Cold-blooded sea creatures seeking refuge from warming ocean waters may find themselves at increasing risk of deadly cold shocks due to changes in ocean currents, new research warns.
Climate change is pushing species to higher latitudes in an attempt to stay within their range of comfortable temperatures, but this migration can come with unforeseen consequences.
The new study, published in Nature, documents a mass mortality event in March 2021 that saw at least 260 dead sea creatures wash up on the shores of South Africa.
Using satellite data, ocean observations and data on the movements of bull sharks, the researchers link the event to a sudden influx of cold water coming up from the deeper ocean.
They also show that such events have been increasing in frequency over the past three decades and forecast that this trend may continue into the future as the world continues to warm.
One of the study authors tells Carbon Brief that “we predict this is going to become a more regular phenomenon and could impact a lot of different species”.
Marine migration
As the Earth warms, many species that are able to do so are migrating to higher latitudes, allowing them to maintain their place within their “thermal niche” – the set of temperatures at which they can comfortably survive.
Nowhere is this effect more pronounced than in the global oceans, where there are fewer barriers to migration than there are on land. On average, highly mobile marine species have been moving polewards by nearly 60km per decade since the 1950s, according to the latest report on climate impacts from the Intergovernmental Panel on Climate Change (IPCC).
But this migration comes with its own risks.
These shifting ranges due to climate change can introduce species to new, unfamiliar stressors – such as shipping lanes or fisheries, says Dr Natalie Posdaljian, a bioacoustician at Scripps Institution of Oceanography in La Jolla, California, who was not involved in the study.
One of these risks is what the researchers describe as a temperature “bait and switch” – where creatures seeking warmer waters can instead be trapped by a sudden cold event. Posdaljian tells Carbon Brief that the new study is the first time that she’s seen evidence of this hazard.
Mass mortality
On 2 March 2021, dead sea creatures started washing up on the south-eastern shores of South Africa between Port Elizabeth and East London. In all, more than 250 individual organisms and 82 separate species were found, including large, migratory species such as manta rays and bull sharks.
In deducing what had happened, the team of researchers examined the temperature data in the days leading up to the event. Using satellite and other observational data, they found that the temperature of the surrounding ocean had dropped by up to 9.2C in less than 24 hours.
The cold event persisted for seven days and had “severe physiological consequences” for the marine organisms there, including hypothermia, malfunction and death, the paper says.
Similar cold shocks have previously occurred in south-eastern South Africa, dating back to at least 1989 and affecting a wide array of creatures, according to the study. But this instance was “probably the biggest cold-water shock [mass mortality event]” ever recorded, Dr Ryan Daly, a marine scientist at the Oceanographic Research Institute in Durban, South Africa, tells Carbon Brief. Daly is one of the authors of the new study.
The influx of cold water was due to a process called “upwelling”, which carries cold, nutrient-rich water from the ocean depths to its surface.
The study identifies three factors that make rapid upwelling events likely to happen: strong currents interacting with the continental shelf, strong winds blowing from the east to the west and meanders in the current. Such winds occur predominantly during the southern hemisphere’s summer, between October and April. They often act as a harbinger of temperature drops occurring in the coming 0-72 hours, the study notes.
All three of these factors are characteristic of both the south-eastern coast of South Africa and the eastern coast of Australia, where strong currents known as the Agulhas and the East Australian Current, respectively, run up against the continental shelf.
‘Trapped’
Dr Camrin Braun, an ocean ecologist at the Woods Hole Oceanographic Institution in Massachusetts, finds it surprising that even large, migratory species such as rays and bull sharks were killed by the cold snap. Braun, who was not involved in the new research, tells Carbon Brief that these animals “can move really far and really fast”.
Daly says that this surprised the research team as well. But it’s possible, he says, that the onset of the cold temperatures was quick enough and large enough that the animals got “trapped” instead of being able to escape.
To underscore this, the researchers use data on bull shark movements and ocean temperatures from tags attached to sharks before, during and after the event.
They find that the sharks consistently demonstrate “attempted avoidance” of lower temperatures – moving closer to the surface while swimming through upwelling areas and only travelling at deeper depths once they reach warmer waters.
The team also observe one shark taking up residence in a sheltered bay during one upwelling event to escape the cold waters. The researchers write that these actions “probably represent behavioural strategies to avoid/survive intense temperature declines”.
On its own, the shark-movement data is “kind of limited” and does not “make a very convincing case”, Braun says. But combining it with other data “really up[s] the ante on the importance” of the research, he adds.
Climate patterns
The researchers also look at several decades’ worth of sea surface temperature and wind data to understand whether these upwelling events are changing in frequency or intensity.
They identify clear increasing trends in the proportion of winds that favour upwelling events across three sites in South Africa. (Previous research has shown a similar increase in such winds in south-eastern Australia.)
Then, for the three South African sites and three Australian sites, they compare temperature data from three locations: “inshore”, defined as between 0-15km from the shore, “midshelf”, which is 15-30km from the shore and “offshore” – located within the warm “core” of the current. The inshore and midshelf locations fall within the upwelling zone, but the offshore ones do not.
If, as they hypothesised, upwelling events were becoming more frequent, the number of cold events inshore would increase over time, while the number of such events offshore would stay the same. Similarly, an upwards trend in the intensity of cold snaps would be revealed in the inshore and midshelf, but not the offshore, data.
The chart below shows that the proportion of upwelling-favourable winds (top left) at three sites in South Africa has been steadily increasing since the “upwelling season” – the period of upwelling-favourable winds stretching from October to April – of 1988-89.
The other three charts show increasing trends in the number of cold events (top right), the average intensity of cold events (bottom left) and the average rate of onset of such cold events (bottom right) for a single site, Port Alfred, over the same period. All three characteristics increase over time for the inshore (blue) and midshelf (pink) locations, but not the offshore (green) one, supporting the idea that the cold snaps are linked to upwelling.
These increases persist over long enough time periods, the authors argue, to be clear evidence of long-term trends, rather than natural variation. Furthermore, the study points to previous research – dating back more than 30 years – that shows evidence of climate change increasing upwelling intensity due in part to increasingly strong winds driven by the land warming faster than the ocean.
This trend analysis is one of the most valuable contributions of the new study, Posdaljian says. She tells Carbon Brief:
“It’s often hard to be able to have that kind of concrete evidence about how something could be increasing in intensity or frequency over time.”
The idea that climate change could lead to an increase in cold snaps may seem counterintuitive. But those increased temperatures “mean more energy in the climate [system] too”, Daly says. He explains:
“This wind-driven upwelling, linked to climate change, is essentially an extreme event – just like we might have more flooding and stronger cyclones and hurricanes.
“If you think about equivalent on land, that might be fires being fuelled by more intense wind. It takes an existing natural phenomenon and basically supercharges that to become [more] intense.”
He adds:
“Going forward, we predict that this is going to become a more regular phenomenon and could impact a lot of different species.”
The researchers “did a really good job of creating this foundational understanding” of how such cold events could hit marine ecosystems in future, Posdaljian says.
Looking ahead, she adds that she would like to see more work focusing on projecting future trends in cold snaps and perhaps even being able to predict them. She tells Carbon Brief:
“A lot of these animals are not just dealing with one stressor from climate change…We can’t necessarily mitigate these [extreme events], but what we can do is maybe reduce the other stressors that we can control.”
The post Climate change ‘bait and switch’ threatens sharks and rays appeared first on Carbon Brief.
Claver Gatete is Executive Secretary of the UN Economic Commission for Africa. Jason Veysey is Energy Modeling Program Director and Senior Scientist at the Stockholm Environment Institute. Lisa Sachs is Director of the Columbia Center on Sustainable Investment at Columbia University.
The case for global energy transition has rarely been clearer. The closure of the Strait of Hormuz earlier this year exposed the cost of unplanned, fossil-dependent systems, while the falling cost of renewables, the rising penetration of electric vehicles, and the growing value of demand flexibility have made the direction of travel obvious. The benefits of a clean, secure, integrated system are no longer in dispute. What remains unclear is how to build it.
Countries around the world have called for faster renewable energy deployment and alternative energy arrangements. A secure, affordable, resilient, decarbonised system requires specific investments in specific places in a specific sequence, optimised across sectors and borders. But very few governments have the analytical foundation to translate those imperatives into investment.
The two instruments that are supposed to determine investment priorities for decarbonisation – Nationally Determined Contributions (NDCs) and country platforms – cannot answer the most basic question facing any country undertaking an energy transition: what should the energy system look like?
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To close this gap, every country needs a bankable, economy-wide optimisation model for its energy system. A model is not a plan, but it can help answer the critical question of what the future energy system should look like. It shows how optimal scenarios vary as assumptions and policies are adjusted, calculates investment requirements and sequencing, and quantifies how system costs are affected by assumptions, policies, and exogenous variables like trade policy and financing terms.
Tool for efficient investment
Optimisation is a simplified way of simulating an energy system, but it can be an extremely powerful tool for moving energy planning from reactive (how do we manage the disparate actions in the energy system?) to intentional (what energy system underpins our national objectives?). A model can show how optimal scenarios vary as assumptions and policies are adjusted, and how investment requirements are quantified and sequenced.
Optimisation models can treat the energy system and the sectors it serves as an integrated whole, optimising across sectors and projects in ways that can be mutually reinforcing. If considered independently, growth in industrial demand, transport electrification, and digital infrastructure can add stress to the energy system. But an optimised plan can arrange these and other changes in an efficient, synergistic way.
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New load can be added where low-cost power is available; industrial customers can ensure the viability of investments in energy supply; electric vehicle charging policy can smooth load curves and reduce costs for all consumers.
Additionally, optimisation modeling can also change the financeability of investments. Taken alone, each project faces uncertainty about the rest of the system, which raises the cost of capital and causes projects to stall or unwind after contracts are signed. A coherent, optimised plan makes visible the coordination that private capital would otherwise have to bet on: identified offtake, sequenced and committed transmission, contracted power supply, and so on.
What COP31 and COP32 should do
The upcoming COPs in Turkey and Ethiopia can shift the center of gravity of international climate cooperation from fragmented commitments to planning. Three moves are urgently needed.
First, optimised, economy-wide, long-term energy system planning must be the foundation on which any meaningful NDC, country platform, or finance commitment rests. NDCs are typically drafted by environment or single-line ministries, with limited cross-sectoral input from ministries of energy, finance, and planning. They contain targets, derived from sectoral strategies or national commitments, not from an analytically grounded picture of what the energy system should look like and what investments would make it work. Country platforms are generally a portfolio of investments assembled from existing project pipelines, rather than derived from a system-level analysis of what an optimised, decarbonised energy system would require.
Second, recognise regions as a key planning unit. Modern integrated energy systems are inherently regional. Renewable endowments are unevenly distributed; balancing variable supply across borders lowers aggregate cost, reduces redundant backup capacity, and unlocks economies of scale no individual nation can achieve. Many energy investments in Southeast Asia, East Africa, Southern Africa and Central Asia may only be financeable in a regional context. Assessing domestic infrastructure without regional optimisation perpetuates the perception that decarbonisation is more expensive than it is.
COP31 leaders unveil global targets, with spotlight on electrification
Third, finance the planning capacity. A coordinated commitment by multilateral development banks, bilateral donors, and philanthropic partners to help every region and its constituent countries develop and maintain their own modelling capability, with open-source tools and regional analytical hubs, would close the most consequential gap in the current architecture. The cost is small relative to current spending on country platforms, failed project preparation, and misallocated infrastructure investment.
This includes supporting regional institutions such as the ASEAN Centre for Energy, the African Energy Commission, regional power pools, and the Latin American and Caribbean Energy Organization to determine what optimised regional systems require. Country-by-country pledging, repeated at every COP, will not deliver what meaningfully integrated systems can.
The 2026 energy crisis made the cost of unplanned, fossil-dependent systems newly visible. That window of clarity will close. The international community should seize the moment to build the planning foundation that has been missing for thirty years, rather than commissioning another round of NDCs or pledges, striving for outcomes neither was designed to deliver.
The post Every country needs a model to help optimise its energy transition appeared first on Climate Home News.
Every country needs a model to help optimise its energy transition
The world is currently experiencing what is expected to become the strongest El Niño on record – dubbed a “super El Niño” by many.
El Niño is the warm phase of a recurring climate pattern in the tropical Pacific that releases heat from the ocean into the atmosphere.
This temporarily raises global temperatures and reshapes rainfall and extreme weather around the world – impacting the lives of billions of people.
The current El Niño event began in June and is expected to last into 2027.
El Niño is part of a wider climate pattern called the El Niño-Southern Oscillation (ENSO) cycle.
The ENSO cycle also has a cool phase, known as La Niña, as well as a “neutral” phase. El Niño and La Niña events typically last between nine and 12 months, but can go on longer.
Below, Carbon Brief explains how the ENSO cycle works, its impacts on extreme weather and global temperatures and why this El Niño event is projected to be the most intense since records began.
The post Explainer: How the ‘super El Niño’ will reshape the world’s weather appeared first on Carbon Brief.
https://interactive.carbonbrief.org/el-nino-explainer/index.html
The second-largest reservoir in the US reached a record-low water height on Saturday – just days after the country’s largest reservoir broke its own record.
Both Lake Mead and Lake Powell are located on the Colorado River.
They provide water for populations across seven US states in the south-western US, with around 40 million people getting some or all of their municipal water from the Colorado River.
The river also provides water for around 5.5m acres (22,258 square kilometres) of farmland across Colorado, Arizona, California and the other states in the river basin.
Experts tell Carbon Brief that climate change, population growth and over-consumption are all contributing to the current record-low levels of the reservoirs.
Record lows
At full capacity, Lakes Mead and Powell can hold a combined 68 cubic kilometres of water – enough to supply all household consumption in the contiguous US for nearly 1.5 years. However, the water level in both reservoirs has been declining for decades.
The chart below shows the water level of Lake Mead, in metres above mean sea level. The reservoir, which began to fill in 1935 following the construction of the Hoover Dam, has a “full pool” maximum capacity of 347.60 metres. The water level in Lake Mead reached a record low of 317.11 metres on 7 August.
The following chart shows the water level of Lake Powell, in metres above mean sea level. Lake Powell’s full-pool level is 1,127.76 metres.
While the reservoir reached its maximum capacity several times in the 1980s, it has not done so since. On 15 August, the water level in Lake Powell was recorded at a new record-low of 1,072.87 metres.
Both reservoirs have continued to decline in the days since breaking their respective records. The downward trend will largely continue in both lakes until next spring, when the snowpack in the mountains of the Upper Colorado River Basin begins to melt, says Dr Jack Schmidt, a senior research scientist at Utah State University’s Center for Colorado River Studies. He tells Carbon Brief:
“The big dilemma of the moment is that we’re only in the middle of August, and we have no assurance of what the coming winter will be. The only thing we can be sure of is that we will be depleting overall total basin reservoir storage from now until, roughly, early April.”
Compounding factors
The record lows across the two reservoirs are the result of several compounding factors, experts tell Carbon Brief.
Since the turn of the 20th century, the amount of water flowing along the Upper Colorado River has declined by about 20%. Research suggests that half of this decline can be attributed to human-induced climate change.
Most of the river’s streamflow comes from the snowpack of the Upper Colorado River Basin, which stretches across five western US states but is primarily located in Colorado and Utah.
This region has been gripped by a historic “megadrought” for more than a quarter of a century. Nearly half of the megadrought’s intensity over 2000-18 is attributable to climate change, according to a 2020 study.
At the same time, the increasing population in the US south-west has put added pressure on the Colorado River’s water supply. The number of people obtaining some or all of their water from the Colorado system has grown by 15 million (around 60%) since 1992.
Schmidt tells Carbon Brief:
“There’s an ultimate cause of the present water crisis, and there’s a proximate cause. The ultimate cause is a warming climate, a warming planet and a pretty clear correlation between warming conditions and decreased runoff in the Colorado River Basin.
“The proximate cause is that in this messy democratic republic of ours, big policy decisions that match the variability of the climate occur painfully slowly – with intense political negotiations – and only incrementally.”
On 31 July, the US Bureau of Reclamation, which manages water resources in the western US, released an environmental impact statement on its proposed post-2026 strategy for managing Lakes Powell and Mead. The strategy itself has not been released yet.
Schmidt notes that the statement does appear to give the Bureau flexibility to “respond to crisis” by reducing the delivery of water to several states. However, he adds:
“They acknowledge it won’t work if we just stay critically dry, and of course every climate model for the 21st century, especially with a continually warming planet, says that that’s exactly what’s going to happen.”
The post Analysis: The two largest reservoirs in the US have hit record-low levels appeared first on Carbon Brief.
Analysis: The two largest reservoirs in the US have hit record-low levels
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