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.

(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.

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.

(The Conversation) – The rhythmic expansion and contraction of Antarctic sea ice is like a heartbeat.

But lately, there’s been a skip in the beat. During each of the last two summers, the ice around Antarctica has retreated farther than ever before.

And just as a change in our heartbeat affects our whole body, a change to sea ice around Antarctica affects the whole world.

Today, researchers at the Australian Antarctic Program Partnership (AAPP) and the Australian Centre for Excellence in Antarctic Science (ACEAS) have joined forces to release a science briefing for policy makers, On Thin Ice.

Together we call for rapid cuts to greenhouse gas emissions, to slow the rate of global heating. We also need to step up research in the field, to get a grip on sea-ice science before it’s too late.

The shrinking white cap on our blue planet

One of the largest seasonal cycles on Earth happens in the ocean around Antarctica. During autumn and winter the surface of the ocean freezes as sea ice advances northwards, and then in the spring the ice melts as the sunlight returns.

We’ve been able to measure sea ice from satellites since the late 1970s. In that time we’ve seen a regular cycle of freezing and melting. At the winter maximum, sea ice covers an area more than twice the size of Australia (roughly 20 million square kilometres), and during summer it retreats to cover less than a fifth of that area (about 3 million square km).

In 2022 the summer minimum was less than 2 million square km for the first time since satellite records began. This summer, the minimum was even lower – just 1.7 million square km.

The annual freeze pumps cold salty water down into the deep ocean abyss. The water then flows northwards. About 40% of the global ocean can be traced back to the Antarctic coastline.

By exchanging water between the surface ocean and the abyss, sea ice formation helps to sequester heat and carbon dioxide in the deep ocean. It also helps to bring long-lost nutrients back up to the surface, supporting ocean life around the world.

Not only does sea ice play a crucial role in pumping seawater across the planet, it insulates the ocean underneath. During the long days of the Antarctic summer, sunlight usually hits the bright white surface of the sea ice and is reflected back into space.

This year, there is less sea ice than normal and so the ocean, which is dark by comparison, is absorbing much more solar energy than normal. This will accelerate ocean warming and will likely impede the wintertime growth of sea ice.

Headed for stormy seas

The Southern Ocean is a stormy place; the epithets “Roaring Forties” and “Furious Fifties” are well deserved. When there is less ice, the coastline is more exposed to storms. Waves pound on coastlines and ice shelves that are normally sheltered behind a broad expanse of sea ice. This battering can lead to the collapse of ice shelves and an increase in the rate of sea level rise as ice sheets slide off the land into the ocean more rapidly.

Sea ice supports many levels of the food web. When sea ice melts it releases iron, which promotes phytoplankton growth. In the spring we see phytoplankton blooms that follow the retreating sea ice edge. If less ice forms, there will be less iron released in the spring, and less phytoplankton growth.

Krill, the small crustaceans that provide food to whales, seals, and penguins, need sea ice. Many larger species such as penguins and seals rely on sea ice to breed. The impact of changes to the sea ice on these larger animals varies dramatically between species, but they are all intimately tied to the rhythm of ice formation and melt. Changes to the sea-ice heartbeat will disrupt the finely balanced ecosystems of the Southern Ocean.

A diagnosis for policy makers

Long term measurements show the subsurface Southern Ocean is getting warmer. This warming is caused by our greenhouse gas emissions. We don’t yet know if this ocean warming directly caused the record lows seen in recent summers, but it is a likely culprit.

As scientists in Australia and around the world work to understand these recent events, new evidence will come to light for a clearer understanding of what is causing the sea ice around Antarctica to melt.

If you noticed a change in your heartbeat, you’d likely see a doctor. Just as doctors run tests and gather information, climate scientists undertake fieldwork, gather observations, and run simulations to better understand the health of our planet.

This crucial work requires specialised icebreakers with sophisticated observational equipment, powerful computers, and high-tech satellites. International cooperation, data sharing, and government support are the only ways to provide the resources required.

After noticing the first signs of heart trouble, a doctor might recommend more exercise or switching to a low-fat diet. Maintaining the health of our planet requires the same sort of intervention – we must rapidly cut our consumption of fossil fuels and improve our scientific capabilities.

Edward Doddridge, Research Associate in Physical Oceanography, University of Tasmania

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

Featured Image: Australian Antarctic Program Partnership, Author provided

The Antarctic Ice Sheet, which covers an area greater than the US and Mexico combined, holds enough water to raise global sea level by more than 57 metres if melted completely. This would flood hundreds of cities worldwide. And evidence suggests it is melting fast. Satellite observations have revealed that grounded ice (ice that is in contact with the bed beneath it) in coastal areas of West Antarctica has been lost at a rate of up to 30 metres per day in recent years.

But the satellite record of ice sheet change is relatively short as there are only 50 years’ worth of observations. This limits our understanding of how ice sheets have evolved over longer periods of time, including the maximum speed at which they can retreat and the parts that are most vulnerable to melting.

So, we set out to investigate how ice sheets responded during a previous period of climatic warming – the last “deglaciation”. This climate shift occurred between roughly 20,000 and 11,000 years ago and spanned Earth’s transition from a glacial period, when ice sheets covered large parts of Europe and North America, to the period in which we currently live (called the Holocene interglacial period).

During the last deglaciation, rates of temperature and sea-level rise were broadly comparable to today. So, studying the changes to ice sheets in this period has allowed us to estimate how Earth’s two remaining ice sheets (Greenland and Antarctica) might respond to an even warmer climate in the future.

Our recently published results show that ice sheets are capable of retreating in bursts of up to 600 metres per day. This is much faster than has been observed so far from space.

Pulses of rapid retreat

Our research used high-resolution maps of the Norwegian seafloor to identify small landforms called “corrugation ridges”. These 1–2 metre high ridges were produced when a former ice sheet retreated during the last deglaciation.

Photo by Jay Ruzesky on Unsplash

Tides lifted the ice sheet up and down. At low tide, the ice sheet rested on the seafloor, which pushed the sediment at the edge of the ice sheet upwards into ridges. Given that there are two low tides each day off Norway, two separate ridges were produced daily. Measuring the space between these ridges enabled us to calculate the pace of the ice sheet’s retreat.

During the last deglaciation, the Scandinavian Ice Sheet that we studied underwent pulses of extremely rapid retreat – at rates between 50 and 600 metres per day. These rates are up to 20 times faster than the highest rate of ice sheet retreat that has so far been measured in Antarctica from satellites.

The highest rates of ice sheet retreat occurred across the flattest areas of the ice sheet’s bed. In flat-bedded areas, only a relatively small amount of melting, of around half a metre per day, is required to instigate a pulse of rapid retreat. Ice sheets in these regions are very lightly attached to their beds and therefore require only minimal amounts of melting to become fully buoyant, which can result in almost instantaneous retreat.

However, rapid “buoyancy-driven” retreat such as this is probably only sustained over short periods of time – from days to months – before a change in the ice sheet bed or ice surface slope farther inland puts the brakes on retreat. This demonstrates how nonlinear, or “pulsed”, the nature of ice sheet retreat was in the past.

This will likely also be the case in the future.

A warning from the past

Our findings reveal how quickly ice sheets are capable of retreating during periods of climate warming. We suggest that pulses of very rapid retreat, from tens to hundreds of metres per day, could take place across flat-bedded parts of the Antarctic Ice Sheet even under current rates of melting.

This has implications for the vast and potentially unstable Thwaites Glacier of West Antarctica. Since scientists began observing ice sheet changes via satellites, Thwaites Glacier has experienced considerable retreat and is now only 4km away from a flat area of its bed. Thwaites Glacier could therefore suffer pulses of rapid retreat in the near future.

Ice losses resulting from retreat across this flat region could accelerate the rate at which ice in the rest of the Thwaites drainage basin collapses into the ocean. The Thwaites drainage basin contains enough ice to raise global sea levels by approximately 65cm.

Our results shed new light on how ice sheets interact with their beds over different timescales. High rates of retreat can occur over decades to centuries where the bed of an ice sheet deepens inland. But we found that ice sheets on flat regions are most vulnerable to extremely rapid retreat over much shorter timescales.

Together with data about the shape of ice sheet beds, incorporating this short-term mechanism of retreat into computer simulations will be critical for accurately predicting rates of ice sheet change and sea-level rise in the future.

Christine Batchelor, Lecturer in Physical Geography, Newcastle University and Frazer Christie, Postdoctoral Research Associate, University of Cambridge

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

(The Conversation) – Ottawa’s famous Rideau Canal, which turns into the world’s largest ice rink every winter, is too thin to open this winter.

Thousands of kilometres to the south, we can see a similar issue on a much larger scale in the Antarctic, where the sea ice is also struggling to form. The Antarctic sea ice extent — region with at least 15 per cent sea ice cover — reached a record low on Feb. 13.

While the mass of the Antarctic ice sheet has been decreasing for a long time, the Antarctic sea ice extent has been strongly decreasing since 2016.

If left unchecked, the complete melting of the West Antarctic ice sheet would cause a global sea level increase of 3.3 metres in the distant future.

The white continent

The ice-covered continent of Antarctica, surrounded by the Southern Ocean, holds 90 per cent of the world’s ice.

This mass of ice that forms the ice cover, or ice sheet, over land has resulted from the accumulation and compaction of the snow over thousands of years. And when it extends over the sea, it forms an ice shelf.

The Antarctic ice sheet comprises the West Antarctic ice sheet and the East Antarctic ice sheet. Most of the West Antarctic ice sheet is below the sea level. Around the Antarctic, the extent of the sea ice — which forms from ocean water — increases in winter and decreases in summer.

The Antarctic warms faster

The Antarctic is not free from climate change. On the contrary, the rise in temperatures at high latitudes is much stronger than the rise in the global mean temperature. This phenomenon is known as polar amplification.

Via Pixabay. File.

This phenomenon can be explained by the ice-albedo feedback. The increase in the near-surface temperature contributes to the melting of the ice, which contributes to the increase in the temperature. Why? Because the albedo — the fraction of solar energy that is reflected by a surface — of the ocean and of the ground underneath is lower than that of the ice.

Over the last four decades, climate change has caused a decrease in the average extent of sea ice in the Arctic, but not in the Antarctic. The reason for this statistically insignificant decrease in the average Antarctic sea ice extent is the regional tendencies — the sea ice extent has increased in some regions and decreased in others — compensate for each other. Another reason is the strong internal variability.

However, the Antarctic sea ice extent has decreased a lot since 2016. The decrease in the surface of the sea ice cover contributes to the increase in the temperature, but not to sea level rise. This is because the volume of water that the ice displaces when it forms is the same as it adds to the ocean when it melts. As for the Antarctic ice sheet, its mass has decreased since at least 1990, with the highest loss rate during the last decade.

In its Sixth Assessment Report, the Intergovernmental Panel on Climate Change (IPCC) found that, in the Antarctic, temperature will continue to increase and the mass of the ice sheet will continue to decrease. The growth of this ice sheet is much slower than its retreat, which means that, if it continues to melt during this century, this melting will not be reversible at a human time scale.

The degree of confidence in the climate projections surrounding the Antarctic sea ice is weak, as the climate model simulations do not accurately capture its observed evolution. And so, we cannot make any definitive conclusions about it.

The consequences of the collapsing ice sheet

The sustained melting of the West Antarctic ice sheet could indicate that an unstable retreat (which reinforces itself) is underway or imminent. However, there is high uncertainty about this phenomenon.

The mechanism that would explain this unstable retreat is known as Marine Ice Sheet Instability.

If the bed, where the ice sheet lies, slopes down towards the interior, it destabilizes the position of the grounding line — zone where this ice sheet starts to float. The thinning of the ice shelf causes this grounding line to retreat, which leads to an influx of ice from the ice sheet to the sea. This, subsequently, causes the thinning of the ice shelf and so on and so forth.

At present, the world is heading towards a warming of 2.8 C by the end of this century. A sustained warming of about 2 C to 3 C would be sufficient to make this ice sheet almost completely disappear, but this phenomenon would take thousands of years.

The bottom line is that the melting of the Antarctic ice sheet contributes to and will continue to contribute to sea level rise for a long time, which will test the adaptive capacity of humanity.

The sea level increase by 2100 will particularly affect the tropical countries. And so, what happens in the Antarctic will definitely not stay in the Antarctic.

Marta Moreno Ibáñez, PhD candidate in Earth and atmospheric sciences, Université du Québec à Montréal (UQAM)

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

Humanity will certainly miss the 1.5 C. goal.

The average temperature of the earth’s surface has already shot up 1.4° F. (0.8° C.) since 1880. The average temperature of the earth in the 20th century was 53.6°F (12.0°C), but that was already warmer than the average in the nineteenth century. The eighteenth century, before the industrial revolution, was positively cold in comparison. In contrast, the first 22 years of the twenty-first century have been unprecedentedly hot. Here’s a visualization from NOAA showing all this:

As with the William J. Ripple article I discussed last week, the Park et al. article tries to build more positive feedback loops into models of ice sheet collapse.

For instance, when ice at the poles melts, it flows as fresh water into the salty seas, tending to occupy the layers of the ocean more toward the surface. As Charles Harvey at ClimateWire put it, “Because fresh water is less dense than salt water, large influxes of meltwater could fail to mix in with the rest of the ocean and instead form a layer that rests on the surface of the water. This cold sheet of liquid traps heat beneath it and causes deeper layers to warm up.”

The Park et al. team tried to build this sort of effect into their model.

They found that if we did keep additional heating to 1.5C above the pre-industrial average, then the ice sheets would be more likely to remain at least somewhat intact.

If we go to 2° C. (3.6F) above the preindustrial average, then the ice sheets are more likely to collapse. In fact, the tipping point may be 1.8° C (3.24° F). They admit that their calculations are conservative, but they see as much as 2.3 feet of sea level rise by 2100, not counting that the hotter ocean will expand and that will additionally contribute to sea level rise.

But beyond 130 years, if we heat the average surface temperature of the earth by 2C, eventually all the ice at the poles would come tumbling down into the seas.

The last time the whole earth was tropical and there was no polar ice cap, there was about a third less land area than there is now.

Even just a few feet of sea level rise will be a big problem for cities such as New York, San Francisco and New Orleans. Lower Manhattan is also lower in elevation and may not be there.

They warn that there are lots of other changes that might accelerate ice sheet melting, such as narrow ocean currents, that are not in their model. Also, scientists still do not understand processes like the “calving” of the ice sheets very well.

But their findings are alarming enough, even though they expect the worst to be felt over many decades.

Positive feedback loops are the ones you have to watch out for. William J. Ripple et al. explain, “For example, warming in the Arctic leads to melting sea ice, which leads to further warming because water has lower albedo (reflectance) than ice.” Here is what they mean: Say the extra carbon dioxide we put into the atmosphere causes the oceans to warm up a bit. The warmer water melts some of the ice at the North Pole. Ice reflects sunlight back out into space, so it cools the earth and its oceans off. When the ice melts, the dark water beneath becomes visible. Dark surfaces absorb sunshine rather than reflecting it. So now the water gets even hotter. And more ice melts. And the dark water absorbs more sunshine and gets even hotter. On and on. A positive feedback loop ratchets things in a single direction so that they get increasingly out of kilter.

So what if the climate emergency is creating not one but 27 positive feedback loops (which, remember, are bad if you are interested in maintaining the status quo)? And what if it is only generating a handful of negative feedback loops, so that these latter cannot hope to offset all the massive changes being provoked by the positive feedback loops? The answer to these “what if?” questions is that we would be well and truly screwed.

That’s the fear expressed in a new scientific paper in One Earth by William J. Ripple et al.

They start out with a graphic showing how several of these positive feedback loops in climate change might reinforce one another:

As noted above, if we want to keep the earth cool, ice is our friend because it is blinding white and reflects the heat of sun rays back out into outer space. So a positive climate feedback loop typically sets in motion the disappearance of more and more ice. For instance, rainfall at the poles melts ice, which causes more global heating because bright surfaces are replaced by dark absorptive ones, and warmer resulting oceans then put more water vapor into the air above them, causing more rainfall, which melts more ice, and so on.

It is worse. Because when oceans warm and put more water vapor into the air above them, they are in effect emitting a greenhouse gas, since water vapor, like carbon dioxide and methane, helps keep the sun’s heat on earth once it strikes it, rather than letting it radiate out to space.

So you have two positive feedback loops going on here, with reduced reflectivity because of ice loss, which increases heat, and also increased heat from emission of a greenhouse gas, i.e. water vapor. Both of these effects reinforce one another and make the earth even hotter.

Not only does the ice melting reduce its ability to reflect away the sun rays, but it causes sea level to rise. Sandy beaches are bright and reflect sunlight. But if they are submerged by dark water they can no longer do this. Loss of beaches because of sea level rise thus can raise the earth’s temperature and melt more ice which causes more sea level rise and loss of bright coastal areas. A positive feedback loop, this process can go on at the same time as the ones mentioned above.

So here’s the bottom line. The authors suggest that if a lot of these positive feedback loops operate at the same time and reinforce one another, as the few examples I chose above do, they could reduce the ability of the ocean to absorb carbon dioxide. For instance, cold water absorbs more CO2 than warm water, so if we heat up the oceans very rapidly we will reduce our carbon budget.

Our carbon budget is the amount of carbon dioxide that the oceans will absorb. Almost all of the massive amounts of CO2 we have put into the atmosphere will go into the oceans. But if we go on producing billions of tons a year of CO2 after 2050, we will outrun the oceans’ absorptive capacity, and then the CO2 will just stay up there, making the earth hot, for thousands or even tens of thousands of years. Since we as a species evolved in relatively cool times, and since our civilization is premised on the stability of a cool climate, we do not know how well we will cope with a very long-term erratic Hot Earth.

That carbon budget we have between now and 2050, however, may not exist. Maybe we only have until 2035 or 2040 to stop producing CO2, in order to avoid pushing our climate system over into chaos. Chaos means super-hurricanes and massive heatwaves and unexpected flooding, etc.

If a lot of these positive climate feedback loops work together, they could reduce our carbon budget. So, the scientists say, governments and companies are unwise to set goals of being carbon neutral by 2050. That may be too late if we take into account all the destructive positive feedback loops, and especially if some of them reinforce one another.

Their message is, in other words, hurry up!

B.E. Schmidt and colleagues write in a paper for Nature that scientists piloted an underwater vehicle beneath the ice shelf and the Thwaites glacier. Eat your heart out, James Cameron! They found that the glacier is melting a little slower than had been feared, but that since 2010 it has nevertheless shrunk consistently and fairly rapidly. Worse, much worse was their finding that there are big cracks in the glacier and terraced indentations from below that they call ‘staircase-like’ structures. These weak spots are exposed to relatively warm water, at a temperature of 2°C, i.e., 35.6°F, from beneath, and the glacier is melting especially rapidly at these weak hot points.

The scientists write that “The varied topography [i.e. the cracks and staircases] of the ice base at the GL [the grounding line where the ice shelf meets the ocean], carved as it flowed over the bed before reaching the ocean, becomes a broadly distributed network of sloped ice surfaces along which melting is promoted.”

The important phrase here is melting is promoted. You never want to hear that in Antarctica.

The National Oceanic and Atmospheric Agency (NOAA) has a neat sea level viewer. I entered two feet of sea level rise into it, and this is what the United States looks like under that condition:

That’s a lot of coast missing. And cities. Doesn’t the map show that Miami, Savannah and New Orleans are not there any more?

Then I put in 10 feet of sea level rise:

It looks like San Diego, San Francisco and Seattle are gone now, too. And Rhode Island and Boston.

We are not talking about hypotheticals. Likely this amount of sea level is locked in, and four to six feet of sea level is predicted by the end of this century by the IPCC. That prediction, however, does not take into account the possibility that the Thwaites Glacier may take a dive.

So the only question is the pace and the time scale of this change. I think what the team that went down in their underwater vehicle found is that weird stuff is going on down there that could speed up T-day, the day when Thwaites takes a swim.

Another team of scientists, as reported by Peter E. D. Davis et al. in Nature, as well, drilled into Thwaites with a warm drill. They found that although some of it is shielded from warm water by a layer of colder water, even a little heat goes a long way toward increasing the rate of melt: “rapid and possibly unstable grounding-line retreat may be associated with relatively modest basal melt rates.” They drilled into a part of the glacier that is melting more slowly, but observe that the “main trunk” is rapidly retreating.

Their conclusion is not encouraging: “Nevertheless, sustained grounding-zone basal melting, weaker ice-shelf buttressing and the advection of increasingly thinner ice over the grounding line will continue to condition TEIS to persistent retreat in the future, even without a strong positive feedback from elevated basal melting.”

In otherwords, the thing is going to go on melting. And that ain’t good.