effects
Port Hills is only the beginning
This article is republished from The Conversation under a Creative Commons license. Read the original article.
___________________________________________________________________________________
Last week, wildfire burnt through 650 hectares of forest and scrub in Christchurch’s Port Hills. This is not the first time the area has faced a terrifying wildfire event.
The 2017 Port Hills fires burnt through almost 2,000 hectares of land, claiming one life and 11 homes. It took 66 days before the fires were fully extinguished.
It is clear New Zealand stands at a pivotal juncture. The country faces an increasingly severe wildfire climate. And our once relatively “safe” regions are now under threat.
At all levels of government, New Zealand needs to consider whether our current investment to combat fires will be enough in the coming decades.
Our research integrating detailed climate simulations with daily observations reveals a stark forecast: an uptick in both the frequency and intensity of wildfires, particularly in the inland areas of the South Island.
It is time to consider what this will mean for Fire and Emergency New Zealand (FENZ), and how a strategic calibration of resources, tactics and technologies will help New Zealand confront this emerging threat.
The climate drivers of wildfires
Last year was the warmest year on record by a large margin. And with El Niño at full throttle into 2024, conditions in late-summer Aotearoa New Zealand are hot and dry. There is also plenty of vegetation fuel from the departing wet La Niña.
The tinder-dry scrub and grass vegetation in the Port Hills – an area that was around 30% above “extreme” drought fire danger thresholds – drove the flammability of the region. And on February 13, when the latest fires started, a strong gusty northwesterly wind was blowing 40-50kph with exceptionally dry relative humidity values.
These conditions resulted in the extreme wildfire behaviour. Only the rapid and coordinated response of FENZ on the ground and in the air prevented this fire from becoming much worse.
While conditions are already bad, our study revealed a concerning trend: the widespread emergence of a new wildfire climate, with regions previously unaffected by “very extreme” wildfire conditions now facing unprecedented threats.
The most severe dangers are projected for areas like the Mackenzie Country, upper Otago and Marlborough, where conditions similar to Australia’s “Black Summer” fires could occur every three to 20 years.
This shift is not merely an environmental concern, it is a socioeconomic one. The increased threat of wildfires will affect communities, the government’s tree-planting initiatives and financial investments in carbon forests.
Enhanced resources and agile response
New Zealand’s firefighting strategy emphases speed and manoeuvrability, especially in the initial attack phase, to prevent wildfires from escalating into large-scale disasters.
Approximately NZ$10 million is allocated annually to general firefighting aviation services, translating into around 11,000 flight hours. The aerial battle over the Port Hills peaked on Thursday and Friday. This effort cost over $1 million, with up to 15 helicopters active over the two days.
FENZ operations are primarily funded by property insurance levies. However, with the severity and frequency of wildfires on the rise, it may be necessary to review this funding model to match the evolving risk portfolio.
Climate change is already driving insurance retreat – a phenomenon whereby coastal properties are unable to renew their insurance due sea level rise. It is plausible insurance companies could take a similar stance in extremely fire-prone areas.
The agility of FENZ and associated rural fire teams, coupled with the investment and integration of advanced technologies and modelling for better wildfire prediction and management, can significantly enhance the effectiveness of firefighting efforts.
Policy adjustments and community engagement
Adjustments in policy and regulatory frameworks are also crucial in mitigating wildfire risks, and should be explored by experts.
To significantly reduce the ignition of new fires, there needs to be greater implementation of restrictions on access, and banning of high-risk activities, when areas are under “extreme fire risk”.
Moreover, community engagement and preparedness initiatives are vital. One successful example is Mt Iron, Wanaka, where a model was developed after interviews, focus groups and workshops with residents identified wildfire risk awareness and mitigation actions.
Educating vulnerable communities about their wildfire risks and preparedness strategies can also enhance community resilience and safety.
The emergence of a more severe wildfire climate in New Zealand calls for a unified response, integrating increased investment in FENZ, strategic planning and community involvement.
By embracing a multifaceted approach that includes technological innovation, enhanced resource, and community empowerment, New Zealand can navigate the complexities of this new era with resilience and foresight.
Once melting glaciers shut down the Gulf Stream, we would see extreme climate change within decades, study shows
Authors: René van Westen, Utrecht University; Henk A. Dijkstra, Utrecht University, and Michael Kliphuis, Utrecht University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
___________________________________________________________________________________
Superstorms, abrupt climate shifts and New York City frozen in ice. That’s how the blockbuster Hollywood movie “The Day After Tomorrow” depicted an abrupt shutdown of the Atlantic Ocean’s circulation and the catastrophic consequences.
While Hollywood’s vision was over the top, the 2004 movie raised a serious question: If global warming shuts down the Atlantic Meridional Overturning Circulation, which is crucial for carrying heat from the tropics to the northern latitudes, how abrupt and severe would the climate changes be?
Twenty years after the movie’s release, we know a lot more about the Atlantic Ocean’s circulation. Instruments deployed in the ocean starting in 2004 show that the Atlantic Ocean circulation has observably slowed over the past two decades, possibly to its weakest state in almost a millennium. Studies also suggest that the circulation has reached a dangerous tipping point in the past that sent it into a precipitous, unstoppable decline, and that it could hit that tipping point again as the planet warms and glaciers and ice sheets melt.
In a new study using the latest generation of Earth’s climate models, we simulated the flow of fresh water until the ocean circulation reached that tipping point.
The results showed that the circulation could fully shut down within a century of hitting the tipping point, and that it’s headed in that direction. If that happened, average temperatures would drop by several degrees in North America, parts of Asia and Europe, and people would see severe and cascading consequences around the world.
We also discovered a physics-based early warning signal that can alert the world when the Atlantic Ocean circulation is nearing its tipping point.
The ocean’s conveyor belt
Ocean currents are driven by winds, tides and water density differences.
In the Atlantic Ocean circulation, the relatively warm and salty surface water near the equator flows toward Greenland. During its journey it crosses the Caribbean Sea, loops up into the Gulf of Mexico, and then flows along the U.S. East Coast before crossing the Atlantic.
This current, also known as the Gulf Stream, brings heat to Europe. As it flows northward and cools, the water mass becomes heavier. By the time it reaches Greenland, it starts to sink and flow southward. The sinking of water near Greenland pulls water from elsewhere in the Atlantic Ocean and the cycle repeats, like a conveyor belt.
Too much fresh water from melting glaciers and the Greenland ice sheet can dilute the saltiness of the water, preventing it from sinking, and weaken this ocean conveyor belt. A weaker conveyor belt transports less heat northward and also enables less heavy water to reach Greenland, which further weakens the conveyor belt’s strength. Once it reaches the tipping point, it shuts down quickly.
What happens to the climate at the tipping point?
The existence of a tipping point was first noticed in an overly simplified model of the Atlantic Ocean circulation in the early 1960s. Today’s more detailed climate models indicate a continued slowing of the conveyor belt’s strength under climate change. However, an abrupt shutdown of the Atlantic Ocean circulation appeared to be absent in these climate models.
This is where our study comes in. We performed an experiment with a detailed climate model to find the tipping point for an abrupt shutdown by slowly increasing the input of fresh water.
We found that once it reaches the tipping point, the conveyor belt shuts down within 100 years. The heat transport toward the north is strongly reduced, leading to abrupt climate shifts.
The result: Dangerous cold in the North
Regions that are influenced by the Gulf Stream receive substantially less heat when the circulation stops. This cools the North American and European continents by a few degrees.
The European climate is much more influenced by the Gulf Stream than other regions. In our experiment, that meant parts of the continent changed at more than 5 degrees Fahrenheit (3 degrees Celsius) per decade – far faster than today’s global warming of about 0.36 F (0.2 C) per decade. We found that parts of Norway would experience temperature drops of more than 36 F (20 C). On the other hand, regions in the Southern Hemisphere would warm by a few degrees.
These temperature changes develop over about 100 years. That might seem like a long time, but on typical climate time scales, it is abrupt.
The conveyor belt shutting down would also affect sea level and precipitation patterns, which can push other ecosystems closer to their tipping points. For example, the Amazon rainforest is vulnerable to declining precipitation. If its forest ecosystem turned to grassland, the transition would release carbon to the atmosphere and result in the loss of a valuable carbon sink, further accelerating climate change.
The Atlantic circulation has slowed significantly in the distant past. During glacial periods when ice sheets that covered large parts of the planet were melting, the influx of fresh water slowed the Atlantic circulation, triggering huge climate fluctuations.
So, when will we see this tipping point?
The big question – when will the Atlantic circulation reach a tipping point – remains unanswered. Observations don’t go back far enough to provide a clear result. While a recent study suggested that the conveyor belt is rapidly approaching its tipping point, possibly within a few years, these statistical analyses made several assumptions that give rise to uncertainty.
Instead, we were able to develop a physics-based and observable early warning signal involving the salinity transport at the southern boundary of the Atlantic Ocean. Once a threshold is reached, the tipping point is likely to follow in one to four decades.
The climate impacts from our study underline the severity of such an abrupt conveyor belt collapse. The temperature, sea level and precipitation changes will severely affect society, and the climate shifts are unstoppable on human time scales.
It might seem counterintuitive to worry about extreme cold as the planet warms, but if the main Atlantic Ocean circulation shuts down from too much meltwater pouring in, that’s the risk ahead.
This article was updated on Feb. 11, 2024, to fix a typo: The experiment found temperatures in parts of Europe changed by more than 5 F per decade.
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.
Authors:Alaa Al Khourdajie, Imperial College London; Chris Bataille, Columbia University, and Lars J Nilsson, Lund University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
___________________________________________________________________________________
The COP28 climate summit in Dubai has adjourned. The result is “The UAE consensus” on fossil fuels.
This text, agreed upon by delegates from nearly 200 countries, calls for the world to move “away from fossil fuels in energy systems in a just, orderly and equitable manner”. Stronger demands to “phase out” fossil fuels were ultimately unsuccessful.
The agreement also acknowledges the need to phase down “unabated” coal burning and transition towards energy systems consistent with net zero emissions by 2050, while accelerating action in “the critical decade” of the 2020s.
As engineers and scientists who research the necessary changes to pull off this energy system transition, we believe this agreement falls short in addressing the use of fossil fuels at the heart of the climate crisis.
Such an approach is inconsistent with the scientific consensus on the urgency of drastically reducing fossil fuel consumption to limit global warming to 1.5°C.
‘Abated’ v ‘unabated’
The combustion of coal, oil and gas accounts for 75% of all global warming to date – and 90% of CO₂ emissions.
So what does the text actually ask countries to do with these fuels – and what loopholes might they exploit to continue using them well into the future?
Those countries advocating for the ongoing use of fossil fuels made every effort to add the term “unabated” whenever a fossil fuel phase-down or phase-out was proposed during negotiations.
“Abatement” in this context typically means using capture capture and storage technology to stop CO₂ emissions from engines and furnaces reaching the atmosphere.
However, there is no clear definition of what abatement would entail in the text. This ambiguity allows for a broad and and easily abused interpretation of what constitutes “abated” fossil fuel use.
Will capturing 30% or 60% of CO₂ emissions from burning a quantity of coal, oil or gas be sufficient? Or will fossil fuel use only be considered “abated” if 90% or more of these emissions are captured and stored permanently along with low leakage of “fugitive” emissions of the potent greenhouse gas methane, which can escape from oil and gas infrastructure?
This is important. Despite the agreement supposedly honouring “the science” on climate change, low capture rates with high residual and fugitive emissions are inconsistent with what research has shown is necessary to limit global warming to the internationally agreed guardrails of 1.5°C and 2°C above pre-industrial temperatures.
In a 2022 report, the Intergovernmental Panel on Climate Change (IPCC) indicated that almost all coal emissions and 33%-66% of natural gas emissions must be captured to be compatible with the 2015 Paris agreement.
That’s assuming that the world will have substantial means of sucking carbon (at least several billion tonnes a year) from the air in future decades. If these miracle machines fail to materialise, our research indicates that carbon capture would need to be near total on all fuels.
The fact that the distinction between “abated” and “unabated” fossil fuels has not been clarified is a missed opportunity to ensure the effectiveness of the Dubai agreement. This lack of clarity can prolong fossil fuel dependence under the guise of “abated” usage.
This would cause wider harm to the transition by allowing continued investment in fossil fuel infrastructure – new coal plants, for instance, as long as some of the carbon they emit is captured (abated) – thereby diverting resources from more sustainable power sources. This could hobble COP28’s other goal: to triple renewable energy capacity by 2030.
By not explicitly defining these terms, COP28 missed the chance to set a firm, scientifically-backed benchmark for future fossil fuel use.
The coming age of carbon dioxide removal
Since the world is increasingly likely to overshoot the temperature goals of the Paris agreement, we must actively remove more CO₂ from the atmosphere – with reforestation and direct air capture (DAC), among other methods – than is emitted in future.
Some carbon removal technologies, such as DAC, are very early in their development and scaling them up to remove the necessary quantity of CO₂ will be difficult. And this effort should not detract from the urgent need to reduce emissions in the first place. This balanced approach is vital to not only halt but reverse the trajectory of warming, aligning with the ambitious goals of the Paris agreement.
There has only really been one unambiguously successful UN climate summit: Paris 2015, when negotiations for a top-down agreement were ended and the era of collectively and voluntarily raising emissions cuts began.
A common commitment to “phase down and then out” clearly defined unabated fossil fuels was not reached at COP28, but it came close with many parties strongly in favour of it. It would not be surprising if coalitions of like-minded governments proceed with climate clubs to implement it.
Authors:
YanaBu, Shutterstock
Katrin Meissner, UNSW Sydney; Deepashree Dutta, University of Cambridge, and Martin Jucker, UNSW Sydney
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Our planet has warmed by about 1.2°C since 1850. But this warming is not uniform. Warming at the poles, especially the Arctic, has been three to four times faster than the rest of the globe. It’s a phenomenon known as “polar amplification”.
Climate models simulate this effect, but when tested against the past 40 years of warming, these models fall short. The situation is even worse when it comes to modelling past climates with very high levels of greenhouse gases.
This is a problem because these are the same models used to project into the future and forecast how the climate will change. They are likely to underestimate what will happen later this century, including risks such as ice sheet melting or permafrost thawing.
In our new research published today in Nature Geoscience we used a high-resolution model of the atmosphere that includes the stratosphere. We found a special type of cloud appears over polar regions when greenhouse gas concentrations are very high. The role of this type of cloud has been overlooked so far. This is one of the reasons why our models are too cold at the poles.
Polar Stratospheric Clouds over Norway (Night Lights Films – Adrien Mauduit)
Back to the future
Looking into past climates can give us glimpses of possible futures for a range of extreme conditions. For us, this means we can use Earth’s history to find out how well our climate models perform. We can test our models by simulating episodes in the past when Earth was much warmer. The advantage of this is that we have temperature reconstructions for these episodes to evaluate the models, as opposed to the future, for which measurements are not available.
If we go back 50 million years or so, our planet was very hot. Carbon dioxide (CO₂) concentrations ranged between 900 and 1,900 parts per million (ppm), compared with 415 ppm today. Methane (CH₄) concentrations were likely also much higher.
Canada’s arctic archipelago was covered in lush rainforests inhabited by alligators, turtles, lizards and mammals.
For these plants and animals to survive, conditions must have been warm and ice-free year-round. Indeed, surface ocean temperatures exceeded 20°C near the north pole (at about 87°N) and 25°C in the Southern Ocean (at about 67°S).
This period called the early Eocene is a perfect test bed for our models, because it was globally very warm, and the poles were even warmer, meaning it was a climate with extreme polar amplification. In addition, the Eocene is recent enough for temperature reconstructions to be available.
But as it turns out, the models fail again. They are much too cold at high latitudes. What are our models missing?
Polar stratospheric clouds
In 1992 American paleoclimatologist Lisa Sloan suggested polar stratospheric clouds might have caused extreme warming at high latitudes in the past.
These clouds are a rare and beautiful sight today. They are also called nacreous or mother-of-pearl clouds for their vivid and sometimes luminous colours.
They form at very high altitudes (in the stratosphere) and at very low temperatures (over the poles). In the present day climate, they appear mainly over Antarctica, but have also been observed during winter months over Scotland, Scandinavia and Alaska, at times when the stratosphere was particularly cold.
Just like greenhouse gases, they absorb infrared radiation emitted by the Earth’s surface and re-emit a portion of this energy back to the surface. This suggests polar stratospheric clouds could be one of the missing puzzle pieces.
They warm the surface. And their effect could be significant, especially in winter, when the sun does not rise. But they are difficult to simulate in a climate model, so most models ignore them. This omission could explain why climate models miss some of the polar warming, because they miss a process that warms the poles.
Three decades after Sloan’s paper, a few atmosphere models are finally complex enough to allow us to test her hypothesis. In our research we use one of them and find that under certain conditions, the additional warming due to these polar stratospheric clouds exceeds 7°C during the winter months. This significantly reduces the gap between climate models and temperature evidence from the early Eocene. Sloan was right.
Implications for future projections
Our research explains why climate models don’t work so well for past climates when greenhouse gas levels were much higher than they are today. But what about the future? Should we be concerned?
There is some good news. While polar stratospheric clouds do warm the poles, they won’t be as common in the future as they were in the distant past, even if both CO₂ and CH₄ reach very high levels.
This is due to another difference between the Eocene and today: the position of continents and mountains, which were different back then and which also influence the formation of polar stratospheric clouds. So even if we hit early Eocene levels of CH₄ and CO₂ in the future, we would expect less polar stratospheric cloud to be formed. This suggests the standard climate models are better at predicting the future than the past.
It’s therefore unlikely the Arctic and Antarctica will be covered by these beautiful clouds anytime soon. But our research shows evidence from past climates can reveal processes that only become important when greenhouse gas concentrations are high. Some of these processes are not included in our models because models are tested against present day observations and other processes simply seemed more important to include. Looking into the past is a way of broadening our horizon and learning for the future.
Authors: Kaitlin Naughten, Ocean-Ice Modeller, British Antarctic Survey; Jan De Rydt, Associate Professor of Polar Glaciology and Oceanography, Northumbria University, Newcastle, and Paul Holland, Ocean and Ice Scientist, British Antarctic Survey
This article is republished from The Conversation under a Creative Commons license. Read the original article.
The rate at which the warming Southern Ocean melts the West Antarctic ice sheet will speed up rapidly over the course of this century, regardless of how much emissions fall in coming decades, our new research suggests. This ocean-driven melting is expected to increase sea-level rise, with consequences for coastal communities around the world.
The Antarctic ice sheet, the world’s largest volume of land-based ice, is a system of interconnected glaciers comprised of snowfall that remains year-round. Coastal ice shelves are the floating edges of this ice sheet which stabilise the glaciers behind them. The ocean melts these ice shelves from below, and if melting increases and an ice shelf thins, the speed at which these glaciers discharge fresh water into the ocean increases too and sea levels rise.
In West Antarctica, particularly the Amundsen Sea, this process has been underway for decades. Ice shelves are thinning, glaciers are flowing faster towards the ocean and the ice sheet is shrinking. While ocean temperature measurements in this region are limited, modelling suggests it may have warmed as a result of climate change.
We chose to model the Amundsen Sea because it is the most vulnerable sector of the ice sheet. We used a regional ocean model to find out how ice-shelf melting will change here between now and 2100. How much melting can be prevented by reducing carbon emissions and slowing the rate of climate change – and how much is now unavoidable, no matter what we do?
Rapid change is locked in
We used the UK’s national supercomputer ARCHER2 to run many different simulations of the 21st century, totalling over 4,000 years of ocean warming and ice-shelf melting in the Amundsen Sea.
We considered different trajectories for fossil fuel burning, from the best-case scenario where global warming is limited to 1.5°C in line with the Paris Agreement, to the worst, in which coal, oil and gas use is uncontrolled. We also considered the influence of natural variations in the climate, such as the timing of events such as El Niño.
The results are worrying. In all simulations there is a rapid increase over the course of this century in the rate of ocean warming and ice-shelf melting. Even the best-case scenario in which warming halts at 1.5°C, something that is considered ambitious by many experts, entails a threefold increase in the historical rate of warming and melting.
What’s more, there is little to no difference between the scenarios up to 2045. Ocean warming and ice-shelf melting in the 1.5°C scenario is statistically the same as in a mid-range scenario, which is closer to what existing pledges to reduce fossil fuel use over the coming decades would produce.
The worst-case scenario shows more melting than the others, but only from around mid-century onwards, and many experts think this amount of future fossil fuel burning is unrealistic anyway.
The results imply that we are now committed to rapid ocean warming in the Amundsen Sea until at least 2100, regardless of international policies on fossil fuels.
The increases in warming and melting are the result of ocean currents strengthening and driving more warm water from the deep ocean towards the shallower ice shelves along the coast. Other studies have suggested this process is behind the ice shelf thinning measured by satellites.
How much will the sea level rise?
Melting ice shelves are a major cause of sea-level rise, but not the whole story. We can’t put a number on how much sea levels will rise without also simulating the flow of Antarctic glaciers and the rate of snow accumulating on the ice sheet, which our model didn’t include.
But we have every reason to believe that increased ice-shelf melting in this region will cause the rate at which sea levels are rising to speed up.
The West Antarctic ice sheet is already contributing substantially to global sea-level rise and is losing about 80 billion tonnes of ice a year. It contains enough ice to cause up to 5 metres of sea-level rise, but we don’t know how much of it will melt, and how quickly. Our colleagues around the world are working hard to answer this question.
Courage and hope
There are some consequences of climate change that can no longer be avoided, no matter how much fossil fuel use falls. Substantial melting of West Antarctica up to 2100 may now be one of them.
How do you tell a bad news story? The conventional wisdom is that you’re supposed to give people hope: to say that there’s a disaster behind one door, but we can avoid it if only we choose a different one. What do you do when your science tells you that all doors lead to the same disaster?
Kate Marvel, an atmospheric scientist, said that when it comes to climate change, “we need courage, not hope … Courage is the resolve to do well without the assurance of a happy ending”. In this case, courage means shifting our attention to the longer term.
The future will not end in 2100, even if most people reading this will no longer be around. Our simulations of the 1.5°C scenario show ice-shelf melting starting to plateau by the end of the century, suggesting that further changes in the 22nd century and beyond may still be preventable. Reducing sea-level rise after 2100, or even slowing it down, could save many coastal cities.
Courage means accepting the need to adapt, protecting coastal communities where it’s possible to do so, and rebuilding or abandoning them where it’s not. By predicting future sea-level rise in advance, we’ll have time to plan for it – rather than wait until the ocean is on our doorstep.
Kaitlin Naughten, Ocean-Ice Modeller, British Antarctic Survey; Jan De Rydt, Associate Professor of Polar Glaciology and Oceanography, Northumbria University, Newcastle, and Paul Holland, Ocean and Ice Scientist, British Antarctic Survey
This article is republished from The Conversation under a Creative Commons license. Read the original article.
“It’s about opportunities; it’s not about obligations.”
Podcast hosted by: Joelle Gergis, Australian National University and Michael Green, The Conversation
Interviewed: Honorary Professor, The University of Melbourne; Senior Lecturer in Climate Science, Imperial College London, Physics Professor, University of the West Indies, Mona Campus
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Last month the United Nations’ Intergovernmental Panel on Climate Change (IPCC) released its Synthesis Report of the Sixth Assessment Report.
It showed global temperatures are now 1.1℃ above pre-industrial levels. This warming has driven widespread and rapid global changes, including more frequent and intense weather extremes that are now impacting people and ecosystems all over the world.
But when an extreme weather event hits, how certain can we be that it was made more likely by climate change? How do we know it wasn’t just a rare, naturally-occuring event that might have happened anyway?
Fear & Wonder is a new podcast from The Conversation that takes you inside the UN’s era-defining climate report via the hearts and minds of the scientists who wrote it.
The show is hosted by Dr Joëlle Gergis – a climate scientist and IPCC lead author – and award-winning journalist Michael Green.
In this episode, we’re delving into one of the major shifts in the public communication of climate change – the attribution of extreme weather events to climate change.
Although in the past we knew climate change was making extreme weather more likely, advances in climate modelling now allow scientists to pinpoint the influence of natural and human-caused factors on individual weather extremes.
We speak to climatologist Dr Friederike Otto about a rapid attribution study of a heatwave in Toulouse, France, as it unfolded in 2019. We also hear from climatologist Professor David Karoly to help us understand how climate models actually work, while Professor Tannecia Stephenson explains how global models are then used to develop regional climate change projections over the Caribbean island of Jamaica.
To listen and subscribe, click here, or click the icon for your favourite podcast app in the graphic above.
Fear and Wonder is sponsored by the Climate Council, an independent, evidence-based organisation working on climate science, impacts and solutions.
By: 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.
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.
Antarctic sea ice is highly variable, but there has been less ice than normal for almost all of the last seven years. This chart of monthly sea ice extent anomaly shows the difference between the long-term average sea ice and the observed sea ice in each month. By removing the annual cycle due to sea ice formation and melt, we can see the longer term variability underneath, and the extreme low sea ice events in recent years. Dr Phil Reid, BoM, Author provided
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.