Surge in marine heatwaves costs lives and billions in storm damage – study. Floods, whale strandings and coral bleaching all more likely, say researchers, as 10% of ocean hits record high temperatures in 2023-24

 

A sperm whale died after stranding at Yeh Malet beach in Bali, in April 2023 – warmer ocean temperatures increase the risk of similar events. Photograph: Dicky Bisinglasi/AFP/Getty Images

 Sophie Kevany

 

The world’s oceans experienced three-and-a-half times as many marine heatwave days last year and in 2023 compared with any other year on record, a study has found.

The sustained spike in ocean temperatures cost lives and caused billions of dollars in storm damage, increased whale and dolphin stranding risks, harmed commercial fishing and sparked a global coral bleaching, according to the paper published on Friday in Nature Climate Change.

 

Like heatwaves on land, a marine heatwave is defined as a period of higher than normal temperature over a longer than usual time. The most recent of these were brought about by human-induced climate change and amplified by El Niño conditions, the report’s authors said, with nearly 10% of the ocean hitting record high temperatures in 2023-24.

“The more regularly our marine ecosystems are being hit by marine heatwaves, the harder it is for them to recover from each event,” said lead author Kathryn Smith from the UK’s Marine Biological Association.

Higher ocean temperatures “supercharge” evaporation, the study said, fuelling storms such as Cyclone Gabrielle which hit New Zealand in February 2023, killing 11 people and costing an estimated NZ$14.5bn (about £6.5bn).

One of the most surprising findings in the study, said Smith, was “how much [marine heatwaves] accentuated storms on land and the number of people that were hit by that – hurt, lost possessions, [suffered a] monetary impact or lost their lives”.

At least 45 people died in April last year when a dam burst in Kenya’s Rift valley, as torrential rains battered the country. Photograph: Luis Tato/AFP/Getty Images

 More worryingly, she said: “There is going to be a huge amount more [about the impacts of marine heatwaves] that we don’t know about [yet] because of the time it takes to publish in scientific literature.”

The effect on species was often devastating. Whales and dolphins venture closer to shore when the water is warm because they follow their prey, so this increased their chances of stranding, said Smith. For Mediterranean fan mussels, which have been dying in their millions since 2016, marine heatwaves may be the final nail in the coffin because the warming waters bring increased risk of diseases, the study said.

An aerial photo from February 2023 showing flooding caused by Cyclone Gabrielle in Awatoto, New Zealand. Photograph: AFP/Getty Images

Although human intervention saved some marine life from the recent heatwaves, the study found damage reduction was mostly lacking, possibly due to limited resources, disconnects between organisations and poor communication.

When there was time to prepare, successful mitigation actions included moving corals and conches in Florida to deeper, cooler water and keeping endangered Tasmanian red handfish in aquariums until they could be returned to the wild.

For corals, the study said initiatives to create new colonies using assisted sexual reproduction that increases genetic diversity showed potential, with increased resilience to bleaching “observed in trial populations of reef-building corals across the Caribbean and Mexico”.

Increased ocean temperatures can sometimes bring small wins, the study noted. In Peru, for example, while the anchovy catch was badly affected by the fish moving outside their normal range – a shift that led to commercial fishery closures and estimated losses of $1.4bn (£1.1bn) – squid landings increased.

 A juvenile queen conch. Scientists in the US moved some of the molluscs into cooler waters to protect them from the warming ocean. Photograph: Jennifer Doerr/NOAA SEFSC Galveston

 

Better forecasting, the study found, is critical to reducing damage from severe marine heatwaves, because it provides “greater confidence” for those making damage limitation decisions.

Valeria Pizarro, a scientist at America’s Perry Institute for Marine Science, who was not part of the study, said watching corals bleach “in the blink of my eyes” made her feel “very sad and frustrated”. In most cases, she said, the paper showed effective responses to marine heatwaves were lacking because “we weren’t prepared, we didn’t have the money or the manpower to do much in such a short period of time”.

More broadly, said Smith, the direct link between the climate crisis and ocean temperatures means that “until we see a switch from fossil fuels to renewable energy”, marine heatwaves, and the damage they do, will continue to increase. 

Total collapse of vital Atlantic currents unlikely this century, study finds. Climate scientists caution, however, that even weakened currents would cause profound harm to humanity

Global heating is weakening the Atlantic meridional overturning circulation (Amoc), which plays a crucial role in global weather conditions. Photograph: Henrik Egede-Lassen/Zoomedia/PA
 

Damian Carrington Environment editor

 

 

Vital Atlantic Ocean currents are unlikely to completely collapse this century, according to a study, but scientists say a severe weakening remains probable and would still have disastrous impacts on billions of people.

The Atlantic meridional overturning circulation (Amoc) is a system of currents that plays a crucial role in the global climate. The climate crisis is weakening the complex system, but determining if and when it will collapse is difficult.

Studies based on ocean measurements indicate that the Amoc is becoming unstable and approaching a tipping point, beyond which a collapse will be unstoppable. They have suggested this would happen this century, but there are only 20 years of direct measurements and data inferred from earlier times bring large uncertainties.

 

Climate models have indicated that a collapse is not likely before 2100, but they might have been unrealistically stable compared with the actual ocean system.

The latest study is important because it uses climate models to reveal the reason that the Amoc is more stable: winds in the Southern Ocean continuing to draw water up to the surface and drive the whole system. The study does not rule out an Amoc collapse after 2100, and other modelling research suggests collapses will occur after that time.

“We found that the Amoc is very likely to weaken under global warming, but it’s unlikely to collapse this century,” said Dr Jonathan Baker at the UK’s Met Office, who led the latest study. He said it was reassuring that an abrupt Amoc crash was improbable, and that the knowledge could help governments plan better for future climate impacts. Amoc weakening would still bring major climate challenges across the globe however, with more floods and droughts and faster sea level rise, he added.

“Of course, unlikely doesn’t mean impossible,” he said. “There’s still a chance that Amoc could collapse [this century], so we still need to cut greenhouse gas emissions urgently. And even a collapse in the next century would cause devastating impacts for climate and society.”

Prof Niklas Boers at the Potsdam Institute for Climate Impact Research (PIK) in Germany said the study delivered a substantial improvement in the understanding of Amoc. “But even a weakening that is not due to a tipping point could have similarly severe impacts on, for example, tropical rains,” he said. “One could even go as far as saying that, in the short term, it doesn’t really matter if we have a strong weakening, say 80%, or a collapse.”

The Amoc system brings warm, salty water northwards towards the Arctic where it cools, sinks, and flows back southwards. Global heating, however, is pushing water temperatures up and increasing the melting of the huge Greenland ice cap, which is flooding the area with fresh water. Both factors mean the water is less dense, reducing sinkage and slowing the currents.

The Amoc was already known to be at its weakest in 1,600 years as a result of global heating, and researchers spotted warning signs of a tipping point in 2021. The Amoc has collapsed in the Earth’s past, Baker said. “So it’s a real risk.”

A collapse of Amoc would have disastrous consequences around the world, severely disrupting the rains that billions of people depend on for food in India, South America and West Africa. It would increase the ferocity of storms and send temperatures plunging in Europe, while pushing up sea levels on the eastern coast of North America and further endangering the Amazon rainforest and Antarctic ice sheets. Scientists have previously said a collapse must be avoided at all costs.

The latest study, published in the journal Nature, used 34 state-of-the-art climate models to assess the Amoc. The researchers used extreme conditions – a quadrupling of carbon dioxide levels or a huge influx of meltwater into the North Atlantic – so that the changes in the modelled ocean currents were clear.

They found that while the Amoc slowed by between 20% and 80% this century, it did not collapse completely in any of the models. This was because winds in the Southern Ocean continued to draw water up to the surface. Balancing this, to the scientists’ surprise, were new downwelling areas in the Pacific and Indian oceans, but they were not strong enough to wholly compensate for the slowing of the Amoc, leaving it significantly weakened.

“Even just a 50% reduction in strength would result in a large drop in heat transport that would alter regional and global climates,” said Dr Aixue Hu at the Global Climate Dynamics Laboratory in Colorado, US. “There is therefore no reason to be complacent about Amoc weakening, and every effort must still be made to combat the global warming that drives it.”

Prof Stefan Rahmstorf, an Amoc expert at PIK, said the latest study considered a collapse to be the total cessation of the currents in the North Atlantic, while previous studies have termed a greatly weakened Amoc a collapse.

Amoc is partly driven by the sinking of dense water and partly by winds, and the latest study provides particular insights on the latter. “It does not, however, change the assessment of the risk and impact of future Amoc changes in response to human-caused global warming, as that is linked to the [density-driven] part of Amoc,” Rahmstorf said. His own research on post-2100 Amoc collapse, currently under review, concludes “a collapse cannot be considered a low-probability event any more”.

Despite the revelations in the latest study, the extent of future Amoc weakening and the timing of any collapse remain uncertain. “There’s a huge amount of work left to do, because there’s still a huge range across models in how much Amoc will weaken,” Baker said, with increasing the resolution of models one important requirement.

“We also show that the Southern Ocean and the Pacific Ocean are more important than we thought for Amoc, so we need better observations and modelling in those regions. That’s crucial to improving the projections so we can better inform policymakers,” he said.

 

Extreme weather expected to cause food price volatility in 2025 after cost of cocoa and coffee doubles

 

Chocolate being added to cups of coffee. The prices for cocoa and coffee rose 163% and 103% respectively in the year to January. Photograph: Luca Bruno/AP

 Damien Gayle

 Trend towards more extreme-weather events will continue to hit crop yields and create price spikes, Inverto says

 

Extreme weather events are expected to lead to volatile food prices throughout 2025, supply chain analysts have said, after cocoa and coffee prices more than doubled over the past year.

In an apparent confirmation of warnings that climate breakdown could lead to food shortages, research by the consultancy Inverto found steep rises in the prices of a number of food commodities in the year to January that correlated with unexpected weather.

Several authorities declared 2024 the hottest year on record, a trend towards higher temperatures that seems to be continuing into 2025. Inverto said a long-term trend towards more extreme weather events would continue to hit regional crop yields, causing price spikes.

The highest price rises were for cocoa and coffee, up 163% and 103% respectively, due to a combination of higher than average rainfall and temperatures in producing regions, according to the research.

 

 

 

Sunflower oil prices increased by 56% after drought caused poor crop yields in Bulgaria and Ukraine, which also continued to be affected by the Russian invasion. Other food commodities with sharp year-on-year price rises included orange juice and butter, both up by more than a third, and beef, up by just over a quarter.

“Food manufacturers and retailers should diversify their supply chains and sourcing strategies to reduce over-reliance on any one region affected by crop failures,” Katharina Erfort, of Inverto, said.

 

In December, the UK government said climate breakdown and related food price inflation was leading to a rise in the number of hungry and malnourished households.

Climate scientists said Inverto’s findings were in line with their expectations.

“Extreme weather events around the globe will continue to increase in severity and frequency in line with the ongoing rise in global temperature,” said Pete Falloon, a food security expert at the Met Office and University of Bristol.

 

 

 

“Crops are often vulnerable to extreme weather, and we can expect to witness ongoing shocks to global agricultural production and supply chains, which ultimately feed into food security concerns.”

Max Kotz, of the Potsdam Institute for Climate Impact Research, said data showed heat extremes were already directly affecting food prices.

“Last year showed numerous examples of this phenomena playing out in real time, as extreme heat across east Asia drove substantial increases in the price of rice in Japan and vegetables in China,” he said.

“Market commodities were also strongly affected, with extreme heat and drought across cocoa-producing west African countries and coffee-producing regions in Brazil and Vietnam driving strong increases in prices. Until greenhouse gas emissions are actually reduced to net zero, heat and drought extremes will continue to intensify across the world, causing greater problems for agriculture and food prices than those we are currently facing.”