The thawing of the Antarctic ice cap as a result of global warming introduces a great complexity in the future evolution of the climate. Also, a study published on August 12 calls for a better consideration of iceberg and meltwater discharges in future projections. It shows, among other things, that these factors tend to mitigate the warming of the southern hemisphere.
As the temperature of the air and water rise, parts of the western Antarctic ice cap become unstable. As a result, increasing amounts of icebergs and meltwater are released into the Southern Ocean – which then escapes to more northern latitudes. However, as a new study shows, the acceleration of these discharges is likely to have a considerable impact on the climate of the southern hemisphere.
An unprecedented study on the role of icebergs
The study focused in particular on the role of icebergs, little studied until then. The influence of the latter, however, may not be the least. Indeed, these giant ice cubes release cold and soft water as they drift towards warmer regions. In doing so, they affect the temperature and salinity of the ocean as they pass – and thus its stratification. Depending on its size and trajectory, the lifespan of an iceberg can be as long as several years.
However, in the future, we expect a substantial increase in their number following the acceleration of the calving process of the calotte under the effect of warming. It is therefore important to know to what extent they modify the operation of the climate machine.
To do this, researchers used a climate model coupled with glacial dynamics. By performing several simulations – with or without the influence of calving – they assessed the impact of icebergs as the ice cap destabilized. This is the first study that explicitly quantifies the importance of this process.
Slowing global warming in the southern hemisphere
One of the main results is the noticeable slowdown in the warming of the southern hemisphere during the destabilization phase of West Antarctica. The additional energy used to melt the icebergs and/or to heat the meltwater.
“Depending on the speed with which the ice sheet disintegrates, the effect of icebergs can delay the expected warming in cities like Buenos Aires or Cape Town by 10 to 50 years,” said Axel Timmermann, co-author of the paper. At the same time, the average sea level would rise by more than 80 centimeters by 2100.
In addition, previous work has suggested that the subsequent modification of ocean currents would induce accelerated warming in the sub-surface. This one would then tend to amplify the retreat of the ice sheet by eroding the ice platforms from below. However, taking into account the dynamics of icebergs, this vicious circle is greatly reduced.
“Our results show that the effects of meltwater and icebergs need to be included in simulations of future climate change,” says Fabian Schloesser, lead author of the study. “The climate models used for the sixth report of the Intergovernmental Panel on Climate Change (IPCC) do not take these processes into account.”