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Human consequences of global warming (1) – Agriculture

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Faced with global warming, the American Academy of Sciences notes, in a 2002 report: “It is important not to adopt a fatalistic attitude in the face of the threats posed by climate change. (…) Societies have had to deal with gradual or abrupt climatic changes for millennia and have been able to adapt through various responses, such as sheltering, developing irrigation or migrating to more hospitable regions. Nevertheless, because climate change is destined to continue in the coming decades, denying the possibility of abrupt weather events or minimizing their impact in the past could prove costly.”

According to a study published in June 2017 by Nature Climate Change, the share of the world population exposed to more than 20 days a year to potentially deadly heatwaves could go from 30% in 2016 to 74% in 2100.

A study commissioned by the European Joint Research Center and published in August 2017 by Lancet Planet Earth, estimates that two out of three Europeans will probably be affected at the end of the century by climate-related disasters, against 5% during the period 1981-2010, and that the number of deaths caused by these disasters will rise from 3,000 per year to 1,500,000 per year if no action is taken to reduce greenhouse gas emissions and the impact of extreme weather events. The risk will be particularly acute for the countries of southern Europe, Portugal, Spain and Italy; where heat waves are by far the most deadly climate catastrophe and would cause 99% of deaths.

Impact on coastal regions

Proiecții ale creșterii globale medii a nivelului mărilor (Projections of global mean sea level rise by Parris and others. Probabilities have not been assigned to these projections. Therefore, none of these projections should be interpreted as a “best estimate” of future sea level rise. Image credit: NOAA.)

The rise in sea level is estimated between 18 and 59 cm by 2100 by the fourth IPCC report.

Populations on some islands in the Pacific Ocean or the Indian Ocean, such as the Maldives or Tuvalu, are under direct threat as part of their territory may be submerged. But all the populations living in coastal regions (more than five hundred million people) risk seeing their environment degraded (coastal erosion, aquifer salinity, disappearance of wetlands, permanent flooding).

Locally, this rise is added to phenomena that are not related to the climate and which lead to a depression of the soil: sediment load in river deltas, groundwater pumping, gas and oil extraction, mining subsidence. .

Fisheries

The warming of the oceans has an impact on marine organisms, especially exploited species. This impact is observed on the biogeography of species and the structure and trophodynamics of the marine ecosystem. Disruptions in the spatial distribution and abundance of fish species, such as Atlantic cod, have been observed in direct or indirect response to climate change.

In the North Atlantic, the majority of species are likely to move northward to stay in an environment that meets their ecological and more specifically thermal requirements. The intensity and speed of expected biogeographic movements, as well as the balance sheet of spatial range gains or losses, differ between species and the intensity of global warming. In the North Sea, species such as pollack, with a narrow ecological niche and strict requirements, may disappear as a result of the contraction of their range. Other, more adapted species will see their abundance increased and/or their upper limit of distribution pushed north, such as black locust. Changing the range of exploited fish species is likely to pose new challenges for fisheries sector stakeholders. Coupled with the depletion of resources from overexploitation, local extinctions of target species may occur, leading fishery professionals to change their patterns of activity in order to predict, anticipate and compensate for potential changes. their resources.

It is also unclear when marine ecosystems will react negatively to ocean acidification caused by the dissolution of increasing amounts of CO2. Organisms such as yeasts or plants (eg Arabidopsis thaliana) are – thanks to a single protein (histone H2A.Z) for the cress – sensitive to temperature variations of less than 1 °C, which are sufficient via this protein to modify the winding of the DNA on itself, which controls the access to the DNA of certain molecules that inhibit or activate several tens of genes. This should help to better understand some effects (on genes) of global warming.

Agriculture

The increase in evaporation is expected to increase winter rainfall locally, except in the Mediterranean countries, which would see drought increase, in a context where the violence and/or the frequency and severity of climatic hazards could increase.

In temperate zones (outside arid zones that could become even more so) and circumpolar zones, the combination of warming and increasing CO2 levels in the air and the rains could increase the productivity of ecosystems. Farming in the northern United States, Canada, Russia and the Nordic countries may be able to benefit, but signs of forest dieback may already be visible in these areas.

The European Economic and Social Committee, in its opinion of 3 February 2009, notes that comparative studies conclude that organic farming is on average better (in terms of raw material and energy consumption and in terms of the carbon stored or greenhouse gas emissions) than that of so-called conventional agriculture, even if we take into account the lower yields of organic farming, which justified the German government’s integration into the means of fight against climate change).

CESRE also recalls that a reoriented and adapted agriculture could, according to various specialists and NGOs, also contribute to stamping or curbing the effects of warming (Cool farming).

The committee does not cite agrofuels as a solution, citing climate scientist Paul Josef Crutzen, who claims that nitrous oxide emissions induced by the cultivation and production of biodiesel are sufficient, under certain conditions, to make rapeseed methyl ester climatic effects worse than those of diesel made with fossil fuel. The committee also raised the issue of traditional manure and wondered “whether full use of plants, as provided for in second generation biofuels, will not undermine the objectives set for development of the humus layer,” that is to say to contribute to further depletion of the organic matter of soils. The committee considers the question of the biofuel eco-balance by quoting a comparative study, from Empa, which concluded that to travel 10,000 km an average car required, with the yields observed in Switzerland, a floor space 5,265 m2 of rapeseed (biodiesel) against 37 m2 of solar panels (134 times less).

Studies are being conducted to adapt crops to global warming, for example to select varieties that grow earlier in the year, or that are more resistant to higher temperatures. One difficulty lies in the fact of combining within the same species mechanisms of adaptation to multiple constraints. Another difficulty is the species planted for several decades. The choice of species or their place of plantation must then be based on still uncertain models of the future climate.

Forest, forestry, agroforestry

Tropical forests are vulnerable to droughts, cyclones and fires; to make them more resilient to climate change, there needs to be a coordinated, multi-level effort to better utilize conservation tools, including the expansion of protected areas, fire control, and the application of REDD (Reduced emissions from deforestation and forest degradation), a tool to protect forest carbon but lacking explicit mechanisms to improve forest resilience.

In North America, Thomas Veblen, professor of geography at the University of Colorado, co-author with the US Institute of Geophysics, studied forest plots in the western United States for the periods 1955/1994 and 1998/2007 . In thirty years, with perhaps other causes, an average warming of 0,5 °C has already doubled the mortality rate of the trees of the great forests of the American west, by favoring the droughts and outbreaks of pests (of which beetles which, for example, destroyed about 1.4 million hectares of pine in northwestern Colorado). The lack of snow has led to a lack of water and an increase in summer droughts, with more fires, which gives rise to fears of cascading impacts on wildlife and ecosystems.

Increased mortality affects both broadleaved and coniferous trees of all sizes and species and at all altitudes. In the northwestern United States and southern British Columbia (Canada), the mortality rate in old coniferous forests has even doubled in 17 years (this is one and a half times faster than the increase in tree mortality of high trees in California where this rate has doubled in 25 years). Mortality has been less rapid in the non-Pacific forests of the west (Colorado and Arizona), but “a doubling of this mortality rate will eventually halve the average age of trees, resulting in a decrease in their average size, “Veblen believes. He also fears a lower CO2 fixation of the atmosphere. He calls for “new policies to reduce the vulnerability of forests and populations”, including limiting residential urbanization in vulnerable areas.

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