The Antarctic ice sheet is not melting in the linear way our climate models predicted it would. Instead, a more detailed model shows that while the rate of ice loss in the South Pole is rapidly accelerating, there are bumps of snowfall and brief reprieves from melt along the way.
“The ice sheet is not changing with a constant rate – it’s more complicated than a linear change,” explains Lei Wang, who researches civil, environmental, and geodetic engineering at Ohio State University.
“The change is more dynamic: The velocity of the melt changes depending on the time.”
Climate projections are imperfect by nature and subject to constant revision as we learn more, but the ones we have for Antarctica’s melting ice sheet are more contested than most.
While the majority of models agree polar ice is on the decline, the extent of melt under different emission scenarios has varied quite a lot.
For many years, in fact, scientists on the Intergovernmental Panel on Climate Change (IPCC) could not come to a consensus on how this melting ice would ultimately contribute to sea level rise. In the end, there was so much debate, the panel simply left out the data.
Today, IPCC models for Antarctic ice have greatly improved, but when it comes to future projections for global sea level rise, scientists say the potential for the South Pole’s massive ice sheet to collapse completely still remains the single largest source of uncertainty.
Ice sheet dynamics are complex and climate variability is unpredictable. Many of our current models, on the other hand, are simple and inflexible, displaying ice loss from the Antarctic ice sheet at a constant rate.
This ignores variability in regions, years, and seasons, leading to large uncertainties in global projections of sea level rise, the researchers argue.
“I’m not saying Antarctica’s ice melt is not an acute problem – it is still very acute,” says Wang.
“All of Antarctica is losing mass, very rapidly. It’s just a time scale problem and a rate problem, and our models that predict sea-level change should reflect that.”
Today, many climate projections do not take Antarctica’s fluctuating weather into account, and this could lead scientists to underestimate the ice sheet’s overall impact on sea level rise or the speed at which that will happen.
By factoring in rates of change in Antarctica using data from NASA satellites, this new and more dynamic model relies on much greater detail than standard regression models.
In the end, its findings reveal that every sector of the Antarctic ice sheet shows “highly variable” seasonal and inter-annual changes in ice loss. What’s more, these factors appear to play a dynamic role in the ice sheet’s overall mass, not a linear one as previous models suggested.
While the West Antarctic ice sheet shows a multi-decadal trend in ice melt, for instance, the East Antarctic ice sheet shows quicker fluctuations.
In the short term, the authors found extreme snowfall events in the East Antarctic can somewhat supplement the continuous loss of ice in the West Antarctic ice sheet. Yet in the long term, those temporary regional dustings have little overall effect on the overall mass of Antarctic ice.
In 2016, for instance, a snowfall anomaly in West Antarctica, unprecedented in the past 60 years, helped offset the net mass loss of Antarctic ice over a period of four years. In a normal year of snowfall, however, West Antarctica loses five times more ice than what East Antarctica gains.
“Despite their historic magnitudes, these extreme snowfall episodes still cannot fully offset contemporary mass loss from the [West Antarctic ice sheet] and the [Antarctic Peninsula ice sheet],” the authors conclude.
“Although models predict increasing accumulation through the 21st century in response to a warmer and wetter atmosphere, it is unlikely they would be able to negate the predicted dynamic loss from the [West Antarctic ice sheet].”
In recent years, ice melt in the southern hemisphere has begun to speed up at an alarming rate, on track with our worst-case scenarios. Since 2012, recent research reveals the rate of ice loss in Antarctica has tripled compared to the two decades before.
As this vast land of ice grows ever more unstable, experts worry the rate of melt will accelerate even more due to positive feedback events. Over half the ice shelves holding up the Antarctic ice sheet are already nearing collapse.
If the world warms by 3 degrees Celsius, some models suggest melting ice in Antarctica could lift the oceans by 6.5 metres, displacing millions of people and sinking numerous coastal cities.
Further monitoring and research is needed, especially in the East Antarctic ice sheet, which has been historically overlooked, and which the authors say represents “a major source of uncertainty in the projection”.
Climate models will always have a certain level of uncertainty, but the better our predictions, the greater our understanding of the actual threat will be – giving us the best chance to actually do something about it before it’s too late.
The study was published in the Geophysical Research Letters.