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carbon dioxide emissions

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Authors: Andrew King, The University of Melbourne and Liam Cassidy, The University of Melbourne

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

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Under the landmark 2015 Paris Agreement on climate change, humanity is seeking to reduce greenhouse gas emissions and keep planetary heating to no more than 1.5°C above the pre-industrial average. In 2024, temperatures on Earth surpassed that limit.

This was not enough to declare the Paris threshold had been crossed, because the temperature goals under the agreement are measured over several decades, rather than short excursions over the 1.5°C mark.

But the two papers just released use a different measure. Both examined historical climate data to determine whether very hot years in the recent past were a sign that a future, long-term warming threshold would be breached.

The answer, alarmingly, was yes. The researchers say the record-hot 2024 indicates Earth is passing the 1.5°C limit, beyond which scientists predict catastrophic harm to the natural systems that support life on Earth.

2024: the first year of many above 1.5°C

Climate organisations around the world agree last year was the hottest on record. The global average temperature in 2024 was about 1.6°C above the average temperatures in the late-19th century, before humans started burning fossil fuels at large scale.

Earth has also recently experienced individual days and months above the 1.5°C warming mark.

But the global temperature varies from one year to the next. For example, the 2024 temperature spike, while in large part due to climate change, was also driven by a natural El Niño pattern early in the year. That pattern has dissipated for now, and 2025 is forecast to be a little cooler.

These year-to-year fluctuations mean climate scientists don’t view a single year exceeding the 1.5°C mark as a failure to meet the Paris Agreement.

However, the new studies published today in Nature Climate Change suggest even a single month or year at 1.5°C global warming may signify Earth is entering a long-term breach of that vital threshold.

What the studies found

The studies were conducted independently by researchers in Europe and Canada. They tackled the same basic question: is a year above 1.5°C global warming a warning sign that we’re already crossing the Paris Agreement threshold?

Both studies used observations and climate model simulations to address this question, with slightly different approaches.

In the European paper, the researchers looked at historical warming trends. They found when Earth’s average temperature reached a certain threshold, the following 20-year period also reached that threshold.

This pattern suggests that, given Earth reached 1.5°C warming last year, we may have entered a 20-year warming period when average temperatures will also reach 1.5°C.

The Canadian paper involved month-to-month data. June last year was the 12th consecutive month of temperatures above the 1.5°C warming level. The researcher found 12 consecutive months above a climate threshold indicates the threshold will be reached over the long term.

Both studies also demonstrate that even if stringent emissions reduction begins now, Earth is still likely to be crossing the 1.5°C threshold.

Heading in the wrong direction

Given these findings, what humanity does next is crucial.

For decades, climate scientists have warned burning fossil fuels for energy releases carbon dioxide and other gases that are warming the planet.

But humanity’s greenhouse gas emissions have continued to increase. Since the Intergovernmental Panel on Climate Change released its first report in 1990, the world’s annual carbon dioxide emissions have risen about 50%.

Put simply, we are not even moving in the right direction, let alone at the required pace.

The science shows greenhouse gas emissions must reach net-zero to end global warming. Even then, some aspects of the climate will continue to change for many centuries, because some regional warming, especially in the oceans, is already locked in and irreversible.

If Earth has indeed already crossed the 1.5°C mark, and humanity wants to get below the threshold again, we will need to cool the planet by reaching “net-negative emissions” – removing more greenhouse gases from the atmosphere than we emit. This would be a highly challenging task.

Feeling the heat

The damaging effects of climate change are already being felt across the globe. The harm will be even worse for future generations.

Australia has already experienced 1.5°C of warming, on average, since 1910.

Our unique ecosystems, such as the Great Barrier Reef, are already suffering because of this warming. Our oceans are hotter and seas are rising, hammering our coastlines and threatening marine life.

Bushfires and extreme weather, especially heatwaves, are becoming more frequent and severe. This puts pressure on nature, society and our economy.

But amid the gloom, there are signs of progress.

Across the world, renewable electricity generation is growing. Fossil fuel use has dropped in many countries. Technological developments are slowing emissions growth in polluting industries such as aviation and construction.

But clearly, there is much more work to be done.

Humanity can turn the tide

These studies are a sobering reminder of how far short humanity is falling in tackling climate change.

They show we must urgently adapt to further global warming. Among the suite of changes needed, richer nations must support the poorer countries set to bear the most severe climate harms. While some progress has been made in this regard, far more is needed.

A major shift is also needed to decarbonise our societies and economies. There is still room for hope, but we must not delay action. Otherwise, humanity will keep warming the planet and causing further damage.The Conversation

Andrew King, Associate Professor in Climate Science, ARC Centre of Excellence for 21st Century Weather, The University of Melbourne and Liam Cassidy, PhD Candidate, The University of Melbourne

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

Global annual average temperatures 2024.

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Author: Robert McLachlan, Te Kunenga ki Pūrehuroa – Massey University

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


It’s now official. Last year was the warmest year on record globally and the first to exceed 1.5°C above pre-industrial levels. This doesn’t mean it’s too late to rein in further warming, but the ambition required rises with each delay in action.

New Zealand is no exception. Current climate policies are no longer a sufficient contribution to the global effort to keep warming at 1.5°C, according to the Climate Change Commission’s first review of the country’s 2050 climate target.

New Zealand’s current 2050 target has two components. Methane emissions from livestock must be cut by 24% to 47% below 2017 levels and emissions of all other greenhouse gases must reach net zero. But the commission has made three main recommendations to raise ambition:

  • a net negative target for emissions of long-lived gases (carbon dioxide and nitrous oxide) by removing 20 million tonnes more from the atmosphere than is released each year

  • a higher target range for biogenic methane emissions to reach at least 35% to 47% below 2017 levels

  • and the inclusion of emissions from international shipping and aviation.

The commission says these changes would bring New Zealand closer to “net zero for all gases”, in line with what is needed to achieve the goals of the Paris Agreement.

The 2050 target review was the last effort for the commission’s outgoing founding chair, Rod Carr, who has become a significant voice for climate action. In his closing words to parliament, he said:

Those who continue to promote the combustion of fossil fuels in the open air without permanent carbon capture and storage are, in my view, committing a crime against humanity.

New Zealand lags behind other countries

The 2050 target is a critical component of New Zealand’s climate response. Under the 2019 Climate Change Response (Zero Carbon) Amendment Act, the commission is charged with reviewing the 2050 target every five years.

The threshold for recommending a change is high. The commission must consider nine key areas and find “significant” developments that justify recommending a different target.

It found three significant changes occurred since the current target was set in 2019.

1. Global action is ahead of New Zealand

While other countries’ current policies, pledges or targets are not sufficient to keep temperature rise at 1.5°C, many countries now have more ambitious targets than New Zealand.

Australia, Japan, US, Canada, EU and Ireland all adopted full net-zero targets in 2021. Finland and Germany have or are considering net negative targets. Among countries with high biogenic methane emissions, several now have full net-zero targets.

2. Scientific understanding of climate change has changed

Climate impacts are appearing sooner and with more severity than the scientific community understood when the target was set in 2019.

3. The burden shifts to future generations

The increased risks and impacts of climate change have implications for inter-generational equity. Delaying action shifts costs and risks to future generations.

The commission’s report also explores New Zealand’s reliance on large-scale commercial exotic afforestation to meet its climate targets. This is one reason why Climate Action Tracker rates New Zealand’s response as highly insufficient and commensurate with a 4°C world.

Carbon in trees is part of the biosphere and will never be stored as permanently as fossil carbon. To take a case in point, Cyclone Gabrielle in 2023 (made worse by climate change) damaged forests, farms and infrastructure, and removed the social licence for forestry in the region.

How the recommended target was set

The commission’s work is tightly prescribed by law. It looked at four possible ways of sharing the global 1.5°C task: equal per capita emissions, national capacity, responsibility for historic warming and the right of all peoples to sustainable development.

New Zealand’s current target does not meet any of these standards, but the commission says the new target would at least meet the “national capacity” criterion and would be feasible and acceptable. However, it would still see New Zealand contributing two to three times its share of global warming this century.

The commission’s assessment is independent of any global warming metrics such as GWP100 (currently the UN standard). Instead, the commission computed New Zealand’s historical and future contribution to temperature rise directly. Both commonly used historical baselines, 1850 and 1990, yield similar results.

New Zealand’s government is currently particularly at odds with the commission’s recommendation on biogenic methane. It appointed a separate advisory panel last year which put forward a target consistent with causing “no additional warming” to the planet from agricultural methane emissions.

This graph shows the warming from emissions from New Zealand (1850–2100) under the current 2050 target and share of 1.5°C warming from 2024.
This graph shows the contribution to warming from emissions in New Zealand (1850–2100) under the current 2050 target. Climate Change Commission, CC BY-SA

But the commission rejects this idea, finding that unless the rest of New Zealand’s target were to be strengthened significantly, this would not be consistent with the Paris Agreement or the country’s own climate law.

International aviation and shipping emissions

In a quirk of climate diplomacy, international aviation and shipping emissions were excluded from the original 2050 target. But as the commission points out, they most definitely contribute to global warming and are covered by the temperature target of the Paris Agreement.

Other countries are moving in these areas and the International Civil Aviation and maritime organisations have net zero 2050 goals in place. Air New Zealand and the global shipping giant Maersk both support including these emissions in the 2050 target, which the commission finds to be achievable under multiple different pathways.

New Zealand’s dependence on shipping and air transport is a challenge. The commission puts the combined emissions from these sectors at 6.7 megatonnes – 20% of total CO₂ emissions and close to all industrial or all passenger car emissions. The aviation industry in particular is planning for growth, which, unless addressed, will blow the 1.5°C carbon budget both for New Zealand and globally.

Drawing on “net zero pathways” prepared by the international aviation and shipping industries, the commission finds that including these sources in New Zealand’s revised 2050 target would be achievable. The sectors would not necessarily have to enter the Emissions Trading Scheme, but the status quo (under which these sectors do not attract GST, fuel tax or a carbon charge) is inequitable with other sources of economic activity.

The author acknowledges the assistance and contribution by Paul Callister.The Conversation

Robert McLachlan, Professor in Applied Mathematics, Te Kunenga ki Pūrehuroa – Massey University

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

wildfire

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Author: Harry Shepherd, Postdoctoral Research Associate, King’s College London

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

Non-native species appear to be better able to resist extreme weather, threatening native plants and animals and potentially creating more favourable conditions for invasive species under climate change. That’s the conclusion of a new study in the scientific journal Nature Ecology and Evolution.

Wildfires, droughts, heavy rainfall and storms are all increasing, and predicted to become more frequent throughout the next century due to human-driven climate change.

At the same time, humans are transporting more species into new areas, despite concerted global efforts to increase biosecurity across borders and to target the eradication of specific species. Some of these non-native species can go on to become invasive, damaging native ecosystems.

Capitalising on opportunities

Invasive species introduced by humans often possess traits that help them survive or even thrive when ecosystems are disturbed (perhaps by wildfire, a storm or human buildings).

Invasive plants are generally fast-growing, for instance, allowing them to quickly fill gaps before native species can recover from disturbances. They are also often very good at dispersing their seeds, allowing them to quickly colonise disturbed areas.

This is why scientists have long suspected that extreme weather and the success of non-native species could be linked.

If extreme weather removes native plants and animals, that increases the availability of resources such as water and space. Non-native species can then capitalise on these new resources to establish themselves.

Even more concerning is the potential for extreme weather and non-native species to interact, exacerbating their effect on native biodiversity. For instance, in a recent field experiment in the US, scientists deliberately started a fire which killed about 10% of the longleaf pine trees in the area studied.

But in areas where an invasive grass – cogongrass, an Asian native – was allowed to establish itself alongside the pines, the fires had more fuel and were larger, hotter and burned for longer.

Where the scientists had added rain shelters to simulate drought conditions, the grass dried out further and the fires became much more lethal. A combination of drought and the invasive species meant longleaf pine mortality soared to 44%.

Similarly, on the small Macquarie Island in the south west Pacific, a combination of extreme rainfall and the presence of invasive European rabbits reduced the breeding success of nesting black-browed albatrosses. Heavy grazing by the invasive rabbits reduced plant cover, exposing the albatross chicks to the harsh weather conditions.

Penguins on grassy surface, sea in background
Macquarie’s grass makes excellent bird nests – and rabbit food. BMJ / shutterstock


This relationship between extreme weather and invasive species – two human-driven drivers of global change – threatens native plants and animals and could cost countries billions of dollars in coming decades. Ecologists must identify priority areas and species that can be targeted in efforts to minimise costs and prevent the loss of native biodiversity.

Bad weather, good for non-natives

To better understand how native and non-native species respond to extreme weather events, the scientists behind the new study reanalysed information from 443 peer-reviewed studies on how species responded to wildfires, droughts and storms. In all, they gathered data on 187 non-native species and 1,852 native species from all major animal groups.

Their results suggest that native and non-native species may indeed respond differently to extreme weather. Across all studies, a total of 24.8% of non-native species benefited from extreme weather events compared to only 12.7% of native species.

'attention invasive plant' sign
Japanese knotweed is an invasive species in much of Europe and North America. Like many invasive plants, it grows quickly and can handle extreme weather. Leon_Brouwer / shutterstock

For example, while native species in both freshwater and land-based ecosystems were harmed by droughts, their non-native counterparts showed no significant response. Notably, marine ecosystems were comparatively more resistant to extreme weather events, with fewer differences between native and non-native species.

The authors did find marine heatwaves harmed native coral species, however, a relationship that has been documented in other scientific studies.

Identifying global hotspots

The authors took this information and combined it with known global hotspots of extreme weather, to identify areas where native species may be particularly vulnerable to the combination of extreme weather and invasive species.

They found high latitude areas such as northern US and Europe, for instance, are both vulnerable to extreme cold spells and possess non-native species that benefit from cold spells. Alternatively, areas of the western Amazon in Brazil and east Asia were identified as vulnerable to flooding and possessing flood-resistant non-native species.

In these regions, non-native species could benefit from increasing cold spells or flooding respectively, posing a greater threat to native plants and animals.

Studies like this are very useful. Regions that are identified as vulnerable can be targeted with early preventative measures to stop the spread of invasive species, or with measures to help native biodiversity cope with climate change.

This research could also allow targeted restoration to remove non-native species and produce invasion-resistant native communities that could better withstand future conditions. This is what happened on Macquarie Island, where invasive rabbits and rats were eventually eliminated and the whole ecosystem soon bounced back.

Such action could be critical as we adapt to a changing climate and a greater mixing of the world’s plants and animals.

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

dairy cows are methane producing machines

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Authors: Milena Bojovic, PhD Candidate, Macquarie University


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

Milena Bojovic, Macquarie University

New Zealand’s dairy sector faces an uncertain future due to several challenges, including water pollution, high emissions, animal welfare concerns and market volatility.

All of these issues are building tensions and changing public perceptions of dairy farming.

In my new research, I argue the time has come for the dairy sector to adopt a “just transition” framework to achieve a fair and more sustainable food future and to navigate the disruptions from alternative protein industries.

The concept of a just transition is typically applied to the energy sector in shifting from fossil fuels to renewable energy sources.

But a growing body of research and advocacy is calling for the same principles to be applied to food systems, especially for shifting away from intensive animal agriculture.

Aotearoa New Zealand’s dairy sector is an exemplary case study for examining the possibilities of a just transition because it is so interconnected in the global production and trade of dairy, with 95% of domestic milk production exported as whole-milk powder to more than 130 countries.

Environmental and economic challenges

New Zealand’s dairy sector faces significant threats. This includes environmental challenges such as alarming levels of nitrate pollution in waterways caused by intensive agriculture.

The sector is also a major source of emissions of biogenic methane from the burps of almost six million cows in the national dairy herd.

Debates about how to account for these emissions have gone on for many years in New Zealand. But last month, the coalition government passed legislation to keep agriculture out of the Emissions Trading Scheme.

This means livestock farmers, agricultural processors, fertiliser importers and manufacturers won’t have to pay for on-farm emissions. Instead, the government intends to implement a pricing system outside the Emissions Trading Scheme by 2030. To meet emissions targets, it relies on the development of technologies such as methane inhibitors.

A cheese board with soem bread and a cheese made from cashews
The development of plant-based and fermentation proteins poses another threat to the dairy sector. Getty Images

In addition to environmental challenges, global growth and domestic initiatives in the development of alternative dairy products are changing the future of milk production and consumption.

New Zealand dairy giant Fonterra is pursuing the growth of alternative dairy with significant investments in a partnership with Dutch multinational corporation Royal-DSM. This supports precision fermentation start-up Vivici, which already has market-ready products such as whey protein powder and protein water.

Fonterra’s annual report states it anticipates a rise in customer preference towards dairy alternatives (plant-based or precision-fermentation dairy) due to climate-related concerns. The company says these shifting preferences could pose significant business risks for future dairy production if sustainability expectations cannot be met.

Pathways to a just transition for dairy

What happens when one the pillars of the economy becomes a major contributor to environmental degradation and undermines its own sustainability? Nitrate pollution and methane emissions threaten the quality of the land and waterways the dairy sector depends on.

In my recent study which draws on interviews with people across New Zealand’s dairy sector, three key transition pathways are identified, which address future challenges and opportunities.

  • Deintensification: reducing the number of dairy cows per farm.

  • Diversification: introducing a broader range of farming practices, landuse options and market opportunities.

  • Dairy alternatives: government and industry support to help farmers participate in emerging plant-based and precision-fermentation industries.

While the pathways are not mutually exclusive, they highlight the socioeconomic and environmental implications of rural change which require active participation and engagement between the farming community and policy makers.

The Ministry of Business, Innovation and Employment recently published a guide to just transitions. It maps out general principles such as social justice and job security.

But the guide is light on advice for agricultural transitions. My work puts forward recommendations to shape future policy for a more just and sustainable dairy future. This includes issues such as navigating intensification pressures, supporting the development of alternative proteins and fundamentally supporting farmer agency in the transition process.

For the dairy transition to be fair and sustainable, we need buy-in from leadership and support from government, the dairy sector and the emerging alternative dairy industry to help primary producers and rural communities. This needs to be specific to different regions and farming methods.

The future of New Zealand’s dairy industry depends on its ability to adapt. Climate adaptation demands balancing social license, sustainable practices and disruptions from novel protein technologies.The Conversation

Milena Bojovic, PhD Candidate, Macquarie University

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

carbon dioxide emissions

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

Polar stratospheric clouds: Night Lights Films - Adrien Mauduit

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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.

Antarctica image: James Eades

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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.

Climate change event attribution - wildfire: image Mike Newbry

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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, Tannecia Stephenson 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.The Conversation

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By: Matthew England, Scientia Professor and Deputy Director of the ARC Australian Centre for Excellence in Antarctic Science (ACEAS), UNSW Sydney; Adele Morrison Research Fellow, Australian National University; Andy Hogg Professor, Australian National University; Qian Li Massachusetts Institute of Technology (MIT); Steve Rintoul CSIRO Fellow, CSIRO.

 Republished in full from The Conversation under a Creative Commons license. See the original article: March 3, 2023

Off the coast of Antarctica, trillions of tonnes of cold salty water sink to great depths. As the water sinks, it drives the deepest flows of the “overturning” circulation – a network of strong currents spanning the world’s oceans. The overturning circulation carries heat, carbon, oxygen and nutrients around the globe, and fundamentally influences climate, sea level and the productivity of marine ecosystems.

But there are worrying signs these currents are slowing down. They may even collapse. If this happens, it would deprive the deep ocean of oxygen, limit the return of nutrients back to the sea surface, and potentially cause further melt back of ice as water near the ice shelves warms in response. There would be major global ramifications for ocean ecosystems, climate, and sea-level rise.

Conveyer overturning schematic showing the pathways of flow in the upper, deep and bottom layers of the ocean.

Our new research, published today in the journal Nature, uses new ocean model projections to look at changes in the deep ocean out to the year 2050. Our projections show a slowing of the Antarctic overturning circulation and deep ocean warming over the next few decades. Physical measurements confirm these changes are already well underway.

Climate change is to blame. As Antarctica melts, more freshwater flows into the oceans. This disrupts the sinking of cold, salty, oxygen-rich water to the bottom of the ocean. From there this water normally spreads northwards to ventilate the far reaches of the deep Indian, Pacific and Atlantic Oceans. But that could all come to an end soon. In our lifetimes.

The authors explain the results of their landmark paper: Is the Southern Ocean about to have its own ‘Day After Tomorrow’ moment? Fact-checked by experts, the video explains how these changes would profoundly alter the ocean’s overturning of heat, freshwater, oxygen, carbon and nutrients, with impacts felt throughout the global ocean for centuries to come.

Why does this matter?

As part of this overturning, about 250 trillion tonnes of icy cold Antarctic surface water sinks to the ocean abyss each year. The sinking near Antarctica is balanced by upwelling at other latitudes. The resulting overturning circulation carries oxygen to the deep ocean and eventually returns nutrients to the sea surface, where they are available to support marine life.

If the Antarctic overturning slows down, nutrient-rich seawater will build up on the seafloor, five kilometres below the surface. These nutrients will be lost to marine ecosystems at or near the surface, damaging fisheries.

Changes in the overturning circulation could also mean more heat gets to the ice, particularly around West Antarctica, the area with the greatest rate of ice mass loss over the past few decades. This would accelerate global sea-level rise.

An overturning slowdown would also reduce the ocean’s ability to take up carbon dioxide, leaving more greenhouse gas emissions in the atmosphere. And more greenhouse gases means more warming, making matters worse.

Meltwater-induced weakening of the Antarctic overturning circulation could also shift tropical rainfall bands around a thousand kilometres to the north.

Put simply, a slowing or collapse of the overturning circulation would change our climate and marine environment in profound and potentially irreversible ways.

Signs of worrying change

The remote reaches of the oceans that surround Antarctica are some of the toughest regions to plan and undertake field campaigns. Voyages are long, weather can be brutal, and sea ice limits access for much of the year.

This means there are few measurements to track how the Antarctic margin is changing. But where sufficient data exist, we can see clear signs of increased transport of warm waters toward Antarctica, which in turn causes ice melt at key locations.

Indeed, the signs of melting around the edges of Antarctica are very clear, with increasingly large volumes of freshwater flowing into the ocean and making nearby waters less salty and therefore less dense. And that’s all that’s needed to slow the overturning circulation. Denser water sinks, lighter water does not.

How did we find this out?

Apart from sparse measurements, incomplete models have limited our understanding of ocean circulation around Antarctica.

For example, the latest set of global coupled model projections analysed by the Intergovernmental Panel on Climate Change exhibit biases in the region. This limits the ability of these models in projecting the future fate of the Antarctic overturning circulation.

To explore future changes, we took a high resolution global ocean model that realistically represents the formation and sinking of dense water near Antarctica.

We ran three different experiments, one where conditions remained unchanged from the 1990s; a second forced by projected changes in temperature and wind; and a third run also including projected changes in meltwater from Antarctica and Greenland.

In this way we could separate the effects of changes in winds and warming, from changes due to ice melt.

The findings were striking. The model projects the overturning circulation around Antarctica will slow by more than 40% over the next three decades, driven almost entirely by pulses of meltwater.

Abyssal ocean warming driven by Antarctic overturning slowdown, Credit: Matthew England and Qian Li.

Over the same period, our modelling also predicts a 20% weakening of the famous North Atlantic overturning circulation which keeps Europe’s climate mild. Both changes would dramatically reduce the renewal and overturning of the ocean interior.

We’ve long known the North Atlantic overturning currents are vulnerable, with observations suggesting a slowdown is already well underway, and projections of a tipping point coming soon. Our results suggest Antarctica looks poised to match its northern hemisphere counterpart – and then some.

What next?

Much of the abyssal ocean has warmed in recent decades, with the most rapid trends detected near Antarctica, in a pattern very similar to our model simulations.

Our projections extend out only to 2050. Beyond 2050, in the absence of strong emissions reductions, the climate will continue to warm and the ice sheets will continue to melt. If so, we anticipate the Southern Ocean overturning will continue to slow to the end of the century and beyond.

The projected slowdown of Antarctic overturning is a direct response to input of freshwater from melting ice. Meltwater flows are directly linked to how much the planet warms, which in turn depends on the greenhouse gases we emit.

Our study shows continuing ice melt will not only raise sea-levels, but also change the massive overturning circulation currents which can drive further ice melt and hence more sea level rise, and damage climate and ecosystems worldwide. It’s yet another reason to address the
climate crisis – and fast.

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