While global warming skeptics are often under the spotlights, for a few decades, reality is slowly catching up with predictions of climate evolution. For instance, the graph below shows the rapid rise in surface temperatures over the last century, especially in the 2000s.
Source : GIEC, 2014
In metropolitan France, the effects of climate change are mainly reflected in rising temperatures. From 1900 to today, we observed a rise in average temperatures of 1.4°C. This value is larger than the world average, estimated at + 0.9°C during the 1901-2012 period.
The warming-up of the French regions is comparable but not steady: it is going quicker since the 1980s. During the 1959-2009 period, the average temperature rised of +0.3°C every ten years, with a peak uring the spring and summer periods. The three hottest years are to date 2014, 2011 and 2003.
The evolution of rainfall accumulation differs according to regions and seasons. During the period 1959-2009, there is a general increase in annual rainfall in the northern half of France and a decrease in its southern half. In spring and autumn, rainfall accumulation is higher on most of the territory. In winter and summer, there is a drop in accumulation in the southern regions.
Since the middle of the 20th century, there has also been an evolution in the frequency and intensity of some extreme events. There are more hot days (maximal temperatures above 25°C) and less frost days than before. Heat waves are also more frequent and intense, and mediterranean rains are stronger. However, for the moment, it does not seem like there is a trend about the impact of global change on storms.
All the changes described above have an impact on the water cycle. For example, the decrease of the period of snow cover in lower montains and the increase in soil evaporation lead to more frequent and intense droughts. Therefore, the dry soil period is about 20 days longer in July and September, which leads to an increase in irrigation needs for crops. We also observe that the recent droughts (2011 and 2003) are consistent with dry soil records since 1959 for the months of May and August.
Whatever the scenario, climate change in France has already been observed and will continue to increase during the 21st century.
Three scenarios are envisaged:
If no climate policy is implemented, compared to the 1976-2005 period, global warming could rise by 4°C during winter periods and by more than 5°C during summer periods, as soon as the horizon of the years 2071-2100. On the other hand, whatever the scenario considered, the estimated climate projections show little change in annual rainfall by the end of the 21st century. Nevertheless, these absences of change mask regional and/or seasonal contrasts. A further reduction in the number of frost days and an increase in the number of hot days will be confirmed throughout the country and for all scenarios.
By 2071-2100, it is estimated that in the lowlands there will be an average increase of 18 hot days per year and a decrease of 17 forst days compared to the1976-2005 period, according to the scenario considering a climate policy to stabilize CO2 concentrations. On the other hand, without a climate policy, twice as many hot days and a decrease in the number of frost days are exepected.
In the near future (2021-2050) and until the end of the century (2071-2100), the frequency and intensity of heat waves in France could increase considerably. Initially, a doubling of the frequency of current events is expected: it will lead at the end of the century to heat waves much more frequent but also more severe and longer, mainly from late May until early October. These dramatic changes will inevitably lead to more and more soil drying in the 21st century, and in all seasons. This development will have an impact on the vegetation and rainfed crops, given that the period of dry soil should extend from 2 months to 4 months in the future, while the wet period will be reduced in the same proportions. In comparison, the average soil moisture at the end of the century would correspond to the extreme drought situations of today.
2003 would be the climatic reference year since similar conditions should happen every other year in 2070.