The Arctic has lost around 12.8% of its surface area every decade between 1979 and 2018, which, although “unprecedented for at least 1,000 years”, could shrink even more if no action is taken. This is according to the Intergovernmental Panel on Climate Change (IPCC). EURACTIV‘s partner le Journal de l’environnement reports.
During the IPCC’s 51st session, it was estimated that Greenland lost an average of 278 billion tonnes of ice each year between 2006 and 2015, twice as much as in 1997-2006.
As for Antarctica, the rate is currently lower (155 billion tonnes of ice per year), but the melting rate has also tripled. This is according to the summary for decision-makers of the Special Report on the Ocean and Cryosphere.
The IPCC report was presented at the end of the IPCC’s 51st session, held from 20 to 23 September in Monaco.
The melting of the poles, combined with the melting of high-altitude glaciers, is the leading cause of the sea-level rise. Each year, it causes the sea level to rise by 1.8 millimetres, which is half a total of 3.6 millimetres sea-level rise observed between 2006 and 2015. If Greenland is currently ahead of Antarctica, Antarctica may well catch up by the end of the 21st century.
A thinning of the ice
The Arctic is the region of the world where the effects of global warming are most pronounced. Between 1979 and 2018, sea ice loss has increased, regardless of the month of the year.
“Between 1979 and 2018, Arctic sea ice extent has very likely decreased for all months of the year. September sea ice reductions are very likely 12.8 ± 2.3% per decade. These sea ice changes in September are likely unprecedented for at least 1,000 years. Arctic sea ice has thinned, concurrent with a transition to younger ice. Between 1979 and 2018, the real proportion of multi-year ice that is at least five years old has declined by approximately 90%,” according to the IPCC.
The melting of sea ice will continue, even in the event of very moderate warming. If it is limited to a 2 °C increase in 2100, the risk of seeing a September without an Arctic ice pack will amount to 10%-35%, against only 1% if it is restricted to a 1.5 °C increase. The same is true on land, where the Arctic snow cover has decreased by 13.4% in size every decade in June since 1967.
However, because of its whiteness, it also plays a crucial role as a reflective mirror against solar rays. Due to this decrease in albedo (a measure of diffuse reflection of solar radiation out of the total solar radiation received), the sea is expected to capture more energy, thus increasing warming.
Permafrost, a significant source of greenhouse gas
As for permafrost, its temperature rose by 0.29 °C between 2007 and 2016. The thawing of this ground, which on a global scale contains twice as much carbon as the atmosphere, is a real “climate bomb”. Permafrost could release vast amounts of CO2 and methane into the atmosphere, further increasing global warming.
For the time being, permafrost is subject to “significant uncertainties: current studies do not allow us to confirm whether CO2 and methane emissions already accompany the large-scale thaw,” said paleoclimatologist Valérie Masson-Delmotte, co-chair of IPCC Group 1.
This is what the experts call “medium evidence with low agreement”.
The uncertainty is dissipating by 2100.
In the event of a Representative Concentration Pathway (RCP) 2.6, a scenario which assumes that global annual greenhouse gas (GHG) emissions peak between 2010-2020 with emissions substantially declining thereafter, the permafrost’s surface area (between 0 and 4 metres), should decrease by 24%.
In an RCP 8.5 scenario, a 69% decline is expected, which would release ten to hundreds of billions of tonnes of carbon. While Arctic vegetation could partially absorb this influx (tundra greening is already taking place), it will not be sufficient to absorb all of it.
In their report, the IPCC experts assessed two types of climate scenarios.
The most optimistic, the RCP 2.6 scenario, forecast an average increase of 1.6 °C over the 2081-2100 period compared to 1850-1900.
The more pessimistic RCP 8.5 scenario (known as “trend” or “business as usual”) forecasts an average increase of 4.3 °C.
The melting of permafrost has climatic effects but it also destabilises soils and could threaten urban, transport and communication infrastructure.
However, “the majority of infrastructure in the Arctic is located in areas where the permafrost thaw is expected to intensify around the middle of the century,” the IPCC noted.
Another human consequence, not necessarily negative for everyone, is that the melting of the ice should give way to new sea routes. In particular, the Northwest Passage (in northern Canada) and the Northeast Passage (in northern Russia), which point to the possibility of faster transportation.
However, this would come at the risk of accelerating the degradation of ecosystems already under high pressure.
Antarctica, a different story
The IPCC summary confirmed that Antarctica has thawed at an accelerated pace, but that the situation of its ice pack is less clear-cut than that of the Arctic.
No clear trend is emerging at the moment, due to high inter-annual variability and conflicting signals from one region to another. The western part is thus declining, while the eastern part is on the contrary tending to expand.
The Arctic Ocean and the Southern Ocean are “two different oceans because the first is surrounded by landmass while the other surrounds it,” according to Théophile Bongarts Lebbe, project manager at the Ocean and Climate Platform.
“The Southern Ocean is separated from the other oceans by the Circumpolar Current, the largest, deepest and fastest in the world. It behaves very differently from the Arctic Ocean, which is why it is currently less impacted. Antarctica is therefore protected by this current, at least to a certain extent,” Lebbe added.