A heat wave in Greenland and a storm in Antarctica. These kinds of individual weather “events” are increasingly being supercharged by a warming climate. But despite being short-term events they can also have a much longer-term effect on the world’s largest ice sheets, and may even lead to tipping points being crossed in the polar regions.

We have just published research looking at these sudden changes in the ice sheets and how they may impact what we know about sea level rise. One reason this is so important is that the global sea level is predicted to rise by anywhere between 28 cm and 100cm by the year 2100, according to the IPCC. This is a huge range – 70 cm extra sea-level rise would affect many millions more people.

Partly this uncertainty is because we simply don’t know whether we’ll curb our emissions or continue with business as usual. But while possible social and economic changes are at least factored in to the above numbers, the IPCC acknowledges its estimate does not take into account deeply uncertain ice-sheet processes.

Sudden accelerations

The sea is rising for two main reasons. First, the water itself is very slightly expanding as it warms, with this process responsible for about a third of the total expected sea-level rise.

Second, the world’s largest ice sheets in Antarctica and Greenland are melting or sliding into the sea. As the ice sheets and glaciers respond relatively slowly, the sea will also continue to rise for centuries.

Photo by Cassie Matias on Unsplash

Scientists have long known that there is a potential for sudden accelerations in the rate at which ice is lost from Greenland and Antarctica which could cause considerably more sea-level rise: perhaps a metre or more in a century. Once started, this would be impossible to stop.

Although there is a lot of uncertainty over how likely this is, there is some evidence that it happened about 130,000 years ago, the last time global temperatures were anything close to the present day. We cannot discount the risk.

To improve predictions of rises in sea level we therefore need a clearer understanding of the Antarctic and Greenland ice sheets. In particular, we need to review if there are weather or climate changes that we can already identify that might lead to abrupt increases in the speed of mass loss.

Weather can have long-term effects

Our new study, involving an international team of 29 ice-sheet experts and published in the journal Nature Reviews Earth & Environment, reviews evidence gained from observational data, geological records, and computer model simulations.

We found several examples from the past few decades where weather “events” – a single storm, a heatwave – have led to important long-term changes.

The ice sheets are built from millennia of snowfall that gradually compresses and starts to flow towards the ocean. The ice sheets, like any glacier, respond to changes in the atmosphere and the ocean when the ice is in contact with sea water.

These changes could take place over a matter of hours or days or they may be long-term changes from months to years or thousands of years. And processes may interact with each other on different timescales, so that a glacier may gradually thin and weaken but remain stable until an abrupt short-term event pushes it over the edge and it rapidly collapses.

Because of these different timescales, we need to coordinate collecting and using more diverse types of data and knowledge.

Historically, we thought of ice sheets as slow-moving and delayed in their response to climate change. In contrast, our research found that these huge glacial ice masses respond in far quicker and more unexpected ways as the climate warms, similarly to the frequency and intensity of hurricanes and heatwaves responding to changes with the climate.

Ground and satellite observations show that sudden heatwaves and large storms can have long-lasting effects on ice sheets. For example a heatwave in July 2023 meant at one point 67% of the Greenland ice sheet surface was melting, compared with around 20% for average July conditions. In 2022 unusually warm rain fell on the Conger ice shelf in Antarctica, causing it to disappear almost overnight.

These weather-driven events have long “tails”. Ice sheets don’t follow a simple uniform response to climate warming when they melt or slide into the sea. Instead their changes are punctuated by short-term extremes.

For example, brief periods of melting in Greenland can melt far more ice and snow than is replaced the following winter. Or the catastrophic break-up of ice shelves along the Antarctic coast can rapidly unplug much larger amounts of ice from further inland.

Failing to adequately account for this short-term variability might mean we underestimate how much ice will be lost in future.

What happens next

Scientists must prioritise research on ice-sheet variability. This means better ice-sheet and ocean monitoring systems that can capture the effects of short but extreme weather events.

This will come from new satellites as well as field data. We’ll also need better computer models of how ice sheets will respond to climate change. Fortunately there are already some promising global collaborative initiatives.

We don’t know exactly how much the global sea level is going to rise some decades in advance, but understanding more about the ice sheets will help to refine our predictions.

Edward Hanna, Professor of Climate Science and Meteorology, University of Lincoln and Ruth Mottram, Climate Scientist, National Centre for Climate Research, Danish Meteorological Institute

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Superstorms, abrupt climate shifts and New York City frozen in ice. That’s how the blockbuster Hollywood movie “The Day After Tomorrow” depicted an abrupt shutdown of the Atlantic Ocean’s circulation and the catastrophic consequences.

While Hollywood’s vision was over the top, the 2004 movie raised a serious question: If global warming shuts down the Atlantic Meridional Overturning Circulation, which is crucial for carrying heat from the tropics to the northern latitudes, how abrupt and severe would the climate changes be?

Twenty years after the movie’s release, we know a lot more about the Atlantic Ocean’s circulation. Instruments deployed in the ocean starting in 2004 show that the Atlantic Ocean circulation has observably slowed over the past two decades, possibly to its weakest state in almost a millennium. Studies also suggest that the circulation has reached a dangerous tipping point in the past that sent it into a precipitous, unstoppable decline, and that it could hit that tipping point again as the planet warms and glaciers and ice sheets melt.

In a new study using the latest generation of Earth’s climate models, we simulated the flow of fresh water until the ocean circulation reached that tipping point.

The results showed that the circulation could fully shut down within a century of hitting the tipping point, and that it’s headed in that direction. If that happened, average temperatures would drop by several degrees in North America, parts of Asia and Europe, and people would see severe and cascading consequences around the world.

We also discovered a physics-based early warning signal that can alert the world when the Atlantic Ocean circulation is nearing its tipping point.

The ocean’s conveyor belt

Ocean currents are driven by winds, tides and water density differences.

In the Atlantic Ocean circulation, the relatively warm and salty surface water near the equator flows toward Greenland. During its journey it crosses the Caribbean Sea, loops up into the Gulf of Mexico, and then flows along the U.S. East Coast before crossing the Atlantic.

This current, also known as the Gulf Stream, brings heat to Europe. As it flows northward and cools, the water mass becomes heavier. By the time it reaches Greenland, it starts to sink and flow southward. The sinking of water near Greenland pulls water from elsewhere in the Atlantic Ocean and the cycle repeats, like a conveyor belt.

Too much fresh water from melting glaciers and the Greenland ice sheet can dilute the saltiness of the water, preventing it from sinking, and weaken this ocean conveyor belt. A weaker conveyor belt transports less heat northward and also enables less heavy water to reach Greenland, which further weakens the conveyor belt’s strength. Once it reaches the tipping point, it shuts down quickly.

What happens to the climate at the tipping point?

The existence of a tipping point was first noticed in an overly simplified model of the Atlantic Ocean circulation in the early 1960s. Today’s more detailed climate models indicate a continued slowing of the conveyor belt’s strength under climate change. However, an abrupt shutdown of the Atlantic Ocean circulation appeared to be absent in these climate models.

Ted-Ed Video: “How do ocean currents work? – Jennifer Verduin”

This is where our study comes in. We performed an experiment with a detailed climate model to find the tipping point for an abrupt shutdown by slowly increasing the input of fresh water.

We found that once it reaches the tipping point, the conveyor belt shuts down within 100 years. The heat transport toward the north is strongly reduced, leading to abrupt climate shifts.

The result: Dangerous cold in the North

Regions that are influenced by the Gulf Stream receive substantially less heat when the circulation stops. This cools the North American and European continents by a few degrees.

The European climate is much more influenced by the Gulf Stream than other regions. In our experiment, that meant parts of the continent changed at more than 5 degrees Fahrenheit (3 degrees Celsius) per decade – far faster than today’s global warming of about 0.36 F (0.2 C) per decade. We found that parts of Norway would experience temperature drops of more than 36 F (20 C). On the other hand, regions in the Southern Hemisphere would warm by a few degrees.

These temperature changes develop over about 100 years. That might seem like a long time, but on typical climate time scales, it is abrupt.

The conveyor belt shutting down would also affect sea level and precipitation patterns, which can push other ecosystems closer to their tipping points. For example, the Amazon rainforest is vulnerable to declining precipitation. If its forest ecosystem turned to grassland, the transition would release carbon to the atmosphere and result in the loss of a valuable carbon sink, further accelerating climate change.

The Atlantic circulation has slowed significantly in the distant past. During glacial periods when ice sheets that covered large parts of the planet were melting, the influx of fresh water slowed the Atlantic circulation, triggering huge climate fluctuations.

So, when will we see this tipping point?

The big question – when will the Atlantic circulation reach a tipping point – remains unanswered. Observations don’t go back far enough to provide a clear result. While a recent study suggested that the conveyor belt is rapidly approaching its tipping point, possibly within a few years, these statistical analyses made several assumptions that give rise to uncertainty.

Instead, we were able to develop a physics-based and observable early warning signal involving the salinity transport at the southern boundary of the Atlantic Ocean. Once a threshold is reached, the tipping point is likely to follow in one to four decades.

The climate impacts from our study underline the severity of such an abrupt conveyor belt collapse. The temperature, sea level and precipitation changes will severely affect society, and the climate shifts are unstoppable on human time scales.

It might seem counterintuitive to worry about extreme cold as the planet warms, but if the main Atlantic Ocean circulation shuts down from too much meltwater pouring in, that’s the risk ahead.

This article was updated on Feb. 11, 2024, to fix a typo: The experiment found temperatures in parts of Europe changed by more than 5 F per decade.

René van Westen, Postdoctoral Researcher in Climate Physics, Utrecht University; Henk A. Dijkstra, Professor of Physics, Utrecht University, and Michael Kliphuis, Climate Model Specialist, Utrecht University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

(The Conversation) – While the Southern Ocean around Antarctica has been warming for decades, the annual extent of winter sea ice seemed relatively stable – compared to the Arctic. In some areas Antarctic sea ice was even increasing.

That was until 2016, when everything changed. The annual extent of winter sea ice stopped increasing. Now we have had two years of record lows.

In 2018 the international scientific community agreed to produce the first marine ecosystem assessment for the Southern Ocean. We modelled the assessment process on a working group of the Intergovernmental Panel on Climate Change (IPCC). So the resulting “summary for policymakers” being released today is like an IPCC report for the Southern Ocean.

This report can now be used to guide decision-making for the protection and conservation of this vital region and the diversity of life it contains.

Why should we care about sea ice?

Sea ice is to life in the Southern Ocean as soil is to a forest. It is the foundation for Antarctic marine ecosystems.

Less sea ice is a danger to all wildlife – from krill to emperor penguins and whales.

The sea ice zone provides essential food and safe-keeping to young Antarctic krill and small fish, and seeds the expansive growth of phytoplankton in spring, nourishing the entire food web. It is a platform upon which penguins breed, seals rest, and around which whales feed.

The international bodies that manage Antarctica and the Southern Ocean under the Antarctic Treaty System urgently need better information on marine ecosystems. Our report helps fill this gap by systematically identifying options for managers to maximise the resilience of Southern Ocean ecosystems in a changing world.

An open and collaborative process

We sought input from a wide range of people across the entire Southern Ocean science community.

We sought to answer questions about the state of the whole Southern Ocean system – with an eye on the past, present and future.

Our team comprised 205 authors from 19 countries. They authored 24 peer-reviewed papers. We then distilled the findings from these papers into our summmary for policymakers.

We deliberately modelled the multi-disciplinary assessment process on a working group of the IPCC to distill the science into an easy-to-read and concise narrative for politicians and the general public alike. It provides a community assessment of levels of certainty around what we know.

We hope this “sea change” summary sets a new benchmark for translating marine research into policy responses.

So what’s in the report?

Southern Ocean habitats, from the ice at the surface to the bottom of the deep sea, are changing. The warming of the ocean, decline in sea ice, melting of glaciers, collapse of ice shelves, changes in acidity, and direct human activities such as fishing, are all impacting different parts of the ocean and their inhabitants.

These organisms, from microscopic plants to whales, face a changing and challenging future. Important foundation species such as Antarctic krill are likely to decline with consequences for the whole ecosystem.

The assessment stresses climate change is the most significant driver of species and ecosystem change in the Southern Ocean and coastal Antarctica. It calls for urgent action to curb global heating and ocean acidification.

It reveals an urgent need for international investment in sustained, year-round and ocean-wide scientific assessment and observations of the health of the ocean.

We also need to develop better integrated models of how individual changes in species along with human impacts will translate to system-level change in the different food webs, communities and species.

What’s next?

Our report was tabled at an international meeting of the Commission for the Conservation of Antarctic Marine Living Resources in Hobart.

The commission is the international body responsible for the conservation of marine ecosystems in the Southern Ocean, with membership of 26 nations and the European Union.

It is but one of the bodies our new report can assist. Currently assessments of change in habitats, species and food webs in the Southern Ocean are compiled separately for at least ten different international organisations or processes.

The Southern Ocean is a crucial life-support system, not just for Antarctica but for the entire planet. So many other bodies will need the information we produced for decision-making in this critical decade for action on climate, including the IPCC itself.

Beyond the science, the assessment team has delivered important lessons about how coordinated, collaborative and consultative approaches can deliver ecosystem information into policymaking. Our first assessment has taken five years, but this is just the beginning. Now we’re up and running, we can continue to support evidence-based conservation of Southern Ocean ecosystems into the future.

Andrew J Constable, Adviser, Antarctica and Marine Systems, Science & Policy, University of Tasmania and Jess Melbourne-Thomas, Transdisciplinary Researcher & Knowledge Broker, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Featured Image: Courtesy Pat James, Australian Antarctic Division.

The global climate is changing and the Arctic is warming rapidly. These are objectively true statements that most people have come to accept.

But it is also true that Earth’s climate has never been stagnant and climate anomalies have been frequent throughout the past.

How then, do we understand our current situation relative to past climate shifts? Are the impacts of modern climate change comparable to those of the medieval warm period (MWP) or the little ice age (LIA)?

Our recently published study in Anthropocene demonstrates a much more substantial impact to polar bears resulting from recent climate change compared to observations over the last 4,000 years. This suggests that current climatic changes are, indeed, unprecedented in human history.

Ecosystem background

Predators at the top of the food chain, like polar bears, reflect changes across the entire ecosystem, all the way down to microscopic algae.

In the Arctic, the base of the food web is sourced from two categories: sea ice-associated algae and open-water phytoplankton, which are distinguishable through their carbon isotopes.

In our study area — centred on Lancaster Sound in the Canadian Arctic Archipelago — the food web is fed by a combination of both sea ice algae and phytoplankton. We can assess the relative importance of these two sources through the stable isotopes incorporated into the tissues of animals.

The relative abundance of carbon isotopes does not change as they are transferred through the food web, so these isotopes tell us about the carbon sources at the base of the food web. Nitrogen isotopes do change as they are passed up the food chain, which tells us who is eating whom.

Results from our study

In our study we examined stable carbon and nitrogen isotopes in polar bear bone collagen.

The polar bears were all from the Lancaster Sound sub-population and spanned the last 4,000 years. We acquired samples of modern polar bear (1998-2007) obtained through hunting and we were able to compare them to samples from archaeological excavations conducted in the region.

The span of time captured by the archaeological samples was vast, but by dividing them into time bins associated with the cultural traditions in the region we were able to compare the samples across time before present (BP): pre-Dorset (4000-2800 years BP), Dorset (1500-700 BP) and Thule (700-500 BP).

The Dorset/Thule cultural transition occurred at the onset of the medieval warm period, so a comparison of these time bins allows us to look at the state of the food web before and during a known climate shift. The Thule time bin also extends into the beginning of the little ice age giving us a glimpse into that period as well.

What it all means

First, the good news. The results of the nitrogen isotopes showed that throughout time, 4,000 years BP to the present, the structure of the Lancaster Sound food web was relatively unchanged. Polar bears eat seals, seals eat cod, cod eat zooplankton, et cetera. There were no surprising shifts in the diets of polar bears despite past and present climate change. This is comforting.

The results of the carbon isotopes tell a less encouraging story, however. Throughout the four millennia encapsulated by the ancient time bins, we saw stability in the mixture of sea ice algae and open water phytoplankton. We did not detect a difference in the origin of carbon at the base of the food web resulting from the medieval warm period or the little ice age.

The modern samples, however, showed a significant difference in the source of carbon, resulting from a greater proportion of open water phytoplankton and less reliance on sea ice algae.

Evidence of a warming climate

Sea ice is an important habitat in the high Arctic. For polar bears it is a platform for hunting. For ringed seals, the primary prey of polar bears, it is a platform for denning and raising young.

The algae that grows in association with sea ice is also very important for jumpstarting biological productivity before the open water season. Our study shows that the loss of biological productivity associated with sea ice is unprecedented on a very long timescale.

Archaeological materials can provide valuable context to the ongoing climate discussion. Much of the valuable work being undertaken is tracking ecosystem changes on a short timescale, seasons to decades. But as we have demonstrated, the Arctic has already changed, so we should not always assume that we are looking at a pristine or undisturbed state.

Image by Peter Fischer from Pixabay

Adding a lens that looks back into the distant past gives resolution and context to our collective understanding of our situation.

In this case, we have illustrated the magnitude of difference occurring in the modern Arctic, relative to past climate anomalies. The medieval warm period and onset of the little ice age were not visible in the isotopes of the Lancaster Sound food web but modern warming is very apparent. We can, therefore, not dismiss calls to action on climate change on the basis that the climate has always fluctuated.

Jennifer Routledge, PhD Candidate, Environmental and Life Sciences, Trent University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Climate change will wreak havoc on small island developing states in the Pacific and elsewhere. Some will be swamped by rising seas. These communities also face more extreme weather, increasingly acidic oceans, coral bleaching and harm to fisheries. Food supplies, human health and livelihoods are at risk. And it’s clear other countries burning fossil fuels are largely to blame.

Yet island states are resourceful. They are not only adapting to change but also seeking legal advice. The international community has certain legal obligations under the law of the sea. These are rules and customs that divvy up the oceans into maritime zones, while recognising certain freedoms and duties.

So island states are asking whether obligations to address climate change might be contained in the United Nations Convention on the Law of the Sea. This is particularly important as marine issues have not received the attention they deserve within international climate negotiations.

If states do have specific obligations to stop greenhouse gas pollution damaging the marine environment, then legal consequences for breaching these obligations could follow. It is possible small island states could one day be compensated for the damage done.

Why seek an advisory opinion?

The International Tribunal for the Law of the Sea is an independent judicial body established by the UN Convention on the Law of the Sea. The tribunal has jurisdiction over any dispute concerning the interpretation or application of the convention and certain legal questions requested of it. The answers to these questions are known as advisory opinions.

Advisory opinions are not legally binding, they are authoritative statements on legal matters. They provide guidance to states and international organisations about the implementation of international law.

The tribunal has delivered two advisory opinions in the past: on deep seabed mining and illegal, unreported and unregulated fishing activities. These proceedings attracted submissions from states, international organisations and non-governmental organisations such as the World Wide Fund for Nature (WWF).

Late last year, the newly established Commission of Small Island States on Climate Change and International Law submitted a request for advice to the tribunal. It concerns the obligations of states to address climate change, including impacts on the marine environment.

Image by David Mark from Pixabay

The tribunal received more than 50 written submissions from states and organisations offering opinions on how it should respond. These submissions, from Australia and New Zealand among others, were recently made public.

While the convention was not designed as a mechanism for regulating climate change, its mandate is broad enough to consider the connection between climate and the oceans. To establish this, the 40-year-old framework agreement must be interpreted in light of changing global circumstances and changing laws, including obligations to strengthen resilience in the high seas. One avenue to achieve this is through an advisory opinion from the tribunal.

The question before the tribunal

The question to the tribunal asks, what are the specific obligations of states:

(a) to prevent, reduce and control pollution of the marine environment in relation to the deleterious effects that result or are likely to result from climate change, including through ocean warming and sea level rise, and ocean acidification, which are caused by anthropogenic greenhouse gas emissions into the atmosphere?

(b) to protect and preserve the marine environment in relation to climate change impacts, including ocean warming and sea level rise, and ocean acidification?

This question invokes specific language from the convention. That provides clues as to which sections of the treaty the tribunal will refer to in its opinion.

The question refers explicitly to the part of the convention entitled “Protection and Preservation of the Marine Environment”. This part sets out the general obligation of states to protect and preserve the marine environment, as well as measures to “prevent, reduce and control pollution”. It also tells states they must not transfer damage or hazards, or transform one type of pollution into another.

Pollution of the marine environment is defined in the convention as:

the introduction by man, directly or indirectly, of substances or energy into the marine environment, including estuaries, which results or is likely to result in such deleterious effects as harm to living resources and marine life, hazards to human health, hindrance to marine activities, including fishing and other legitimate uses of the sea, impairment of quality for use of sea water and reduction of amenities.

What if states do not meet their obligations?

The tribunal will need to answer a key question for the law of the sea: can the convention be understood as referring to the drivers and effects of climate change? And if so, in what ways does the convention require that they be addressed by states?

What the commission’s question does not ask is, what happens when states do not meet their obligations? The answer is particularly important to small island states, who are dissatisfied with ongoing negotiations on addressing loss and damage associated with climate change impacts.

Obligations relating to climate change are contained within other treaties and rules, including the UN Framework Convention on Climate Change and the Paris Agreement. Small island states have sought advice from different courts to clarify these obligations.

The International Court of Justice will consider a wider set of legal issues on climate obligations next year.

The fact that the court has authorised the commission to participate in this separate advisory opinion request signals the UN’s main judicial body will take account of the tribunal’s opinion. It’s also worth noting the tribunal is likely to deliver its views on the law of the sea first, setting the stage for a broader interpretation of international law when it comes to taking responsibility for polluting the atmosphere.

Sustained pressure from small island states is advancing our understanding of the obligations of states to address climate change.

Ellycia Harrould-Kolieb, Lecturer and Research Fellow in Ocean Governance, University of Melbourne and Postdoctoral Researcher, UEF Law School, University of Eastern Finland, The University of Melbourne and Margaret Young, Professor, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

About 400,000 years ago, large parts of Greenland were ice-free. Scrubby tundra basked in the Sun’s rays on the island’s northwest highlands. Evidence suggests that a forest of spruce trees, buzzing with insects, covered the southern part of Greenland. Global sea level was much higher then, between 20 and 40 feet above today’s levels. Around the world, land that today is home to hundreds of millions of people was under water.

Scientists have known for awhile that the Greenland ice sheet had mostly disappeared at some point in the past million years, but not precisely when.

In a new study in the journal Science,
we determined the date, using frozen soil extracted during the Cold War from beneath a nearly mile-thick section of the Greenland ice sheet.

NSF UVM Community “Greenland’s ice is vulnerable: a mile of ice vanished from northwest Greenland 400,000 years ago”

The timing – about 416,000 years ago, with largely ice-free conditions lasting for as much as 14,000 years – is important. At that time, Earth and its early humans were going through one of the longest interglacial periods since ice sheets first covered the high latitudes 2.5 million years ago.

The length, magnitude and effects of that natural warming can help us understand the Earth that modern humans are now creating for the future.

A world preserved under the ice

In July 1966, American scientists and U.S. Army engineers completed a six-year effort to drill through the Greenland ice sheet. The drilling took place at Camp Century, one of the military’s most unusual bases – it was nuclear powered and made up of a series of tunnels dug into the Greenland ice sheet.

The drill site in northwest Greenland was 138 miles from the coast and underlain by 4,560 feet of ice. Once they reached the bottom of the ice, the team kept drilling 12 more feet into the frozen, rocky soil below.

In 1969, geophysicist Willi Dansgaard’s analysis of the ice core from Camp Century revealed for the first time the details of how Earth’s climate had changed dramatically over the last 125,000 years. Extended cold glacial periods when the ice expanded quickly gave way to warm interglacial periods when the ice melted and sea level rose, flooding coastal areas around the world.

For nearly 30 years, scientists paid little attention to the 12 feet of frozen soil from Camp Century. One study analyzed the pebbles to understand the bedrock beneath the ice sheet. Another suggested intriguingly that the frozen soil preserved evidence of a time warmer than today. But with no way to date the material, few people paid attention to these studies. By the 1990s, the frozen soil core had vanished.

Several years ago, our Danish colleagues found the lost soil buried deep in a Copenhagen freezer, and we formed an international team to analyze this unique frozen climate archive.

In the uppermost sample, we found perfectly preserved fossil plants – proof positive that the land far below Camp Century had been ice-free some time in the past – but when?

Dating ancient rock, twigs and dirt

Using samples cut from the center of the sediment core and prepared and analyzed in the dark so that the material retained an accurate memory of its last exposure to sunlight, we now know that the ice sheet covering northwest Greenland – nearly a mile thick today – vanished during the extended natural warm period known to climate scientists as MIS 11, between 424,000 and 374,000 years ago.

To determine more precisely when the ice sheet melted away, one of us, Tammy Rittenour, used a technique known as luminescence dating.

Over time, minerals accumulate energy as radioactive elements like uranium, thorium, and potassium decay and release radiation. The longer the sediment is buried, the more radiation accumulates as trapped electrons.

In the lab, specialized instruments measure tiny bits of energy, released as light from those minerals. That signal can be used to calculate how long the grains were buried, since the last exposure to sunlight would have released the trapped energy.

Paul Bierman’s laboratory at the University of Vermont dated the sample’s last time near the surface in a different way, using rare radioactive isotopes of aluminum and beryllium.

These isotopes form when cosmic rays, originating far from our solar system, slam into the rocks on Earth. Each isotope has a different half-life, meaning it decays at a different rate when buried.

By measuring both isotopes in the same sample, glacial geologist Drew Christ was able to determine that melting ice had exposed the sediment at the land surface for less than 14,000 years.

Ice sheet models run by Benjamin Keisling, now incorporating our new knowledge that Camp Century was ice-free 416,000 years ago, show that Greenland’s ice sheet must have shrunk significantly then.

At minimum, the edge of the ice retreated tens to hundreds of miles around much of the island during that period. Water from that melting ice raised global sea level at least 5 feet and perhaps as much as 20 feet compared to today.

Warnings for the future

The ancient frozen soil from beneath Greenland’s ice sheet warns of trouble ahead.

During the MIS 11 interglacial, Earth was warm and ice sheets were restricted to the high latitudes, a lot like today. Carbon dioxide levels in the atmosphere remained between 265 and 280 parts per million for about 30,000 years. MIS 11 lasted longer than most interglacials because of the impact of the shape of Earth’s orbit around the sun on solar radiation reaching the Arctic. Over these 30 millennia, that level of carbon dioxide triggered enough warming to melt much of the Greenland’s ice.

Today, our atmosphere contains 1.5 times more carbon dioxide than it did at MIS 11, around 420 parts per million, a concentration that has risen each year. Carbon dioxide traps heat, warming the planet. Too much of it in the atmosphere raises the global temperature, as the world is seeing now.

Over the past decade, as greenhouse gas emissions continued to rise, humans experienced the eight warmest years on record. July 2023 saw the hottest week on record, based on preliminary data. Such heat melts ice sheets, and the loss of ice further warms the planet as dark rock soaks up sunlight that bright white ice and snow once reflected.

Even if everyone stopped burning fossil fuels tomorrow, carbon dioxide levels in the atmosphere would remain elevated for thousands to tens of thousands of years. That’s because it takes a long time for carbon dioxide to move into soils, plants, the ocean and rocks. We are creating conditions conducive to a very long period of warmth, just like MIS 11.

Unless people dramatically lower the concentration of carbon dioxide in the atmosphere, evidence we found of Greenland’s past suggests a largely ice-free future for the island.

Everything we can do to reduce carbon emissions and sequester carbon that is already in the atmosphere will increase the chances that more of Greenland’s ice survives.

The alternative is a world that could look a lot like MIS 11 – or even more extreme: a warm Earth, shrinking ice sheets, rising sea level, and waves rolling over Miami, Mumbai, India and Venice, Italy.

Paul Bierman, Fellow of the Gund Institute for Environment, Professor of Natural Resources and Environmental Science, University of Vermont and Tammy Rittenour, Professor of Geosciences and Director of Luminescence Lab, Utah State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

I’m striding along the steep bank of a raging white-water torrent, and even though the canyon is only about the width of a highway, the river’s flow is greater than that of London’s Thames. The deafening roar and rumble of the cascading water is incredible – a humbling reminder of the raw power of nature.

As I round a corner, I am awestruck at a completely surreal sight: A gaping fissure has opened in the riverbed, and it is swallowing the water in a massive whirlpool, sending up huge spumes of spray. This might sound like a computer-generated scene from a blockbuster action movie – but it’s real.

A moulin is forming right in front of me on the Greenland ice sheet. Only this really shouldn’t be happening here – current scientific understanding doesn’t accommodate this reality.

As a glaciologist, I’ve spent 35 years investigating how meltwater affects the flow and stability of glaciers and ice sheets.

This gaping hole that’s opening up at the surface is merely the beginning of the meltwater’s journey through the guts of the ice sheet. As it funnels into moulins, it bores a complex network of tunnels through the ice sheet that extend many hundreds of meters down, all the way to the ice sheet bed.

When it reaches the bed, the meltwater decants into the ice sheet’s subglacial drainage system – much like an urban stormwater network, though one that is constantly evolving and backing up. It carries the meltwater to the ice margins and ultimately ends up in the ocean, with major consequences for the thermodynamics and flow of the overlying ice sheet.

Scenes like this and new research into the ice sheet’s mechanics are challenging traditional thinking about what happens inside and under ice sheets, where observations are extremely challenging yet have stark implications. They suggest that Earth’s remaining ice sheets in Greenland and Antarctica are far more vulnerable to climate warming than models predict, and that the ice sheets may be destabilizing from inside.

This is a tragedy in the making for the half a billion people who populate vulnerable coastal regions, since the Greenland and Antarctic ice sheets are effectively giant frozen freshwater reservoirs locking up in excess of 65 meters (over 200 feet) of equivalent global sea level rise. Since the 1990s their mass loss has been accelerating, becoming both the primary contributor to and the wild card in future sea level rise.

How narrow cracks become gaping maws in ice

Moulins are near-vertical conduits that capture and funnel the meltwater runoff from the ice surface each summer. There are many thousands across Greenland, and they can grow to impressive sizes because of the thickness of the ice coupled with the exceptionally high surface melt rates experienced. These gaping chasms can be as large as tennis courts at the surface, with chambers hidden in the ice beneath that could swallow cathedrals.

But this new moulin I’ve witnessed is really far from any crevasse fields and melt lakes, where current scientific understanding dictates that they should form.

In a new paper, Dave Chandler and I demonstrate that ice sheets are littered with millions of tiny hairline cracks that are forced open by the meltwater from the rivers and streams that intercept them.

Because glacier ice is so brittle at the surface, such cracks are ubiquitous across the melt zones of all glaciers, ice sheets and ice shelves. Yet because they are so tiny, they can’t be detected by satellite remote sensing.

Under most conditions, we find that stream-fed hydrofracture like this allows water to penetrate hundreds of meters down before freezing closed, without the crack’s necessarily penetrating to the bed to form a full-fledged moulin. But, even these partial-depth hydrofractures have considerable impact on ice sheet stability.

As the water pours in, it damages the ice sheet structure and releases its latent heat. The ice fabric warms and softens and, hence, flows and melts faster, just like warmed-up candle wax.

The stream-driven hydrofractures mechanically damage the ice and transfer heat into the guts of the ice sheet, destabilizing it from the inside. Ultimately, the internal fabric and structural integrity of ice sheets is becoming more vulnerable to climate warming.

Emerging processes that speed up ice loss

Over the past two decades that scientists have tracked ice sheet melt and flow in earnest, melt events have become more common and more intense as global temperatures rise – further exacerbated by Arctic warming of almost four times the global mean.

The ice sheet is also flowing and calving icebergs much faster. It has lost about 270 billion metric tons of ice per year since 2002: over a centimeter and a half (half an inch) of global sea-level rise. Greenland is now, on average, contributing around 1 millimeter (0.04 inches) to the sea level budget annually.

A 2022 study found that even if atmospheric warming stopped now, at least 27 centimeters – nearly 1 foot – of sea level rise is inevitable because of Greenland’s imbalance with its past two decades of climate.

Understanding the risks ahead is crucial. However, the current generation of ice sheet models used to assess how Greenland and Antarctica will respond to warming in the future don’t account for amplification processes that are being discovered. That means the models’ sea-level rise estimates, used to inform Intergovernmental Panel on Climate Change (IPCC) reports and policymakers worldwide, are conservative and lowballing the rates of global sea rise in a warming world.

Our new finding is just the latest. Recent studies have shown that:

• Warming ocean currents are intruding into the Antarctic and Greenland coastlines, flowing under the ice shelves to undercut outlet glaciers and destabilize their calving fronts.

• Increasing rainfall across the Greenland ice sheet not only depletes snow accumulation, it also accelerates surface melting and ice flow.

• Algae and microbes, along with surface snowpack melt, darken the ice sheet surface, absorbing more solar radiation, which also accelerates ice melt.

• Superimposed ice slabs within the snowpack are forming across the accumulation zone, forming an impermeable barrier that depletes meltwater retention and drives extraordinary runoff.

• Water at the base of the ice sheet thaws and softens the frozen bed, thereby triggering basal sliding and accelerating interior ice sheet flow to the margins.

In the last months, other papers also described previously unknown feedback processes underway beneath ice sheets that computer models currently can’t include. Often these processes happen at too fine a scale for models to pick up, or the model’s simplistic physics means the processes themselves can’t be captured.

Two such studies independently identify enhanced submarine melting at the grounding line in Greenland and Antarctica, where large outlet glaciers and ice streams drain into the sea and start to lift off their beds as floating ice shelves. These processes greatly accelerate ice sheet response to climate change and, in the case of Greenland, could potentially double future mass loss and its contribution to rising sea level.

Current climate models lowball the risks

Along with other applied glaciologists, “structured expert judgment” and a few candid modelers, I contend that the current generation of ice sheet models used to inform the IPCC are not capturing the abrupt changes being observed in Greenland and Antarctica, or the risks that lie ahead.

Ice sheet models don’t include these emerging feedbacks and respond over millennia to strong-warming perturbations, leading to sluggish sea level forecasts that are lulling policymakers into a false sense of security. We’ve come a long way since the first IPCC reports in the early 1990s, which treated polar ice sheets as completely static entities, but we’re still short of capturing reality.

As a committed field scientist, I am keenly aware of how privileged I am to work in these sublime environments, where what I observe inspires and humbles. But it also fills me with foreboding for our low-lying coastal regions and what’s ahead for the 10% or so of the world’s population that lives in them.

Alun Hubbard, Professor of Glaciology, Arctic Five Chair, University of Tromsø

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Featured Image: Richard Bates and Alun Hubbard kayak a meltwater stream on Greenland’s Petermann Glacier, towing an ice radar that reveals it’s riddled with fractures.
Nick Cobbing.

There’s more to Antarctic ice than meets the eye. Sea ice is not a uniform crust overlying the salty Southern Ocean.

Our new research is the first to review the many crucial roles of “landfast” sea ice around Antarctica. Landfast ice is frozen seawater that is fastened to the coast. It acts like a belt around the Antarctic coast, regulating the flow of ice shelves and glaciers into the sea. And it’s crucial habitat for Weddell seals and emperor penguins.

Satellites can easily estimate the horizontal extent of sea ice, but determining the type of ice is far more difficult. Our deeper analysis of satellite images reveals landfast sea ice extent declined to a record low of just 123,200 square km in March 2022. That’s well below the normal March range of 168,600-295,200 square km.

Much of the ice lost in 2022 had been present since 2000, when high-quality records began. If this trend persists, the consequences for the climate and for Southern Ocean ecosystems could be catastrophic.

Getting a grip on landfast ice

Antarctic sea ice drives the circulation of the world’s oceans. The “overturning” circulation begins in Antarctica when very salty, dense brine (created as the ice forms) sinks to the bottom of the ocean. This “bottom water” spreads away from Antarctica to reach the northern hemisphere.

This crucial circulation is projected to slow due to glacial melt, because the input of more buoyant fresh water dilutes the denser brine. This raises the spectre of a further slowing or worse, total shut down of deep ocean currents as in the disaster movie, “The Day After Tomorrow”. We know concentrated regions of sea ice formation tend to occur next to landfast ice, so the changes we are seeing are likely to further reduce this deep ocean circulation.

Global climate models are not particularly skilful at reproducing the recent history of Antarctic sea ice, giving limited confidence in our ability to predict its future. There are many reasons for this, but one of the main ones is an overly simplistic representation of the sea ice.

Landfast sea ice is not represented in any global climate model. These models treat all sea ice as if it’s able to drift, whereas in reality up to 15% of ice should be held still by being anchored to land or grounded icebergs.

This is a big problem because, as our study reveals, if we don’t properly simulate it, we are likely to get all kinds of inaccurate flow-on effects, including an incorrect amount of sea ice (and hence dense water) produced by our models?.

Wildlife depends on landfast ice

Landfast ice supports a unique community of algae, krill, small crustaceans called copepods, molluscs and fish. They are adapted to live within and below the ice where conditions are harsh.

These species form a complex food web around ice algae, using the ice as a nursery ground. Life within landfast ice requires wide-ranging survival strategies. Drastic changes could mean cascading effects on the entire food web.

Seals and penguins rely on this environment for resting, hunting and breeding. Emperor penguins have a unique approach to raising a family that requires stable ice, which only landfast ice can provide. Reduced ice extent, increased fragmentation and earlier breakup can lead to population declines of this iconic species.

Deeper knowledge is crucial for climate forecasts

Only a few areas of Antarctic landfast ice are regularly sampled. These areas are found near Antarctic research stations and are generally separated by thousands of kilometres of coast.

Additionally, scientists can often only safely collect sea ice cores from smooth ice thick enough to support people. So sampling is skewed to favour the unbroken crème brûlée-type crust over the shattered meringue of rough landfast ice.

To better understand rough landfast ice and a slew of other poorly understood ice types, we need repeat ice core measurements along with more detailed satellite studies. We also need the capability to model each ice type accurately.

Our research has ensured landfast ice is earmarked for inclusion in the next iteration of our national climate model, which aims to better simulate the interactions between sea ice of all types and the Southern Ocean. Without this ability, we are missing a key ingredient in the recipe of Australia’s climate future.

Alexander Fraser, Senior Researcher in Antarctic Remote Sensing, University of Tasmania; Christine Weldrick, Postdoctoral research fellow, University of Tasmania; Laura Dalman, PhD candidate, University of Tasmania; Matthew Corkill, PhD candidate, University of Tasmania, and Pat Wongpan, Quantitative Sea Ice Biogeochemist/Ecologist, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Featured Image: Landfast ice ‘breaks out’, Justin Chambers/AAD, Author provided.

Pakistan is a nuclear-armed country of some 220 million people, the fifth most populous in the world It has a nominal GDP per annum of some $350 billion (in the same general range as South Africa, Egypt, Iran and Chile). Its most fertile regions comprise the Indus River basin. Water is the country’s lifeblood, and it is estimated that some 74% of the Indus Valley run-off derives from Himalayan snowmelt and glacier melt. It is likely to decrease by 5% to 12% by 2050. The melting of the glaciers and the retreat of the snow cover there at the top of the world are therefore an existential issue for Pakistan.

Image by lutz from Pixabay

If the world goes on putting 36 billion metric tons of carbon dioxide into the atmosphere every year and doesn’t pull back significantly, actually the melting could be twice as bad. And under the worse case scenario, where human beings just do nothing to fight climate change, by the end of this century, 2081-2100, fully 80% of the lower-lying Himalayan ice will be gone.

These findings, by the way, pertain not only to the lower levels of the Himalayas but also the European Alps, the Rockies, and the Andes.

The reason for the melting of the surface ice in the Hindu Kush Himalayas is obvious. Glacier mass changes have been accelerating because of increased heat owing to human-induced climate change. Temperatures have been going up by an average of +0.28 °C (about half a degree Fahrenheit) every decade since 1951.

The rate of mass loss in the ice between the 1970s and 2019 has increased 65%. Even just in this century, the amount of ice mass lost in 2000-2009 was -0.17 meters water equivalent. But in 2010-2019 it jumped up to -0.28 meters water equivalent.

Seasonal snow cover in the Himalayas is decreasing at an alarming rate. At the lower elevations, there has been a loss of 5 snow-cover days per decade since the 1970s.