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Melting polar ice caps means climate turbulence expected to felt globally

Credits : Video screenshot / NASA Goddard's Scientific Visualization Studio.

As our climate is becoming warmer, polar ice caps are starting to lose their mass more quickly.  There are many environmental consequences of this evolution.  However climate change models which policymakers rely on do not explicitly take into account the interactions between climate change and polar ice caps. However, it appears that including the coupling between ice sheets and global climate significantly changes the global climate situation. At least this is what a study published this February 6 suggests.  It suggest that  the likelihood of extreme weather events is even higher than before. 

Loss of glacial mass in the Greenland and Antarctica ice sheets and mountain glaciers has accelerated in the last few decades.  This acceleration is largely due to the rapid increase in temperature of our atmosphere and oceans following the growth of greenhouse gases released into the atmosphere by human activity.

Rising sea levels is largely due to the gigantic mass of water which is filling our oceans.  Melting ice sheets, as mentioned above, are considered to be the greatest possible factor for this increase.  As a result, our ice sheets could become major contributors to climate change in the next few decades.

What is more, the partial melting of polar ice caps has an impact on many other aspects of the climactic system.  This includes atmosphere or ocean circulation or even the ocean’s thermal stratification.  These induced disturbances could then have a negative effect on ice caps by increasing their melting rate.  This could be a real vicious circle.

Credits : NASA – Nathan Kurtz

However

However, the projections made in the fifth coupled model inter-comparison exercise (CMIP-5) – used to inform policymakers – do not explicitly consider interactions between climate and ice caps *. The interactions between ice, oceans and atmosphere and the consequences are therefore not adequately represented.

Polar ice caps need to be considered

A study published on the 6 February in the Nature journal presents what will happen when this dynamic coupling is taken into consideration.  A high-resolution digital representation of the two ice caps has been included in a global model simulating a marked global warming. This is a first in this domain. The authors also produced an identical but uncoupled control stimulation so there could be a comparison.

If ice caps are couple to the global modal global warming is mitigated. On a global scale, the difference with the control simulation remains relatively low (around -0.3 ° C). But at medium and high latitudes of the southern hemisphere, there is a more significant difference (-2 ° C locally -4 ° C). This limitation of rising atmospheric temperatures could play a negative feedback role for the Antarctic ice cap and temperate its melting.

The same structure can be seen for the surface temperature of the sea with anomalies that are a slightly less pronounced. However several hundred metres below the surface of our oceans their are more pronounced signs of warming.  Ice cap melt waters stratifies the ocean and decreases vertical mixing. Heat is then trapped beneath the surface. Overtime, this accelerates the flow of continental ice to the ocean.

calotte polaire
Credits : Calyponte / Wikimedia Commons.

Necessary for more realistic climate projections

What does ocean circulation involve? Unsurprisingly ocean circulation is significantly slowed down in the Atlantic sector. As a result, heat is less efficiently transported to the north. As a result, warming in northwestern Europe has been weakened, but is increasing in central and eastern North America and in the tropics. A robust footprint already noted by previous studies. A redistribution of thermal contrasts whose consequences are still poorly understood.

The researchers also highlighted that coupling with the caps amplified meteorological extremes. Compared to the control simulation, thermal variability from one year to the next is much greater – almost +50% overall on average. The same thing is observed with regards to the sea surface temperature. It is therefore more likely that we could have weather of cold or hot extremes.

Overall, the inclusion of meltwater releases in climate simulations appears to result in a complex set of atmospheric and oceanic changes, including increased inter-annual variability in some areas, which could lead to more frequent extreme weather events“,  says the study. In conclusion, in order to provide more realistic climate projections, simultaneous consideration of both ice sheets and their coupling with the global climate is necessary. This subject will undoubtedly be one of many future works.

* A deficit to be linked to the numerical challenge posed by the representation of the climate system as a whole. 

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