Climate models

Antarctica is melting in a way our climate models never predicted, scientists say


The Antarctic ice sheet is not melting in the linear way our climate models predicted. Instead, a more detailed model shows that as the rate of ice loss at the South Pole accelerates rapidly, there is snowfall and brief respite from melting along the way.

“The ice sheet doesn’t change at a constant rate – it’s more complicated than linear change,” says Lei Wang, who does civil, environmental and geodetic engineering research at Ohio State University.

“Change is more dynamic: the speed of melting changes over time.”

Climate projections are imperfect by nature and subject to constant revision as we learn more, but those we have for the melting of the Antarctic ice sheet are more disputed than most.

While the majority of models agree on the decline of polar ice, the extent of the melt under different emission scenarios has varied widely.

For many years, in fact, scientists at the Intergovernmental Panel on Climate Change (IPCC) were unable to reach a consensus on how this melting ice would ultimately contribute to the level rise. of the sea. In the end, there was so much debate that the panel simply left out the data.

Today, IPCC models for Antarctic ice have improved dramatically, but when it comes to future projections of global sea level rise, scientists say the potential for complete collapse of the huge ice cap at the South Pole remains the main source of uncertainty.

The dynamics of ice caps are complex and climate variability is unpredictable. Many of our current models, on the other hand, are simple and rigid, displaying the loss of ice from the Antarctic ice sheet at a constant rate.

This ignores the variability of regions, years and seasons, which leads to large uncertainties in global projections of sea level rise, the researchers say.

“I am not saying that the melting ice in Antarctica is not an acute problem – it is still very serious,” Wang said.

“All of Antarctica is losing mass, very quickly. It’s just a time scale issue and a rate issue, and our models that predict sea level change should reflect that.”

Today, many climate projections do not take into account Antarctic weather fluctuations, which could lead scientists to underestimate the overall impact of the ice sheet on sea level rise or speed. to which this will occur.

By accounting for rates of change in Antarctica using data from NASA satellites, this new, more dynamic model relies on much more detailed detail than standard regression models.

Ultimately, his results reveal that each sector of the Antarctic ice sheet exhibits “highly variable” seasonal and interannual changes in ice loss. In addition, these factors appear to play a dynamic role in the overall mass of the ice sheet, and not linear as suggested by previous models.

While the West Antarctic ice sheet shows a trend of melting ice over several decades, for example, the East Antarctic ice sheet shows more rapid fluctuations.

In the short term, the authors found that extreme snowfall in East Antarctica may somewhat complement the continued loss of ice in the West Antarctic ice sheet. Yet in the long term, these temporary regional dusts have little overall effect on the overall mass of Antarctic ice.

In 2016, for example, a snowfall anomaly in West Antarctica, unprecedented in the past 60 years, offset the loss of net Antarctic ice mass over a four-year period. In a normal snowfall year, however, West Antarctica loses five times more ice than East Antarctica gains.

“Despite their historical magnitude, these episodes of extreme snowfall still cannot fully compensate for the contemporary mass loss of the [West Antarctic ice sheet] and the [Antarctic Peninsula ice sheet], conclude the authors.

“Although models predict increasing accumulation over the 21st century in response to a warmer, more humid atmosphere, it is unlikely that they will be able to reverse the predicted dynamic loss of the [West Antarctic ice sheet]. “

In recent years, the melting ice in the southern hemisphere has started to accelerate at an alarming rate, in line with our worst-case scenarios. Since 2012, recent research shows that the rate of ice loss in Antarctica has tripled compared to the previous two decades.

As this vast land of ice becomes increasingly unstable, experts fear the rate of melting will accelerate even further due to positive feedback events. More than half of the ice shelves supporting the Antarctic ice sheet are already on the verge of collapse.

If the world warms by 3 degrees Celsius, some models suggest that the melting ice in Antarctica could lift the oceans 6.5 meters, displacing millions of people and sinking many coastal cities.

Further monitoring and research is needed, particularly in the historically neglected East Antarctic Ice Sheet, which the authors say represents “a major source of uncertainty in the projection.”

Climate models will always have some level of uncertainty, but the better our predictions, the better our understanding of the real threat will be, which will give us the best chance of doing something before it’s too late.

The study was published in the Geophysical research letters.