right side of each panel. The number of models from Phase 5 of the Coupled Model Intercomparison Project (CMIP5) used to calculate the multi-model mean is given (source: IPCC 2014).
Figure 1.9. (a) Change in mean surface temperature. (b) Change in mean precipitation based on the multi-model mean projections for 2081-2100 compared to 1986-2005 in the RCP2.6 (left) and RCP8.5 (right) scenarios. For a color version of this figure, see www.iste.co.uk/mercier/climate.zip
COMMENT ON FIGURE 1.9.- The number of models used to calculate the multi-model average is shown in the upper right corner of each panel. The dotted lines show
regions where the projected change is large relative to the natural internal variability, and where at least 90% of the models agree on the sign of the change. Hatching shows regions where the projected change is less than one standard deviation of the natural internal variability (source: IPCC 2014).
Maps of climate change projected to the end of the 21st Century show that the continents and the Arctic basin are most affected by this warming under any scenario with an increase of 2.6 watts per square meter (RCP2.6), accentuated by an increase of 8.5 watts per square meter (RCP8.5). For the amount of average annual precipitation considered by 2100, the maps show that the cold regions of the Arctic and Antarctic should logically receive more water in relation to a higher moisture content of the air in these cold regions associated with the increase in the evaporation potential over the Arctic basin with less ice pack in summer.
On the other hand, regarding land masses, it is mainly the Mediterranean regions and certain regions of South America and South Africa that would experience a decrease in rainfall, which would have a significant impact on agricultural yields (see Chapter 10).
1.4. Future Arctic-wide climate change
The polar projections in Figures 1.10 and 1.11 provide a better understanding of the magnitude of the projected warming in the Arctic Basin by 2050 and 2100 for summer (June to August) and winter (December to February), regardless of the scenario selected, RCP4.5 or RCP8.5. For the summer months, the continental regions surrounding the Arctic Basin would warm up the most.
On the other hand, the magnitude of warming would be exacerbated over the marine areas of the Arctic Basin during the winter months. Indeed, as the melting of the summer ice pack increased in summer during the 21st Century, the thermal inertia of the oceans, which accumulate more heat in summer through solar radiation, also makes it possible to halt the spatial expansion of sea ice in the winter period, even though winter temperatures continue to be favorable to its formation.
This amplifying role of the oceans shows what is at stake in the interactions between the atmosphere and the hydrosphere, with or without the central role of the sea ice filter.
For example, the average winter temperature in the Longyearbyen region of Svalbard at the end of the 21st Century is expected to be about 10°C higher than the current climate (F0rland et al. 2012).
Figure 1.10. Projected changes in summer surface temperatures (June to August) compared to the 1986-2005 average under scenario 4.5 and 8.5, for the years 2050 and 2080
(source: AMAP 2017). For a color version of this figure, see www.iste.co.uk/mercier/climate.zip
Figure 1.11. Projected changes in winter (December to February) surface temperatures relative to the 1986-2005 average under scenarios 4.5 and 8.5, for the years 2050 and 2080
(source: AMAP 2017). For a color version of this figure, see www.iste.co.uk/mercier/climate.zip
1.5. The causes of climate change
1.5.1. Solar radiation
Depending on the time scales considered, orbital variations concerning the Earth and the sun play a fundamental role in understanding climate change. Thus, the astronomical cycles (eccentricity, obliquity and precession) highlighted by Milutin Milanković allow us to understand the large climatic oscillations between long cold sequences separated by shorter interglacial periods. The change in global average surface temperature between the last glacial maximum (21,000 years ago) and the pre-industrial climate is estimated to be about 5°C (between 3 and 8°C). It would have been a few degrees in the tropics and 10°C at the poles (Masson-Delmotte et al. 2015). During the Eemian interglacial period (128,000 to 116,000 years ago), estimated temperatures were 3 to 5°C higher than in the pre-industrial period, resulting in the melting of a significant fraction of the cryosphere and a sea level rise of about 6.6 to 9.4 m above the present level (Lageat 2019).
On another time scale, it has been shown that solar radiation varies in intensity with minimums, such as the Maunder minimum in the 17th Century or the Dalton minimum from 1800 to 1830. The latter corresponds to the coldest period of the Little Ice Age. At the century scale, a linear relationship between the air temperature series at the Longyearbyen station in Svalbard and the length of a solar cycle has been demonstrated (Solheim et al. 2011). Thus, the contemporary evolution of temperatures, which records sequences of warming (1910-1940 and since 1980), separated by sequences of stagnation or even slight cooling (from 1880 to 1910 and then from 1940 to 1980), could be partly explained by these variations in solar radiation intensity.
