The melting rate of the Antarctic ice sheet is mainly controlled by the increase in ocean temperatures around Antarctica. Using a new, higher resolution simulation of climate models, scientists from Utrecht University found a much slower increase in ocean temperature compared to current simulations with a coarser resolution. As a result, the projected sea level rise in 100 years is about 25% lower than the current simulations expected. These results were published in the journal Science Advances.
Estimates for future sea level rise are based on a large ensemble of climate model simulations. The results of these simulations help to understand future climate change and its effects on sea level. Climate scientists are constantly striving to improve these models, for example by using a much higher spatial resolution that takes more detail into account. “High-resolution simulations can determine the circulation of the ocean much more accurately,” says prof. Henk Dijkstra. Together with his PhD candidate René van Westen, he has been studying ocean currents in high-resolution simulations of climate models for the past few years.
Ocean eddies
The new high-resolution model takes ocean vortex processes into account. A vortex is a large (10 – 200 km) swirling and turbulent feature in the circulation of the ocean, which contributes to the transport of heat and salt. The addition of ocean vortices in the simulation results in a more realistic representation of the ocean temperatures around Antarctica, which is the key to determining the mass loss of the Antarctic ice sheet. “The ice sheet of Antarctica is surrounded by ice shelves that reduce the flow of land ice to the ocean,” Van Westen explains. “Higher ocean temperatures around Antarctica increase the melting of these ice shelves, leading to an acceleration of land ice in the ocean and leading to more sea level rise.”
Current simulations of climate models, which do not take ocean vortices into account, indicate that ocean temperatures around Antarctica are rising under climate change. The new high-resolution simulation shows very different behaviors and some regions near Antarctica are even cooler under climate change. “These regions seem to be more resilient under climate change,” says Van Westen. Dijkstra adds: “One gets a very different temperature response due to effects on the ocean.”
Supercomputer
The new high-resolution model projects a smaller mass loss due to the melting of the ice shelf: only one-third compared to current climate models. This will reduce the projected global sea level rise by 25% in the next 100 years, Van Westen says. ‘Although sea levels will continue to rise, this is good news for low-lying regions. In our simulation, ocean vortices play a crucial role in sea level projections, showing that these small-scale ocean functions can have a global impact. ‘It took the team about a year to complete the high-resolution simulation on the national supercomputer at SURFsara in Amsterdam. Dijkstra: “These high-resolution models require many calculations, but are valuable because they show smaller-scale physical processes that must be taken into account when studying climate change.”
Reference: “Ocean vortices strongly influence global average sea level projections” by René M. van Westen and Henk A. Dijkstra, 9 April 2021, Scientific progress.
DOI: 10.1126 / sciadv.abf1674