I stand at the edge of the Greenland ice cap, mesmerized by a breathtaking scene of natural destruction. A mile-wide section of the ice 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 tremors through the ground.
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 ice sheets for over 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 study published on 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 find that loss of ice from Greenland at current temperatures will raise global sea levels by 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 were 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 emerging processes that we believe are amplifying Greenland’s ice loss.
The Greenland Ice Sheet is a massive, frozen reservoir that looks like an inverted bowl of pudding. The ice is in constant flux, flowing from the interior – where it is more than 3 kilometers thick, cold and snowy – to its edges, where the ice melts or forms banks.
In total, the ice sheet locks in enough fresh water to raise global sea level by 24 feet (7.4 meters).
Greenland’s land ice has been around for about 2.6 million years and has expanded and contracted with about 20 “ice age” cycles lasting 70,000 or 100,000 years, punctuated by warm interglacials about 10,000 years old. Each glacier is driven by changes in the Earth’s orbit that modulate the amount of solar radiation reaching 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 and stable climate with an ice cap in balance, 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.
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 has contributed about 0.04 inches (1 millimeter) per year to global sea level rise over the past decade.
This net loss is split between surface melting and dynamical processes that accelerate outlet glacier flow 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.
What the future will bring is harder to answer.
Models used by the Intergovernmental Panel on Climate Change predict a contribution to Greenland’s sea level rise of about 4 inches (10 centimeters) by 2100, with a worst-case scenario of 6 inches (15 centimeters).
But this prediction is at odds with what field scientists observe from the ice sheet itself.
According to our findings, Greenland will lose at least 3.3% of its ice, or more than 100 trillion metric tons. This loss is already underway – the ice that must melt and calve icebergs to 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:
- The increase in rain accelerates the melting of the surface and the flow of the ice.
- Large areas of the ice surface undergo bio-albedo darkening, which accelerates surface melting, as well as the impact of melting and refreezing snow on the surface. These darker surfaces absorb more solar radiation, resulting in even more melting.
- Warm ocean currents of subtropical origin enter Greenland fjords and rapidly erode outlet glaciers, undermining and destabilizing their calving fronts.
- Supraglacial lakes and river systems drain into fractures and mills, bringing with them large amounts of latent heat. This “cryo-hydraulic heating” within and at the base of the ice sheet softens and thaws the bed, thereby accelerating the interior ice flow to the margins.
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 advanced 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 aren’t fit for purpose.
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.
Therefore, rather than using models, we base our study on proven glaciological theory constrained by two decades of actual measurements from weather stations, satellites, and ice geophysics.
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.
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 the ice sheet and the information our new study provides, 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.
Alun Hubbard is Professor of Glaciology and Arctic Five Chair at the University of Tromsø