Antarctica is melting faster than models predict due to climate variability

Shrinking ice levels in Antarctica, along with future sea level rise, have been underestimated. In a new study from Penn State, researchers found that existing models do not account for climate variability, which has a significant influence on the Antarctic ice sheet. 

“We know ice sheets are melting as global temperatures increase, but uncertainties remain about how much and how fast that will happen,” said study co-author Professor Chris Forest. “Our findings shed new light on one area of uncertainty, suggesting climate variability has a significant impact on melting ice sheets and sea level rise.”

Before accounting for climate variability, the experts found that models projected roughly 10.6 to 14.9 inches of sea level rise by the end of this century. When climate variability was incorporated into the models, those forecasts increased by as much as 4.3 inches. 

“That increase alone is comparable to the amount of sea level rise we have seen over the last few decades,” said Professor Forest. “Every bit adds on to the storm surge, which we expect to see during hurricanes and other severe weather events, and the results can be devastating.”

It requires thousands of simulations to project how the Antarctic ice sheet will evolve under future climate conditions. Scientists use the average temperature that is derived from all of those results. 

However, the process smooths out peaks caused by climate variability and reduces the average number of days above temperature thresholds that can impact the ice sheet melt, creating a bias in the results, the scientists said.

“If we include variability in the simulations, we are going to have more warm days and more sunshine, and therefore when the daily temperature gets above a certain threshold it will melt the ice,” said Professor Forest. “If we’re just running with average conditions, we’re not seeing these extremes happening on yearly or decadal timescales.”

To study the effects of climate variability, the scientists incorporated relevant atmospheric and oceanic data into a three-dimensional Antarctic ice sheet model. The analysis showed that atmospheric variations had a great impact on the ice sheet with immediate effects. Variability in ocean temperatures were found to have a smaller, yet significant, impact. 

The results of previous studies suggest that warming oceans could cause large chunks to break away, exposing massive ice cliffs that would collapse under their own weight.

According to the experts, model simulations which did not include the effects of climate variability delayed the retreat of the ice sheet by up to 20 years and underestimated future sea level rise.

“This additional ice melt will impact the hurricane storm surges across the globe. Additionally, for years, the IPCC reports have been looking at sea level rise without considering this additional variability and have been underestimating what the impact may be,” said Professor Forest. “It’s important to better understand these processes contributing to the additional ice loss because the ice sheets are melting much faster than we expected.”

The study is published in the journal Climate Dynamics.

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By Chrissy Sexton, Earth.com Staff Writer