The climate science community is tasked with striking a difficult balance: inspiring precisely the amount of alarm commensurate to the climate crisis. Make estimates that are too conservative, and the public might not react with appropriate urgency; make estimates that are too extreme, and the public might distrust future climate science. Now, researchers from the Utrecht University are using the power of supercomputing to evaluate the accuracy of climate models’ estimates of future sea level rise.

The Utrecht researchers ran a series of high-resolution climate models over the course of several years. The latest incorporates ocean eddies, which help move heat and salt around the ocean. The idea behind incorporating ocean eddies was simple: if the researchers knew where the heat would be concentrated, they could more accurately understand what heat would surround Antarctica and, ipso facto, how fast that ice would melt and contribute to sea level rise.

“The Antarctic ice sheet is surrounded by ice shelves which reduce the flow of land ice into the ocean,” explained René Van Westen, a PhD candidate at Utrecht and first author on the paper. “Higher ocean temperatures around Antarctica increase the melting of these ice shelves, resulting in an acceleration of land ice into the ocean and consequently leading to more sea level rise.”

To run these high-resolution simulations, the researchers used the Dutch national supercomputer, Cartesius, hosted by SURFsara. Cartesius is an Atos system with a combination of Intel Haswell, Ivy Bridge, Knights Landing, Sandy Bridge and Broadwell nodes, along with 132 GPUs and 130 TB of memory. All told, Cartesius delivers 1.84 petaflops of peak performance. 

The researchers took a year to perform the simulation on Cartesius. “These high-resolution models require an immense amount of computation, but are valuable as they reveal smaller-scale physical processes which should be taken into account when studying climate change,” said Henk Dijkstra, a professor of oceanography at Utrecht and lead author on the paper.

The results of the high-resolution simulation compared to a low-resolution simulation.

The simulation yielded surprising results: compared to models that did not incorporate eddies, it showed substantially less heat and melting in Antarctic regions – just a third of what had previously been estimated by major ensemble models, which corresponds to a 25 percent decrease in projected sea level rise. “These regions appear to be more resilient under climate change,” Van Westen said. “Although sea levels will continue to rise, this is good news for low-lying regions. 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.”