What’s going on with the Greenland Ice Sheet? | Kiowa County Press

A turbulent meltwater river dumps a million tons of water a day into a mill, where it cuts through the subglacial environment and eventually reaches the ocean. Ted Gifford

Alun Hubbard, University of Tromsø

I stand at the edge of the Greenland ice cap, mesmerized by a breathtaking scene of natural destruction. A mile-long section of glacier front has fractured and is collapsing into the ocean, calving a huge iceberg.

Seracs, giant columns of ice the height of three-storey houses, are thrown like dice. And the previously submerged part of this huge block of glacial ice has just broken through the ocean – a foaming maelstrom hurling ice cubes several tons high into the air. The resulting tsunami inundates everything in its path as it radiates from the calving front of the glacier.

Luckily, I’m watching from a cliff a few miles away. But even here I can feel the earthquake shaking through the ground.

A large iceberg breaks off from a glacier.
A fast-flowing outlet glacier creates a ‘megaberg’ in Uummannaq Fjord in Greenland. Alun Hubbard

Despite the spectacle, I am fully aware that this means even more bad news for the world’s low coasts.

As a field glaciologist, I have worked on the ice caps for more than 30 years. During this time, I have witnessed impressive changes. The last few years in particular have been troubling because of the speed and magnitude of the changes taking place. My revered textbooks taught me that ice sheets react on millennial timescales, but that’s not what we see today.

A published study August 29, 2022 demonstrates – for the first time – that the Greenland Ice Sheet is now so out of balance with the prevailing Arctic climate that it can no longer maintain its current size. It is irreversibly committed to retreating at least 59,000 square kilometers (22,780 square miles), an area considerably larger than Denmark, the protectorate state of Greenland.

Even if all greenhouse gas emissions that cause global warming cease today, we see that Greenland’s loss of ice at current temperatures raise global sea level at least 10.8 inches (27.4 centimeters). This is more than predicted by current models, and it is a very conservative estimate. If every year was like 2012, when Greenland experienced a heat wave, this irreversible commitment to sea level rise would triple. This is an ominous omen given that these are climatic conditions we have seen before, not a hypothetical future scenario.

Our study takes a completely new approach – it is based on observations and glaciological theory rather than sophisticated numerical models. The current generation of coupled climate and ice sheet models used to predict future sea level rise fail to capture the emergent processes we see amplifying Greenland’s ice loss.

How Greenland got here

The Greenland ice sheet is a huge frozen tank that looks like an inverted bowl of pudding. The ice is in constant flowflowing from the interior – where it is more than 1.9 miles (3 kilometers) thick, cold and snowy – to its edges, where ice melts or bergs calves.

In total, the ice sheet contains enough fresh water to raise global sea level by 24 feet (7.4 meters).

David Attenborough takes us on a virtuoso tour of the Greenland Ice Cap.

from Greenland land ice has been around for about 2.6 million years and has expanded and contracted with about two dozen “ice age” cycles with a duration of 70,000 or 100,000 years, punctuated by warm interglacials of about 10,000 years. Each glacier is driven by changes in earth’s orbit which modulate how much solar radiation reaches the Earth’s surface. These variations are then reinforced by the reflectivity of the snow, or albedo; atmospheric greenhouse gases; and the ocean circulation which redistributes this heat around the planet.

We are currently living in an interglacial period – the Holocene. For 6,000 years, Greenland, like the rest of the planet, has enjoyed a mild, stable climate with a balanced ice cap – until recently. Since 1990, as the atmosphere and ocean have warmed due to rapidly increasing greenhouse gas emissions, Greenland’s mass balance has turned red. Ice losses from increased melting, rain, ice flow and calving now far exceed the net gain from snow accumulation.

Greenland’s ice mass loss measured by NASA’s Grace satellites.

What does the future hold?

The key questions are: how fast is Greenland losing its ice and what does this mean for future sea level rise?

Greenland’s ice loss was contributing about 0.04 inch (1 millimeter) per year for global sea level rise during the last decade.

This net loss is split between surface melting and dynamic processes which accelerate outflow from the outlet glacier and are greatly exacerbated by atmospheric and oceanic warming, respectively. Although complex in its manifestation, the concept is simple: ice caps don’t like hot weather or baths, and the heat is on.

A large area of ​​meltwater pools on the snow-covered surface of Greenland forms a river and streams.
Meltwater lakes feed the rivers that meander through the ice cap – until they meet a mill. Alun Hubbard

What the future will bring is harder to answer.

The models used by the Intergovernmental Panel on Climate Change predict a contribution to sea level rise from Greenland of about 4 inches (10 centimeters) by 2100with a worst-case scenario of 6 inches (15 centimeters).

But this prediction is at odds with which area scientists witness the ice sheet itself.

According to our conclusions, Greenland will lose at least 3.3% of its ice, more than 100 trillion metric tons. This loss is already incurred – ice that must melt and calve the icebergs restore Greenland’s balance with the prevailing climate.

We observe many emerging processes that are not captured by models and that increase the vulnerability of the ice sheet. For instance:

Weather stations sit on wet snow in Greenland
In August 2021, rain fell atop the Greenland Ice Sheet for the first time on record. Meteorological stations in Greenland have recorded a rapid melting of the ice. European Space Agency

The model problem

Part of the problem is that the models used for predictions are mathematical abstractions that only include processes that are fully understood, quantifiable and deemed important.

Models reduce reality to a set of equations that are solved over and over on very fast computer benches. Anyone interested in cutting-edge engineering—including me—knows the intrinsic value of models for experimenting and testing ideas. But they do not replace reality and observation. It is evident that current global sea level rise model predictions underestimate its real threat in the 21st century. Developers are making constant improvements, but it’s tricky, and you realize that the complex models used for long-term sea level forecasting are not suitable for use.

Several brightly colored research tents dot a landscape with streams and snow on the ice cap.
Author Alun Hubbard’s science camp in the melting area of ​​the Greenland Ice Sheet. Alun Hubbard

There are also “unknown unknowns” – those processes and feedbacks that we don’t yet realize and that models can never anticipate. They can only be understood by direct observation and literally by drilling into the ice.

This is why, rather than using models, we base our study on proven glaciological theory limited by two decades of actual measurements from weather stations, satellites and ice geophysics.

It is not too late

It is an understatement that the societal stakes are high and the risk is tragically real in the future. The consequences of catastrophic coastal flooding with sea level rise are still unimaginable for the majority of the one billion people who live in the low-lying coastal areas of the planet.

A tall ship with an even bigger iceberg behind it and a glacier in the distance.
A large tabular iceberg that calved from Store Glacier in Uummannaq Fjord. Alun Hubbard

Personally, I remain hopeful that we can get on the right track. I do not believe we have passed a catastrophic tipping point that is irreversibly flooding the shores of the planet. From what I understand of ice cap and insight our new study bring, it is not too late to act.

But fossil fuels and emissions need to be cut now, because time is running out and the water is rising – faster than expected.

The conversation

Alun HubbardProfessor of Glaciology, Arctic Five Chair, University of Tromso

This article is republished from The conversation under Creative Commons license. Read it original article.

About Florence M. Sorensen

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