Tag Archives: Sheet

New projections warn that Greenland’s ice sheet will see 60% more melt than we’ve estimated

New research warns that the Greenland ice sheet is likely to melt even more than previously estimated — a solid 60% more.

Bad news keeps piling up for the Greenland ice sheet. A study earlier this month reported that in around 600 years or so, it will melt enough that it won’t ever be able to recover (the ice sheet creates its own microclimate, meaning it is making itself possible right now). Despite this, new research suggests that we’ve underestimated how large the problem truly is.

Melt a-plenty

The team, headed by researchers from the Universities of Liège and Oslo, used multiple climate models with the latest observations, finding that we’re likely to see a 60% greater melting of the Greenland ice sheet by 2100 than previously predicted. That melt will, obviously, contribute to a rising sea level.

“The MAR model (one of the models used for the paper) was the first to demonstrate that the Greenland ice sheet would melt further with a warming of the Arctic in summer. While our MAR model suggested that in 2100 the surface melting of the Greenland ice sheet would contribute to a rise in the oceans of around ten centimeters in the worst-case scenario (i.e. if we do not change our habits),” explains Stefan Hofer, a post-doc researcher at the University of Oslo.

“Our new projections now suggest a rise of 18 cm.”

The results of this paper will be integrated into the next Intergovernmental Panel on Climate Change (IPCC) report, AR6, the team adds. As they will be based on our most up-to-date models, the findings outlined by the paper should be more reliable than anything we’ve had previously.

Greenland’s ice sheet is the second-largest in the world after the Antarctic one, covering some 1.7 million square kilometers. A complete melt of this sheet would cause a rise in ocean levels by up to 7 meters, which is immense. Although the estimations in this paper are nowhere near that figure, they’re still higher than previous estimates, which is cause for concern.

The current paper reports that we’re looking at an 18cm (~7 in) increase in sea levels by 2100, which is 8cm higher than the previous estimation used by the IPCC. The researchers also used their MAR model to ‘downscale’ on previous IPCC scenarios. Keeping the same emission estimates that these used, the current model shows 60% more surface melting of the Greenland ice cap until the end of the century. Downscaling basically means turning a model with coarse resolution (i.e. low detail) into one with a higher resolution (more, finer detail).

“It would now be interesting”, says Xavier Fettweis, researcher and director of the Laboratory,” to analyze how these future projections are sensitive to the MAR model that we are developing by downscaling these scenarios with other models than MAR as we have done on the present climate.”

This was the first attempt to downscale the future scenarios regarding Greenland that the IPCC uses, the team notes. Future efforts to refine our climate models will receive support from various international projects such as the EU’s Horizon 2020, which should help the team gain access to even more cutting-edge data. Since melting processes are influenced by a wide variety of factors, our ability to predict them hinges on having as much reliable data factored in as possible.

The paper “GrSMBMIP: intercomparison of the modelled 1980-2012 surface mass balance over the Greenland Ice Sheet” has been published in the journal The Cryosphere.

Greenland’s ice sheet is poised to melt forever — we have 600 years to stop it

New research suggests that the Greenland Ice Sheet is inching in towards a dangerous threshold: in around 600 years, it will melt enough that the sheet won’t ever recover, no matter what we do, and sea levels remain permanently higher. This scenario assumes that current rates of melt remain constant.

The glaciers and landscape in northeast Greenland, captured in 2014. Here you can see refrozen meltwater ponds from last year’s summer cover with snow that has fallen during the winter months. Image credits Credits: NASA /Michael Studinger.

The team from the National Centre for Atmospheric Science and the University of Reading show that climate change is leading to an irreversible rise in the sea level alongside a declining Greenland ice sheet. Worse yet, this sheet is closing in on a point of no return, past which it will never fully regrow — leaving a permanent mark on the global sea level.

Big Ice, Big Loss

The Greenland ice sheet is roughly three times the size of Texas and stores an important quantity of Earth’s frozen water. Under current melting rates, it contributes around 1mm of sea level rise per year (around one-quarter, 25%, of the total increase). It’s estimated that it lost a total of three-and-a-half trillion tonnes of ice since 2003, even with seasonal growth periods factored in.

Needless to say, that’s a lot of water. Rising seas threaten all coastal areas around the world, and can affect potentially millions of people who live in low-lying areas.

If the current target of the Paris Agreement (keeping global warming from going above 2°C compared to pre-industrial temperatures) is not met, we should expect the sea level to rise by several meters and significant ice loss, the authors note. Both would last for tens of thousands of years, and the worse global warming gets, the more dramatic these shifts would be.

The current paper shows that even if temperatures are brought back under control at a later time, the Greenland ice sheet will never fully regrow after it passes its critical threshold. If that point is passed, the sea level would permanently rise by at least 2 meters (with other sources adding to that figure).

Being so large, the sheet has a significant cooling effect on its local climate. In essence, there’s so much ice in Greenland that it’s making Greenland colder and more icy — not a bad trick. But if the sheet declines, local temperatures would increase, which increases melting rates, and snowfall levels would drop dramatically, which would slow down the formation of ice. The team estimates that if the Greenland ice sheet retreats from the northern part of Greenland, that area would remain permanently ice-free. All in all, we have around 600 years before that threshold is passed, the team estimates based on data from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

The team simulated the effects of the Greenland ice sheet melting under a range of scenarios, from minimal warming to worst-case conditions. All scenarios led to a decline in size of the sheet and contributed to rising sea levels to one extent or another.

So what’s to be done? Well we need to stop and then reverse climate warming before that threshold is reached.

“Our experiments underline the importance of mitigating global temperature rise. To avoid partially irreversible loss of the ice sheet, climate change must be reversed — not just stabilised — before we reach the critical point where the ice sheet has declined too far,” says Professor Jonathan Gregory, climate scientist from the National Centre for Atmospheric Science and University of Reading, a co-author of the paper.

There were some scenarios the team found where the ice sheet could be stabilized before reaching its point of no return. All of them, however, hinged on steps being taken ahead of time to reverse global warming.

The paper “Large and irreversible future decline of the Greenland ice sheet” has been published in the journal The Cryosphere.

Greenland is losing ice seven times faster than in the 1990s

Greenland’s rate of ice loss is increasing faster than expected, a new metastudy reports.

The increased influx of water from Greenland’s ice sheet puts us on track for sea-level rise consistent with the Intergovernmental Panel on Climate Change’s (IPCC) high-end climate warming scenario. Projections for this scenario estimate that coastal flooding will displace 400 million people by 2100.

Image credits Jean-Christophe Andre.

The study is a collaboration between 96 polar scientists from 50 international organizations — The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) team — and takes the most complete look at Greenland’s long-term ice loss to date. It combined 26 separate surveys to track changes in the ice mass of Greenland between 1992 and 2018. Data from 11 different satellite missions was used to measure the ice sheet’s changing volume, flow, and mass.

Melting quick

“On current trends, Greenland ice melting will cause 100 million people to be flooded each year [by 2100], so 400 million in total due to all sea level rise,” says Professor Andrew Shepherd at the University of Leeds, one of the study’s co-lead authors.

Melt rate in Greenland has risen from 33 billion tons, on average, per year in the 1990s to 254 billion tons per year over the last decade. In total, the island lost roughly 3.8 trillion tons of ice since 1992.

The IPCC mid-warming scenario set out in 2013 estimated 60 centimeters of sea-level rise by 2100, with associated coastal flooding displacing an estimated 360 million people. The rates of melt reported on in this study push those estimates by an additional 5 to 12 cm — consistent with the projection for the high-warming climate scenario.

“As a rule of thumb, for every centimeter rise in global sea level another six million people are exposed to coastal flooding around the planet,” Professor Shepherd explains.

The report shows that half of the ice losses recorded between 1992 and today have been caused by higher average temperatures, which promoted surface melting. The rest, around 48% of the total ice mass lost, was caused by increased glacier flow into the ocean due to warmer waters. Melting peaked 335 billion tonnes per year in 2011 but has since decreased to 238 billion tonnes per year “as atmospheric circulation favored cooler conditions”.

https://www.youtube.com/watch?v=HlApT0-2LT4

The team notes that this lower rate is still seven times higher than that in the 1990s, and that the dataset didn’t include all of 2019. Higher rates of melt expected in the summer could push Greenland to see record quantities of ice loss.

“Satellite observations of polar ice are essential for monitoring and predicting how climate change could affect ice losses and sea level rise” said Erik Ivins at NASA’s Jet Propulsion Laboratory in California, and co-lead author of the study.

Researchers from the European Space Agency (ESA) and the US National Aeronautics and Space Administration (NASA) also took part in the IMBIE report.

The paper “Mass balance of the Greenland Ice Sheet from 1992 to 2018” has been published in the journal Nature.

Greenland set to accelerate sea level change in the near future

Greenland’s contribution to sea-level rise is increasing, as climate change makes the region release meltwater into the ocean.

Image via Pixabay.

Greenland’s ice sheet is experiencing an increase in ice slab thickness at its interior regions. These ice sheets are normally porous, allowing meltwater to percolate (drain through) them, but the extra thickness makes them impermeable — so all the meltwater is draining into the ocean.

The process could see the country’s contribution to sea level rise increase by as much as 2.9 inches by 2100.

Thicc ice

“Even under moderate climate projections, ice slabs could double the size of the runoff zone by 2100,” said Mike MacFerrin, a CIRES (Cooperative Institute for Research In Environmental Sciences) and University of Colorado Boulder researcher who led the new study. “Under higher emissions scenarios, the runoff zone nearly triples in size.”

Runoff from ice slabs only amounts to a one-millimeter increase in global sea levels so far, the team explains, but that contribution will expand substantially under climate warming.

In the year 2000, Greenland’s runoff zone — the region of the ice sheet where runoff contributes to sea level rise — was roughly equivalent to the size of New Mexico. Between 2001 and 2013, it expanded by an average of two American football fields per minute, reaching roughly 65,000 sq km.

Even under a moderate emissions scenario, the team adds, it could reach the size of Colorado by 2100. That would raise sea levels by an extra 7-33 mm (one-quarter to one inch) by the same timeframe. Under a high emissions scenario, the situation looks even bleaker: the runoff zone could increase by the size of Texas, according to the new paper, contributing an extra 17-74 mm (half-inch to nearly three inches) of sea-level rise.

The runoff estimates from ice slabs are in addition to other sources of sea-level rise from Greenland, such as calving icebergs.

The team explains that Greenland’s ice sheets are made of layers with different textures. Fresh snow that falls each winter either melts into surface lakes or builds-up and helps compact older snow into glacial ice. Snow that partially melts over summer later re-freezes into thin ice “lenses” between 2 to 5 mm (one or two inches) thick within the compacted snow.

Normally, meltwater can percolate through and around ice lenses, refreezing in place without running off to sea. As mean temperatures over the Arctic increase and melting events become more frequent and extreme, however, these ice lenses solidify into slabs between 1 and 16-meter (3- to 50-foot) thick. These slabs block water from flowing through, which ends up flowing downhill into the ocean.

Climate warming is also increasing the quantity of meltwater in Greenland. In July of 2012, snow and ice melted from 97% of Greenland’s ice sheet surface, which the team says has never before been seen the 33-year-long satellite record. This spring, which was particularly warm and sunny in Greenland, resulted in a record-setting 80 billion tons of Greenland ice melted.

“As the climate continues to warm, these ice slabs will continue to grow and enhance other meltwater feedbacks,” said Mahsa Moussavi, a coauthor on the paper. “It’s a snowball effect: more melting creates more ice slabs, which create more melting, which creates again more ice slabs.”

All in all, this process will fundamentally alter the ice sheet’s equilibrium. The team warns that we need to understand Arctic feedbacks like this one because they show just how much, and how quickly, a warming climate can change Earth’s most vulnerable regions.

“Humans have a choice about which way this goes,” MacFerrin said.

The paper “Rapid expansion of Greenland’s low-permeability ice slabs” has been published in the journal Nature.

Iceland.

Our emissions could melt all the ice in Greenland by the year 3000 — and raise sea levels by 24 ft

Greenland may actually be green by the end of the millennium if greenhouse emissions continue unabated.

Iceland.

Image credits Marcel Prueske.

New research shows that, if greenhouse gas emissions continue on their current trajectory, Greenland could lose 4.5% of its ice by the end of the century, and all of it by the year 3000. That 4.5% loss of ice is equivalent to roughly 13 inches of sea level rise, the team explains.

Actually Green land

“How Greenland will look in the future — in a couple of hundred years or in 1,000 years — whether there will be Greenland, or at least a Greenland similar to today, it’s up to us,” said first author Andy Aschwanden, a research associate professor at the University of Alaska Fairbanks Geophysical Institute.

Greenland houses a lot of ice — around 660,000 square miles of solid ice sheet, which contains around 8% of all the planet’s fresh water. Between 1991 and 2015, melting here has added about 0.02 inches per year to the sea level. Needless to say, we need to know how all that ice is faring and whether there’s any cause for concern. Turns out that there is.

The team used recent topography (landscape) data of Greenland’s terrain today to model how its ice sheets will evolve in the future. This data was recorded by a NASA airborne science campaign (Operation IceBridge) during which aircraft fitted with a full suite of scientific instruments scanned Greenland’s ice sheets recording its surface, the individual layers within, and the shape of the bedrock. On average, Greenland’s ice sheet is 1.6 miles thick, but there was a lot of variation.

A wide range of scenarios concerning ice loss and changes in sea level are possible based on how greenhouse gas concentrations and atmospheric conditions evolve. The team ran 500 simulations for each emission scenario using the Parallel Ice Sheet Model, developed at the Geophysical Institute, to create a picture of how Greenland’s ice would respond to different climate conditions. The model included parameters on ocean and atmospheric conditions as well as ice geometry, flow, and thickness.

Under a business as usual scenario, we could see around 24 feet to global sea level rise by the year 3000 due to melting in Greenland alone — which would put much of San Francisco, Los Angeles, New Orleans and other cities under water. However, if we do manage to slash greenhouse gas emissions significantly, the prospects improve. Reduced emission scenarios showed between 8% to 25% melting of Greenland’s ice, which would lead to approximately 6.5 feet of sea level rise

Projections for both the end of the century and 2200 tell a similar story. A wide range of outcomes are possible, including saving the ice sheet, but it all depends on emission levels, the team explains.

The team explains that modeling ice sheet behavior is tricky because ice loss is primarily driven by the retreat of outlet glaciers. These are the glaciers at the margin of the ice sheets, and they ‘drain’ ice from deeper in the sheets through through-like structures in the bedrock. This study was the first to include these outlet glaciers in its modeling and found that their discharge could contribute as much as 45% of the total mass of ice loss in Greenland by 2200. Outlet glaciers come into contact with water, the team explains, which makes ice melt much faster than air. The more ice that comes into contact with water, the faster the rate of melting — which creates a feedback loop that dramatically affects the ice sheet’s stability.

Previous research lacked data as comprehensive as that recorded by IceBridge, so it couldn’t simulate the ice sheets’ evolution in such detail.

“Ice is in very remote locations,” says Mark Fahnestock, a researcher at the University of Alaska Fairbanks Geophysical Institute and paper co-author. “You can go there and make localized measurements. But the view from space and the view from airborne campaigns, like IceBridge, has just fundamentally transformed our ability to make a model to mimic those changes.”

“What we know from the last two decades of just watching Greenland is not because we were geniuses and figured it out, but because we just saw it happen,” he adds. As for what we will see in the future, “it depends on what we are going to do next.”

The paper “Contribution of the Greenland Ice Sheet to sea level over the next millennium” has been published in the journal Science Advances.

The Greenland ice sheet is losing some 270 billion tons of ice each year, a new study finds

A new study focusing on the Greenland Ice Sheet found that the rate of ice loss has accelerated over the past few years, confirming previous measurements. To put it into perspective, the sheet is now losing some 110 million Olympic-size swimming pools of water every year.

Image credits NASA Goddard Space Flight Center / Flickr.

One direct consequence of all the greenhouse gases we’re emitting into the atmosphere is melting ice. Doesn’t sound so dramatic — ice on my front lawn melts every spring, there’s ice-covered lakes and ice-bergs that sometimes melt and a little water never hurt anybody, right? For those things, yes. It’s a small quantity of ice, and it’s already floating on bodies of water so it won’t affect the volume of the world’s oceans if it melts.

But our planet has one huge deposit of water that doesn’t take part in the liquid’s natural cycle — ice sheets. When these melt, the water finds its way into the ocean and raises the sea level of the world’s oceans. So knowing how melting happens every year is important not only to help us quantify our activity’s effect on climate, but also because it helps us estimate how much sea levels rise.

However, you can’t simply hammer a tap into the ice and measure how much water flows out. What we can do is measure the volume of ice. This requires high-precision measurements of the ice sheets’ sizes over a long period of time to yield reliable results. In a new study, an international team reports the findings of one such high-precision measurement of the Greenland Ice Sheet, and their results confirm previous estimates of its rate of melting.

Malcolm McMillan from the Centre for Polar Observation and Modeling and his colleagues mapped the ice-sheet with incredibly high resolution (5 km distances,) by using data from the CryoSat 2 satellite. It relies on a technique called radar altimetry to measure terrain height, and with it the team was able to track the behavior of Greenland’s ice sheets with more precision than ever before.

In theory, if an ice sheet gains in altitude, it means that it’s also gaining in volume, so there’s more ice. A drop in altitude would correspond to a thinning of the ice caused by melting. But the processes that create the sheets are a little more complex — the Greenland sheets are thousands of meters thick, but the top layers are made up of snow and firn which gradually compress into solid ice. Accounting for the constitution of the sheet thus becomes very important in determining how much water gets trapped or released into the ocean.

After accounting for changes in density, surface roughness, and water content the authors found how much ice Greenland is losing, and how this melt varies by location and time. For example, 2012 saw a huge amount of ice loss compared to other years. The western side of the ice sheet is also melting much faster than the eastern side. The team found that a small part of the ice sheet (less than 1% of the sheet) is responsible for more than 10% of the mass loss.

Rate of mass change between January 2011 and December 2014 from CryoSat-2 radar altimetry. The color wheel indicates ice mass lost each year, with the radius scaled according to the magnitude of the total losses. The boundaries between the four sectors are shown in gray. Image provided by authors.

Rate of mass change between January 2011 and December 2014 from CryoSat-2 radar altimetry. The color wheel indicates ice mass lost each year, with the radius scaled according to the magnitude of the total losses. The boundaries between the four sectors are shown in gray.
Image credits Malcolm MacMillan et. al, 2016.

They estimate that between 2011 and 2014, some 270 gigatons of ice have melted away from Greenland — that’s enough water to fill 110 million Olympic swimming pools each year. This matches other independent measurements almost perfectly, helping to confirm the numbers.

“Using high resolution satellite data from ESA’s CryoSat-2 mission, we have produced a detailed and comprehensive picture of how Greenland has changed in recent years. In particular, we have been able to map the changing ice sheet in fine detail, and pinpoint where, and when, the greatest ice losses have occurred,” McMillan said in an interview for The Guardian.

The measurements allow scientists to calculate how much ice has been lost every year and determine the relationship between mean temperatures and melt — by looking at melt during the record summertime temperatures of 2012, for example. The variations in ice quantity show to what extent Greenland contributes to the sea level rise we’ve seen in recent years. And, thanks to their high resolution, researchers can also highlight which glaciers are experiencing the most melt.

The duration of this study was a relatively short 4 years. Hopefully, the team will continue their measurements in the following years, so we can get a better understanding of how sea levels will evolve in the future.

The full paper, titled “A high-resolution record of Greenland mass balance” has been published online in the journal Geophysical Research Letters.