Beyond the direct physical and climatic consequences of global warming, it will affect ecosystems, especially by modifying biodiversity.
Scientists are beginning to propose relatively reliable projections of the future of biodiversity based on 5 determinants: habitat degradation and destruction, climate change, nutrient availability, overexploitation of biological resources and invasive species.
The Convention on Biological Diversity (CBD) in 2010 proposed scenarios of biodiversity responses to global change. These prospective tools based on statistical models, experiments and observed trends aim to help the dialogue. Based on work published in peer-reviewed scientific journals, the CBD (via DIVERSITAS, UNEP-WCMC) produced these “biodiversity scenarios” with the participation of about forty experts.
In the world, according to the IPCC, the ability of many ecosystems to adapt naturally will probably be overwhelmed by the unprecedented combination of:
- climatic upheavals: floods, forest fires, drought, insects, ocean acidification;
- global changes: land-use changes (deforestation, dams …), pollution, overexploitation of resources.
The ensuing natural imbalance could lead to the disappearance of several animal and plant species. This is a concern that states are starting to take into account. For all human populations, these “physical” and “ecological” effects will have a strong impact. The very great complexity of the ecological, economic and social systems affected by global warming does not make it possible to make quantified forecasts as for the physical modeling of the Earth.
At the biological and ecological level, a scientific consensus has been reached on the following points:
- The overall balance of global warming in terms of biodiversity will be negative according to a number of studies and according to the consensus of the fourth report of the IPCC that envisages the disappearance of 40 to 70% of the species evaluated; some species may see (and perhaps temporarily) their population and range increase (eg for yellow-bellied marmots).
- Some natural systems will be more affected than others by global warming. The most sensitive systems would be: glaciers, coral reefs, mangroves, boreal and tropical forests, polar and alpine ecosystems, wet meadows. The bleaching of coral reefs was observed for the first time in 1979 in the West Indies. This phenomenon has grown steadily in space and time on ever-increasing scales, for example at the Indian Ocean level in 1998. In 2017, 2015, 2016 and 2017 are recorded as the most measured since 2000, with an average increase in ocean temperature of 0.17 °C per decade. Their upper part (up to 700 meters deep) accumulated an unprecedented amount of heat resulting in a massive bleaching of corals from June 2014 to May 2017, causing, in the Atlantic, Indian and Pacific Oceans, unprecedented mortalities, going as far as 95% for some coral formations.
- The damage to natural systems, whether by geographical extent or intensity, will be proportional to the intensity and speed of global warming.
Negative consequences for humanity
The IPCC predicts major negative consequences for humanity in the 21st century:
- a decline in potential agricultural yields in most tropical and subtropical areas;
- a decrease in water resources in most tropical and subtropical dry regions;
- a decrease in the flow of water sources resulting from melting ice and snow, following the disappearance of these ice and snow.
- an increase in extreme weather events such as torrential rains, storms and droughts, as well as an increase in the impact of these phenomena on agriculture;
- an increase in wildfires during warmer summers;
- the extension of areas infested with diseases such as cholera or malaria. This risk is greatly minimized by specialist professor Paul Reiter, but the UK government points out that this professor has chosen to ignore all recent reports that contradict him;
- increased flood risk, both because of rising sea levels and changes in climate;
- higher energy consumption for air conditioning purposes;
- a decline in potential agricultural yields at mid and high latitudes (assuming strong warming).
Positive consequences for humanity
They are also associated with the warming expected in the 21st century:
- lower winter mortality at medium and high latitudes;
- a possible increase in water resources in some tropical and subtropical dry regions;
- an increase in potential agricultural yields in some mid-latitude regions (assuming low warming);
- the opening of new shipping lanes in the Canadian Arctic following the melting of ice in the Northwest Passage.