Antarctic ice sheet warning
Alarming stories from Antarctica are happening more often than ever before; surface ice is melting, floating ice sheets are collapsing and glaciers are flowing faster into the ocean.
Antarctica will be the biggest source of future sea level rise. But scientists don’t know exactly how this melting will happen as the climate warms.
Our latest research looks at how the Antarctic ice sheet has advanced and retreated over the last 10,000 years. It holds strong warnings, and perhaps some hope, for the future.
Current imbalance
Future sea level rise presents one of the most significant challenges of climate change, with the expected economic, environmental and social impacts on coastal communities around the world.
Although it may seem like a distant problem, change in Antarctica will soon be felt at our doorstep, in the form of rising sea levels.
Antarctica is home to the single largest ice mass in the world: the Antarctic ice sheet. This glacier’s ice body is several kilometers thick, lying on solid ground. It covers the entire mountain range below.
The ice sheet “flows” over land from the Antarctic interior and into the surrounding ocean. Overall it remains a solid mass, but slowly changes shape as the ice crystals move.
While the ice sheet flows out, the snowfall from above fills it back up. This cycle is supposed to keep the system in balance, where equilibrium is reached when the ice sheet gains the same amount of ice it loses to the ocean each year.
However, the satellite watching from above shows the current ice sheet no in balance. Over the past 40 years, it has lost more ice than it has gained. The result is rising sea levels globally.
But these historical observations lasted only four decades, limiting our understanding of how ice sheets respond to climate change over longer periods.
We want to look further into the past – before satellites – and even before the first polar explorers. For this, we need natural archives.
Digging into Antarctica’s past
We compiled various natural archives to explore how the Antarctic ice sheet has changed over the last 10,000 years or so. This includes:
- ice cores collected from the remote interior of Antarctica, which could show us how snow accumulated in the past
- rocks collected from exposed mountain peaks, which reveal how the ice sheet has thickened or thinned over time
- a core of sediment collected from the ocean floor, which reveals how the ice sheet boundary – where the edge of land ice meets the ocean – is advancing or retreating
- mud lakes and old beaches, which reveal how coastlines are changing in response to growing or shrinking ice sheets.
When we started our research, I wasn’t sure what to expect. After all, this period of time had long been considered quite boring, with only slight changes to the ice boundary.
However, we study many different natural archives one by one. The work feels like a 1000-piece jigsaw puzzle, full of irregularly shaped pieces and apparently not having straight edges. But once we put it together, the pieces lined up and the picture was clear.
Most striking is the period of ice loss that occurred in all of Antarctica some 10,000 to 5,000 years ago. This resulted in several meters of sea level rise globally.
In some areas of Antarctica, however, this ice loss was then followed by ice rise over the last 5,000 years – and a corresponding decline in global sea levels – as ice sheet margins rose to where they are today.
A warning
Understand how and why Antarctica’s ice sheet changing in this way offers lessons for the future.
The first lesson is more of a warning. The period of ice loss from 10,000 to 5,000 years ago was rapid, occurring at the same rate as parts of the Antarctic ice sheet that are changing most dramatically today.
We think it may be the result of warm ocean water melting the bottom of the floating ice shelf – something that has also happened in recent decades. These ice shelves hold ice on land, so once they are moved, ice on land flows faster into the sea.
In the future, it is expected that ice loss will accelerate as the ice sheet retreats into the basin below sea level. This may already be happening in some areas of Antarctica. And based on what happened in the past, the resulting ice loss could last for centuries.
Bouncing back
A second lesson from our work may bring hope. About 5000 years ago the ice sheet boundaries stopped shrinking in most locations, and in some areas actually started to increase. One explanation for this has to do with earlier periods of ice loss.
Before the ice began to melt, the Antarctic ice sheet was much heavier, and its weight was pushed down into the Earth’s crust (which is above the molten interior). As the ice sheet melts and becomes lighter, the ground beneath will lift up – effectively transporting the ice out of the ocean.
Another possible explanation is climate change. On the shores of Antarctica, the oceans may have transitioned temporarily from warmer to cooler waters by the time the ice sheets began to advance again. At the same time, more snowfall occurs at the top of the ice sheet.
Our research supports the idea that the Antarctic ice sheet is poised to lose more ice and raise sea levels – especially if the oceans continue to warm.
It also suggests ground uplift and increased snowfall could potentially slow or offset ice loss. However, this effect is uncertain.
The past can never be a perfect test for the future. And given that the planet is warming faster now than it was then, we must be careful.
Read more: Scientists in Antarctica discover vast, salty groundwater systems beneath ice sheets – with implications for sea level rise
This article originally appeared on The Conversation.
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