Menu

Antarctica

file-20260928-50-m9ewz1

, , , , ,

Over the long term, when it comes to future sea-level rise, one place matters more than any other: Antarctica.

The frozen continent holds enough ice to raise global sea level by about 190 feet (58 meters). Yet scientists have disagreed on a fundamental question: Will Antarctica gain more ice than it loses this century or lose more ice than it gains?

In a new study published in the scientific journal Nature Geoscience, we looked at hundreds of thousands of potential futures and the impact of each on the ice sheet.

We found that Antarctica’s ice loss this century is locked in – even if the world limits global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit), the 2015 international Paris climate agreement’s most ambitious goal.

Why the Antarctic ice sheet is so hard to predict

The Antarctic ice sheet’s future depends on a chain of events.

Greenhouse gas emissions from vehicles, coal- and natural gas-fueled power plants and other sources around the world determine how much the ocean and air around Antarctica warms. That warming shapes how ice shelves around the continent’s margins melt, and how quickly the glaciers behind them slide over the bedrock. When those ice shelves thin or collapse, studies show the glacier flow speeds up.

A European research team explains ways Antarctica is vulnerable to ice loss from the ocean and how models work. TiPACCS.

Each step relies on assumptions that scientists have yet to agree on, such as how ice shelves collapse. Different assumptions give different answers, and because each step feeds the next, the differences grow – what scientists call cascading uncertainty. As a result, research teams around the world can’t agree on whether Antarctica will gain or lose ice this century.

Snow is part of the puzzle. Warmer air holds more moisture, so as temperatures rise, more snow will likely fall on Antarctica. In some projections, that extra snow outweighs the ice lost to the warming ocean, and the ice sheet actually grows.

Auditioning possible futures

A big reason for this persistent disagreement involves the cost of computing.

Each ice-sheet simulation runs with just one set of assumptions for every step in the chain, from how much greenhouse gas we emit to how the ice behaves. One run can keep a supercomputer busy for days, so no team can test every plausible combination.

Our team of data scientists, glaciologists and oceanographers took a shortcut. An international project called the Ice Sheet Model Intercomparison Project, or ISMIP6, has built a large archive of Antarctic simulations showing how the ice responds under different circumstances. We trained a physics-informed machine learning model on that archive to learn how each simulation’s outcome depends on its physical assumptions, such as how easily ice slides over bedrock. The machine learning model does in a fraction of a second what took the original models days, predicting sea-level change with similar accuracy.


NASA’s Grace satellite has tracked ice mass loss over the years. NASA

That speed let us run millions of combinations and check hundreds of thousands of possible futures against data from satellites that weigh the ice sheet from space by sensing tiny changes in Earth’s gravity. Only scenarios that were able to match what the satellites have seen since 2002 made the cut.

The scenarios that did make the cut point one direction: Antarctica will lose more ice than it gains this century, even if humanity is able to limit global warming to 1.5 C.

That means Antarctica will contribute more to sea-level rise that’s already being driven by melting of the Greenland ice sheet and mountain glaciers and from warming ocean temperatures that cause water to expand.

What a clearer forecast can do

The biggest lessons from our study are that greenhouse gas emissions matter and extra snowfall won’t save Antarctica. Every ton of greenhouse gas that humans can avoid releasing today reduces how much ice Antarctica loses this century, and the benefit – slower and less sea-level rise – lasts for hundreds of years.

In a scenario with very high emissions, our results show a potential faster domino effect. A fast-warming ocean thins the ice shelves, weakened shelves break apart, and glacier ice flows into the ocean faster. Each step makes the next one easier. Together, these steps could add up to 10 inches (25 centimeters) of sea-level rise from Antarctica alone by 2100 – enough to permanently flood the homes of more than 10 million people.

What different types of models help scientists understand about ice melt, and how they are connected to help predict the Antarctic ice sheet’s future. On the left, how greenhouse gas emissions change the climate, including sea ice, ocean and atmospheric dynamics, which influence one another and levels of global warming. On the right, what goes into an ice sheet model, including ice shelf melt and collapse and how the ice slides. Every stage adds uncertainty. Yucheng Lin

Of more than 20 physical assumptions about Antarctica, three matter most for understanding future sea-level rise: how ice shelves respond to a warming ocean, how ice slides over bedrock, and how fast the ocean and air around Antarctica warm. Gaining a better understanding of these processes would do the most to sharpen sea-level projections.

What’s still missing

Our study is far from the final word.

Some processes are missing from today’s simulations, so our machine learning model can’t learn about them – for example, how ice cracks and breaks, and how rivers and lakes beneath the ice sheet change over time. Any of these could change our understanding of how quickly Antarctica’s ice reaches the sea and whether coastal communities have enough time to adapt.

What our study does offer is a much faster way to test combinations of assumptions that are too costly to simulate one by one. That provides a clearer basis for the decisions coastal communities around the world are already having to make.

Antarctica: Sonny Whitelaw

, , , , , , ,

Top image: Antarctic ice : Sonny Whitelaw

Authors: Nerilie Abram, Chief Scientist, Australian Antarctic Division and Professor of Climate Science, Australian National University; Ariaan Purich, Senior Lecturer in Climate Science, Monash University; Felicity McCormack, Antarctic Research Fellow and Senior Lecturer, Monash University; Jan Strugnell, Professor of Marine Biology and Aquaculture, James Cook University, and Matthew England, Deputy Director of the ARC Australian Centre for Excellence in Antarctic Science and Scientia Professor in Oceanography, UNSW Sydney

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

Antarctica has long been seen as a remote, unchanging environment. Not any more.

The ice-covered continent and the surrounding Southern Ocean are undergoing abrupt and alarming changes. Sea ice is shrinking rapidly, the floating glaciers known as ice shelves are melting faster, the ice sheets carpeting the continent are approaching tipping points and vital ocean currents show signs of slowing down.

Published today in Nature, our new research shows these abrupt changes are already underway – and likely to significantly intensify in the future.

Several authors of this article have witnessed these startling changes during fieldwork on the ice. These changes spell bad news for wildlife, both iconic and lesser known. But the changes will reach much further. What’s happening in Antarctica right now will affect the world for generations to come, from rising sea levels to extreme changes in the climate system.

Antarctica: melting iceberg image: Sonny WhitelawAntarctica’s enormity can give the illusion of permanence. But abrupt changes are arriving. Image: Sonny Whitelaw

What is an abrupt change?

Scientists define an abrupt change as a climatic or environmental shift taking place much faster than expected.

What makes abrupt changes so concerning is they can amplify themselves. For example, melting sea ice allows oceans to warm more rapidly, which melts more sea ice. Once triggered, they can be difficult or even impossible to reverse on timescales meaningful to humans.

While it’s common to assume incremental warming will translate to gradual change, we’re seeing something very different in Antarctica. Over past decades, the Antarctic environment had a much more muted response overall to human-caused climate warming compared to the Arctic. But about a decade ago, abrupt changes began to occur.

Shrinking sea ice brings cascading change

Antarctica’s natural systems are tightly interwoven. When one system is thrown out of balance, it can trigger cascading effects in others.

Sea ice around Antarctica has been declining dramatically since 2014. The expanse of sea ice is now shrinking at double the rate of Arctic sea ice. We found these unfolding changes are unprecedented – far outside the natural variability of past centuries.

The implications are far reaching. Sea ice has a reflective, high-albedo surface which reflects heat back to space. When there’s less sea ice, more heat is absorbed by darker oceans. Emperor penguins and other species reliant on sea ice for habitat and breeding face real threats. Less sea ice also means Antarctica’s ice shelves are more exposed to waves.

Antarctica: Sonny Whitelaw The expanse of ocean covered by sea ice began shrinking in 2014 and the rate is accelerating. image: Sonny Whitelaw 


Vital ocean currents are slowing

The melting of ice is actually slowing down the deep ocean circulation around Antarctica. This system of deep currents, known as the Antarctic Overturning Circulation, plays a critical role in regulating Earth’s climate by absorbing carbon dioxide and distributing heat.

In the northern hemisphere, the Atlantic Meridional Overturning Circulation is facing a slowdown.

We’re now observing a similar risk in Southern Ocean currents. Changes to the Antarctic Overturning Circulation may unfold at twice the rate of the more famous North Atlantic counterpart.

A slowdown could reduce how much oxygen and carbon dioxide the ocean absorbs and leave vital nutrients at the seafloor. Less oxygen and fewer nutrients would have major consequences for marine ecosystems and climate regulation.

Melting giants

The West Antarctic Ice Sheet as well as some regions of East Antarctica are now losing ice and contributing to sea level rise. Ice loss has increased sixfold since the 1990s.

The West Antarctic Ice Sheet alone has enough ice to raise global sea levels by more than five metres – and scientists warn we could be nearing the point where this ice sheet could collapse even without substantial further warming, though this might take centuries to millennia.

These enormous ice sheets represent the risk of a global tipping point. They contribute the greatest uncertainty to projections of future sea level rise because we don’t know just how quickly they could collapse.

Worldwide, at least 750 million people live in low-lying areas near the sea. Rising sea levels threaten coastal infrastructure and communities globally.

Wildlife and ecosystems under threat

Antarctica’s biological systems are also undergoing sudden shifts. Ecosystems both under the sea and on land are being reshaped by warming temperatures, unreliable ice conditions and human activity bringing pollution and the arrival of invasive species.

It’s essential to protect these ecosystems through the Antarctic Treaty, including creating protected areas of land and sea and restricting some human activities. But these conservation measures won’t be enough to ensure emperor penguins and leopard seals survive. That will require decisive global action to reduce greenhouse gas emissions.

Which future?

Antarctica is often seen as a symbol of isolation and permanence. But the continent is now changing with disturbing speed – much faster than scientists anticipated.

These abrupt changes stem largely from the extra heat trapped by decades of unchecked greenhouse gas emissions. The only way to avoid further abrupt changes is to slash emissions rapidly enough to hold warming as close to 1.5°C as possible.

Even if we achieve this, much change has already been set in motion. Governments, businesses and coastal communities must prepare for a future of abrupt change. What happens in Antarctica won’t stay there.

The stakes could not be higher. The choices made now will determine whether we face a future of worsening impacts and irreversible change or one of managed resilience to the changes already locked in.The Conversation

Antarctic sea ice 2023 Sonny Whitelaw

, , , , ,

Top image: Antarctica | Sonny Whitelaw

Story: Steven Chown, Director, Securing Antarctica’s Environmental Future and Professor of Biological Sciences, Monash University

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

Our planet continues to warm because of greenhouse gas emissions from human activities. The polar regions are especially vulnerable to this warming. Sea ice extent is already declining in both the Arctic and Antarctic. The Greenland and Antarctic ice sheets are melting, and abrupt changes in both polar environments are underway.

These changes have significant implications for society through sea level rise, changes to ocean circulation and climate extremes. They also have substantial consequences for polar ecosystems, including polar bears and emperor penguins, which have become iconic symbols of the impacts of climate change.

The most effective way to mitigate these changes, and lower the risk of widespread impacts, is reducing greenhouse gas emissions. Yet decarbonisation is slow, and current projections suggest temperature increases of roughly 3°C by 2100.

Given the expected change, and the importance of the polar regions for planetary health, some scientists and engineers have proposed technological approaches, known as geoengineering, to soften the blow to the Arctic and Antarctic.

In research published today in Frontiers in Science, my colleagues and I assessed five of the most developed geoengineering concepts being considered for the polar regions. We found none of them should be used in the coming decades. They are extremely unlikely to mitigate the effects of global warming in polar regions, and are likely to have serious adverse and unintended consequences.

 

What is polar geoengineering?

Geoengineering encompasses a wide range of ideas for deliberate large-scale attempts to modify Earth’s climate. The two broadest classes involve removing carbon dioxide from the atmosphere and increasing the amount of sunlight reflected back into space (known as “solar radiation modification”).

For the polar regions, here are the five most developed concepts.

Stratospheric aerosol injection is a solar radiation modification approach that involves introducing finer particles (such as sulphur dioxide or titanium dioxide) into the stratosphere to reflect sunlight back out to space. In this case, the focus is specifically on the polar regions.

Sea curtains are flexible, buoyant structures anchored to the seafloor at 700 metres to 1,000m depth and rising 150m to 500m. The aim is to prevent warm ocean water from reaching and melting ice shelves (floating extensions of ice that slow the movement of ice from Greenland and Antarctica into the ocean) and the grounding lines of ice sheets (where the land, ice sheet and ocean meet).

A diagram showing a large curtain in the sea against a wall of ice.
Sea curtains are flexible, buoyant structures anchored to the seafloor at 700m to 1,000m depth and rising 150m to 500m.

Sea ice management includes two concepts. The first is the scattering of glass microbeads over fresh Arctic sea ice to make it more reflective and help it survive longer. The second is pumping seawater onto the sea ice surface, where it will freeze, with the aim of thickening the ice – or into the air to produce snow, to the same general effect, using wind-powered pumps.

Basal water removal targets the ice streams found in the Antarctic and Greenland ice sheets. These streams are fast-moving rivers of ice that flow toward the coast, where they can enter the ocean and raise sea levels. Water at their base acts as a lubricant. This concept proposes to remove water from their base to increase friction and slow the flow. The concept is thought to be especially relevant to Antarctica, which has much less surface melting than Greenland, and therefore melt is more about the base of the ice sheet than its surface.

Ocean fertilisation involves adding nutrients such as iron to polar oceans to promote the growth of phytoplankton. These tiny creatures absorb carbon dioxide from the atmosphere, which gets stored in the deep ocean when they die and sink.

A diagram showing nutrients being added to an ocean to promote the growth of phytoplankton
Ocean fertilization aims to promote the growth of phytoplankton.

 

The risk of false hopes

In our research, we assessed each of these concepts against six criteria. These included: scope of implementation; feasibility; financial costs; effectiveness; environmental risks; and governance challenges.

This framework offers an objective way of assessing all such concepts for their merits.

None of the proposed polar geoengineering concepts passed scrutiny as concepts that are workable over the coming decades. The criteria we used show each of the concepts faces multiple difficulties.

For example, to cover 10% of the Arctic Ocean with pumps to deliver seawater to freeze within ten years, one million pumps per year would need to be deployed. The estimated costs of sea curtains (US$1 billion per kilometre) are underestimates of similar-scale projects in easier environments, such as the Thames Barrier near London, by six to 25 times.

One project that planned to spread glass microbeads on ice has also been shut down citing environmental risks. And at their most recent meeting, the majority of Antarctic Treaty Consultative Parties made clear their view that geoengineering should not be conducted in the region.

Polar geoengineering proposals raise false hopes for averting some disastrous consequences of climate change without rapidly cutting greenhouse gas emissions.

They risk encouraging complacency about the urgency of achieving net zero emissions by 2050 or may be used by powerful actors as an excuse to justify continued emissions.

The climate crisis is a crisis. Over the time available, efforts are best focused on decarbonisation. The benefits are rapidly realisable within the near term.The Conversation

Steven Chown, Director, Securing Antarctica’s Environmental Future and Professor of Biological Sciences, Monash University

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

NIWA: New Zealand Scientists Unlock Antarctic Ice Melt Mystery

, , , , , , , , , ,

Top image: NIWA
 
A groundbreaking Antarctic research expedition, led by New Zealand scientists, has for the first time directly observed water flowing out from beneath the West Antarctic Ice Sheet—revealing how massive, hidden floods beneath the ice are contributing to the melting of the continent’s largest ice shelves.
 
The findings, recently published in Nature Geoscience, offer dramatic new insights into how meltwater beneath Antarctica flows and affects sea level rise, says expedition lead Victoria University of Wellington Associate Professor Huw Horgan:
 

“Researchers have long suspected that water, from geothermal heat and other sources, flows from under the ice sheets. Satellite observations from elsewhere in West and East Antarctica have revealed active lakes under the ice caps. Our quest was not just to discover the network of hidden lakes and streams that can’t be seen from the surface, but to complete the first close-up observation of these watercourses meeting the ocean in cavities under the ice shelf. These sub-glacial watercourses play a central role in the melting of the ice shelf, so the findings will enable us to predict sea level rise more accurately.”

Supported by New Zealand’s Antarctic Science Platform, the scientists from NIWA, Victoria University, GNS Science and the University of Otago, as well as researchers in the UK and the US including Cornell University, undertook the fieldwork in the autumn of 2021. It took two weeks for the international team to travel from Scott Base 1,200 kilometres towards the Kamb Ice Stream across the Ross Ice Shelf, a floating ice sheet about the area of France.

“The first challenge was just to get there,” says Associate Professor Horgan, who also works in Switzerland for ETH Zurich’s Laboratory of Hydraulics, Hydrology and Glaciology.

“Fortunately, Antarctica New Zealand has developed long-range ice traverse capabilities to safely move people and gear over vast distances. The second challenge was drilling half a kilometre into the Kamb Ice Stream, a major glacier feeding into the Ross Ice Shelf. Vital to the expedition’s success were the skills of the drilling team from the Antarctic Research Centre at the Victoria University of Wellington who, using high-pressure hot water at 80°C, drilled a 500-metre-deep borehole through the Kamb Ice Stream.”
Drilling team from the Antarctic Research Centre at the Victoria University of Wellington. Image: NIWA
Once the team melted through the ice down into the ocean, they were able to film the under-ice watercourse and collect unique data on its temperature, salinity, sediment, and flow behaviour using a range of NIWA’s specialist ocean equipment—as well as Cornell University’s IceFin remotely operated vehicle. 
Camera being lowered down through the ice. Image: NIWA

“With the help of our camera, we even discovered a school of lobster-like (amphipods) creatures, 400 kilometres from the open ocean.”

The measurements provided many surprises for the team, says NIWA and University of Auckland physical oceanographer Professor Craig Stevens:

“Our first discovery was the unique shape of the under-ice cavity where the meltwater was flowing. The size of the watercourse—about 250 metres deep and 150 metres wide—was larger than expected and mostly filled with ocean water, with only a small portion being freshwater from beneath the ice sheet.”

Using sediment cores the team concluded that the water comes from sub-glacial lakes upstream, which fill and empty the lakes in cycles – when they empty, a flood of water rushes towards the sea.

“Understanding these hidden systems is crucial to improving climate models and predicting sea level rise more accurately. The Ross Ice Shelf and others like it play a critical role in slowing the flow of inland glaciers to the sea. Their decline will significantly accelerate global sea level rise.”

“Antarctica may be remote, but what happens there affects us all,” says Professor Stevens. “We need to understand this distant changing environment, so we can prepare for future challenges here at home.”
Denman Glacier Pete Harmsen AAD

, , , , , , , , , , , ,

Top image: An icebreaker approaches Denman Glacier in March, when there was 70% less Antarctic sea ice than usual. Pete Harmsen AAD

Author: Edward Doddridge, University of Tasmania
_______________________________________________________________________________

On her first dedicated scientific voyage to Antarctica in March, the Australian icebreaker RSV Nuyina found the area sea-ice free. Scientists were able to reach places never sampled before.

Over the past four summers, Antarctic sea ice extent has hit new lows.

I’m part of a large group of scientists who set out to explore the consequences of summer sea ice loss after the record lows of 2022 and 2023. Together we rounded up the latest publications, then gathered new evidence using satellites, computer modelling, and robotic ocean sampling devices. Today we can finally reveal what we found.

It’s bad news on many levels, because Antarctic sea ice is vital for the world’s climate and ecosystems. But we need to get a grip on what’s happening – and use this concerning data to prompt faster action on climate change.

Sea ice around Antarctica waxes and wanes with the seasons, growing in the cold months and melting in warm ones. But this rhythmic cycle is changing. 

What we did and what we found

Our team used a huge range of approaches to study the consequences of sea ice loss.

We used satellites to understand sea ice loss over summer, measuring everything from ice thickness and extent to the length of time each year when sea ice is absent.

Satellite data was also used to calculate how much of the Antarctic coast was exposed to open ocean waves. We were then able to quantify the relationship between sea ice loss and iceberg calving.

Data from free-drifting ocean robots was used to understand how sea ice loss affects the tiny plants that support the marine food web.

Every other kind of available data was then harnessed to explore the full impact of sea ice changes on ecosystems.

Voyage reports from international colleagues came in handy when studying how sea ice loss affected Antarctic resupply missions.

We also used computer models to simulate the impact of dramatic summer sea ice loss on the ocean.

In summary, our extensive research reveals four key consequences of summer sea ice loss in Antarctica.

1. Ocean warming is compounding

Bright white sea ice reflects about 90% of the incoming energy from sunlight, while the darker ocean absorbs about 90%. So if there’s less summer sea ice, the ocean absorbs much more heat.

This means the ocean surface warms more in an extreme low sea ice year, such as 2016 – when everything changed.

Until recently, the Southern Ocean would reset over winter. If there was a summer with low sea ice cover, the ocean would warm a bit. But over winter, the extra heat would shift into the atmosphere.

That’s not working anymore. We know this from measuring sea surface temperatures, but we have also confirmed this relationship using computer models.

What’s happening instead is when summer sea ice is very low, as in 2016, it triggers ocean warming that persists. It takes about three years for the system to fully recover. But recovery is becoming less and less likely, given warming is building from year to year.

Artwork illustrating the consequences of sea ice loss around Antarctica, showing more warming, and less area available to wildlife
Comparing an average sea ice summer (a) to an extreme low sea ice summer (b) in which there is less sea ice for wildlife and more sunlight is absorbed by the ocean. The ice shelf is more exposed to ocean waves, calving more icebergs. The ocean is also less productive and tourist vessels can make a closer approach. Doddridge, E., W., et al. (2025) PNAS Nexus., CC BY-NC-ND


2. More icebergs are forming

Sea ice protects Antarctica’s coast from ocean waves.

On average, about a third of the continent’s coastline is exposed over summer. But this is changing. In 2022 and 2023, more than half of the Antarctic coast was exposed.

Our research shows more icebergs break away from Antarctic ice sheets in years with less sea ice. During an average summer, about 100 icebergs break away. Summers with low sea ice produce about twice as many icebergs.

3. Wildlife squeezed off the ice

Many species of seals and penguins rely on sea ice, especially for breeding and moulting.

Entire colonies of emperor penguins experienced “catastrophic breeding failure” in 2022, when sea ice melted before chicks were ready to go to sea.

After giving birth, crabeater seals need large, stable sea ice platforms for 2–3 weeks until their pups are weaned. The ice provides shelter and protection from predators. Less summer sea-ice cover makes large platforms harder to find.

Many seal and penguin species also take refuge on the sea ice when moulting. These species must avoid the icy water while their new feathers or fur grows, or risk dying of hypothermia.

Antarctica: melting iceberg image: Sonny Whitelaw Antarctic ice sheets without sea ice are more exposed to waves. Image: Sonny Whitelaw


4. Logistical challenges at the end of the world

Low summer sea ice makes it harder for people working in Antarctica. Shrinking summer sea ice will narrow the time window during which Antarctic bases can be resupplied over the ice. These bases may soon need to be resupplied from different locations, or using more difficult methods such as small boats.

An icebreaker delivers supplies to the Antarctic base
Supply ships typically unload their cargo directly onto the sea ice, but that may have to change.
Jared McGhie, Australian Antarctic Division

 

No longer safe

Anarctic sea ice began to change rapidly in 2015 and 2016. Since then it has remained well below the long-term average.

The dataset we use relies on measurements from US Department of Defense satellites. Late last month, the department announced it would no longer provide this data to the scientific community. While this has since been delayed to July 31, significant uncertainty remains.

One of the biggest challenges in climate science is gathering and maintaining consistent long-term datasets. Without these, we don’t accurately know how much our climate is changing. Observing the entire Earth is hard enough when we all work together. It’s going to be almost impossible if we don’t share our data.

A chart showing the variation in Antarctic sea ice extent compared to the long-term average, trending towards less sea ice since 2016.
Antarctic sea ice extent anomalies (the difference between the long-term average and the measurement) for the entire satellite record since the late 1970s. Edward Doddridge, using data from the US NSIDC Sea Ice Index, version 3., CC BY

Recent low sea ice summers present a scientific challenge. The system is currently changing faster than our scientific community can study it.

But vanishing sea ice also presents a challenge to society. The only way to prevent even more drastic changes in the future is to rapidly transition away from fossil fuels and reach net zero emissions.The Conversation

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

space

, , , , , , , , , , , , ,

Top image: NASA, CC BY-NC-ND

Steven Sherwood, Professor of Atmospheric Sciences, Climate Change Research Centre, UNSW Sydney; Benoit Meyssignac, Associate Research Scientist in Climate Science, Université de Toulouse, and Thorsten Mauritsen, Professor of Climate Science, Stockholm University

______________________________________________________________________________

How do you measure climate change? One way is by recording temperatures in different places over a long period of time. While this works well, natural variation can make it harder to see longer-term trends.

But another approach can give us a very clear sense of what’s going on: track how much heat enters Earth’s atmosphere and how much heat leaves. This is Earth’s energy budget, and it’s now well and truly out of balance.

Our recent research found this imbalance has more than doubled over the last 20 years. Other researchers have come to the same conclusions. This imbalance is now substantially more than climate models have suggested.

In the mid-2000s, the energy imbalance was about 0.6 watts per square metre (W/m2) on average. In recent years, the average was about 1.3 W/m2. This means the rate at which energy is accumulating near the planet’s surface has doubled.

These findings suggest climate change might well accelerate in the coming years. Worse still, this worrying imbalance is emerging even as funding uncertainty in the United States threatens our ability to track the flows of heat.

Energy in, energy out

Earth’s energy budget functions a bit like your bank account, where money comes in and money goes out. If you reduce your spending, you’ll build up cash in your account. Here, energy is the currency.

Life on Earth depends on a balance between heat coming in from the Sun and heat leaving. This balance is tipping to one side.

Solar energy hits Earth and warms it. The atmosphere’s heat-trapping greenhouse gases keep some of this energy.

But the burning of coal, oil and gas has now added more than two trillion tonnes of carbon dioxide and other greenhouse gases to the atmosphere. These trap more and more heat, preventing it from leaving.

Some of this extra heat is warming the land or melting sea ice, glaciers and ice sheets. But this is a tiny fraction. Fully 90% has gone into the oceans due to their huge heat capacity.

Earth naturally sheds heat in several ways. One way is by reflecting incoming heat off of clouds, snow and ice and back out to space. Infrared radiation is also emitted back to space.

From the beginning of human civilisation up until just a century ago, the average surface temperature was about 14°C. The accumulating energy imbalance has now pushed average temperatures 1.3-1.5°C higher.

Ilulissat Greenland, midnight sun over iceberg from the Jacobshavn glacier Photo: Cody Whitelaw
Ice and reflective clouds reflect heat back to space. As the Earth heats up, most trapped heat goes into the oceans but some melts ice and heats the land and air. Pictured: Icebergs from the Jacobshavn glacier in Greenland, the largest outside Antarctica. Photo: Cody Whitelaw


Tracking faster than the models

Scientists keep track of the energy budget in two ways.

First, we can directly measure the heat coming from the Sun and going back out to space, using the sensitive radiometers on monitoring satellites. This dataset and its predecessors date back to the late 1980s.

Second, we can accurately track the build-up of heat in the oceans and atmosphere by taking temperature readings. Thousands of robotic floats have monitored temperatures in the world’s oceans since the 1990s.

Both methods show the energy imbalance has grown rapidly.

The doubling of the energy imbalance has come as a shock, because the sophisticated climate models we use largely didn’t predict such a large and rapid change.

Typically, the models forecast less than half of the change we’re seeing in the real world.

Why has it changed so fast?

We don’t yet have a full explanation. But new research suggests changes in clouds is a big factor.

Clouds have a cooling effect overall. But the area covered by highly reflective white clouds has shrunk, while the area of jumbled, less reflective clouds has grown.

It isn’t clear why the clouds are changing. One possible factor could be the consequences of successful efforts to reduce sulfur in shipping fuel from 2020, as burning the dirtier fuel may have had a brightening effect on clouds. However, the accelerating energy budget imbalance began before this change.

Natural fluctuations in the climate system such as the Pacific Decadal Oscillation might also be playing a role. Finally – and most worryingly – the cloud changes might be part of a trend caused by global warming itself, that is, a positive feedback on climate change.

Clouds by Vladimir Anikeev | Unsplash
Dense blankets of white clouds reflect the most heat. But the area covered by these clouds is shrinking. Image: Vladimir Anikeev | Unsplash.

What does this mean?

These findings suggest recent extremely hot years are not one-offs but may reflect a strengthening of warming over the coming decade or longer.

This will mean a higher chance of more intense climate impacts from searing heatwaves, droughts and extreme rains on land, and more intense and long lasting marine heatwaves.

This imbalance may lead to worse longer-term consequences. New research shows the only climate models coming close to simulating real world measurements are those with a higher “climate sensitivity”. That means these models predict more severe warming beyond the next few decades in scenarios where emissions are not rapidly reduced.

We don’t know yet whether other factors are at play, however. It’s still too early to definitively say we are on a high-sensitivity trajectory.

Our eyes in the sky

We’ve known the solution for a long time: stop the routine burning of fossil fuels and phase out human activities causing emissions such as deforestation.

Keeping accurate records over long periods of time is essential if we are to spot unexpected changes.

Satellites, in particular, are our advance warning system, telling us about heat storage changes roughly a decade before other methods.

But funding cuts and drastic priority shifts in the United States may threaten essential satellite climate monitoring.The Conversation

Steven Sherwood, Professor of Atmospheric Sciences, Climate Change Research Centre, UNSW Sydney; Benoit Meyssignac, Associate Research Scientist in Climate Science, Université de Toulouse, and Thorsten Mauritsen, Professor of Climate Science, Stockholm University

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

Antarctic sea ice 2023 Sonny Whitelaw

, , , , , , , , , , , ,

Author: Alessandro Silvano, NERC Independent Research Fellow in Oceanography, University of Southampton

The ocean around Antarctica is rapidly getting saltier at the same time as sea ice is retreating at a record pace. Since 2015, the frozen continent has lost sea ice similar to the size of Greenland. That ice hasn’t returned, marking the largest global environmental change during the past decade.

This finding caught us off guard – melting ice typically makes the ocean fresher. But new satellite data shows the opposite is happening, and that’s a big problem. Saltier water at the ocean surface behaves differently than fresher seawater by drawing up heat from the deep ocean and making it harder for sea ice to regrow.

The loss of Antarctic sea ice has global consequences. Less sea ice means less habitat for penguins and other ice-dwelling species. More of the heat stored in the ocean is released into the atmosphere when ice melts, increasing the number and intensity of storms and accelerating global warming. This brings heatwaves on land and melts even more of the Antarctic ice sheet, which raises sea levels globally.

Our new study has revealed that the Southern Ocean is changing, but in a different way to what we expected. We may have passed a tipping point and entered a new state defined by persistent sea ice decline, sustained by a newly discovered feedback loop.

A satellite image of Antarctica with sea ice and Southern Ocean noted. 

The Southern Ocean surrounds Antarctica, which is fringed by sea ice. Image: NASA

A surprising discovery

Monitoring the Southern Ocean is no small task. It’s one of the most remote and stormy places on Earth, and is covered in darkness for several months a year. Thanks to new European Space Agency satellites and underwater robots which stay below the ocean surface measuring temperature and salinity, we can now observe what is happening in real time.

Our team at the University of Southampton worked with colleagues at the Barcelona Expert Centre and the European Space Agency to develop new algorithms to track ocean surface conditions in polar regions from satellites. By combining satellite observations with data from underwater robots, we built a 15-year picture of changes in ocean salinity, temperature and sea ice.

What we found was astonishing. Around 2015, surface salinity in the Southern Ocean began rising sharply – just as sea ice extent started to crash. This reversal was completely unexpected. For decades, the surface had been getting fresher and colder, helping sea ice expand.


A line graph showing a steady and then sudden decline in sea ice extent. 

The annual summer minimum extent of Antarctic sea ice dropped precipitously in 2015.
Image: NOAA Climate.gov/National Snow and Ice Data Center

To understand why this matters, it helps to think of the Southern Ocean as a series of layers. Normally, the cold, fresh surface water sits on top of warmer, saltier water deep below. This layering (or stratification, as scientists call it) traps heat in the ocean depths, keeping surface waters cool and helping sea ice to form.

Saltier water is denser and therefore heavier. So, when surface waters become saltier, they sink more readily, stirring the ocean’s layers and allowing heat from the deep to rise. This upward heat flux can melt sea ice from below, even during winter, making it harder for ice to reform. This vertical circulation also draws up more salt from deeper layers, reinforcing the cycle.

A powerful feedback loop is created: more salinity brings more heat to the surface, which melts more ice, which then allows more heat to be absorbed from the Sun. My colleagues and I saw these processes first hand in 2016-2017 with the return of the Maud Rise polynya, which is a gaping hole in the sea ice that is nearly four times the size of Wales and last appeared in the 1970s.

What happens in Antarctica doesn’t stay there

Losing Antarctic sea ice is a planetary problem. Sea ice acts like a giant mirror reflecting sunlight back into space. Without it, more energy stays in the Earth system, speeding up global warming, intensifying storms and driving sea level rise in coastal cities worldwide.

Wildlife also suffers. Emperor penguins rely on sea ice to breed and raise their chicks. Tiny krill – shrimp-like crustaceans which form the foundation of the Antarctic food chain as food for whales and seals – feed on algae that grow beneath the ice. Without that ice, entire ecosystems start to unravel.

What’s happening at the bottom of the world is rippling outward, reshaping weather systems, ocean currents and life on land and sea.

An aerial view of sea ice. 

Feedback loops are accelerating the loss of Antarctic sea ice. Image: University of Southampton

 

Antarctica is no longer the stable, frozen continent we once believed it to be. It is changing rapidly, and in ways that current climate models didn’t foresee. Until recently, those models assumed a warming world would increase precipitation and ice-melting, freshening surface waters and helping keep Antarctic sea ice relatively stable. That assumption no longer holds.

Our findings show that the salinity of surface water is rising, the ocean’s layered structure is breaking down and sea ice is declining faster than expected. If we don’t update our scientific models, we risk being caught off guard by changes we could have prepared for. Indeed, the ultimate driver of the 2015 salinity increase remains uncertain, underscoring the need for scientists to revise their perspective on the Antarctic system and highlighting the urgency of further research.

We need to keep watching, yet ongoing satellite and ocean monitoring is threatened by funding cuts. This research offers us an early warning signal, a planetary thermometer and a strategic tool for tracking a rapidly shifting climate. Without accurate, continuous data, it will be impossible to adapt to the changes in store.

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

Glacier terminal undercut by warm water image by Sonny Whitelaw

, , , , , , , ,

Shaun Eaves, Te Herenga Waka — Victoria University of Wellington; Andrew Mackintosh, Monash University; Helen Bostock, The University of Queensland, and Joel Pedro

Recent assessments suggest the ocean current known as Atlantic Meridional Overturning Circulation (AMOC) is slowing down, with collapse a real possibility this century.

The AMOC is a globally important current in the Atlantic Ocean, where surface water moves northward as part of the Gulf Stream and transports warm water towards the Arctic. There it cools and sinks to return southward as a deep ocean current.

Map of sea surface temperatures in the North Atlantic with a schematic diagram of ocean currents.
The Atlantic meridional overturning current (AMOC) transfers heat to the North Atlantic. Recent trends indicate this current may be slowing. Ruijian Gou, CC BY-ND

Collapse of the AMOC would have a devastating effect on climate in Europe. Temperatures in the UK and Scandinavia could drop by 5–15°C in a matter of decades.

However, because Earth’s climate system is interconnected, these impacts could have a global reach. Our new research shows past changes in AMOC have had significant impact on temperatures in New Zealand and across the southern hemisphere. These results imply that future collapse of AMOC may accelerate ongoing warming trends.

Lessons from the past

Between 20,000 and 10,000 years ago, Earth transitioned from peak ice-age conditions to a climate more like today’s. This interval featured rising global temperatures, melting ice sheets and climbing sea levels – all phenomena associated with present-day climate change.

Evidence from ice cores in Greenland and marine sediments in the North Atlantic suggests this natural warming event featured several abrupt changes associated with AMOC variability.

Using this interval as a natural experiment, we have undertaken research to learn more about how AMOC variability can affect climate in New Zealand.

Two merged photographs show a glacial basin and people among snow-covered rocks.
Evidence preserved in the landscape shows cooling and glacier growth in New Zealand coincided with a strengthening AMOC 14,500 years ago. Huw Horgan, Shaun Eaves, CC BY-ND.

To reconstruct how air temperature changed in New Zealand, we examined the past extent of mountain glaciers using evidence preserved in the landscape. Glaciers grow and shrink primarily in response to changing air temperature, which affects the annual balance of snowfall and snow or ice melt. As glaciers change in size, they deposit moraines (rock debris) in the landscape, which can persist for tens of thousands of years.

A female scientist wearing a hard hat inspects mud layers in a sediment core.
The analysis of microfossils in marine sediment cores allows scientists to reconstruct past changes in sea-surface temperature. Jenni Hopkins, CC BY-ND

We combined these land-based observations with reconstructions of sea-surface temperature in the Tasman Sea, which we derived from microfossils (smaller than one millimetre in size) known as foraminifera. These microfossils come in a wide range of species and each has a preferred water temperature.

We quantified changes in foraminifera species in a core of marine sediment to trace how local temperature in the Tasman Sea has varied through time.


Global climate connections

Our results show that changes in air and sea-surface temperature followed a similar pattern in the New Zealand region as Earth warmed following the last ice age.

Warming began in both air and sea at about 18,000 years ago, followed by a cooling event at about 14,500 years ago – the Antarctic Cold Reversal. The timing of these changes matches past changes in the AMOC, as recorded in geological climate records from the North Atlantic region.

We examined computer simulations to test the physical connection between changes in the AMOC and New Zealand’s climate. These simulations used a physics-based climate model that captures atmospheric and ocean circulation and their interaction.

Outputs from climate models show southern hemisphere temperature changes due to AMOC variability.
Climate model experiments show the impact of past AMOC variability on surface temperature in the Southern Hemisphere. Shaun Eaves, CC BY-ND

The model simulations support our geological evidence, showing air and sea surface temperatures in New Zealand respond sensitively to changes in AMOC intensity. When the AMOC weakens and Europe cools, New Zealand and the southern mid-latitudes undergo warming, and vice versa.

The models also indicate changes in the AMOC are transported rapidly, within decades, to New Zealand via shifting global wind systems. Changes in the AMOC disrupt the temperature gradient between the hemispheres, which is a key control on the strength of westerly wind belts in the southern hemisphere, between the latitudes of 40°S and 60°S where New Zealand is.

The westerly winds are important for New Zealand’s climate. They control the path of atmospheric storms and regional ocean currents.

Stronger winds over New Zealand bring regional cooling, as more storms track over the country and warm ocean currents are diverted away from the Tasman Sea into the south Pacific. In contrast, when the AMOC weakens, New Zealand has clearer skies and the Tasman Sea receives more tropical water masses, causing regional warming.

Future implications

Scientists have identified several “tipping points” in Earth’s climate system that may be triggered by human-caused climate change. Once these thresholds are crossed, the consequences cannot be easily undone.

Climbing greenhouse gas concentrations have raised air temperatures in New Zealand, and globally, by about 1.1°C since the late 19th century. Projections suggest New Zealand may end this century 1°C to 3°C warmer than now. However, these estimates do not include the potential impacts of a future AMOC collapse.

Our insights from the recent geological past show this AMOC tipping point has global reach, and could accelerate future warming in New Zealand.The Conversation

Shaun Eaves, Senior Lecturer in Physical Geography, Te Herenga Waka — Victoria University of Wellington; Andrew Mackintosh, Chief Investigator in Antarctic environmental science, Monash University; Helen Bostock, Associate Professor in Marine Geology, The University of Queensland, and Joel Pedro, Palaeoclimatologist

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

Antarctic sea ice loss 2023 Image: Sonny Whitelaw

, , , ,

Originally published under Creative Commons by 360info™ .

360Info is an open access global information agency of journalists working with academics to address the world’s biggest challenges and offer practical solutions. More by 360info.

Throughout 2023, the area of ocean around Antarctica covered by sea ice was so far below the norm that scientists have struggled to communicate their shock.
 
This month, as the sea ice shrinks to its smallest point of the year, it is once again tracking well below its previous levels.
 
 Research released in September 2023 shows that ocean warming was a key contributor to the dramatic change in sea ice.
 
The question is where the heat comes from.
 

A new satellite launched recently may provide the key to understanding how the ocean transports heat to Antarctica’s margins where it has a devastating impact on sea ice and ice shelves.

Sea ice insulates the ocean, reflects heat, drives currents, supports ecosystems and protects ice shelves.

 

 

Parts of the ocean 100–200m below the surface began to warm in 2015, and those same regions lost substantial sea ice in 2016. Since then, the warm subsurface ocean seems to have maintained the low sea-ice coverage.

The record-breaking low sea ice of 2023 may be the new abnormal, the beginning of the inevitable decline in Antarctic sea ice, long projected by climate models.

For millions of years, the icy continent has been ring-fenced by the Antarctic Circumpolar Current, separating the warm northern waters from the cold polar ocean.

Flowing clockwise around Antarctica and driven by westerly winds, the current is the world’s strongest, with a flow 100 times stronger than all rivers combined.

The Antarctic Circumpolar Current flows around Antarctica, keeping warm water out — but eddies can let heat through.

The current ‘feels’ the seafloor and the mountains in its path. Where it encounters barriers like ridges or seamounts, ‘wiggles’ are created in the water flow that form eddies.

Ocean eddies are the weather systems of the seas, and they play a key role in transporting heat through the circumpolar current to the ocean around Antarctica. But they’re small and hard for satellites to see.

Broad-scale ocean mapping identifies at least five major ‘heat flux gates’ or eddy hotspots in the circumpolar current.

One is south of Australia, about halfway between Tasmania and Antarctica.

To understand the ocean dynamics happening now and how these may change in the future, we need much higher-resolution data to see smaller-scale features like the eddy hotspots.

Enter the Surface Water and Ocean Topography (Swot) satellite. Jointly developed by Nasa and French space agency Centre National d’Études Spatiales (CNES), the Swot satellite measures differences in the height of the ocean within a few centimetres from an orbit of more than 890km above the surface.

The advanced radar altimeters on the two-tonne satellite detect surface water features with 10 times better resolution than previous technologies.

Oceanographers say it’s like a short-sighted person looking at a tree in the distance, and then putting on glasses to reveal all the leaves.

As Swot passes over the Southern Ocean, the high-resolution topography it records of the shape of the ocean surface shows the fine streams of current to capture the eddy hotspots spinning off the Antarctic Circumpolar Current.

This means scientists can monitor these smaller-scale circulation features thought to be responsible for transporting most of the heat and carbon from the upper ocean to deeper layers – a critical buffer against global warming.

For the first time we can see them on the surface in detail – but we still need to work out what’s happening beneath the waves.

In November 2023, scientists were able to validate the Swot satellite data from an eddy hotspot in the Southern Ocean in an ambitious voyage on CSIRO research vessel investigator.

The five-week FOCUS voyage travelled 850 nautical miles south of Hobart to the Macquarie meander, one of the five eddy hotspots.

A meander may sound gentle and slow, but in fact it’s where the world’s strongest current races through a series of hairpin bends, steered by mountains on the seafloor.

As the satellite passed overhead, the team led by CSIRO and the Australian Antarctic Program Partnership deployed a variety of high-tech observational equipment.

Researchers and crew anchored a tall mooring 3.6km high at the centre of the survey area, carrying over 54 instruments on a cable stretching from the seafloor to near the surface.

They also released free-floating autonomous instruments like floats, drifters and gliders into the eddies, while more than a hundred CTDs – conductivity, temperature, and depth sensors – plumbed the depths and a Triaxus was towed behind the ship through the satellite’s path.

Researchers use a variety of instruments to understand the ocean. Some float along the surface, some dive deep in the water, and some follow directed paths using motors.

The wealth of information gathered by all these instruments ‘ground-truths’ and validates the satellite data from the surface.

The Antarctic is rapidly changing, and with further disruptions to the sea-ice cycle on the cards, there’s a race to understand why.

Strong winds over the Southern Ocean have been increasing for decades and are likely to continue. It’s expected this will send more heat southward through leaky meanders, accelerating ice shelf melting in Antarctica and sea level rise.

Ultimately, this research aims to turn daily maps of ocean sea surface height from satellites into daily maps of the movement of heat in the Southern Ocean toward Antarctica.

This is vital information in a climate crisis. It will help governments plan how to respond to ocean warming and rising sea levels and how quickly action is needed.

At the same time, as the transition to a net-zero world gathers momentum and carbon levels in the atmosphere start to level out, we need to be able to track the response of the Southern Ocean and the global climate system.

Ariaan Purich is a lecturer in the School of Earth, Atmosphere and Environment at Monash University, and a Chief Investigator with the Australian Research Council Special Research Initiative Securing Antarctica’s Environmental Future. She has worked previously with CSIRO.

Edward Doddridge is a physical oceanographer working in the Australian Antarctic Program Partnership (AAPP) based at the Institute for Marine and Antarctic Studies (IMAS) in Hobart, Tasmania.

Benoit Legresy works with CSIRO as climate scientist leading the Oceans group and is a co-leader of the oceanography project with the Australian Antarctic Program Partnership.

Edward Doddridge (University of Tasmania) and Ariaan Purich (Monash University) both receive funding from the Australian Research Council.

The research of the FOCUS voyage is supported by a grant of sea time on RV Investigator from the CSIRO Marine National Facility which is supported by the Australian Government’s National Collaborative Research Infrastructure Strategy (NCRIS).

The Australian Antarctic Program Partnership is funded by the Australian Government Department of Climate Change, Energy, the Environment and Water through the Antarctic Science Collaboration Initiative.
 
Authors:
 

Ariaan Purich is a lecturer in the School of Earth, Atmosphere and Environment at Monash University, and a Chief Investigator with the Australian Research Council Special Research Initiative Securing Antarctica’s Environmental Future. She has worked previously with CSIRO.

Edward Doddridge is a physical oceanographer working in the Australian Antarctic Program Partnership (AAPP) based at the Institute for Marine and Antarctic Studies (IMAS) in Hobart, Tasmania.

Benoit Legresy works with CSIRO as climate scientist leading the Oceans group and is a co-leader of the oceanography project with the Australian Antarctic Program Partnership.

Edward Doddridge (University of Tasmania) and Ariaan Purich (Monash University) both receive funding from the Australian Research Council.

The research of the FOCUS voyage is supported by a grant of sea time on RV Investigator from the CSIRO Marine National Facility which is supported by the Australian Government’s National Collaborative Research Infrastructure Strategy (NCRIS).

The Australian Antarctic Program Partnership is funded by the Australian Government Department of Climate Change, Energy, the Environment and Water through the Antarctic Science Collaboration Initiative.

Load More