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El Niño August 2026

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This article is republished from The Conversation under a Creative Commons license. Read the original article.
Mandy Freund, The University of Melbourne

The United Nations has made the grim prediction that our planet now sits in the “danger zone” of extreme weather. That’s based on data suggesting the current El Niño will break all previous records.

El Niño is a naturally occurring weather phenomenon that drives variations in temperature and winds across the Pacific Ocean and influences weather around the globe.

Globally, we have endured many strong El Niños in the past, but none have been as exceptionally strong and developed as quick as this one.

So what’s behind this potentially record-breaking El Niño? And how might it affect weather across the globe?

An exceptional El Niño

Scientists track El Niño activity using temperature data from the tropical Pacific Ocean near the equator. Historically, this involved measuring how high or low temperatures were across this region.

However, scientists and weather organisations – including Australia’s Bureau of Meteorology – now use a relative index. Instead of simply measuring temperatures, this relative index accounts for any background warming due to climate change. This makes it much easier for scientists to identify how intense an El Niño is in a warming climate.

The current El Niño stands out for two main reasons.

Extra early

El Niño typically peaks in the period between November and January, but this one is already unusually warm this early in the season and is yet to peak during summer.

Extra hot

Recent data shows the relative index for August were 2.3°C above average, stronger compared to other El Niño years. In Australia, El Niño years tend to coincide with hotter and drier conditions. However, every El Niño is different and can lead to different impacts. However, this El Niño will lead to record breaking global temperatures in 2027.

How is it affecting the world’s weather?

This historic El Niño is already altering weather around the globe.

We see its most direct and severe impacts in countries surrounding the Pacific Ocean. Indonesia, for example, just this month was battling massive wildfires. Scientists understand the current El Niño is a major driver of these increasingly fierce blazes.

El Niño is also reshaping how and where cyclones form. Satellite pictures reveal there are currently four active tropical cyclones in the Pacific, from near Japan to as far away as Hawaii. This is extremely unusual. El Niño typically boosts cyclone activity in the eastern and central Pacific by carrying warmer water to those regions. Usually we only see one or two such cyclones.

In Australia, we are slightly more removed from the effects of El Niño. However, we can expect to feel its presence more strongly as we head into spring.

The Bureau of Meteorology’s seasonal forecast suggests Australia has so far had a textbook response to El Niño. Temperatures are rising – up to an unseasonable 37°C this week in parts of northern Australia – and conditions are getting drier. Much of eastern and central Australia can expect an unusually dry spring and summer, potentially heightening bushfire risk.

However, a record-breaking El Niño will not necesssarily trigger catastrophic bushfires in Australia. Consider three of the last strong El Niño we’ve experienced. In 1982, a robust El Niño coincided with drought-like conditions. In contrast, during the El Niño years of 1997–98 and 2015–16, some parts of Australia received drenching rain while other regions barely registered any moisture.

What may lie ahead

The intensifying El Niño will likely exacerbate the consequences of climate change.

As El Niño strengthens, countries around the world will be forced to grapple with increasingly extreme weather. Tragically, the most disadvantaged will be the hardest hit, with nearly 50 million people in vulnerable communities likely to be pushed into acute hunger. Farmers across the globe face more unpredictable weather, from crop-destroying floods in South America to severe drought in parts of Africa.

To protect the world’s people and ecosystems, governments must invest in robust research. We urgently need more modelling capability to identify which regions will be worst affected by the strengthening El Niño. This is particularly true for Australia, where a lack of understanding of how climate change on top of a strong El Niño will affect local conditions.

This record-shattering El Niño is already compounding the destructive effects of climate change. But it may be just the catalyst we need to finally abandon fossil fuels and curb our world-warming emissions.

Our lives in your hands Paddy O'Sullivan Unsplash

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Top image: Paddy O’Sullivan Unsplash

Authors: Sarah Perkins-Kirkpatrick, Deputy Director, Engagement and Impact, The ARC Centre of Excellence for the Weather of the 21st Century, Australian National University; Andrew King, ARC Future Fellow and Associate Professor in Climate Science, ARC Centre of Excellence for 21st Century Weather, The University of Melbourne; Nicola Maher, DECRA/Research Fellow, Climate Science, Australian National University, and Wesley Morgan, Research Associate, Institute for Climate Risk and Response, UNSW Sydney

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

Global warming from Woodside’s massive Scarborough gas project off Western Australia would lead to 484 additional heat-related deaths in Europe alone this century, and kill about 16 million additional corals on the Great Barrier Reef during each future mass bleaching event, our new research has revealed.

The findings were made possible by a robust, well-established formula that can determine the extent to which an individual fossil fuel project will warm the planet. The results can be used to calculate the subsequent harms to society and nature.

The results close a fundamental gap between science and decision-making about fossil fuel projects. They also challenge claims by proponents that climate risks posed by a fossil fuel project are negligible or cannot be quantified.

Each new investment in coal and gas, such as the Scarborough project, can now be linked to harmful effects both today and in the future. It means decision-makers can properly assess the range of risks a project poses to humanity and the planet, before deciding if it should proceed.


Every tonne of CO₂ matters

Scientists know every tonne of carbon dioxide (CO₂) emissions makes global warming worse.

But proponents of new fossil fuel projects in Australia routinely say their future greenhouse gas emissions are negligible compared to the scale of global emissions, or say the effects of these emissions on global warming can’t be measured.

The Scarborough project is approved for development and is expected to produce gas from next year. Located off WA, it includes wells connected by a 430km pipeline to an onshore processing facility. The gas will be liquefied and burned for energy, both in Australia and overseas. Production is expected to last more than 30 years. When natural gas is burned, more than 99% of it converts to CO₂.

Woodside – in its own evaluation of the Scarborough gas project – claimed:

it is not possible to link GHG [greenhouse gas] emissions from Scarborough with climate change or any particular climate-related impacts given the estimated […] emissions associated with Scarborough are negligible in the context of existing and future predicted global GHG concentrations.

But what if there was a way to measure the harms? That’s the question our research set out to answer.

A method already exists to directly link global emissions to the climate warming they cause. It uses scientific understanding of Earth’s systems, direct observations and climate model simulations.

According to the IPCC, every 1,000 billion tonnes of CO₂ emissions causes about 0.45°C of additional global warming. This arithmetic forms the basis for calculating how much more CO₂ humanity can emit to keep warming within the Paris Agreement goals.

But decisions about future emissions are not made at the global scale. Instead, Earth’s climate trajectory will be determined by the aggregation of decisions on many individual projects.

That’s why our research extended the IPCC method to the level of individual projects – an approach that we illustrate using the Scarborough gas project.


Scarborough’s harms laid bare

Over its lifetime, the Scarborough project is expected to emit 876 million tonnes of CO₂.

We estimate these emissions will cause 0.00039°C of additional global warming. Estimates such as these are typically expressed as a range, alongside a measure of confidence in the projection. In this case, there is a 66–100% likelihood that the Scarborough project will cause additional global warming of between 0.00024°C and 0.00055°C.

This additional warming might seem small – but it will cause tangible damage.

The human cost of global warming can be quantified by considering how many people will be left outside the “human climate niche” – in other words, the climate conditions in which societies have historically thrived.

We calculated that the additional warming from the Scarborough project will expose 516,000 people globally to a local climate that’s beyond the hot extreme of the human climate niche. We drilled down into specific impacts in Europe, where suitable health data was available across 854 cities. Our best estimate is that this project would cause an additional 484 heat-related deaths in Europe by the end of this century.

Richard Vanlerberghe Unsplash


















The project would cause an additional 484 heat-related deaths in Europe by the end of this century.
Richard Vanlerberghe/Unsplash

And what about harm to nature? Using research into how accumulated exposure to heat affects coral reefs, we found about 16 million corals on the Great Barrier Reef would be lost in each new mass bleaching. The existential threat to the Great Barrier Reef from human-caused global warming is already being realised. Additional warming instigated by new fossil fuel projects will ratchet up pressure on this natural wonder.

Some 16 million corals on the Great Barrier Reef would be lost in each new mass bleaching. Naja Bertolt Jensen/Unsplash

As climate change worsens, countries are seeking to slash emissions to meet their commitments under the Paris Agreement. So, we looked at the impact of Scarborough’s emissions on Australia’s climate targets.

We calculated that by 2049, the anticipated emissions from the Scarborough project alone – from production, processing and domestic use – will comprise 49% of Australia’s entire annual CO₂ emissions budget under our commitment to net-zero by 2050.

Beyond the 2050 deadline, all emissions from the Scarborough project would require technologies to permanently remove CO₂ from the atmosphere. Achieving that would require a massive scale-up of current technologies. It would be more prudent to reduce greenhouse gas emissions where possible.


‘Negligible’ impacts? Hardly

Our findings mean the best-available scientific evidence can now be used by companies, governments and regulators when deciding if a fossil fuel project will proceed.

Crucially, it is no longer defensible for companies proposing new or extended fossil fuel projects to claim the climate harms will be negligible. Our research shows the harms are, in fact, tangible and quantifiable – and no project is too small to matter.

In response to issues raised in this article, a spokesperson for Woodside said:

Woodside is committed to playing a role in the energy transition. The Scarborough reservoir contains less than 0.1% carbon dioxide. Combined with processing design efficiencies at the offshore floating production unit and onshore Pluto Train 2, the project is expected to be one of the lowest carbon intensity sources of LNG delivered into north Asian markets.

We will reduce the Scarborough Energy Project’s direct greenhouse gas emissions to as low as reasonably practicable by incorporating energy efficiency measures in design and operations. Further information on how this is being achieved is included in the Scarborough Offshore Project Proposal, sections 4.5.4.1 and 7.1.3 and in approved Australian Government environment plans, available on the regulator’s website.

A report prepared by consultancy ACIL Allen has found that Woodside’s Scarborough Energy Project is expected to generate an estimated A$52.8 billion in taxation and royalty payments, boost GDP by billions of dollars between 2024 and 2056 and employ 3,200 people during peak construction in Western Australia.The Conversation

Event attribution: Cyclone Gabrielle

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Top image: NASA/Cyclone Gabrielle  Aotearoa New Zealand March 2023

New high-resolution modelling predicts that rainfall from tropical cyclones will significantly increase under global warming. Earth Sciences New Zealand and the University of Waikato found that, under a high emissions scenario, extreme rainfall from cyclones could rise by up to 35% across the southwest Pacific, including for ex-tropical cyclones impacting Aotearoa New Zealand.  
 
Researchers used the latest climate change projections released last year by Earth Sciences NZ (then NIWA) with the Ministry for the Environment.  Study lead and climate scientist Dr Peter Gibson says they simulated more than 1,800 years of data from different climate models and levels of greenhouse gas emissions.   
“We wanted to assess how the frequency and severity of tropical cyclones in the southwest Pacific may change by the end of the century. Under the full range of climate scenarios examined there was an increase in tropical cyclone rainfall. This was proportional to the rate of emissions, with the most pronounced rise in extreme rainfall occurring under the highest emissions.

“If that scenario plays out, we can expect around 30 – 35% more extreme rainfall during tropical cyclones than we experience today. Even under the best-case scenario, we will still see an increase proportional to the warming experienced. Extreme windspeeds are also likely to increase, but not to the same extent.”

The more greenhouse gases that are emitted, the higher temperatures get, with a high emissions scenario representing around a 3°C increase by the end of the century. A warmer atmosphere holds more water, so when storms develop, they have access to more water vapour that can be released as heavier rainfall.

And while the model simulations didn’t show an overall increase in the total number of cyclones by the end of the century, there is compelling evidence that the strongest (category 4 and above) will become more frequent.

“One or two ex-tropical cyclones typically effect New Zealand each year. However, it’s the really big, much rarer events that cause the most damage. And the difference between a river flooding or not can often be small, so any increase in rainfall is significant and potentially very impactful.

The February 2023 Cyclone Gabrielle [top image], which at its peak reached category 3, and the Auckland Anniversary weekend event, resulted in total estimated costs of $14.5 billion, with the total insured losses for both events totalling $3.8 billion, with $1.8 billion from Cyclone Gabrielle claims, and $2 billion from the Auckland anniversary weekend event. Most the claims were because of widespread flooding.
 
Until now, most projections of tropical cyclones have relied on global climate models, which have a relatively low spatial resolution. This work refines those models to a regional scale that can zoom in closer and get a much more accurate picture. 

“The eye of a cyclone is fairly compact, at only tens of kilometres across. Global climate models are coarse, with each pixel going down to around 100km, meaning they miss much of the crucial detail and small-scale physics of a storm. Our refined regional model goes down to around a 12km resolution, making it a state-of-the-art dataset for assessing ex-tropical cyclones that impact New Zealand.”

These findings, published in the Journal of Geophysical Research: Atmospheres, are consistent with other studies around the world, highlighting the potential for more intense tropical cyclones and heavier rainfall in the future, said Dr Gibson. This indicates increasing risks for vulnerable communities across the southwest Pacific and New Zealand. 

“It’s clear that if we reduce emissions, we reduce warming, and we mitigate the worst impacts of severe weather events. As computing capabilities improve, newer, high-resolution models will become available to create even more accurate and reliable long term climate projections of cyclones and their impacts. More research is being undertaken by Earth Sciences NZ into specific weather and climate hazards in the projections, to provide clarity on the future climate New Zealanders are likely to face in the decades to come.”

Denman Glacier Pete Harmsen AAD

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

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

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

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

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

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

What we did and what we found

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

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

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

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

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

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

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

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

1. Ocean warming is compounding

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

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

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

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

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

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


2. More icebergs are forming

Sea ice protects Antarctica’s coast from ocean waves.

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

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

3. Wildlife squeezed off the ice

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

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

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

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

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


4. Logistical challenges at the end of the world

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

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

 

No longer safe

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

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

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

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

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

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

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

space

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Top image: NASA, CC BY-NC-ND

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

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

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

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

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

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

Energy in, energy out

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

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

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

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

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

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

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

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


Tracking faster than the models

Scientists keep track of the energy budget in two ways.

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

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

Both methods show the energy imbalance has grown rapidly.

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

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

Why has it changed so fast?

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

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

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

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

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

What does this mean?

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

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

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

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

Our eyes in the sky

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

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

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

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

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

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

Global warming will continue to rise: image Peggy Anke

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Authors: Andrew King, Senior Lecturer in Climate Science, The University of Melbourne and Tilo Ziehn, Principal Research Scientist, CSIRO

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

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The world is striving to reach net-zero emissions as we try to ward off dangerous global warming. But will getting to net-zero actually avert climate instability, as many assume?

Our new study examined that question. Alarmingly, we found reaching net-zero in the next few decades will not bring an immediate end to the global heating problem. Earth’s climate will change for many centuries to come.

And this continuing climate change will not be evenly spread. Australia would keep warming more than almost any other land area. For example if net-zero emissions are reached by 2060, the Australian city of Melbourne is still predicted to warm by 1°C after that point.

But that’s not to say the world shouldn’t push to reach net-zero emissions as quickly as possible. The sooner we get there, the less damaging change the planet will experience in the long run.

Reaching net-zero is vital

Global greenhouse gas emissions hit record highs in 2023. At the same time, Earth experienced its hottest year.

Analysis suggests emissions may peak in the next couple of years then start to fall. But as long as emissions remain substantial, the planet will keep warming.

Most of the world’s nations, including Australia, have signed up to the Paris climate agreement. The deal aims to keep global warming well below 2°C, and requires major emitters to reach net-zero as soon as possible. Australia, along with many other nations, is aiming to reach the goal by 2050.

Getting to net-zero essentially means nations must reduce human-caused greenhouse gas emissions as much as possible, and compensate for remaining emissions by removing greenhouse gases from the atmosphere elsewhere. Methods for doing this include planting additional vegetation to draw down and store carbon, or using technology to suck carbon out of the air.

Getting to net-zero is widely considered the point at which global warming will stop. But is that assumption correct? And does it mean warming would stop everywhere across the planet? Our research sought to find out.

Centuries of change

Computer models simulating Earth’s climate under different scenarios are an important tool for climate scientists. Our research used a model known as the Australian Community Climate and Earth System Simulator.

Such models are like lab experiments for climate scientists to test ideas. Models are fed with information about greenhouse gas emissions. They then use equations to predict how those emissions would affect the movement of air and the ocean, and the transfer of carbon and heat, across Earth over time.

We wanted to see what would happen once the world hit net-zero carbon dioxide at various points in time, and maintained it for 1,000 years.

We ran seven simulations from different start points in the 21st century, at five-year increments from 2030 to 2060. These staggered simulations allowed us to measure the effect of various delays in reaching net-zero.

We found Earth’s climate would continue to evolve under all simulations, even if net-zero emissions was maintained for 1,000 years. But importantly, the later net-zero is reached, the larger the climate changes Earth would experience.

Warming oceans and melting ice

Earth’s average temperature across land and sea is the main indicator of climate change. So we looked at that first.

We found this temperature would continue to rise slowly under net-zero emissions – albeit at a much slower rate than we see today. Most warming would take place on the ocean surface; average temperature on land would only change a little.

We also looked at temperatures below the ocean surface. There, the ocean would warm strongly even under net-zero emissions – and this continues for many centuries. This is because seawater absorbs a lot of energy before warming up, which means some ocean warming is inevitable even after emissions fall.

Over the last few decades of high greenhouse gas emissions, sea ice extent fell in the Arctic – and more recently, around Antarctica. Under net-zero emissions, we anticipate Arctic sea ice extent would stabilise but not recover.

In contrast, Antarctic sea ice extent is projected to fall under net-zero emissions for many centuries. This is associated with continued slow warming of the Southern Ocean around Antarctica.

Importantly, we found long-term impacts on the climate worsen the later we reach net-zero emissions. Even just a five-year delay would affect on the projected climate 1,000 years later.

Delaying net-zero by five years results in a higher global average surface temperature, a much warmer ocean and reduced sea ice extent for many centuries.

Australia’s evolving climate

The effect on the climate of reaching net-zero emissions differs across the world.

For example, Australia is close to the Southern Ocean, which is projected to continue warming for many centuries even under net-zero emissions. This warming to Australia’s south means even under a net-zero emissions pathway, we expect the continent to continue to warm more than almost all other land areas on Earth.

For example, the models predict Melbourne would experience 1°C of warming over centuries if net-zero was reached in 2060.

Net-zero would also lead to changes in rainfall in Australia. Winter rainfall across the continent would increase – a trend in contrast to drying currently underway in parts of Australia, particularly in the southwest and southeast.

Knowns and unknowns

There is much more to discover about how the climate might behave under net-zero.

But our analysis provides some clues about what climate changes to expect if humanity struggles to achieve large-scale “net-negative” emissions – that is, removing carbon from the atmosphere at a greater rate than it is emitted.

Experiments with more models will help improve scientists’ understanding of climate change beyond net-zero emissions. These simulations may include scenarios in which carbon removal methods are so successful, Earth actually cools and some climate changes are reversed.

Despite the unknowns, one thing is very clear: there is a pressing need to push for net-zero emissions as fast as possible.The Conversation

Glacier terminal undercut by warm water image by Sonny Whitelaw

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

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

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

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

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

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

Lessons from the past

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

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

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

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

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

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

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

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


Global climate connections

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

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

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

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

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

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

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

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

Future implications

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

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

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

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

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

Thunderstorm

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Authors: Andrew Dowdy, The University of Melbourne; Conrad Wasko, University of Sydney; Jennifer Catto, University of Exeter, and Seth Westra, University of Adelaide

In media articles about unprecedented flooding, you’ll often come across the statement that for every 1°C of warming, the atmosphere can hold about 7% more moisture.

This figure comes from research undertaken by the French engineer Sadi Carnot and published 200 years ago this year.

We now know there’s more to the story. Yes, a hotter atmosphere has the capacity to hold more moisture. But the condensation of water vapour to make rain droplets releases heat. This, in turn, can fuel stronger convection in thunderstorms, which can then dump substantially more rain.

This means that the intensity of extreme rainfall could increase by much more than 7% per degree of warming. What we’re seeing is that thunderstorms can likely dump about double or triple that rate – around 14–21% more rain for each degree of warming.

Thunderstorms are a major cause of extreme flooding around the world, contributing to Brazil’s disastrous floods, which have submerged hundreds of towns, and Dubai’s flooded airport and roads.

For Australia, we helped develop a comprehensive review of the latest climate science to guide preparedness for future floods. This showed the increase per degree of global warming was about 7–28% for hourly or shorter duration extreme rain, and 2–15% for daily or longer extreme rain. This is much higher than figures in the existing flood planning standards recommending a general increase of 5% per degree of warming.

Why are thunderstorms important for extreme rain?

For thunderstorms to form, you need ingredients such as moisture in the air and a large temperature difference between lower and higher air masses to create instability.

We typically associate thunderstorms with intense localised rain over a short period. What we’re seeing now, though, is a shift towards more intense thunderstorm downpours, particularly for short periods.

Extreme rain events are also more likely when thunderstorms form in combination with other weather systems, such as east coast lows, intense low pressure systems near eastern Australia. The record floods which hit Lismore in February 2022 and claimed the lives of many people came from extreme rain over many days, which came in part from severe thunderstorms in combination with an east coast low.

Climate change pumps up extreme flood risk factors

The latest report from the Intergovernmental Panel on Climate Change (IPCC) states that:

frequency and intensity of heavy precipitation events have increased since the 1950s over most land areas for which observational data are sufficient for trend analysis (high confidence), and human-induced climate change is likely the main driver

This increase is particularly clear in short-duration extreme rains, such as those caused by thunderstorms.

Why? In part, it’s because of the 7% figure – warmer air is able to hold more water vapour.

But that doesn’t explain everything. There’s something else going on. Condensation produces heat. So as water vapour turns into droplets, more heat becomes available, and hot air rises by convection. In thunderstorms, more heat fuels stronger convection, where warm, moisture-laden air is driven up high.

This explains why thunderstorms can now drive such extreme rainfall in our warming world. As water vapour condenses to make rain, it also makes heat, supercharging storms.

We are seeing these very rapid rates of rainfall increase in recent decades in Australia.

Daily rainfall associated with thunderstorms has increased much more than the 7% figure would suggest – about 2-3 times more.

Hourly rainfall extremes have also increased in intensity at similar rates.

What about very sudden, extreme rains? Here, the rate of increase could potentially be even larger. One recent study examined extreme rain for periods shorter than one hour near Sydney, suggesting about a 40% increase or more over the past 20 years.

Rapid trends in extreme rainfall intensity are also clear in other lines of evidence, such as fine-resolution modelling.

To model complex climate systems, we need the grunt of supercomputers. But even so, many of our models for climate projections don’t drill down to grid resolutions smaller than about 100 kilometres.

While this can work well for large-scale climate modelling, it’s not suitable for directly simulating thunderstorms. That’s because the convection processes needed to make thunderstorms form happen on much smaller scales than this.

There’s now a concerted effort underway to perform more model simulations at very fine scales, so we can improve the modelling of convection.

Recent results from these very fine scale models for Europe suggest convection will play a more important role in triggering extreme rainfall including in combined storms, such as thunderstorms mingling with low pressure systems and other combinations.

This matches Australian observations, with a trend towards increased rain from thunderstorms combining with other storm types such as cold fronts and cyclones (including low-pressure systems in southern Australia).


Does this change how we plan for floods?

The evidence for supercharged thunderstorm rainfall has grown in recent years.

Australia’s current flood guidance recommendations, which influence how infrastructure projects have been built, are based on extreme rain increasing by just 5% for each degree of warming.

Our research review has shown the real figure is substantially higher.

This means roads, bridges, tunnels built for the 5% figure may not be ready to deal with extreme rain we are already seeing from supercharged thunderstorms.

While Australia has become more conscious of links between climate change and bushfires, studies show we are less likely to link climate change and more intense storms and floods.

This will have to change. We still face some uncertainties in precisely linking climate change to a single extreme rain event. But the bigger picture is now very clear: a hotter world is likely one with higher risk of extreme floods, often driven by extreme rain from supercharged thunderstorms.

So what should we do? The first step is to take climate change influences on storms and flood risk as seriously as we now do for bushfires.

The next is to embed the best available evidence in how we plan for these future storms and floods.

We have already loaded the dice for more extreme floods, due to existing human-caused climate change and more to come, unless we can quickly reduce our greenhouse gas emissions.The Conversation

__________________________________________________________________________________

Andrew Dowdy, Principal Research Scientist in Extreme Weather, The University of Melbourne; Conrad Wasko, ARC DECRA Fellow in Hydrology, University of Sydney; Jennifer Catto, Associate Professor of Mathematics and Statistics, University of Exeter, and Seth Westra, Hydrologist, University of Adelaide

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

Thunderstorm

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First published 19 September 2023, in Environmental Research Letters 18; reproduced here under Creative Commons Attribution 4.0 licence

Authors:

  1. Giorgia Di Capua:Magdeburg-Stendal University of Applied Sciences, 39114 Magdeburg, Germany

  2. Stefan Rahmstorf: Potsdam Institute for Climate Impact Research (PIK), Member of the Leibniz Association, PO Box 6012 03, D-14412 Potsdam, Germany | E-mail: dicapua@pik-potsdam.de

Abstract

Extreme weather events are rising at a pace which exceeds expectations based on thermodynamic arguments only, changing the way we perceive our climate system and climate change issues. Every year, heatwaves, floods and wildfires, bring death and devastation worldwide, increasing the evidence about the role of anthropogenic climate change in the increase of extremes. In this viewpoint article, we summarize some of the most recent extremes and put them in the context of the most recent research on atmospheric and climate sciences, especially focusing on changes in thermodynamics and dynamics of the atmosphere. While some changes in extremes are to be expected and are clearly attributable to rising greenhouse gas emissions, other seem counterintuitive, highlighting the need for further research in the field. In this context, research on changes in atmospheric dynamics plays a crucial role in explaining some of these extremes and more needs to be done to improve our understanding of the physical mechanisms involved.

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A rise in weather extremes is probably the most severe early impact of rising global temperatures. Extreme weather events have a high impact on both human activities and natural ecosystems. In recent decades the world has seen an increase in heatwaves, droughts, flooding events and fire weather conditions, as expected in a warming climate. 2022 has been no exception, with record-breaking high temperatures registered across large portions of Western Europe, China and Pakistan (Hausfather 2023). In Pakistan, extreme monsoon rains and Himalayan glaciers melting away in a heat wave have flooded approximately 85 000 km2 (USAID 2022), killing more than 1700 people and causing $15 billion of damage (World Bank), while the Horn of Africa has seen an unprecedented drought that has pushed more than three million people into emergency food insecurity (NASA Earth Observatory 2022). Many of these events have been made more likely by anthropogenic warming and represent a serious threat to human society, with effects ranging from health and mortal- ity to economy and national security issues.

Even for lay persons it will be obvious that heat extremes will increase in a warming world. But it may be unexpected by how much: monthly heat extremes

that were three standard deviations above average during the baseline period 1951–1980 have already increased over 90-fold in frequency over the global land area, while the formerly near-unprecedented 4-sigma events have increased 1000-fold to affect 3% of the land area in any given month, data show (Robinson et al 2021). July 2023 was the hot- test month on record on Earth by a large margin (Copernicus 2023a), and likely the hottest for at least 10 000 years. Marine heatwaves have also doubled in the last few decades, and they are expected to see a 23-fold increase under a 2 ◦C warming scenario (Frölicher et al 2018)—the off-the charts sea surface temperatures in the North Atlantic in summer 2023 are a stern foretaste of this (Copernicus 2023b), while in Florida the marine heatwave caused wide spread bleaching turning into one of the worst events in the region on record (Dennis et al 2023).

Part of this is as expected simply by shifting a Gaussian normal distribution towards warmer values; the more extreme an event, the larger is the factor by which its likelihood increases. However, explaining the full extent of the global increase in extreme heat requires additional, dynamical effects (which we will discuss below).

And heat—especially lasting heat—is a silent killer. The death toll of the 2003 European heat wave has been estimated as ∼70 000 (Robine et al 2008), with a mortality peak in France higher than dur- ing any Covid19 wave (Ferrer and Breteau 2020). A first estimate for summer 2022 came in at ∼62 000 (Ballester et al 2023), when even in Britain temperatures soared above 40◦C for the first time in history. Temperature-related excess mortality is expected to increase with unmitigated global warming, even when accounting for a decrease in cold-related deaths (Gasparrini et al 2017).

Since early 2012, the fingerprint of climate change can be detected in any single day in the observed record. There are no more days on Earth where global weather is not significantly different from what it would be without human influence—on nearly all days even when just considering the weather pat- terns without the increase in global-mean temperature (Sippel et al 2020). Observations show that nearly the entire Earth surface has warmed since the late 19th century (except for the prominent ‘warming hole’ south of Greenland and Iceland, Rahmstorf et al 2015) and the annual global mean temperature has increased by 1.2◦C since the late 19th Century (Intergovernmental Panel on Climate Change 2021). The intensity and speed of warming differ by region, with land areas warming twice as much as the ocean surface since 1970 (Intergovernmental Panel on Climate Change 2021). Warming is more prominent in the Arctic, Eastern Europe, North Africa, the Middle East, East Asia and western North America. Key heatwave characteristics, such as frequency, duration and cumulative heat (i.e. the heat produced by heatwaves days inside a season), show increasing trends since 1950 at global scale, with stronger trends in tropical and northern latitudes. Trends for these key variables have been accelerating in the past few decades (Perkins-Kirkpatrick and Lewis 2020). Summer 2023 was no exception, with record breaking temperature recorded in Southeastern US, China, Spain, Morocco, rendered more likely by current climate change (Zachariah et al 2023).

While the world-wide rise in heat extremes is easily understood given the rise in global mean temperature, mean global rainfall and extreme precipitation trends depict a more complex relationship. Global rainfall is expected to increase as evaporation from warmer oceans increases. Indeed, the IPCC AR6 WGI (2021) reports an increase in globally averaged land precipitation since 1950, though with medium confidence given the large variability and spatial heterogeneity of precipitation. However, extreme rainfall events have shown a steep increase in the last few decades (especially in tropical regions), with 1 in 4 record breaking rainfall events being attributable to climate change (Robinson et al 2021). In August 2023, the region surrounding Beijing was hit by a severe flood event which saw the highest rainfall record of

the last 140 years (744.8 mm in less the 4 d) (Hawkins 2023) Perhaps counterintuitively, some areas even show opposite trends in mean precipitation rates and extreme rainfall events. One such example is the Indian summer monsoon system, which shows a slight decrease in its mean seasonal precipitation rates together with a three-fold increase in extreme rainfall events during the 1950–2015 period (Roxy et al 2017). Therefore, when considering the effect of climate change on extremes, it is not enough to look at trends in mean values.

Another example of that is that despite the global-mean (and often also local) rainfall increase, the frequency and severity of droughts has also increased in some regions, for a number of reasons. One overall reason is that with approximately constant relative humidity, air will contain (and at some point rain out) 7% more moisture per degree of warming, while the resupply of water via evaporation increases only by 2%–3% per degree (Allan et al 2020). The additional evaporation and rain- fall tends to end up in heavy rain rather than alleviating drought: Half of it comes down in the wet- test 6 d each year (Pendergrass and Knutti 2018), and the heaviest rainfall events increase most strongly (Fischer and Knutti 2015). Also, increasing agricultural and ecological droughts (i.e. loss of soil moisture and drying vegetation) can be caused not just by declining precipitation but also by rising temperatures causing faster evapotranspiration. In different regions, either of these effects can be the more important one (Cook et al 2018). Major droughts can also result from natural climate variability and are rare events (compared to the length of available observational data). Thus, studying their trend and, more importantly, attributing them to anthropogenic global warming is not an easy task (Cook et al 2018). Several regions in the world have shown an increase in drought risk, such as Western North America, the Mediterranean, East Southern Africa, East Asia and South Australia, at least partly attributable to anthropogenic warming, with the Mediterranean and the North-Western North America showing the highest confidence (Intergovernmental Panel on Climate Change 2021).

In the past decade, wildfire activity has produced some new extreme fires that are unprecedented regarding propagation speed, intensity, location, timing and burnt area (Descals et al 2022, Senande- Rivera et al 2022). For example, the Australian ‘Black Summer’ wildfire disaster in 2019/2020 fol- lowed Australia’s hottest and driest year on record, burned more than half of the habitat for over 1600 native species and directly caused 33 human deaths and almost 450 more from smoke inhalation (Himbrechts 2021). An increase in extreme fire weather conditions can already be detected at global scale, although trend magnitude and spatial patterns vary at regional scale (Jain et al 2022). Globally, anthropogenic global warming is projected to cause unprecedented increases in extreme fire weather risk in the 21st century (Touma et al 2021). Model experiments estimate that anthropogenic induced changes in fire weather indices have already emerged from natural variability for 22% of the burnable land area globally by 2019, while by the mid twenty-first century the emergence will reach 30%–60% (Abatzoglou et al 2019). Meanwhile, in August 2023, Hawaii has experienced its worst wildfire on record, and one of the worst in US history, where dry conditions and hurricane-force winds fueled the flames bringing utter devastation to the town of Lahaina, killing at least 93 people and thus surpassing the death toll of the Camp fire in California in 2018 (Gabbat and Anguiano 2023).

While warm extremes are to be expected due to anthropogenic global warming, cold extreme are projected to decrease in this century. Nevertheless, despite the general increase in global surface temperatures, a few regions show a cooling trend in the historical record. One such example is central Siberia, which features a cooling trend during boreal winter (Inoue et al 2012). While both natural variability and anthropogenic forcing are debated as causes of this trend (Inoue et al 2012), the cooling trend is mainly associated with an increase in cold extremes over the region. Cold air outbreaks in central Siberia and North America have been shown to result from sudden stratospheric warming events and a disruption of the stratospheric Polar vortex (Kretschmer et al 2018).

Detecting climate change signals can be challenging depending on the region and the variable selected, and attributing trends in temperature or precipitation fields to changes in thermodynamic or dynamic features of the atmosphere represent an even greater challenge (Shepherd 2014). In general, the largest portion of the change is to be attributed to thermodynamic effects. However, dynamic changes can further exacerbate thermodynamic driven changes and atmosphere dynamics and changes in weather patterns play an important role at regional scale (Rousi et al 2022). Amplified Rossby waves with preferred phase position, in particular waves with wave numbers 5 and 7, can lead to concurrent heatwaves (and crop failures) in the mid-latitudes (Kornhuber et al 2020), raising concerns about future food security. Arctic amplification, despite being more prominent in winter than summer, may also affect westerly winds, storm tracks and wave-guides in the mid-latitudes (Coumou et al 2018). Analyzing the ability of models to reproduce amplified waves 5 and 7 shows that even a small bias in upper tropospheric circulation features can have a strong impact on surface temperature and rainfall patterns (Luo et al 2022), highlighting that it is difficult for global climate models to simulate all mechanisms that contribute to making weather more extreme.

Europe has emerged as a hot-spot of heat extremes: it has seen a stronger increase in summer heat than other regions in the northern mid-latitudes. This enhanced warming has been related to dynamical changes such as an increase of double jet patterns, which could explain all of the additional rise in heat waves beyond what is expected simply by thermodynamics (Rousi et al 2022). Both observation and model experiment support the hypothesis that shrinking Arctic sea ice and reduced snow cover over northern Eurasia in spring can also contribute to increased blocking over Europe and consequent frequency of heatwaves (Zhang et al 2020). Sea surface temperature anomalies (in particular the northern Atlantic ‘warming hole’ mentioned earlier) can also reinforce heatwaves in central Europe, such as in 2015 (Duchez et al 2015).

In summary, it is now clear that global warming is already greatly increasing the number and intensity of many types of weather extremes, as has been predicted by climate science for decades. Much of this is due to thermodynamics. With that we mean that the atmosphere is warmer, which means it holds more energy and water to power extreme weather. The ocean is also warmer and can provide more energy and moisture as fuel to tropical cyclones. However, increasingly the attention of researchers has turned to dynamic effects. With that we refer to changes in circulation and stability of atmosphere and ocean. It includes changes to the jet stream, polar vortex, atmospheric planetary waves or to the Atlantic meridional overturning circulation.

Obtaining robust conclusions about changes in weather extremes requires long time series, given that extreme events are by definition rare events and are not easy to model. Nevertheless, the signal of climate change has now clearly emerged from the noise for many types of extremes. Disentangling the dynamic mechanisms is harder again and represents a current frontline of research. Driving forces behind dynamic changes are often regionally diverse temperature changes, such as Arctic amplification, enhanced land warming and sea surface temperature anomalies. Many facets of the dynamic mechanisms are still being debated in the scientific literature. Even if not everything is fully understood, researchers and journalists should not be shy to use every opportunity to educate the public about the fact that human-caused global warming is making weather extremes worse, already causing serious harm to many millions of people.

Even once global warming is stopped, we will see unprecedented extremes for a long time to come. Just think of a former once-in-5000 year event which at 1.5◦C warming may have become a once-in-50 year event. Thus, it will take many decades until we have seen all the possible extreme events a 1.5◦C warmer world has in store for us.


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