Climate change - heating of oceans increasing

 

The world’s oceans are the hottest on record for June – and El Niño is set to turn up the heat even more

Artur Debat/Getty

Matthew England, UNSW Sydney; Alex Sen Gupta, UNSW Sydney, and Alistair Hobday, CSIRO

The world’s oceans are the hottest on record for June, pushing past records set during the 2023–24 El Niño years.

Right now, the average sea surface temperature is just under 21°C across the world’s tropical and temperate oceans. Before widespread industrialisation in 1870, the temperature was about 19.6°C.

That may not sound like a big difference. But heating the world’s oceans this much requires a truly enormous amount of energy. Of all the extra heat trapped by greenhouse gases from burning coal, gas and oil, more than 90% has gone into the world’s oceans.

As a result, the oceans are getting rapidly warmer. In 2025, the heat added was the equivalent of about 12 Hiroshima-scale nuclear bombs exploding every second of every day.

To find a climate analogue comparable to what’s happening now in the oceans, we would have to go back around 120,000 years to before the last ice age. Back then, slow shifts in Earth’s orbit led it to heat up gradually over thousands of years. Humans have accomplished a similar result in a little over a century.

But the heat in the ocean doesn’t just stay there. Hotter oceans fuel stronger cyclones, a more humid atmosphere, more intense rainfall and more heat in air masses over the seas, which can in turn make heatwaves over land more likely and more intense.

The El Niño forming in the tropical Pacific right now is likely to be a big one. As it develops, we can expect to see warmer temperatures and extreme events such as marine heatwaves in the western Indian, tropical Atlantic and eastern Pacific Oceans.

Global ocean sea surface temperatures are at the highest level recorded during June. HadISST, CC BY-NC-ND

Where are the hotspots on land and in the ocean?

Europe is sweltering through a record-breaking heatwave. The oceans surrounding the region and in enclosed seas are also exceptionally hot.

Parts of the Mediterranean are up to 6°C hotter than the long-term average.

Parts of the North Sea are up to 3°C warmer than average.

The seas around Europe have been much warmer than average. This map shows temperature anomalies from June 29 2026. opernicus Marine Service Data/European Union, CC BY-NC-ND

The forming El Niño has led to sea surface temperatures about 1.24°C warmer than average across a large area of the central eastern Pacific.

There’s much more heat below the surface as well. Subsurface conditions in the eastern Pacific are more than 6°C above average.

A typical El Niño lasts about a year. The full effect on atmospheric heat becomes clearest towards the end of the cycle. That means while we can expect 2026 to be very hot – perhaps a new record – next year is very likely to be even hotter, as ocean heat is moved back to the surface. We saw this during El Niño events over 2023–24 and 2015–16.

Steady ocean warming coupled with longer-lasting and more intense marine heatwaves pose huge threats to marine ecosystems such as coral reefs, sea grass meadows and coastal reefs. Research on the 2023–24 El Niño and the warm 2024 year showed widespread impacts.

Regions such as the eastern Pacific and the Mediterranean are unusually hot at present. This map shows temperature anomalies on June 30th 2026. Climate Reanalyzer, CC BY-NC-ND

From oceans to land

What happens in the oceans doesn’t stay there.

In June 2023, a record-breaking marine heatwave broke previous temperature records across the North Atlantic Ocean. Soon afterwards, large areas of Europe were hit by intense heatwaves, while extreme rains triggered deadly floods in Spain and severe bushfires broke out around the Mediterranean.

Rising ocean temperatures have many consequences.

A warmer ocean is less able to cool the land over summer. Warmer oceans also lead to more evaporation, boosting humidity and fuelling more intense and more sudden extreme rain and floods. These can have devastating consequences.

During El Niño events, there’s a clear geographical pattern. The regions we expect to be warmer or cooler during an El Niño roughly reflect where we are more or less likely to get marine heatwaves and more intense tropical cyclones.

Typical cyclone areas such as the western Indian Ocean could see stronger cyclones dumping heavier rainfall when they hit land. El Niño tends to bring extreme rain and floods to the western South America and dry conditions over parts of Australia and Southeast Asia.

Global surface temperatures tend to spike during strong El Nino years (red) and fall back during La Nina years, even as climate change drives the baseline higher. HadCRUT, CC BY-NC-ND

Can we prepare?

We are gaining a better understanding of how big climate drivers like El Niño shape weather and how to use ocean data from around the world to develop better seasonal forecasts authorities can use to prepare.

Over the past two years, we have improved our ability to forecast marine heatwaves three to four months ahead in Australia, the United States and other regions. Forecasts give marine authorities a chance to act early by reducing allowable fishery catches and beginning conservation efforts for vulnerable species.

The world’s oceans have been steadily warming since the 1870s, as this climate stripes visualisation shows. El Niño years (red tag above) tend to boost ocean warming while La Niña years (blue tag below) tend to be cooler. Tag width represents strength of the event. HadISST (before 1982)/NOAA OISST (1982 onward), CC BY-NC-ND

This early success in ocean forecasting may be short-lived. The current US administration last year slashed funding for climate data gathering networks and has worked to dismantle the National Center for Atmospheric Research.

This year, the administration announced it would end funding for a key ocean monitoring network before backing down.

Ongoing collection of ocean data is crucial for ocean and land forecasts. If they are weakened or discontinued, we could face the challenge of dealing with worsening climate impacts blind.

Ending the measuring of climate change won’t stop it happening. The only way to keep climate change from steadily worsening is to reach net zero as soon as humanly possible. Until then, we must use forecasts to prepare for what we can’t avoid.

Matthew England, Director of the ARC Centre of Excellence for Our Future Oceans and Scientia Professor in Oceanography, UNSW Sydney; Alex Sen Gupta, Associate Professor in Climate Science, UNSW Sydney, and Alistair Hobday, Chief Research Scientist - Environment, CSIRO

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

Climate change destroys underwater forests

 

Heat is destroying Australia’s underwater forests. Seaweed biobanks could help save them

Tom Burd, CC BY-NC-ND

Catalina A. Musrri, University of Sydney and Georgina Wood, Flinders University

Australia’s Great Southern Reef is built not by coral but by seaweed. The seaweed forests on these rocky reefs stretch more than 8,000 kilometres around southern Australia.

Amid the swaying fronds live seadragons, rock lobsters, giant cuttlefish and southern blue devils. The reef is home to more than 1,500 seaweed species and contributes billions to the economy each year.

But these remarkable cold water forests face a worsening threat. The ocean is getting steadily warmer, pushing seaweed species outside their survival zone. Much of this damage is done by sudden marine heatwaves, where temperatures spike and remain high for some time. Heatwaves have driven the decline of seaweed forests across the country.

To protect these underwater forests, we need to preserve their genetic diversity. We led the first attempt to cryopreserve (freezing and storing reproductive material at ultra-low temperatures) a key Australian seaweed, crayweed, and found the idea shows promise, though the techniques need to be perfected.

Why does seaweed matter?

Most of us encounter seaweed as a slightly stinky mass spotted when walking along a beach. But underwater, these large algae (not plants) form beautiful forests swaying in the current – some as tall as 30 metres.

Seaweed forests are among the most productive ecosystems on Earth. Like forests on land, they provide habitat, shelter and food for many creatures. They underpin valuable fisheries such as lobster and abalone.

When local populations are wiped out, they take something important with them – genetic diversity. Species with high genetic diversity can better adapt to change. Some populations will be able to tolerate heat better, for instance. But if these populations disappear, their unique genes go with them.

In 2011, an extreme marine heatwave in Western Australia led to two common seaweed species losing an estimated 30 to 65% of their genetic diversity. These losses may mean poorer outcomes in response to intensifying threats.

Seaweed forests are home to many species, such as this shovelnose ray in Australia’s first named seaweed forest, Yanggaa, at Coogee Beach in New South Wales. Operation Crayweed, CC BY-NC-ND

Consider the crayweed

Golden-brown crayweed (Phyllospora comosa) once formed extensive underwater forests along Sydney’s coastline. Many of these disappeared in the 1980s, likely due to sewage pollution. But crayweed didn’t return even after pollution levels fell.

Over the past 14 years, scientists and divers have replanted this species around Sydney through Operation Crayweed. Their work has led to the return of self-sustaining populations, including Australia’s first named seaweed forest – Yanggaa forest at Coogee Beach.

But restoration may not be enough in a rapidly warming ocean. Our research shows separate crayweed populations harbour unique genetic diversity – and some individuals appear better equipped to tolerate heat. It may make sense to plant germlings (baby seaweed) from these individuals in vulnerable populations to boost their chances of survival.

We tested storing crayweed reproductive material at very low temperatures using cryopreservation in liquid nitrogen. Rachel Venhuizen, CC BY-NC-ND

Of seed banks, biobanks and cryopreservation

For decades, thousands of land-based plant species have had their genetic diversity preserved through seed banks. The seeds stored are sleeping but still alive. If planted in the right conditions, they will grow.

Some kelp species can also be kept alive in biobanks – not as seeds, but in a microscopic form (gametophytes) able to be kept alive in laboratories for years. Current kelp collections support research, aquaculture and restoration programs around the world, including in Australia.

These banks are important. But they won’t be enough. The majority of seaweed species dominating the Great Southern Reef are known as fucoids. Unlike true kelps, fucoids don’t have this microscopic life stage – they release sperm and eggs directly into seawater that fertilise and form germlings. This makes species such as crayweed, bull kelp (Durvillaea potatorum), Cystophora sp. and Scytothalia dorycarpa more challenging to conserve.

It is possible to bank species which rely on sexual reproduction, such as humans, cows, corals and fucoids. Assisted reproduction methods such as IVF rely on cryopreservation: storing reproductive material, tissue or early life stages at ultra-low temperatures (around –196 °C) so it remains viable for future use.

Our recent research tested whether frozen crayweed sperm and germlings were viable after being thawed. We found the sperm did well, but the germlings did not (for now). Our ultimate goal is to develop proven methods able to work across a broader range of Australian seaweed species.

Preserving the genetic diversity of seaweed species would mean these genes can be drawn on to bring them back. This buys valuable time and keeps the door open for new methods such as assisted gene flow, where individuals from better-adapted populations are used to help vulnerable ones cope with warmer conditions.

Time for seaweed biobanks?

Australia already has an impressive algal culture collection and is a global leader in coral cryobanking.

Even so, it will take real work to develop methods of preserving the forest-forming seaweed species that rely on sexual reproduction. We need to learn which populations contain unique or threatened genetic diversity, understand which are most vulnerable to climate change and improve freezing and recovery techniques.

Choosing which species and populations should be done alongside Indigenous custodians, governments, conservation organisations and local communities.

Cryobanking doesn’t solve climate change or replace the need to protect habitat. It’s an insurance policy for biodiversity. Much has already been lost. Preserving the remaining genetic diversity of our seaweed forests may well be critical to the survival of the Great Southern Reef.

Catalina A. Musrri, Postdoctoral Research Fellow in Marine Biology, University of Sydney and Georgina Wood, ARC Research Fellow in Marine Science, Flinders University

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

Climate change - sea levels will rise even if the global temperature increase is only 1.5°C

                          Daytona, Florida, United States                  Shutterstock

With all the focus and debate on the target of limiting the temperature increase on the planet to 1.5°C pre-industrial levels, a very real concern is often overlooked. That concern is the impact of the temperature increase that has already happened. The reality is that even if the target of limiting the  increase to 1.5°C was achieved, ocean levels will still rise and at a rate much faster than previously predicted. Scientists at Durham University in the UK have reviewed three lines of evidence on the current situation: satellite observations of ice loss and sea level rise over the past three decades; studies of warm periods in the past; and computer models of ice sheets.

The conclusion was startling. The Greenland and West Antarctica ice sheets are already melting, decades earlier forecast in the last report of the Intergovernmental Panel and Climate Change (IPCC). The melting of the ice sheets is also accelerating. As the scientists at Durham concluded, every fraction of a degree of temperature increase really matters for ice sheets. To merely slow down but not stop the ice sheets melting, the global temrperature increase would need to be reduced to 1°C above the pre-industrial baseline.

In 2024, the average temperature increase world-wide was 1.51°C which makes a mockery of the desired target as it has already been surpassed. The world is on course with current trends to reach a 2.9°C increase in temperature by the end of the century.

The research article can be found at this link: Ice loss at 1.5C 

Climate change and the loss of coral reefs

Reality check: coral restoration won’t save the world’s reefs

A coral ‘rope’ nursery in the Maldives. Luca Saponari/University of Milan, CC BY-ND

Corey J. A. Bradshaw, Flinders University; Clelia Mulà, The University of Western Australia, and Giovanni Strona, University of Helsinki

Coral reefs are much more than just a pretty place to visit. They are among the world’s richest ecosystems, hosting about a third of all marine species.

These reefs also directly benefit more than a billion people, providing livelihoods and food security, as well as protection from storms and coastal erosion.

Without coral reefs, the world would be a much poorer place. So when corals die or become damaged, many people try to restore them. But the enormity of the task is growing as the climate keeps warming.

In our new research, we examined the full extent of existing coral restoration projects worldwide. We looked at what drives their success or failure, and how much it would actually cost to restore what’s already been lost. Restoring the reefs we’ve already lost around the world could cost up to A$26 trillion.

Bleached Acropora corals in the Maldives. Davide Seveso/University of Milan

Global losses

Sadly, coral reefs are suffering all over the world. Global warming and marine heatwaves are the main culprits. But overfishing and pollution make matters worse.

When sea temperatures climb above the seasonal average for sustained periods, corals can become bleached. They lose colour as they expel their symbiotic algae when stressed, revealing the white skeleton underneath. Severe bleaching can kill coral.

Coral bleaching and mass coral deaths are now commonplace. Last month, a massive warm-water plume bleached large areas of Ningaloo Reef on Australia’s northwest coast just as large sections of the northern Great Barrier Reef were bleaching on the northeast coast.

Since early 2023, mass coral bleaching has occurred in throughout the tropics and parts of the Indian Ocean.

Over the past 40 years, the extent of coral reefs has halved. As climate change continues, bleaching events and coral deaths will become more common. More than 90% of coral reefs are at risk of long-term degradation by the end of the century.

Dead corals in the Maldives following a bleaching event. Simone Montano/University of Milan

Direct intervention

Coral reef restoration can take many forms, including removing coral-eating species such as parrot fish, transferring coral spawn, or even manipulating the local community of microbes to improve coral survival.

But by far the most common type of restoration is “coral gardening”, where coral fragments grown in nurseries are transplanted back to the reef.

The problem is scale. Coral restoration can only be done successfully at a small scale. Most projects only operate over several hundred or a few thousand square metres. Compare that with nearly 12,000 square km of loss and degradation between 2009 and 2018. Restoration projects come nowhere near the scale needed to offset losses from climate change and other threats.

Conservationists work to garden coral and help preserve these unique life forms.

Sky-high costs

Coral restoration is expensive, ranging from around $10,000 to $226 million per hectare. The wide range reflects the variable costs of different techniques used, ease of access, and cost of labour. For example, coral gardening (coral fragments grown in nurseries transplanted back to the reef) is relatively cheap (median cost $558,000 per hectare) compared with seeding coral larvae (median $830,000 per hectare). Building artificial reefs can cost up to $226 million per hectare.

We estimated it would cost more than $1.6 billion to restore just 10% of degraded coral areas globally. This is using the lowest cost per hectare and assuming all restoration projects are successful.

Even our conservative estimate is four times more than the total investment in coral restoration over the past decade ($410 million).

But it’s reasonable to use the highest cost per hectare, given high failure rates, the need to use several techniques at the same site, and the great expense of working on remote reefs. Restoring 10% of degraded coral areas globally, at $226 million a hectare, would cost more than $26 trillion – almost ten times Australia’s annual GDP.

It is therefore financially impossible to tackle the ongoing loss of coral reefs with restoration, even if local projects can still provide some benefits.

Rope nurseries nurture coral fragments until they’re ready to be planted out. Luca Saponari/University of Milan

Location, location, location

Our research also looked at what drives the choice of restoration sites. We found it depends mostly on how close a reef is to human settlements.

By itself, this isn’t necessarily a bad thing. But we also found restoration actions were more likely to occur in reefs already degraded by human activity and with fewer coral species.

This means we’re not necessarily targeting sites where restoration is most likely to succeed, or of greatest ecological importance.

Another limitation is coral gardening normally involves only a few coral species – the easiest to rear and transplant. While this can still increase coral cover, it does not restore coral diversity to the extent necessary for healthy, resilient ecosystems.

Measuring ‘success’

Another sad reality is that more than a third of all coral restoration efforts fail. The reasons why can include poor planning, unproven technologies, insufficient monitoring, and subsequent heatwaves.

Unfortunately, there’s no standard way to collect data or report on restoration projects. This makes it difficult – or impossible – to identify conditions leading to success, and reduces the pace of improvement.

Succeed now, fail later

Most coral transplants are monitored for less than 18 months. Even if they survive that period, there’s no guarantee they will last longer. The long-term success rate is unknown.

When we examined the likelihood of extreme heat events immediately following restoration and in coming decades, we found most restored sites had already experienced severe bleaching shortly after restoration. It will be difficult to find locations that will be spared from future global warming.

Sometimes the young coral is bleached before the restoration project is complete. Davide Seveso/University of Milan

No substitute for climate action

Coral restoration has the potential to be a valuable tool in certain circumstances: when it promotes community engagement and addresses local needs. But it is not yet – and might never be – feasible to scale up sufficiently to have meaningful long-term positive effects on coral reef ecosystems.

This reality check should stimulate constructive debate about when and where restoration is worthwhile. Without stemming the pace and magnitude of climate change, we have little power to save coral reefs from massive losses over the coming century and beyond.

Other conservation approaches such as establishing, maintaining and enforcing marine protected areas, and improving water quality, could improve the chance a coral restoration project will work. These efforts could also support local human communities with incentives for conservation.

Reinforcing complementary strategies could therefore bolster ecosystem resilience, extending the reach and success of coral restoration projects.

Corey J. A. Bradshaw, Matthew Flinders Professor of Global Ecology and Node Leader in the ARC Centre of Excellence for Indigenous and Environmental Histories and Futures, Flinders University; Clelia Mulà, PhD student in Marine Ecology, The University of Western Australia, and Giovanni Strona, Doctoral program supervisor, University of Helsinki

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

Coral reefs in jeopardy

Devastating coral bleaching will be more common, start earlier and last longer unless we cut emissions

Sarah_lewis/Shutterstock

Camille Mellin, University of Adelaide and Damien Fordham, University of Adelaide

Coral bleaching is becoming much more common as a result of increasingly severe and frequent marine heatwaves. Four global mass bleaching events have happened since 1998. Two of these were in the past decade.

Unless greenhouse gas emissions are cut to slow global warming, our new research shows that, by 2080, coral bleaching will start in spring, rather than late summer. Some events will last into autumn. The Great Barrier Reef’s maximum annual heat stress will double by 2050 if emissions do not slow.

Marine heatwaves stress corals, which then expel the symbiotic algae living in their tissue. These corals are left white and weakened. While not all bleached corals die immediately, prolonged heat stress harms their health and reproduction.

Our research used daily data on sea surface temperatures (instead of monthly data that models typically use) and supercomputing to produce high-resolution projections of marine heatwaves. We showed the risk of coral bleaching will be greatest along the equator. That’s also where the most biodiverse coral reefs are found.

Coral reefs cover only 1% of our oceans, but host at least 25% of all marine species. More than half a billion people worldwide depend on coral reefs for food.

So coral reefs are vital for the health of the ocean and people. They are also among the ecosystems most at risk from climate change.

Longer bleaching season will hit spawning

The US National Oceanic and Atmospheric Administration monitors marine heatwaves globally. Seasonal coral bleaching alerts are based on this data. Predicting coral bleaching risk over entire decades has proved much more challenging.

Recent improvements in climate modelling now allow marine heatwaves and coral bleaching risks to be predicted with high accuracy. Using daily projections of heat stress from many global climate models, we show the severity and duration of coral bleaching will soon reach uncharted territory.

By mid-century coral bleaching is expected to start in spring for most of Earth’s reefs, rather than late summer as is typical today. In equatorial regions, corals will be at high risk of bleaching all year round by the end of the century.

In many regions, corals spawn only once a year. These spectacular mass spawning events happen in a single week following a full moon in spring.

By 2040, this spawning event could coincide with severe bleaching risk. This would greatly reduce their reproductive success, causing large-scale coral loss.

Acropora coral spawning on Magnetic Island in Queensland, Australia. Coral Brunner/Shutterstock

Equatorial regions most at risk

We show the future risk of severe coral bleaching is uneven globally.

The greatest risk is along the equator. Equatorial regions are home to the most biodiverse coral reefs, including conservation hotspots such as the Coral Triangle. To make matters worse, marine life in these regions is particularly vulnerable to accelerated climate change.

Many equatorial species are already living at temperatures near their upper tolerance. They also generally have low abilities to move to track shifting climates. This leaves them at high risk of extinction.

Future risk of coral bleaching under a high-emission scenario (top) and benefit from climate mitigation (bottom). Adapted from Mellin et al. Science Advances 2024

Our research shows equatorial regions are set to benefit least from efforts to curb emissions. We expect significant emission cuts will reduce the annual duration of severe bleaching conditions in all areas except these regions.

The projected highest climate impacts coincide with highest social reliance on coral reefs. This will challenge human populations that rely heavily on their local reefs for their livelihoods and nutrition.

Improving coral reef management

Our research identifies Earth’s reef regions that are at lowest risk of increased bleaching. This will help conservation managers and policymakers prioritise efforts to limit loss of coral reef biodiversity.

We predict much less risk of coral bleaching in regions such as the northern coasts of Venezuela and Colombia, Socotra Island (opposite the Gulf of Aden) and Alor Kecil in Indonesia. Seasonal upwellings occur here, bringing cooler water to the surface that’s likely to limit the severity of heatwaves.

Identifying these future havens for coral reefs will help maximise the success of coral conservation strategies such as assisted evolution, coral restoration or transplantation.

These strategies can help maintain healthy coral populations at local scales, particularly if used on reefs where future climate impacts will be lower. By pinpointing these havens, our research will strengthen coral conservation.

Our research includes a user-friendly web-based tool for mapping future coral bleaching. It will help pinpoint locations for effective management interventions.

Curbing greenhouse gas emissions is the main solution to reduce future climate impacts on corals. However, other strategies are also vital to maximise coral reefs’ adaptation to climate change.

Camille Mellin, Senior Lecturer and ARC Future Fellow, School of Biological Sciences, University of Adelaide and Damien Fordham, Associate Professor of Global Change Ecology, University of Adelaide

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

The risk of ocean change and climate impact

Atlantic Ocean is headed for a tipping point − once melting glaciers shut down the Gulf Stream, we would see extreme climate change within decades, study shows

Too much fresh water from Greenland’s ice sheet can slow the Atlantic Ocean’s circulation. Paul Souders/Stone via Getty Images

René van Westen, Utrecht University; Henk A. Dijkstra, Utrecht University, and Michael Kliphuis, Utrecht University

Superstorms, abrupt climate shifts and New York City frozen in ice. That’s how the blockbuster Hollywood movie “The Day After Tomorrow” depicted an abrupt shutdown of the Atlantic Ocean’s circulation and the catastrophic consequences.

While Hollywood’s vision was over the top, the 2004 movie raised a serious question: If global warming shuts down the Atlantic Meridional Overturning Circulation, which is crucial for carrying heat from the tropics to the northern latitudes, how abrupt and severe would the climate changes be?

Twenty years after the movie’s release, we know a lot more about the Atlantic Ocean’s circulation. Instruments deployed in the ocean starting in 2004 show that the Atlantic Ocean circulation has observably slowed over the past two decades, possibly to its weakest state in almost a millennium. Studies also suggest that the circulation has reached a dangerous tipping point in the past that sent it into a precipitous, unstoppable decline, and that it could hit that tipping point again as the planet warms and glaciers and ice sheets melt.

In a new study using the latest generation of Earth’s climate models, we simulated the flow of fresh water until the ocean circulation reached that tipping point.

The results showed that the circulation could fully shut down within a century of hitting the tipping point, and that it’s headed in that direction. If that happened, average temperatures would drop by several degrees in North America, parts of Asia and Europe, and people would see severe and cascading consequences around the world.

We also discovered a physics-based early warning signal that can alert the world when the Atlantic Ocean circulation is nearing its tipping point.

The ocean’s conveyor belt

Ocean currents are driven by winds, tides and water density differences.

In the Atlantic Ocean circulation, the relatively warm and salty surface water near the equator flows toward Greenland. During its journey it crosses the Caribbean Sea, loops up into the Gulf of Mexico, and then flows along the U.S. East Coast before crossing the Atlantic.

How the Atlantic Ocean circulation changes as it slows. IPCC 6th Assessment Report

This current, also known as the Gulf Stream, brings heat to Europe. As it flows northward and cools, the water mass becomes heavier. By the time it reaches Greenland, it starts to sink and flow southward. The sinking of water near Greenland pulls water from elsewhere in the Atlantic Ocean and the cycle repeats, like a conveyor belt.

Too much fresh water from melting glaciers and the Greenland ice sheet can dilute the saltiness of the water, preventing it from sinking, and weaken this ocean conveyor belt. A weaker conveyor belt transports less heat northward and also enables less heavy water to reach Greenland, which further weakens the conveyor belt’s strength. Once it reaches the tipping point, it shuts down quickly.

What happens to the climate at the tipping point?

The existence of a tipping point was first noticed in an overly simplified model of the Atlantic Ocean circulation in the early 1960s. Today’s more detailed climate models indicate a continued slowing of the conveyor belt’s strength under climate change. However, an abrupt shutdown of the Atlantic Ocean circulation appeared to be absent in these climate models.

How the ocean conveyor belt works.

This is where our study comes in. We performed an experiment with a detailed climate model to find the tipping point for an abrupt shutdown by slowly increasing the input of fresh water.

We found that once it reaches the tipping point, the conveyor belt shuts down within 100 years. The heat transport toward the north is strongly reduced, leading to abrupt climate shifts.

The result: Dangerous cold in the North

Regions that are influenced by the Gulf Stream receive substantially less heat when the circulation stops. This cools the North American and European continents by a few degrees.

The European climate is much more influenced by the Gulf Stream than other regions. In our experiment, that meant parts of the continent changed at more than 5 degrees Fahrenheit (3 degrees Celsius) per decade – far faster than today’s global warming of about 0.36 F (0.2 C) per decade. We found that parts of Norway would experience temperature drops of more than 36 F (20 C). On the other hand, regions in the Southern Hemisphere would warm by a few degrees.

The annual mean temperature changes after the conveyor belt stops reflect an extreme temperature drop in northern Europe in particular. René M. van Westen

These temperature changes develop over about 100 years. That might seem like a long time, but on typical climate time scales, it is abrupt.

The conveyor belt shutting down would also affect sea level and precipitation patterns, which can push other ecosystems closer to their tipping points. For example, the Amazon rainforest is vulnerable to declining precipitation. If its forest ecosystem turned to grassland, the transition would release carbon to the atmosphere and result in the loss of a valuable carbon sink, further accelerating climate change.

The Atlantic circulation has slowed significantly in the distant past. During glacial periods when ice sheets that covered large parts of the planet were melting, the influx of fresh water slowed the Atlantic circulation, triggering huge climate fluctuations.

So, when will we see this tipping point?

The big question – when will the Atlantic circulation reach a tipping point – remains unanswered. Observations don’t go back far enough to provide a clear result. While a recent study suggested that the conveyor belt is rapidly approaching its tipping point, possibly within a few years, these statistical analyses made several assumptions that give rise to uncertainty.

Instead, we were able to develop a physics-based and observable early warning signal involving the salinity transport at the southern boundary of the Atlantic Ocean. Once a threshold is reached, the tipping point is likely to follow in one to four decades.

A climate model experiment shows how quickly the AMOC slows once it reaches a tipping point with a threshold of fresh water entering the ocean. How soon that will happen remains an open question. René M. van Westen

The climate impacts from our study underline the severity of such an abrupt conveyor belt collapse. The temperature, sea level and precipitation changes will severely affect society, and the climate shifts are unstoppable on human time scales.

It might seem counterintuitive to worry about extreme cold as the planet warms, but if the main Atlantic Ocean circulation shuts down from too much meltwater pouring in, that’s the risk ahead.

This article was updated on Feb. 11, 2024, to fix a typo: The experiment found temperatures in parts of Europe changed by more than 5 F per decade.

René van Westen, Postdoctoral Researcher in Climate Physics, Utrecht University; Henk A. Dijkstra, Professor of Physics, Utrecht University, and Michael Kliphuis, Climate Model Specialist, Utrecht University

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

The changing composition of the world's oceans - acidification

The 12th meeting of the Parties to the Convention on Biological Diversity is currently underway at Pyeongchang in South Korea (6-17 October, 2014). One of the research papers presented at the meeting has addressed the issue of ocean acidification. Acidification of the ocean, caused by increased level of absorption of carbon emissions, has often been cited and identified as major threat to the environment and marine life in particular. Increasingly the evidence of this serious threat to marine life has needed quantification which at last appears to have occured. The sea's acidity level has increased by over 26% during the past 200 years with impacts on corals, shellfish and other calcium-making organisms. The effect of acidification is most strongly felt by tropical coral reefs such as the Great Barrier Reef which is already exposed to warmer water. The impact extends beyond marine organisms and ecosystems but also to over 400 million people who depend on the ocean habitats for survival.

The link is below:

12th Meeting of the Convention on Biological Diversity

Climate Change Insight: Impact of cooler oceans is only temporary

Researchers at UCLA in San Diego in the United States have just released research that shows that the cooling of eastern Pacific Ocean waters has been counteracting the warming effect of greenhouse gases. The impact from this natural variability in ocean cycles is responsible for the pause or “hiatus” in global warming over the last ten years. This is not a permanent effect and will end leading to a resumption in global warming as before.

The UCLA  study examines the tropical Pacific Decadal Oscillation, a climate cycle that occurs over the course of several decades. Within this large pattern are the El Niño and La Niña  cycles that cause shifts in the distribution of warm water in the equatorial Pacific Ocean. While El Niño and La Niña last only a few years, the Pacific Decadal Oscillation lasts several decades. The Oscillation has been in a cooling phase since 1998.

When the climate cycle that governs that ocean cooling reverses and begins warming again, the planet-wide direction toward higher temperatures will resume.

As the researchers have noted, before 2000, global temperatures had risen at a rate of 0.13C per decade since 1950. The hiatus in warming has happened while levels of carbon dioxide, the main greenhouse gas, continue rising steadily. In May 2013, carbon dioxide reached 400 parts per million in the atmosphere for the first time in human history. This study does not refute climate change models, but only reinforces the understanding of the various dynamic forces at work in the environment.

UNESCO's concern over the future of Australia's Great Barrier Reef

Bleached coral - Great Barrier Reef, Australia

The latest report from the World Heritage Committee of the United Nations Educational, Scientific and Cultural Organisation (UNESCO) tabled at the thirty-seventh session in June 2013, raises the uncomfortable proposal to list the Great Barrier Reef on the list of World Heritage sites in danger. UNESCO routinely monitors World Heritage sites and comments on efforts by states parties to maintain these listed valuable sites within their geographical borders. The UN body has raised concerns about coastal development, particularly the Port of Gladstone, and water quality with the Australian and Queensland Governments in previous years but found that key issues were not being fully addressed. In addition there was a lack of transparency in information being provided by the Queensland Government.

In relation to the Great Barrier Reef and Australia, the UN report specifically states:

The World Heritage Centre and IUCN recommend that the World Heritage Committee reiterate its request to the State Party (Australia) to undertake the following actions:

a) make a clear financial commitment to maintain the Reef Rescue programme and ensure water quality continues to improve,
 
b) halt the approval of coastal development projects that could individually or cumulatively impact on the property’s Oustanding Universal Value (OUV) and compromise the ongoing Strategic Assessment, and
 
c) ensure that the legislation protecting the property remains strong and adequate to maintain and enhance its OUV.
 
They further recommend that the Committee consider the Great Barrier Reef for inscription on the List of World Heritage in Danger at its 38th session in 2014 in the absence of a firm and demonstrable commitment on these priority issues by the State Party.

The Great Barrier Reef is one of the wonders of the world and the largest coral reef on the planet. The international recognition of serious threats to its' survival should galvanise further action domestically as warnings from local marine scientists appear to have been largely unsuccessful.