- 2020-02-01 09:34:30.0
Climate change is profoundly disrupting wild and cultivated ecosystems. It affects the growth of plants and the activity of crop pests. It exacerbates tensions over the management of water resources. Extreme weather events are increasing in frequency and intensity, posing significant risks to agricultural production.
The rate of increase in average temperature - of the order of several degrees per century (Figure 2) - is a sudden event that has, according to our current knowledge, no equivalent since the last mass extinction of living things 65 million years ago . Due to the persistence time of CO2 in the atmosphere, and the inertia of the climate system, the near climate future is essentially already written, and the already observable effects of the current disruption will worsen over the years. next decades. While drastically reducing our greenhouse gas emissions is an absolute necessity, it is also essential to prepare our food system to absorb this climate "shock", which is now inevitable.
Figure 2 : Evolution of the atmospheric concentration of carbon dioxide (CO2) and the average temperature of the earth's surface over the past 800,000 years. CO2 is a greenhouse gas, increasing its concentration in the atmosphere causes global warming. Symmetrically, the increase in the average temperature leads to an increase in the level of CO2 by various feedback mechanisms. Since the industrial revolution, the burning of fossil fuels and deforestation have caused a massive release of CO2. The resulting current temperature rise is a hundred times faster than when the last Ice Age emerged from -20,000 to -10,000 years.ource : Les Greniers d’Abondance, and data from Snyder (2016).
Background degradation : variability and drop in yields, pressures on water use, spread of new pests, instability of world markets The growing instability of climatic conditions and the scarcity of water resources will have negative effects on agricultural production at the national level. The spring and summer drought of the soils will increase (Figure 3), while the average temperatures will increase and the "hot spells" will multiply, bringing together unfavorable conditions for large cereal crops. Medium-term climate projections (2050) suggest average drought levels equivalent to the worst years of recent decades, in particular in highly productive agricultural regions such as Beauce, Champagne and Picardy (Figure 3).
The agricultural sector consumes around half of the fresh water withdrawn in France, and this use is concentrated in the summer months, which coincide with the low flow of rivers (see resilience path No. 5). In irrigated crop regions, agricultural withdrawals will therefore compete directly with priority domestic uses . Water use restriction orders are likely to multiply and last over time, like 2019. Farms dependent on irrigation could face significant economic hardship.
Figure 3 : Regionalized projections of the relative soil humidity index, on average for spring, compared to 1970. The scenario considered corresponds to a trajectory of greenhouse gas emissions causing a warming of around 3 ° C by now 2100 (equivalent to the RCP 6.0 scenario of the IPCC). Reading: In 2055, the soil moisture index will have an average value corresponding to today's "dry" to "extremely dry" levels in most departments. An extremely dry level corresponds to the drought of 2003. Source : Météo-France/CLIMSEC (2012).
The rapid rise of certain bioclimatic zones to the North will deeply disrupt ecosystems and promote the activity, migration and development of certain pathogens and crop pests . This risk of destabilization is all the greater as wild and cultivated biodiversity is degraded.
Crisis situations : extreme weather events (droughts, heat waves, storms and floods) causing agricultural disasters and damaging critical infrastructure In France, the majority of crops are "rainfed": this means that they are not irrigated and depend on natural rainfall. A drought can therefore jeopardize their proper development. This is what happened during the marked episodes of 1976 and 2003, during which the yields of the main crops fell on average by 20 to 30% in the territory. At the scale of an agricultural region, some crops can be totally lost. Intense droughts in Europe could be ten times more frequent and 70% longer by 2060 . Heat waves can also have serious consequences on crops and livestock depending on their intensity and the period in which they occur.
In Hérault in 2019, grapevine burned (in June) and fire causing the closure of the A9 motorway (in September). During the summer of 2019, thousands of hectares of vines were burnt by the heat in Hérault and Gard. These extreme heat waves will increase in intensity and duration. Crédits : © Chai d'Emilien; © SDIS 34.
Other extreme weather phenomena such as floods and storms are bound to multiply and intensify , jeopardizing crops and affecting certain links essential to our food security such as road transport.
Two consequences of the floods on the food system: a flooded field in the Manche in February 2020 and the A10 motorway submerged in the Loiret in May 2016. The floods and humidity of spring 2016 reduced wheat yields in the departments by more than half. the most affected, such as Loiret or Seine-et-Marne, while blocking certain major traffic axes. Crédits : © Thibault Lorin ; Roland45, CC BY-SA, Wikimedia Commons.
Ways of resilience : diversify cultivated varieties and develop autonomy in seeds, adopt integrated management of water resources, generalize agroecology, simplify and shorten food logistics, eat more plants.