Models used to predict future global warming can also be used to simulate the consequences of this warming on other physical parameters of the Earth, such as ice caps, precipitation, or sea levels. In this area, a number of consequences of global warming are the subject of consensus among climatologists.
Rising waters
One of the consequences of global warming on which scientists agree is a rise in the level of the oceans. Two phenomena generate this elevation:
- the increase in the volume of water due to its warming (thermal expansion);
- additional water supply from melting continental glaciers and polar ice caps. This last phenomenon is spread over a long period, the melting of glaciers being measured on the scale of several decades, and that of the polar ice caps over several centuries or millennia.
As with temperatures, sea level uncertainties are related to models, on the one hand, and future greenhouse gas emissions, on the other.
The increase between 1993 and 2003 is estimated at 3.1 mm per year (plus or minus 0.7 mm). The predicted elevation of sea level in 2100 is 18 to 59 cm, according to the fourth report of the Giec. This is probably a minimalist estimate, as Giec’s predictions are based solely on future ocean warming and expected melting of mountain glaciers, excluding phenomena related to possible ice cap instability, recently highlighted.
A rising water of a few centimeters does not have a very visible impact on the rocky coast, but can have very significant effects on the sedimentary dynamics of the flat coasts: in these regions, which are in dynamic equilibrium, the rising waters reinforces the erosive capacities of the sea, and thus globally shifts the balance towards a resumption of erosion that pushes back the coasts. The rise of the mean sea level thus has much greater effects than the simple translation of the coastline to the corresponding contour lines.
Precipitation and lightning
According to the 2007 IPCC report, an increase in precipitation at high latitudes is very likely, while in subtropics a decrease is expected, continuing a trend already noted, although other experts are tempering this, estimating the data as too rare and incomplete in order to identify a current upward or downward trend. According to studies published in 2007-2008, by 2025, one third of the world’s population could be in a state of water stress; the warming would have sometimes a positive effect, sometimes a negative effect, the balance between the two depending on the counting mode adopted.
According to a study published in November 2014 in the journal Science, global warming is expected to increase by 50% the number of lightning strikes in the 21st century; the risk of lightning could increase by 12% per additional degree Celsius in the United States.
Degradation of air quality
Climate disruption could have synergistic, aggravating and delocalised effects on many air pollutants, particularly through the risk of increased water and wind erosion and through an increased risk of forest fires and a lower level of ability of environment to fix dust. Acidification of the environment may also make toxic metals and metalloids more mobile (and more bioassimilable), including in the atmospheric compartment.
Thermohaline circulation
The thermohaline circulation refers to the movement of cold and salty water to the ocean floor at high latitudes in the northern hemisphere. This phenomenon, along with others, is responsible for the renewal of the deep ocean waters and the relative mildness of the European climate.
In the event of global warming, the engine which animates the marine currents would be threatened. Indeed, the currents acquire their kinetic energy during the dive of cold and salty waters, and therefore dense, in the depths of the Arctic Ocean. However, the increase in temperature is expected to increase evaporation in the tropics and rainfall in higher latitude areas. The warmer Atlantic Ocean would then receive more rain, and in parallel the ice cap could partially melt (see Heinrich Event). In such circumstances, one of the direct consequences would be a massive influx of fresh water to the vicinity of the poles, leading to a decrease in marine salinity and thus in the density of surface water. This can prevent their dive into the ocean abyss. Thus, currents such as the Gulf Stream could slow down or stop, and no longer ensure current heat exchange between the equator and the temperate zones. For the twenty-first century, the IPCC considered in its 2007 report as very likely a slowdown of the thermohaline circulation in the Atlantic, but as very unlikely a sudden change in this circulation.
Stop of the thermohaline circulation
According to one theory, a possible halt of the thermohaline circulation, due to global warming, could lead to a significant drop in temperature or even an ice age in Europe and in high latitude regions. In fact, Europe is at the same latitude as Quebec, and the Detlef Quadfasel study published in Nature in December 2005 shows that part of the difference in climate seems to lie in the fact that Europe benefits from the thermal contribution of the Gulf Stream. The equator, on the other hand, would then accumulate stimulating heat as a result of the continuous formation of hurricanes leading to large-scale precipitation.
This hypothesis of a cooling of Europe that would follow global warming is however not validated. Indeed, it is by no means established that the Gulf Stream is the only cause of mild winters in Europe. In 2002, Richard Seager published a scientific study on the influence of the Gulf Stream on the climate. According to him the effect of the Gulf Stream is a myth and has only a minor effect on the climate in Europe. The difference between winter temperatures between North America and Europe is due to the direction of the prevailing winds (icy continental wind from the north on the east coast of North America and the oceanic wind from the west in Europe) and to the configuration of the Rocky Mountains.
Ice and snow cover
IPCC scientists predict a reduction in snow cover for the 21st century and a retreat of pack ice. Glaciers and ice caps in the northern hemisphere are also expected to continue to retreat, with glaciers at altitudes less than 3,400 m above sea level.
On the other hand, the evolution of the Antarctic icecap during the 21st century is more difficult to predict.
In 2006 a team of American researchers highlighted a link between human activity and the collapse of ice shelves in Antarctica. Local warming would be due to a change in the direction of the prevailing winds, this change being itself due to the increase in the concentration of air in greenhouse gases and the degradation of the ozone layer in Antarctica due to the CFCs of human origin.
However, according to a letter sent to the journal Nature, these warmings are observed only locally. In fact, Antarctica is generally experiencing an increasingly cold climate and its icy cover is expanding, as the temperature rises in these very cold areas are favorable to an increase in snowfall, so in the long term, to an increase in volumes of ice.
However, the amount of Antarctic ice discharged into the sea has increased by 75% in the ten years prior to 2008. This phenomenon is likely to increase due to the disappearance of the pack ice, which ceases to spilling glaciers into the ocean.
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