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Home POLITICS Greenland ice sheet shrinking faster than predicted, blocking sea level rise: study

Greenland ice sheet shrinking faster than predicted, blocking sea level rise: study

This article is part of the TPM Cafe, TPM’s home for sentiment analysis and news. It was first published in The conversation.

I am standing on the edge of the Greenland ice sheet, mesmerized by a mind-boggling scene of natural destruction. A mile-wide section of the glacier front has fractured and is collapsing into the ocean, calving a massive iceberg.

Seracs, gigantic columns of ice the height of three-story houses, are being thrown like dice. And the previously submerged portion of this immense block of glacial ice has just broken out of the ocean: a foamy whirlwind that launches multi-ton ice cubes into the air. The resulting tsunami inundates everything in its path as it radiates from the torn front of the glacier.

Happily, I’m looking down from a clifftop a couple of miles away. But even here, I can feel the seismic shocks through the ground.

A fast-flowing outlet glacier forms a ‘megaberg’ in Greenland’s Uummannaq Fjord. (Alun Hubbard)

Despite the spectacle, I am well aware that this means even more unpleasant news for the low-lying shores of the world.

ace a field glaciologist, I have worked on ice sheets for over 30 years. In that time, I have witnessed some amazing changes. The last few years in particular have been bewildering in the speed and magnitude of change underway. My revered textbooks taught me that ice sheets respond on millennial timescales, but that’s not what we’re seeing 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 a withdrawal of at least 59,000 square kilometers (22,780 square miles), in an area considerably larger than Denmark, Greenland’s protectorate state.

Even if all greenhouse gas emissions that cause global warming were to cease today, we will find that Greenland’s ice loss under current temperatures raise global sea level at least 10.8 inches (27.4 centimeters). That’s more than current models predict, and it’s a very conservative estimate. If every year was like 2012, when Greenland experienced a heat wave, that irreversible commitment to sea level rise would triple. That’s an ominous omen given that these are weather conditions we’ve already seen, not a hypothetical future scenario.

Our study takes a completely new approach: it is based on observations and glaciological theory instead of sophisticated numerical models. The current generation of Combined climate and ice sheet models used to forecast future sea level rise fail to capture the emergent processes we see amplifying Greenland ice loss.

How did Greenland get to this point?

the Greenland ice sheet it is a huge frozen deposit that resembles an inverted pudding bowl. 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 the ice melts or crumbles.

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

David Attenborough takes us on a virtuous tour of the Greenland ice sheet.

Greenland Land’s ice has been around for about 2.6 million years and has expanded and contracted with about two dozen “ice age” cycles. lasting 70,000 or 100,000 years, punctuated by about 10,000 warm interglacial years. Each glacier is powered by changes to Earth’s orbit that modulate the amount of solar radiation that reaches the earth’s surface. These variations are enhanced by the reflectivity of the snow, or albedo; atmospheric greenhouse gases; and the ocean circulation that redistributes that heat around the planet.

We are currently enjoying an interglacial period: the Holocene. For the past 6,000 years, Greenland, like the rest of the planet, has benefited from a stable, temperate climate with a balanced ice sheet, 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 due to increased melting, rainfall, ice flow, and shedding now far outweigh the net gain from snow accumulation.

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

What does the future hold?

The critical questions are, how fast is Greenland losing its ice and what does it mean for future sea level rise?

Greenland ice loss has been contributing about 0.04 inches (1 millimeter) per year at global sea level rise in the last decade.

This net loss is divided between surface melting and dynamic processes. that accelerate outflow from glacial outflows and are greatly exacerbated by atmospheric and ocean warming, respectively. Though complex in its manifestation, the concept is simple: Ice sheets don’t like hot weather or baths, and the heat is on.

A large area of ​​meltwater pools on the snowy surface of Greenland and forms a river and streams.
Meltwater lakes feed rivers that wind through the ice cap, until they meet a moulin. (Alun Hubbard)

What the future will bring is more difficult to answer.

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

But that prediction is at odds with which field scientists are witnessing from the ice sheet itself.

Based on our findings, Greenland wants to lose at least 3.3% of its ice, more than 100 billion metric tons. This loss is already compromised – ice that must melt and calve icebergs to bring Greenland back into balance with the prevailing climate.

We are seeing many emerging processes that are not taken into account by the models and that increase the vulnerability of the ice sheet. For example:

Weather stations sit on top of wet snow in Greenland
In August 2021, rain fell on the summit of the Greenland Ice Sheet for the first time on record. Greenland weather stations captured the rapid melting of the ice. European Space Agency

The problem with models

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

Models reduce reality to a set of equations that are repeatedly solved on banks of very fast computers. Anyone interested in cutting-edge engineering, myself included, knows the intrinsic value of models for experimentation and testing of ideas. But they do not replace reality and observation. It is clear that current model forecasts of global sea level rise underestimate its actual threat during the 21st century. Developers are making constant improvements, but it’s complicated, and it’s increasingly realized that the complex models used for long-term sea level prediction are not fit for purpose.

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 zone of the Greenland ice sheet. (Alun Hubbard)

There are also “unknown unknowns”: those processes and feedbacks that we are not yet aware of and that models can never anticipate. They can only be understood through direct observations and literally drilling through the ice.

Therefore, instead of 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’s not too late

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

A tall ship with an even larger iceberg behind it and a glacier in the distance.
A large tabular iceberg that calved off Store Glacier within Uummannaq Fjord. (Alun Hubbard)

Personally, I remain hopeful that we can get back on track. I don’t think we’ve passed any doom-laden tipping point that irreversibly floods the planet’s shores. From what I understand of the ice cap and intuition our new studio bring, it’s not too late to act.

But fossil fuels and emissions must be reduced now, because time is short and the water level is rising, faster than anticipated.

Alun Hubbard is a professor of glaciology and holder of the Arctic Five Chair at the University of Tromso in Norway.

This article is republished from The conversation under a Creative Commons license. Read the Original article.

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