Current climate model simulations overestimate future sea level rise

The rate of melting of the Antarctic ice sheet is primarily controlled by the rising temperatures of the oceans surrounding Antarctica. Using a new, higher-resolution climate model simulation, scientists at Utrecht University found a much slower rise in ocean temperature than current simulations with coarser resolution. Therefore, the projected sea level rise in 100 years is about 25% lower than expected from current simulations. These results are published today in the journal Scientific progress.

Estimates of future sea level rise are based on a large set of climate model simulations. The results of these simulations help to understand future climate change and its effects on sea level. Climatologists continually seek to improve these models, for example by using a much higher spatial resolution that takes into account more detail. “High-resolution simulations can determine ocean circulation much more accurately,” says Professor Henk Dijkstra. With his doctorate. candidate René van Westen, he has studied ocean currents in high-resolution climate model simulations over the past few years.

Ocean eddies

The new high-resolution model takes into account the processes of ocean vortices. A vortex is a large (10-200 km) swirling and turbulent feature in the ocean circulation, which contributes to the transport of heat and salt. Adding ocean eddies to the simulation leads to a more realistic representation of the ocean temperatures surrounding Antarctica, which is essential in determining the mass loss of the Antarctic ice sheet. “The Antarctic ice sheet is surrounded by ice shelves that reduce the flow of land ice into the ocean,” says Van Westen. “The warmer ocean temperatures around Antarctica increase the melting of these ice shelves, causing land ice to accelerate in the ocean and, as a result, rise in sea level. .

Current climate model simulations, which do not take into account ocean eddies, predict that ocean temperatures around Antarctica will increase with climate change. The new high-resolution simulation shows quite different behavior and some areas near Antarctica are cooling even under climate change. “These regions appear to be more resilient to climate change,” says Van Westen. Dijkstra adds: “You get a very different temperature response due to the ocean-vortex effects.”

Supercomputer

The new high-resolution model projects less mass loss due to melting sea ice: only a third compared to current climate models. This reduces the projected global sea-level rise by 25% over the next 100 years, says Van Westen. “Although sea level continues to rise, this is good news for low lying areas. In our simulation, ocean eddies play a crucial role in sea level projections, showing that these small-scale ocean features can have a global effect.

It took about a year for the team to complete the high-resolution model simulation on SURFsara’s national supercomputer in Amsterdam. Dijkstra: “These high-resolution models require a huge amount of computation, but are valuable because they reveal smaller-scale physical processes that should be taken into account when studying climate change.”