Geophysical and seismic effects
(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 rapid melting of part of the cryosphere (high mountain glaciers, but especially ice caps) has geophysical effects; the melting of any large mass of ice is accompanied by shifts in gravity and as a result in a deformation of the Earth considered viscoelastic (measurable by GPS, inclinometer measurements (also used to measure soil deformations induced by the dams or aquifers)) and gravimetric near affected areas, the magnitude of these effects is greater in the polar and sub-polar regions.
In the wake of the postglacial rebound, which it could exacerbate, this melting induces a new distribution of the water bodies (volumes of ice that are not very mobile, transformed into a mass of liquid and very mobile water, contributing to a rapid spatial and temporal redistribution of mass) that we can begin to measure better and that could change the shape of the geoid. The oceans become heavy while inland seas are evaporated (Caspian Sea, for example, which has lost 1.5 meters in 20 years).
According to data collected by the European Goce satellite (Gravity Field and steady-state Ocean Circulation Explorer), from 2009 to 2012 and by his predecessor Grace (less accurate), the melting of some of the ice in West Antarctica significantly altered the gravity field of a region where since 2009 the annual loss of ice has tripled (from 2011 and 2014, the overall volume of the southern ice cap has decreased by an average of about 125 cubic kilometers per year ), which is confirmed by the radar altimetry (radio altimeter) of the CryoSat satellite.
By rebalancing or “glacial-isostatic adjustment” (GIA), some faults and volcanic systems could be reactivated (correlations between massive melting of caps and seismic events were evoked and confirmed in 2009 to recent geological periods, between 12,000 and 7,000 years, when volcanism seems to have been six times more intense, and in Iceland more than thirty times what it is today). In addition to the lightening of the poles, we must also take into account the additional weight of the global ocean related to the rise of the oceans.
Finally, the destabilizing thaw of mountain permafrost and the water that cements certain mountainous rock masses (eg the Alps) are reflected in mass displacements and collapses of mountain blocks (150 km collapses recorded in 2015 in the Mont-Blanc massif, essentially “between 3,100 and 3,500 meters of altitude”), sources of additional materials that will be carried by the torrents. The collapse occurs in winter after the heat of summer has penetrated the interior of the mountains and when the cold returns, according to Ludovic Ravanel.
Effects on agricultural practices
The climate, and especially the temperatures, have an effect on the date of the agricultural harvest. Anticipation of the key dates of plant development (budding, flowering, harvest) was observed for all crops in temperate and Mediterranean climates. Thus, for wheat, the exit of the ears takes place 8 to 10 days earlier than twenty years ago. In many cases, the harvest dates are regularly advanced, as in Burgundy. Moreover these phenomena can be described over several decades because these dates of harvest were recorded in the past and archived. Such documents are used to determine temperatures at times when thermometers did not exist or lacked precision. Global warming since the twentieth century is clearly established by the study of these archives (thus, the date of the beginning of the grape harvest in Châteauneuf-du-Pape has advanced three weeks in fifty years).
Effects on fauna, flora, fungi and biodiversity
(As the climate change melts sea ice, the U.S. Geological Survey projects that two-thirds of polar bears will disappear by 2050. )
Range changes
At sea, many species of fish go back to the poles. On Earth, there is also a change in the range of different animal and plant species. This modification is complex and heterogeneous.
In some cases, species and ecosystems shrink from desertification or salinization. Some range boundaries rise higher in altitude, especially when the species’ range is moving north (or south in the southern hemisphere), which should not hide the fact that in reality, at least locally, the optimum for a species has been able to descend strongly at altitude (where the environments are wetter, for example as a result of an increased melting of glaciers). For example in California, for 64 plant species whose range has been monitored since 1930 to 2010, the climatic optimum zone of these plants has decreased by 80 meters of altitude on average. A follow-up done in 13 European states shows that mountain plants “climb” at altitude, but are then faced with increased competition. Some foresters thought that warming would increase the growth of Alaskan trees, but in fact it is declining, probably because of the stress of summer drought.
Climate change is often proposed as explaining global ecological changes. Paradoxically, locally, as a result of cold currents resulting from the accelerated melting of the ice cap, winter chills can also affect wildlife. Thus in early February 2011, 1,600 green turtles (endangered species) numbed by unusually cold water washed up on and around South Padre Island (Texas). They are then more vulnerable to collisions with boats, their predators and strandings (of the first 860 turtles recovered by volunteers, 750 survived and were later released). As of January 2010, more than 4,600 turtles had been stranded in Florida.
This also applies to terrestrial wildlife. For example, the range of the pine processionary caterpillar is expanding and reached Orléans in 1992 and Fontainebleau in 2005. The colonization of the species could reach Paris in 2025. According to INRA, this expansion is emblematic of the spread of pests of forest species through global warming. The temporal monitoring of common birds (STOC) shows, for example, that in twenty years, bird communities in France have globally moved 100 km to the north.
Physiological changes of organisms
In many species, ecological insularization (which increases during glaciations (phenomenon of glacial refugia) but also increases in case of warming on the coastlines, because of the rise of the oceans, changes in precipitation or seasonality, but also the warming of the range of an animal species can lead to a decrease in the size of the body (“adaptive dwarfism”).
According to palaeontologists Philip Gingerich and his colleagues, if the warming trend were to continue in the long term, a decrease in size or even a real dwarfism of some wild animals (mammals such as primates, horses and deer in particular) could reappear in adaptation in hot climates. Such a phenomenon has already occurred during the Paleocene-Eocene Passage Thermal (or PETM) heat that occurred about 56 million years ago and lasted about 160,000 years with global temperatures rising from 9 to 14 degrees Fahrenheit at its peak. Similarly, during another global warming of lesser magnitude (+ 5 °F at max.) and less long (80,000 to 100,000 years), which is ETM2 (Eocene Thermal Maximum 2), about 2 million years after PETM (53 million years ago). During these two global warmings, the size of the ancestors of our horses (Hyracotherium which had the size of a dog), respectively decreased by 30% and 19% during the PETm then the ETM2.
This phenomenon also concerns the fauna of the soil and those living in the water where the increase of the temperature brings about a drop of the oxygen level, an increase of the CO2 and an acidification (which modifies the bioavailability of the iron for the marine phytoplankton, and increases everywhere that of many toxic metals). Dryness or increased metabolism of ectotherms seems to disadvantage large individuals compared to small ones, and a majority of advanced organisms appear to be adapting with lower growth, by a cascading narrowing effect (from primary producers to consumers) to following the decline of food resources in the food chain.
Moreover, global warming affects the survival of species in a wide variety of ways. Polar bears, for example, are threatened because of the greater presence of holes in the pack ice, allowing seals to breathe out of reach of this predator. Color polyphenism affecting a large number of arctic species, such as the polar fox that becomes white in winter, is very often dependent on the length of the day, thus inducing hiatus more and more frequent (a white coat while there is no snow yet).
Extinctions of species, disappearance of habitats
According to the selected scenarios and methodologies, the studies published between the years 1990 and 2015 concluded with varied results: some concluding to minimal changes and others to the disappearance of up to 54% of the species due to climate change.
In 2015, a meta-analysis focused on 131 studies, all of which focused on the risk of extinction of more than one species due to climate change. This meta-analysis concluded that “up to one sixth of the species on Earth could disappear if climate change stays on its current trajectory” (2010-2015). But locally, in more critical areas, extinction rates may be higher.
Extinguishing factors are, for example, a natural slowness of dispersion, or the existence of obstacles to migration to milder areas. These barriers are, for example, mountain ranges, deforestation, intensive agriculture or urban development. In other cases, the habitat will disappear entirely, or the vital area will become too small to ensure the survival of the species. To formulate this prospective scenario by avoiding extrapolated biases from studies of few species or small territory, the authors chose to overweight the value of work for a large number of species. The authors estimate that in 2015, about 2.8% of the species on Earth are already in danger of extinction for climatic reasons. The (likely) warming of 2 °C in 2100 is expected to lead to a further 5.2 per cent of the species at probable extinction. And if the average warming was to reach 4.3 °C above pre-industrial levels (a scenario deemed credible by some studies) one in six species could disappear.
Due to the complexity of ecosystem phenomena, however, these figures must be taken with caution. Sax recognizes that “we are only right at the beginning of the assessment of these risks”.
Prospective issues and management of natural heritage
In addition to the risk of extinction of species, the elements described above may be of great importance for climate change adaptation and protection strategies for the protection and restoration of biodiversity and the green and blue networks required for their movement (including climatic corridors where appropriate). National parks, especially those located in the mountains, may not be able to take into account a discreet but important phenomenon of descent of the “optimums” of certain plants that will often extend to urbanized and agricultural areas. Countries like Australia have created climate corridors to facilitate “climate” migration of wildlife. Prospective studies could also help scientists and policymakers better choose protected areas and change their perimeters according to climatic constraints (“An area set aside as a natural reserve to preserve species in a contemporary ecosystem may become ecologically unsuitable for a few decades. “). This applies to the marine environment: NOAA and others call for the creation of marine sanctuaries and networks of other protected habitats to create climate migration corridors to help marine life adapt to climate change.
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