Spatial Impacts of Climate Change. Denis Mercier
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World Glacier Monitoring Service (WGMS) provides standardized statistical data, such as ice front variations and mass balances1.
Figure 2.9. Annual mass balance of reference glaciers with more than 30 years of glaciological measurements from 1950 to 2018. The values of annual mass change are given on the y-axis in water equivalent (w.e.) per meter of water, which corresponds to tons per square meter (t/m2). For a color version of this figure, see www.iste.co.uk/mercier/climate.zip
(source: Zemp et al. 2017)
In particular, this graph (Figure 2.9) shows that seven of the ten most negative mass balance sheet years were recorded after 2010. A value of -1.0 m water equivalent per year represents a mass loss of 1,000 kg per square meter of ice cover or an annual loss of glacier-wide ice thickness of about 1.1 m per year, since the density of ice is only 0.9 times the density of water (Zemp et al. 2017).
Data at regional scales show that all of the world's glaciated mountain areas have been melting over the last few decades. Glaciers in North America and Central Europe are suffering the greatest losses. Between 2006 and 2015, the world's other glaciers melted at an average rate of 220 ± 30 billion tons per year, equivalent to 0.61 ± 0.08 mm per year in sea level rise (IPCC 2019).
Figure 2.10. Cumulative mass change from 1976 for regional and global averages based on reference glacier data. For a color version of this figure, see www.iste.co.uk/mercier/climate.zip
(source: Zemp et al. 2017)
Recent studies are trying to determine the date of disappearance of some glaciers. For example, the evolution and characteristics such as volume, area, ice thickness, runoff and duration and mode of disappearance of glaciers have been projected for the Austre Lovénbreen glacier on the BrØgger peninsula in northwestern Spitsbergen in the Svalbard archipelago (Wang et al. 2019; see Figures 2.11 and 2.12). Based on the 21st Century warming trend of the Arctic in the IPCC Fifth Assessment Report, glacier evolution was simulated under three hypothetical climate scenarios: pessimistic, high probability and optimistic. The results predicted that the glacier would retreat until it disappeared under all three scenarios, and its time to disappear would likely be about 111 years, that is by 2120.
Figure 2.11. Area and thickness of the Austre Lovénbreen glacier (Svalbard) simulated for different years: (i) 50th year (2060); (ii) disappearance of the western tributary; (iii) break between the main current and the eastern tributary; (iv) late decomposition according to the scenarios (a) optimistic; (b) high probability; (c) pessimistic. For a color version of this figure, see www.iste.co.uk/mercier/climate.zip
(source: Wang et al. 2019)
Figure 2.12. The Austre Lovenbreen glacier in northwestern Spitsbergen (Svalbard) in the background. The flat space in front of the glacier corresponds to the space freed by its melting since the beginning of the 20th Century. In the foreground, the prograding deltas on the Kongsfjorden are fed with sediments by the meltwater runoff from the glacier. For a color version of this figure, see www.iste.co.uk/mercier/climate.zip
(source: © photo by D. Mercier taken on August 24, 2017)
2.4.3. Decreasing permafrost
The IPCC Cryosphere Synthesis (IPCC 2019) provides information on the increase in permafrost temperatures since the 1980s. From 2007 to 2016, permafrost temperatures increased by an average of 0.29°C ± 0.12°C in the polar and high mountain regions of the world. The intensity of climate warming in the Arctic is exacerbated by this melting of Arctic and boreal permafrost, which may eventually release between 1,460 and 1,600 Gt of organic carbon, nearly twice the carbon in the atmosphere (IPCC 2019).
2.4.4. Melting snow
The decrease in land snow cover extent in June for the Arctic was 13.4 ± 5.4% per decade between 1967 and 2018, a total loss of approximately 2.5 million km2, mainly due to the increase in surface air temperature (IPCC 2019).
In almost all high mountain regions, the depth, extent and duration of snow cover has decreased in recent decades, especially at low altitudes in relation to rising temperatures and the rising rain-snow limit (IPCC 2019).
2.5. Consequences of the melting cryosphere
2.5.1. On a global scale: rising sea levels
At this scale, the most important consequence of the melting of the cryosphere is sea level rise. In addition to the thermal expansion of the oceans, the main sources of this sea level rise are the melting of the Greenland ice sheet and the Antarctic ice sheet, the contribution of mountain glaciers and permafrost. It was 18 cm during the 20th Century, and the various IPCC scenarios envisage a rise of around 60 to 100 cm by the end of the 21st Century (IPCC 2019).
However, we should not think in terms of this deadline alone, but rather that the rise of the seas and oceans will continue over the coming centuries as part of the melting of continental ice that has begun since the beginning of the Holocene interglacial period in which we live.
Thus, an increase (rise) of 5 m will surely be recorded by 2300. The consequences for low-lying coastal areas such as estuaries, tidal marshes, deltas, etc. will affect the economic activities and human occupation of millions of citizens (see Chapter 4).
A recent assessment by Zemp et al. (2019) shows that glaciers alone lost more than 9 billion tons of ice between 1961 and 2016, raising water levels by 27 millimeters (see Figure 2.13).
With more than 3,000 Gt, the Alaska Glaciers (ALA) have contributed the most to sea level rise. The glaciers of Southwest Asia (ASW, green circle) were the only ones to record an increase in mass.
Glaciers in the European Alps, the Caucasus mountain range and New Zealand have also suffered significant ice loss. However, because of their relatively small glacial areas, they have played only a minor role in sea-level rise (Zemp et al. 2019).
Figure 2.13. Regional share of glaciers in sea-level rise from 1961 to 2016. The cumulative change in regional and global glacier mass (in gigatons, 1 Gt = 1,000,000,000 tons) corresponds to the size of the