Marine life found in ancient Antarctica ice helps solve a carbon dioxide puzzle from the ice age



Chris Fogwill, Author provided

Chris Turney, UNSW and Chris Fogwill, Keele University

Evidence of minute amounts of marine life in an ancient Antarctic ice sheet helps explain a longstanding puzzle of why rising carbon dioxide (CO₂) levels stalled for hundreds of years as Earth warmed from the last ice age.

Our study
shows there was an explosion in productivity of marine life at the surface of the Southern Ocean thousands of years ago.




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Ancient Antarctic ice melt caused extreme sea level rise 129,000 years ago – and it could happen again


And surprisingly, this marine life once played a part regulating the climate. Hence, this finding has big implications for future climate change projections.

Walking into the past

Our research took us on a four-hour flight from Chile to the Weddell Sea, at the extreme southern end of the Atlantic Ocean, to land on an ice runway at a frigid latitude of 79° south.

Our Ilyshion aircraft landed on the Union Glacier (Antarctic Logistics and Expeditions).
Chris Turney, Author provided

The Weddell Sea is frequently choked with sea ice and has been hazardous to ships since the earliest explorers ventured south.

In 1914, the Anglo-Irish explorer Ernest Shackleton and his men became stuck here for two years, 1,000 kilometres from civilisation. They faced isolation, starvation, freezing temperatures, gangrene, wandering icebergs and the threat of cannibalism.

Surviving here is tough, as is undertaking science.




Read more:
What an ocean hidden under Antarctic ice reveals about our planet’s future climate


We spent three weeks in the nearby Patriot Hills, drilling through ice to collect samples.

Normally when scientists collect ice samples, they drill a deep core vertically down through the annual layers of snow and ice. We did something quite different: we went horizontal by drilling a series of shorter cores across the icescape.

That’s because the Patriot Hills is a fiercely wild place strafed by Weddell Sea cyclones that dump large snowfalls, followed by strong frigid winds (called katabatic winds) pouring off the polar plateau.

Those katabatic winds blowing hard.

As the winds blow throughout the year, they remove the surface ice in a process called sublimation. Older, deeper ice is drawn up to the surface. This means walking across the blue ice towards Patriot Hills is effectively like travelling back through time.

A walk across the blue ice is a walk back in time.
Matthew Harris, Keele University, Author provided

The exposed ice reveals what was happening during the transition from the last ice age around 20,000 years ago into our present warmer world, known as the Holocene.

The Antarctic Cold Reversal

As Earth was warming, carbon dioxide levels in the atmosphere were rising rapidly from around 190 to 280 parts per million.

But the warming trend wasn’t all one way.

Starting around 14,600 years ago, there was a 2,000 year-long period of cooling in the Southern Hemisphere. This period is called the Antarctic Cold Reversal, and is where CO₂ levels stalled at around 240 parts per million.

Why that happened was the puzzle, but understanding it could be crucial for improving today’s climate change projections.

Finding life in the ice

Over three weeks we battled the winds and snow to make a detailed collection of ice samples spanning the end of the last ice age.

We collected sample of ice to study later in the lab.
Chris Turney, Author provided

To our surprise, hidden in our ice samples were organic molecules – remnants of marine life thousands of years ago. They came from the cyclones off the Weddell Sea, which swept up organic molecules from the ocean surface and dumped them onshore to be preserved in the ice.

Antarctic ice, which forms from snowfall, usually only tells scientists about the climate. What’s exciting about finding evidence of lifẻ in ancient Antarctic ice is that, for the first time, we can reconstruct what was happening offshore in the Southern Ocean at the same time, thousands of years ago.

We found an unusual period, displaying high concentrations and a diverse range of marine microplankton. This increased ocean productivity coincided with the Antarctic Cold Reversal.

Melting sea ice in summer sustains marine life

Our climate modelling reveals the Antarctic Cold Reversal was a time of massive change in the amount of sea ice across the Southern Ocean.

Sea ice formed in winter melts in summer, and dumps nutrients into the ocean.
Shutterstock

As the world lurched out of the last ice age, the summer warmth destroyed large amounts of sea ice that had formed through winter. When the sea ice melts, it releases valuable nutrients into the Southern Ocean, and fuelled the explosion in marine productivity we found in the ice on the continent.

This marine life caused more carbon dioxide to be drawn from the atmosphere as it photosynthesised, similar to the way plants use carbon dioxide. When the marine life die they sink to the floor, locking away the carbon. The amount of carbon dioxide absorbed in the ocean was sufficiently large to register around the world.

What this mean for climate change today

Today, the Southern Ocean absorbs some 40% of all carbon put in the atmosphere by human activity, so we urgently need a better understand the drivers of this important part of the carbon cycle.




Read more:
The last ice age tells us why we need to care about a 2℃ change in temperature


Marine life in the Southern Ocean still plays an important role in regulating the amount of atmospheric carbon dioxide.

But as the world warms with climate change, less sea ice will be formed in polar regions. This natural carbon sink of marine life will only weaken, increasing global temperatures further.

It’s a timely reminder that while the Antarctic may seem remote, it’s impact on our future climate is closer and more connected than we might think.The Conversation

Chris Turney, Professor of Earth Science and Climate Change, Director of the Changing Earth Research Centre and the Chronos 14Carbon-Cycle Facility at UNSW, and Node Director of the ARC Centre of Excellence for Australian Biodiversity and Heritage, UNSW and Chris Fogwill, Professor of Glaciology and Palaeoclimatology, Head of School Geography, Geology and the Environment and Director of the Institute for Sustainable Futures, Keele University

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

What an ocean hidden under Antarctic ice reveals about our planet’s future climate



Craig Stevens, Author provided

Craig Stevens, National Institute of Water and Atmospheric Research and Christina Hulbe, University of Otago

Jules Verne sent his fictional submarine, the Nautilus, to the South Pole through a hidden ocean beneath a thick ice cap. Written 40 years before any explorer had reached the pole, his story was nevertheless only half fiction.

There are indeed hidden ocean cavities around Antarctica, and our latest research explores how the ocean circulates underneath the continent’s ice shelves – large floating extensions of the ice on land that rise and fall with the tides.

These ice shelves buttress the continent’s massive land-based ice cap and play an important role in the assessment of future sea level rise. Our work sheds new light on how ocean currents contribute to melting in Antarctica, which is one of the largest uncertainties in climate model predictions.

The field camp on top of the Ross Ice Shelf.
Craig Stevens, Author provided



Read more:
Climate scientists explore hidden ocean beneath Antarctica’s largest ice shelf


An unexplored ocean

The Ross Ice Shelf is the largest floating slab of ice on Earth, at 480,000 square kilometres. The ocean cavity it conceals extends 700km south from Antarctica’s coast and remains largely unexplored.

We know ice shelves mainly melt from below, washed by a warming ocean. But we have very little data available about how the water mixes underneath the ice. This is often overlooked in climate models, but our new measurements will help redress this.

The only other expedition to the ocean cavity underneath the central Ross Ice Shelf goes back to the 1970s and came back with intriguing results. Despite the limited technology of the time, it showed the ocean cavity was not a static bathtub. Instead, it found fine layering of water masses, with subtly different temperatures and salinities between the layers.

Other ocean studies have been conducted from the edges or from high above. They have provided insight into how the system works but to really understand it, we needed to take measurements directly from the ocean under hundreds of metres of ice.

The team used a hot-water jet to drill through the ice to the ocean below.
Craig Stevens, Author provided

In 2017, we used a hot-water jet, modelled on a British Antarctic Survey design, to drill through 350 metres of ice to the ocean below. We were able to keep the hole liquid long enough to make detailed ocean measurements as well as leave instruments behind to continue monitoring ocean currents and temperature. These data are still coming in via satellite.

We found the hidden ocean acts like a massive estuary with comparatively warm (2℃) seawater coming in at the seabed to cycle close to the surface in a combination of meltwater and sub-glacial freshwater squeezed out from the ice sheet and Antarctica’s hidden rocky foundation.

The hundreds of metres of ice isolate the ocean cavity from the furious winds and freezing air temperatures of Antarctica. But nothing stops the tides. Our data suggest tides push the stratified ocean back and forth past undulations on the underside of the ice and mix parts of the ocean cavity.




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How solar heat drives rapid melting of parts of Antarctica’s largest ice shelf


Antarctica’s ice isolates the ocean cavity from furious winds and freezing air temperatures.
Craig Stevens, Author provided

Future projections

This sort of discovery is the ultimate challenge for climate science. How do we represent processes that work at daily scales in models that make projections over centuries? Our data show the daily changes can add up, so finding a solution matters.

For example, data collected outside the ocean cavity and computer models suggest that any given parcel of water spends one to six years making its way through the cavity. Our new data indicate the lower end of the range is more likely and that we should not be thinking in terms of one grand circuit anyway.

The Ross is not the ice shelf in most danger from warming oceans. But its sheer size and its relationship with the neighbouring Ross Sea means it is a vital cog in the planetary ocean system.




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Ice melt in Greenland and Antarctica predicted to bring more frequent extreme weather


The importance of these ice shelves for sea level rise over the next few centuries is very apparent. Research shows that if atmospheric warming exceeds 2℃, major Antarctic ice shelves would collapse and release ice flowing from the continent’s ice cap – lifting the sea level by up to 3 metres by 2300.

What is less well understood, but also potentially a massive agent for change, is the impact of meltwater on the global thermohaline circulation, an oceanic transport loop that sees the ocean cycle from the abyss off the coast of Antarctica to tropical surface waters every 1,000 years or so.

Antarctic ice shelves are like a pit stop in this loop and so what happens in Antarctica resonates globally. Faster melting ice shelves will change the ocean stratification, with repercussions for global ocean circulation – and one result of this appears to be greater climate variability.The Conversation

Craig Stevens, Associate Professor in Ocean Physics, National Institute of Water and Atmospheric Research and Christina Hulbe, Professor and Dean of the School of Surveying (glaciology specialisation), University of Otago

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

New research shows the South Pole is warming faster than the rest of the world



Elaine Hood/NSF

Kyle Clem, Te Herenga Waka — Victoria University of Wellington

Climate scientists long thought Antarctica’s interior may not be very sensitive to warming, but our research, published today, shows a dramatic change.

Over the past 30 years, the South Pole has been one of the fastest changing places on Earth, warming more than three times more rapidly than the rest of the world.

My colleagues and I argue these warming trends are unlikely the result of natural climate variability alone. The effects of human-made climate change appear to have worked in tandem with the significant influence natural variability in the tropics has on Antarctica’s climate. Together they make the South Pole warming one of the strongest warming trends on Earth.




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The Amundsen-Scott South Pole station is the Earth’s southern-most weather observatory.
Craig Knott/NSF

The South Pole is not immune to warming

The South Pole lies within the coldest region on Earth: the Antarctic plateau. Average temperatures here range from -60℃ during winter to just -20℃ during summer.

Antarctica’s climate generally has a huge range in temperature over the course of a year, with strong regional contrasts. Most of West Antarctica and the Antarctic Peninsula were warming during the late 20th century. But the South Pole — in the remote and high-altitude continental interior — cooled until the 1980s.

Scientists have been tracking temperature at the Amundsen-Scott South Pole Station, Earth’s southernmost weather observatory, since 1957. It is one of the longest-running complete temperature records on the Antarctic continent.

Our analysis of weather station data from the South Pole shows it has warmed by 1.8℃ between 1989 and 2018, changing more rapidly since the start of the 2000s. Over the same period, the warming in West Antarctica suddenly stopped and the Antarctic Peninsula began cooling.

One of the reasons for the South Pole warming was stronger low-pressure systems and stormier weather east of the Antarctic Peninsula in the Weddell Sea. With clockwise flow around the low-pressure systems, this has been transporting warm, moist air onto the Antarctic plateau.

South Pole warming linked to the tropics

Our study also shows the ocean in the western tropical Pacific started warming rapidly at the same time as the South Pole. We found nearly 20% of the year-to-year temperature variations at the South Pole were linked to ocean temperatures in the tropical Pacific, and several of the warmest years at the South Pole in the past two decades happened when the western tropical Pacific ocean was also unusually warm.

To investigate this possible mechanism, we performed a climate model experiment and found this ocean warming produces an atmospheric wave pattern that extends across the South Pacific to Antarctica. This results in a stronger low-pressure system in the Weddell Sea.

Map of the Antarctic continent.
National Science Foundation

We know from earlier studies that strong regional variations in temperature trends are partly due to Antarctica’s shape.

The East Antarctic Ice Sheet, bordered by the South Atlantic and Indian oceans, extends further north than the West Antarctic Ice Sheet, in the South Pacific. This causes two distinctly different weather patterns with different climate impacts.

More steady, westerly winds around East Antarctica keep the local climate relatively stable, while frequent intense storms in the high-latitude South Pacific transport warm, moist air to parts of West Antarctica.

Scientists have suggested these two different weather patterns, and the mechanisms driving their variability, are the likely reason for strong regional variability in Antarctica’s temperature trends.




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How solar heat drives rapid melting of parts of Antarctica’s largest ice shelf


What this means for the South Pole

Our analysis reveals extreme variations in South Pole temperatures can be explained in part by natural tropical variability.

To estimate the influence of human-induced climate change, we analysed more than 200 climate model simulations with observed greenhouse gas concentrations over the period between 1989 and 2018. These climate models show recent increases in greenhouse gases have possibly contributed around 1℃ of the total 1.8℃ of warming at the South Pole.

We also used the models to compare the recent warming rate to all possible 30-year South Pole temperature trends that would occur naturally without human influence. The observed warming exceeds 99.9% of all possible trends without human influence – and this means the recent warming is extremely unlikely under natural conditions, albeit not impossible. It appears the effects from tropical variability have worked together with increasing greenhouse gases, and the end result is one of the strongest warming trends on the planet.

The temperature variability at the South Pole is so extreme it masks anthropogenic effects.
Keith Vanderlinde/NSF

These climate model simulations reveal the remarkable nature of South Pole temperature variations. The observed South Pole temperature, with measurements dating back to 1957, shows 30-year temperature swings ranging from more than 1℃ of cooling during the 20th century to more than 1.8℃ of warming in the past 30 years.

This means multi-decadal temperature swings are three times stronger than the estimated warming from human-caused climate change of around 1℃.

The temperature variability at the South Pole is so extreme it currently masks human-caused effects. The Antarctic interior is one of the few places left on Earth where human-caused warming cannot be precisely determined, which means it is a challenge to say whether, or for how long, the warming will continue.

But our study reveals extreme and abrupt climate shifts are part of the climate of Antarctica’s interior. These will likely continue into the future, working to either hide human-induced warming or intensify it when natural warming processes and the human greenhouse effect work in tandem.The Conversation

Kyle Clem, Research Fellow in Climate Science, Te Herenga Waka — Victoria University of Wellington

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

Climate change threatens Antarctic krill and the sea life that depends on it



Brett Wilks

Devi Veytia, University of Tasmania and Stuart Corney, University of Tasmania

The Southern Ocean circling Antarctica is one of Earth’s richest marine ecosystems. Its food webs support an abundance of life, from tiny micro-organisms to seals, penguins and several species of whales. But climate change is set to disrupt this delicate balance.

Antarctic krill – finger-sized, swarming crustaceans – might be small but they underpin the Southern Ocean’s food web. Our research published today suggests climate change will cause the ocean habitat supporting krill growth to move south. The habitat will also deteriorate in summer and autumn.

The ramifications will reverberate up the food chain, with implications for other Antarctic animals. This includes humpback whales that feed on krill at the end of their annual migration to the Southern Ocean.

Changes in krill habitat could affect species up the food chain including the humpback whale.
Mike Hutchings/AAP

What we found

Antarctic krill are one of the most abundant animal species in the world. About 500 million tonnes of Antarctic krill are estimated to exist in the Southern Ocean.

Antarctic krill play a critical role in the ocean’s food webs. But their survival depends on a delicate balance of food and temperature. Scientists are concerned at how climate change may affect their population and the broader marine ecosystem.

We wanted to project how climate change will affect the Southern Ocean’s krill “growth habitat” – essentially, ocean areas where krill can thrive in high numbers.

Krill growth depends largely on ocean temperature and the abundance of its main food source, phytoplankton (microscopic single-celled plants).




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Anatomy of a heatwave: how Antarctica recorded a 20.75°C day last month


Under a “business as usual” climate change scenario, future changes in ocean temperature and phytoplankton varied depending on the region and season.

In the mid-low latitudes, our projections showed temperatures warmed towards the limits krill can tolerate. For example, by 2100 the waters during summer around South Georgia island warmed by 1.8℃.

Warming water was often accompanied by decreases in phytoplankton; in the Bellingshausen Sea during summer a 1.7℃ rise halved the available phytoplankton.

However, phytoplankton increased closer to the continent in spring and summer – most dramatically by 175% in the Weddell Sea in spring.

Antarctic krill habitat will shift south under climate change.
Simon Payne, Australian Antarctic Division

Shifting habitat

Across all seasons, krill growth habitat remained relatively stable for 85% of the Southern Ocean. But important regional changes still occurred.

Krill growth habitat shifted south as suitable ocean temperatures contracted towards the poles. Combined with changes in phytoplankton distribution, growth habitat improved in spring but deteriorated in summer and autumn.




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This early end to the growth season could have profound consequences for krill populations. The krill life cycle is synchronised with the Southern Ocean’s dramatic seasonal cycles. Typically this allows krill to both maximise growth and reproduction and store reserves to survive the winter.

A shift in habitat timing could create a mismatch between these two cycles.

For example, female krill need access to plentiful food during the summer in order to spawn. Since larger females produce exponentially more eggs, a decline in summer growth habitat could result in smaller females and far less spawning success.

Antarctic predators including penguins rely on krill for survival.
Royal Navy

Why this matters

Krill’s significant role in the food chain means the impacts of these changes may play out through the entire ecosystem.

If krill shift south to follow their retreating habitat, less food would be available for predators on sub-Antarctic islands such as Antarctic fur seals, penguins and albatrosses for whom krill forms a significant portion of the diet.

In the past, years of low krill densities has coincided with declines in reproductive success for these species.

Shifts in krill habitat timing may also affect migratory predators. For example, each year humpback whales migrate from the tropics to the poles to feed on the huge amount of summer krill. If the krill peak occurs earlier in the season, the whales must adapt by arriving earlier, or be left hungry.

Krill predators. a. crabeater seal (Lobodon carcinophaga), b. Adelie penguins (Pygoscelis adeliae), c. Antarctic fur seal (Arctocephalus gazella), d. humpback whale (Megaptera novaeangliae).
Photo credits (in order a-d): Kevin Neff, Australian Antarctic Division; Mark Hindell, Institute for Marine and Antarctic Studies; Colin Lee Hong, Australian Antarctic Division; Anthony Hull, Australian Antarctic Division.

Looking ahead

Changes to krill growth habitat may damage more than the ocean food web. Demand for krill oil in health supplements and aquaculture feed is on the rise, and krill are the target of the Southern Ocean’s largest fishery. Anticipating changes in krill availability is crucial to informing the fishery’s sustainable management.

Many environmental drivers interact to create good krill habitat. More research is required, including better models, and an improved understanding of what drives krill to reproduce and survive.

But by examining changes in phytoplankton, we’ve taken significant strides towards predicting climate change impacts on krill and the wider Antarctic marine ecosystem.




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The Conversation


Devi Veytia, PhD student , University of Tasmania and Stuart Corney, Senior lecturer, University of Tasmania

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

5 big environment stories you probably missed while you’ve been watching coronavirus



Shutterstock

Rod Lamberts, Australian National University and Will J Grant, Australian National University

Good news: COVID-19 is not the only thing going on right now!

Bad news: while we’ve all been deep in the corona-hole, the climate crisis has been ticking along in the background, and there are many things you may have missed.

Fair enough – it’s what people do. When we are faced with immediate, unambiguous threats, we all focus on what’s confronting us right now. The loss of winter snow in five or ten years looks trivial against images of hospitals pushed to breaking point now.




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While we fixate on coronavirus, Earth is hurtling towards a catastrophe worse than the dinosaur extinction


As humans, we also tend to prefer smaller, short-term rewards over larger long-term ones. It’s why some people would risk illness and possible prosecution (or worse, public shaming) to go to the beach with their friends even weeks after social distancing messages have become ubiquitous.

But while we might need to ignore climate change right now if only to save our sanity, it certainly hasn’t been ignoring us.

So here’s what you may have missed while coronavirus dominates the news cycle.

Heatwave in Antarctica

Antarctica is experiencing alarmingly balmy weather.
Shutterstock

On February 6 this year, the northernmost part of Antarctica set a new maximum temperature record of 18.4℃. That’s a pleasant temperature for an early autumn day in Canberra, but a record for Antarctica, beating the old record by nearly 1℃.

That’s alarming, but not as alarming as the 20.75℃ reported just three days later to the east of the Antarctic Peninsula at Marambio station on Seymour Island.




Read more:
Anatomy of a heatwave: how Antarctica recorded a 20.75°C day last month


Bleaching the reef

The Intergovernmental Panel on Climate Change has warned a global average temperature rise of 1.5℃ could wipe out 90% of the world’s coral.

As the world looks less likely to keep temperature rises to 1.5℃, in 2019 the five-year outlook for Australia’s Great Barrier Reef was downgraded from “poor” to “very poor”. The downgrading came in the wake of two mass bleaching events, one in 2016 and another in 2017, damaging two-thirds of the reef.

And now, in 2020, it has just experienced its third in five years.

Of course, extreme Antarctic temperatures and reef bleaching are the products of human-induced climate change writ large.

But in the short time since the COVID-19 crisis began, several examples of environmental vandalism have been deliberately and specifically set in motion as well.




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Coal mining under a Sydney water reservoir

The Berejiklian government in New South Wales has just approved the extension of coal mining by Peabody Energy – a significant funder of climate change denial – under one of Greater Sydney’s reservoirs. This is the first time such an approval has been granted in two decades.

While environmental groups have pointed to significant local environmental impacts – arguing mining like this can cause subsidence in the reservoir up to 25 years after the mining is finished – the mine also means more fossil carbon will be spewed into our atmosphere.

Peabody Energy argues this coal will be used in steel-making rather than energy production. But it’s still more coal that should be left in the ground. And despite what many argue, you don’t need to use coal to make steel.




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Victoria green-lights onshore gas exploration

In Victoria, the Andrews government has announced it will introduce new laws into Parliament for what it calls the “orderly restart” of onshore gas exploration. In this legislation, conventional gas exploration will be permitted, but an existing temporary ban on fracking and coal seam gas drilling will be made permanent.

The announcement followed a three-year investigation led by Victoria’s lead scientist, Amanda Caples. It found gas reserves in Victoria “could be extracted without harming the environment”.

Sure, you could probably do that (though the word “could” is working pretty hard there, what with local environmental impacts and the problem of fugitive emissions). But extraction is only a fraction of the problem of natural gas. It’s the subsequent burning that matters.




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Trump rolls back environmental rules

Meanwhile, in the United States, the Trump administration is taking the axe to some key pieces of environmental legislation.

One is an Obama-era car pollution standard, which required an average 5% reduction in greenhouse emissions annually from cars and light truck fleets. Instead, the Trump administration’s “Safer Affordable Fuel Efficient Vehicles” requires just 1.5%.

The health impact of this will be stark. According to the Environmental Defense Fund, the shift will mean 18,500 premature deaths, 250,000 more asthma attacks, 350,000 more other respiratory problems, and US$190 billion in additional health costs between now and 2050.

And then there are the climate costs: if manufacturers followed the Trump administration’s new looser guidelines it would add 1.5 billion tonnes of carbon dioxide to the atmosphere, the equivalent of 17 additional coal-fired power plants.




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And so…

The challenges COVID-19 presents right now are huge. But they will pass.

The challenges of climate change are not being met with anything like COVID-19 intensity. For now, that makes perfect sense. COVID-19 is unambiguously today. Against this imperative, climate change is still tomorrow.

But like hangovers after a large celebration, tomorrows come sooner than we expect, and they never forgive us for yesterday’s behaviour.The Conversation

Rod Lamberts, Deputy Director, Australian National Centre for Public Awareness of Science, Australian National University and Will J Grant, Senior Lecturer, Australian National Centre for the Public Awareness of Science, Australian National University

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

Anatomy of a heatwave: how Antarctica recorded a 20.75°C day last month


Dana M Bergstrom, University of Wollongong; Andrew Klekociuk, University of Tasmania; Diana King, University of Wollongong, and Sharon Robinson, University of Wollongong

While the world rightfully focuses on the COVID-19 pandemic, the planet is still warming. This summer’s Antarctic weather, as elsewhere in the world, was unprecedented in the observed record.

Our research, published today in Global Change Biology, describes the recent heatwave in Antarctica. Beginning in late spring east of the Antarctic Peninsula, it circumnavigated the continent over the next four months. Some of our team spent the summer in Antarctica observing these temperatures and the effect on natural systems, witnessing the heatwave first-hand.

Antarctica may be isolated from other continents by the Southern Ocean, but has worldwide impacts. It drives the global ocean conveyor belt, a constant system of deep-ocean circulation which transfers oceanic heat around the planet, and its melting ice sheet adds to global sea level rise.

Antarctica represents the simple, extreme end of conditions for life. It can be seen as a ‘canary in the mine’, demonstrating patterns of change we can expect to see elsewhere.

A heatwave in the coldest place on Earth

Most of Antarctica is ice-covered, but there are small ice-free oases, predominantly on the coast. Collectively 0.44% of the continent, these unique areas are important biodiversity hotspots for penguins and other seabirds, mosses, lichens, lakes, ponds and associated invertebrates.

This summer, Casey Research Station, in the Windmill Islands oasis, experienced its first recorded heat wave. For three days, minimum temperatures exceeded zero and daily maximums were all above 7.5°C. On January 24, its highest maximum of 9.2°C was recorded, almost 7°C above Casey’s 30-year mean for the month.




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The arrival of warm, moist air during this weather event brought rain to Davis Research Station in the normally frigid, ice-free desert of the Vestfold Hills. The warm conditions triggered extensive meltwater pools and surface streams on local glaciers. These, together with melting snowbanks, contributed to high-flowing rivers and flooding lakes.

By February, most heat was concentrated in the Antarctic Peninsula at the northernmost part of the continent. A new Antarctic maximum temperature of 18.4°C was recorded on February 6 at Argentina’s Esperanza research station on the Peninsula – almost 1°C above the previous record. Three days later this was eclipsed when 20.75°C was reported at Brazil’s Marambio station, on Seymour Island east of the Peninsula.

What caused the heatwave?

The pace of warming from global climate change has been generally slower in East Antarctica compared with West Antarctica and the Antarctic Peninsula. This is in part due to the ozone hole, which has occurred in spring over Antarctica since the late 1970s.

The hole has tended to strengthen jet stream winds over the Southern Ocean promoting a generally more ‘positive’ state of the Southern Annular Mode in summer. This means the Southern Ocean’s westerly wind belt has tended to stay close to Antarctica at that time of year creating a seasonal ‘shield’, reducing the transfer of warm air from the Earth’s temperate regions to Antarctica.




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But during the spring of 2019 a strong warming of the stratosphere over Antarctica significantly reduced the size of the ozone hole. This helped to support a more ‘negative’ state of the Southern Annular Mode and weakened the shield.

Other factors in late 2019 may have also helped to warm Antarctica. The Indian Ocean Dipole was in a strong ‘positive’ state due to a late retreat of the Indian monsoon. This meant that water in the western Indian Ocean was warmer than normal. Air rising from this and other warm ocean patches in the Pacific Ocean provided energy sources that altered the path of weather systems and helped to disturb and warm the stratosphere.

Is a warming Antarctica good or bad?

Localised flooding appeared to benefit some Vestfold Hills’ moss banks which were previously very drought-stressed. Prior to the flood event, most mosses were grey and moribund, but one month later many moss shoots were green.

Given the generally cold conditions of Antarctica, the warmth may have benefited the flora (mosses, lichens and two vascular plants), and microbes and invertebrates, but only where liquid water formed. Areas in the Vestfold Hills away from the flooding became more drought-stressed over the summer.

High temperatures may have caused heat stress in some organisms. Antarctic mosses and lichens are often dark in colour, allowing sunlight to be absorbed to create warm microclimates. This is a great strategy when temperatures are just above freezing, but heat stress can occur once 10°C is exceeded.

On King George Island, near the Antarctic Peninsula, our measurements showed that in January 2019 moss surface temperatures only exceeded 14°C for 3% of the time, but in 2020 this increased fourfold (to 12% of the time).

Based on our experience from previous anomalous hot Antarctic summers, we can expect many biological impacts, positive and negative, in coming years. The most recent event highlights the connectedness of our climate systems: from the surface to the stratosphere, and from the monsoon tropics to the southernmost continent.

Under climate change, extreme events are predicted to increase in frequency and severity, and Antarctica is not immune.




Read more:
The ozone hole leaves a lasting impression on southern climate


The Conversation


Dana M Bergstrom, Principal Research Scientist, University of Wollongong; Andrew Klekociuk, Adjunct Senior Lecturer, University of Tasmania; Diana King, Research officer, University of Wollongong, and Sharon Robinson, Professor, University of Wollongong

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

Antarctica now has more than 65,000 ‘meltwater lakes’ as summer ice melts



Meltwater on the ice shelf near the McMurdo research station, Antarctica.
Nicholas Bayou / UNAVCO, Author provided

Jennifer Arthur, Durham University

During the Antarctic summer, thousands of mesmerising blue lakes form around the edges of the continent’s ice sheet, as warmer temperatures cause snow and ice to melt and collect into depressions on the surface. Colleagues of mine at Durham University have recently used satellites to record more than 65,000 of these lakes.

Though seasonal meltwater lakes have formed on the continent for decades, lakes had not been recorded before in such great numbers across coastal areas of East Antarctica. This means parts of the world’s largest ice sheet may be more vulnerable to a warming climate than previously thought.

Lakes affect ice shelves

Much of Antarctica is surrounded by floating platforms of ice, often as tall as a skyscraper. These are “ice shelves”. And when some of these ice shelves have collapsed in the past, satellites have recorded networks of lakes growing and then abruptly disappearing shortly beforehand. For instance, several hundred lakes disappeared in the weeks before the the catastrophic disintegration of the Larsen B Ice Shelf – when 3,250 km² of ice broke up in just two months in 2002.

Blue meltwater ponds cover the surface of Larsen B Ice Shelf in January 2002 (left) before its abrupt collapse two months later (right). Open ocean appears as black in both images.
NASA/Goddard Space Flight Center

The collapse may have depended on water from these lakes filling crevasses and then acting like a wedge as the weight of the water expanded the crevasses, triggering a network of fractures. The weight of lakes can also cause the ice shelf surface to flex, leading to further fracturing, which is thought to have helped the shelf become unstable and collapse.

Ice shelves act as door stops, supporting the huge mass of ice further inland. Their removal means the glaciers feeding the ice shelf are no longer held back and flow faster into the ocean, contributing to sea-level rise.

Melting the ice sheet surface

Scientists already knew that lakes form on the Antarctic ice sheet. But the latest study, published in Scientific Reports, shows that many more lakes are forming than previously thought, including in new parts of the ice sheet and much further inland and at higher elevations.

Since the cold and remoteness makes it logistically challenging to measure and monitor Antarctica’s lakes in the field, we largely know all this thanks to satellite imagery. In this case, one of the satellites used was the European Space Agency’s Sentinel-2 which provides global coverage of the Earth’s surface every five days and can detect features as small as ten metres.

Meltwater lakes on Sørsdal Glacier, Antarctica (red dot on larger map).
Google Maps

My colleagues analysed satellite images of the East Antarctic Ice Sheet taken in January 2017. In total, the images covered 5,000,000 km² (that’s more than 20 times the area of the United Kingdom).

Because water reflects certain wavelengths very strongly compared to ice, lakes can be detected in these images by classifying pixels in the image as “water” or “non-water”. From these images we can pinpoint when lakes form, their growth and drainage, and how their extent and depth change over time. The largest lake detected so far was nearly 30 km long and estimated to hold enough water to fill 40,000 Olympic-sized swimming pools.

Cause for concern?

In a warming world, scientists are particularly interested in these lakes because they may contribute to destabilising the ice shelves and ice sheet in future.

Like a sponge, the more that ice shelves become saturated with meltwater, the less they are able to absorb, meaning more water pools on their surfaces as lakes. More surface lakes mean a greater likelihood that water will drain out, fill crevasses and potentially trigger flexing and fracturing. If this were to occur, other ice shelves around Antarctica may start to disintegrate like Larsen B. Glaciers with floating ice tongues protruding into the ocean may also be vulnerable.

Meltwater drains away through a
Sanne Bosteels

Meanwhile in Greenland, scientists have observed entire lakes draining away within a matter of days, as meltwater plunges through vertical shafts in the ice sheet known as “moulins”. A warm, wet base lubricated by meltwater allows the ice to slide quicker and flow faster into the ocean.

Could something similar be happening in Antarctica? Lakes disappearing in satellite imagery suggests they could be draining in this way, but scientists have yet to observe this directly. If we are to understand how much ice the continent could lose, and how much it could contribute to global sea-level rise, we must understand how these surface meltwater lakes behave. Though captivating, they are potentially a warning sign of future instability in Antarctica.


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Jennifer Arthur, PhD student, Cryospheric Remote Sensing, Durham University

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

If warming exceeds 2°C, Antarctica’s melting ice sheets could raise seas 20 metres in coming centuries



During the Pliocene, up to one third of Antarctica’s ice sheet melted, causing sea-level rise of 20 metres.
from http://www.shutterstock.com, CC BY-ND

Georgia Rose Grant, GNS Science and Timothy Naish, Victoria University of Wellington

We know that our planet has experienced warmer periods in the past, during the Pliocene geological epoch around three million years ago.

Our research, published today, shows that up to one third of Antarctica’s ice sheet melted during this period, causing sea levels to rise by as much as 20 metres above present levels in coming centuries.

We were able to measure past changes in sea level by drilling cores at a site in New Zealand, known as the Whanganui Basin, which contains shallow marine sediments of arguably the highest resolution in the world.

Using a new method we developed to predict the water level from the size of sand particle moved by waves, we constructed a record of global sea-level change with significantly more precision than previously possible.

The Pliocene was the last time atmospheric carbon dioxide concentrations were above 400 parts per million and Earth’s temperature was 2°C warmer than pre-industrial times. We show that warming of more than 2°C could set off widespread melting in Antarctica once again and our planet could be hurtling back to the future, towards a climate that existed three million years ago.




Read more:
Not convinced on the need for urgent climate action? Here’s what happens to our planet between 1.5°C and 2°C of global warming


Overshooting the Paris climate target

Last week we saw unprecedented global protests under the banner of Greta Thunberg’s #FridaysForFuture climate strikes, as the urgency of keeping global warming below the Paris Agreement target of 2°C hit home. Thunberg captured collective frustration when she chastised the United Nations for not acting earlier on the scientific evidence. Her plea resonated as she reminded us that:

With today’s emissions levels, that remaining CO₂ budget [1.5°C] will be entirely gone in less than eight and a half years.

At the current rate of global emissions we may be back in the Pliocene by 2030 and we will have exceeded the 2°C Paris target. One of the most critical questions facing humanity is how much and how fast global sea levels will rise.

According to the recent special report on the world’s oceans and cryosphere by the Intergovernmental Panel on Climate Change (IPCC), glaciers and polar ice sheets continue to lose mass at an accelerating rate, but the contribution of polar ice sheets, in particular the Antarctic ice sheet, to future sea level rise remains difficult to constrain.

If we continue to follow our current emissions trajectory, the median (66% probability) global sea level reached by the end of the century will be 1.2 metres higher than now, with two metres a plausible upper limit (5% probability). But of course climate change doesn’t magically stop after the year 2100.




Read more:
With 15 other children, Greta Thunberg has filed a UN complaint against 5 countries. Here’s what it’ll achieve


Drilling back to the future

To better predict what we are committing the world’s future coastlines to we need to understand polar ice sheet sensitivity. If we want to know how much the oceans will rise at 400ppm CO₂, the Pliocene epoch is a good comparison.

Back in 2015, we drilled cores of sediment deposited during the Pliocene, preserved beneath the rugged hill country at the Whanganui Basin. One of us (Timothy Naish) has worked in this area for almost 30 years and identified more than 50 fluctuations in global sea level during the last 3.5 million years of Earth’s history. Global sea levels had gone up and down in response to natural climate cycles, known as Milankovitch cycles, which are caused by long-term changes in Earths solar orbit every 20,000, 40,000 and 100,000 years. These changes in turn cause polar ice sheets to grow or melt.

While sea levels were thought to have fluctuated by several tens of metres, up until now efforts to reconstruct the precise amplitude had been thwarted by difficulties due to Earth deformation processes and the incomplete nature of many of the cycles.

Our research used a well-established theoretical relationship between the size of the particles transported by waves on the continental shelf and the depth to the seabed. We then applied this method to 800 metres of drill core and outcrop, representing continuous sediment sequences that span a time period from 2.5 to 3.3 million years ago.

We show that during the Pliocene, global sea levels regularly fluctuated between five to 25 metres. We accounted for local tectonic land movements and regional sea-level changes caused by gravitational and crustal changes to determine the sea-level estimates, known as the PlioSeaNZ sea-level record. This provides an approximation of changes in global mean sea level.

Antarctica’s contribution to sea-level rise

Our study also shows that most of the sea-level rise during the Pliocene came from Antarctica’s ice sheets. During the warm Pliocene, the geography of Earth’s continents and oceans and the size of polar ice sheets were similar to today, with only a small ice sheet on Greenland during the warmest period. The melting of the Greenland ice sheet would have contributed at most five metres to the maximum 25 metres of global sea-level rise recorded at Whanganui Basin.

Of critical concern is that over 90% of the heat from global warming to date has gone into the ocean. Much of it has gone into the Southern Ocean, which bathes the margins of Antarctica’s ice sheet.




Read more:
New research shows that Antarctica’s largest floating ice shelf is highly sensitive to warming of the ocean


Already, we are observing warm circumpolar deep water upwelling and entering ice shelf cavities in several sites around Antarctica today. Along the Amundsen Sea coast of West Antarctica, where the ocean has been heating the most, the ice sheet is thinning and retreating the fastest. One third of Antarctica’s ice sheet — the equivalent to up to 20 metres of sea-level rise — is grounded below sea level and vulnerable to widespread collapse from ocean heating.

Our study has important implications for the stability and sensitivity of the Antarctic ice sheet and its potential to contribute to future sea levels. It supports the concept that a tipping point in the Antarctic ice sheet may be crossed if global temperatures are allowed to rise by more than 2℃. This could result in large parts of the ice sheet being committed to melt-down over the coming centuries, reshaping shorelines around the world.The Conversation

Georgia Rose Grant, Postdoctoral Research Assistant, Paleontology Team, GNS Science and Timothy Naish, Professor, Victoria University of Wellington

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