While climate-skeptics are regularly in the news, reality is slowly catching up with climate forecasts for a few decades now. The graph below shows for instance the rapid rise in temperatures over the last century, especially in the 2000s.
In metropolitan France, the effects of climate change are mainly reflected in rising temperatures. From 1900 to today, a rise in average temperatures of 1.4 ° C has been observed. This value is larger than the world average, estimated at + 0.9 ° C during the period 1901-2012.
The warming of the French regions is comparable but not regular: an acceleration is observed since the 1980s. During the period 1959-2009, we observe an average temperature rise of + 0.3 ° C every ten years, accentuated during 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 and a decrease in the southern half.
In the spring and autumn cumulations are up on most of the territory. In winter and summer, there is a drop in accumulations in the southern regions.
Since the middle of the 20th century, there has also been an evolution in the frequency and intensity of certain extreme events. Not to believe that the rainy episodes or even the storms have increased, no trend is marked by the evolution of these events. On the contrary, it is observed that the number of hot days (temperatures higher than 25 ° C) does not cease. increase at the expense of the number of freezing days.
High temperatures have become more frequent and more intense due to the increased evaporation of soils. Indeed, these changes have real impacts on the evolution of the water cycle and particularly on the duration of the average mountain snow period.
As a result, the dry soil period of about 20 days in July and September is longer, leading to greater irrigation needs for crops.
Recent droughts (2011 and 2003) are consistent with dry soil records since 1959 for the months of May and August.
Source : Fotolia
Whatever the different scenarios imaginable, climate change in France has already been observed and will continue to increase during the 21st century.
Three scenarios are envisaged:
Considering that no climate policy has been taken, compared to the period 1976-2005, global warming could rise by 4 ° C during winter periods, and by more than 5 ° C during summer periods. 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 freezing 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 days of heat per year and a decrease of 17 days of freezing compared to the period 1976-2005, according to the scenario considering a policy climate change to stabilize CO2 concentrations. On the other hand, without a climate policy, one expects twice as many days of heat and a decrease in freezing days.
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, since it is considered that the period of dry soil will 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 it would be reproduced every other year in 2070.