The overlapping crises of extreme heat and Covid-19 “severely stretched” an already overwhelmed healthcare system in the UK with “deadly consequences”, a new study finds.
The research, published in Nature Climate Change, estimates the number of heat- and cold-related deaths in England and Wales before and during the Covid-19 pandemic.
The study finds that pressure on the health system during heatwaves was as much as three times higher for the pandemic years than it was in the previous decade. The authors find a similar result during cold periods.
The number of heat-related deaths “shifted higher” in the Covid-19 years, the study says, suggesting that Covid “may have impacted temperature-related mortality during extreme weather events”.
The authors warn that “if health services are already operating at capacity because of one crisis, the additional health burden from another crisis can break the system entirely, endangering the lives of many people”.
One expert not involved in the study tells Carbon Brief that any future pandemic is likely to be a “syndemic”, where its impacts intertwine with those of a changing climate.
And as similar groups tend to be most vulnerable to both major disease outbreaks and extreme weather, anticipating and preparing for the co-occurrence of such events “would be lifesaving”, the study authors conclude.
Heat, cold and Covid
Extreme weather events and pandemics are among the most serious risks facing the UK, according to the UK National Risk Register. Since 2020, both have claimed thousands of lives in the UK.
Between the UK’s first documented Covid-19 case on 30 January 2020 and the end of 2022, around 190,000 people in England and Wales died of the virus, according to death certificates.
Over this two-year study period, the UK has also seen extreme hot and cold temperatures – from the coldest UK temperature in more than 20 years during February 2021 to the country’s first recorded instance of 40C heat in July 2022.
To assess the link between temperature and mortality, the authors produced “epidemiological models” that analyse exposure to different temperatures and human mortality in different regions of the UK.
Dr Eunice Lo is a research fellow in climate change and health at the University of Bristol and lead author on the study. She tells Carbon Brief that “heatstroke and heat exhaustion can occur quite rapidly” and that, in her models, “we expect the mortality outcome to be within three days of exposure to heat”. In contrast, it takes longer for cold snaps to cause mortality, she adds.
The plot below illustrates the example of London. The lowest point on the curve – indicated by a “relative risk” level of one – shows the optimum temperature, when people are at lowest risk of physiological harm from temperature extremes.
If the temperature rises above (red) or falls below (blue) the optimum temperature, the risk of temperature-related mortality increases. This is indicated by a relative risk level greater than one.
Cumulative relative risk of death in London for the overall population, using data from 1981-2022. Source: Lo et al (2024).
The authors developed a series of models for locations across England and Wales. The study estimates that, over the study period, almost 8,500 excess deaths were attributable to high temperatures and more than 125,000 deaths to cold.
The study points out that cold-related deaths are more common in the UK as “most days of the year are considered moderately cold”. As the planet continues to warm, heat-related deaths are expected to rise, while cold-related deaths will likely fall.
Lo tells Carbon Brief that factors including age and socioeconomic status also affect temperature-related mortality, but these were not included in the model.
Extreme temperatures
The chart below, from the study, shows a timeseries of daily deaths attributable to heat (red), cold (blue) and Covid-19 (purple) in England and Wales over the study period. The black line shows deaths in the UK from all causes. The right-hand section of the chart focuses on the July 2022 heatwave, when daily heat-related mortality peaked at 580 deaths – higher than at any time of over the previous decade.
Annual “all-cause mortality” in England and Wales was higher during the pandemic than it was in the preceding decade, as Covid-19 drove up mortality rates, the study finds.
The authors note that cold-related mortality “dominated” heat-related mortality in all months other than July, August and September – adding that spikes in cold-related mortality often coincided with spikes in deaths due to Covid.
There are a range of reasons for this. For example, low humidity in winter allows droplets containing the virus to spread further. And peoples’ immune systems are weaker in the winter due to a lack of vitamin D, making them more vulnerable to the virus.
The study also notes that, over the whole study period, “cumulative temperature-related deaths exceeded cumulative Covid-19 deaths by 8% in south-west England”. And while total temperature-related deaths did not exceed those from Covid in other regions, they did amount to 58% (East Midlands) to 75% (London) of Covid-19 deaths by the end of 2022.
The approach used in the study assumes that deaths caused by Covid-19 and temperature extremes are independent of each other. In other words, individuals are assumed to die either due to Covid or as a result of extreme temperature exposure, but not a combination of the two.
Nonetheless, the findings suggest that Covid “may have impacted temperature-related mortality during extreme weather events”, the study says. For example, “heat-related mortality shifted higher in the Covid-19 years”, compared to extreme events that were not affected by the disease, the authors note.
At the same time, “extreme heat may have exacerbated Covid-19 mortality”, the authors note, pointing out that on 19 July 2022 – the day that 40C heat was recorded – Covid caused 91 more deaths than the daily average over 10-25 July.
The results “highlight the complex interplay between extreme temperatures and the Covid-19 pandemic, as well as its implications on population health and health services capacity”, the study says.
Mapped
The study maps out Covid- and temperature-related deaths to see how they vary regionally.
The authors select 70 heatwave days and 70 cold days from the 30 January 2020 to 31 December 2022 study period. They then calculate regional mortality rates due to Covid, heat and cold during these days.
The maps below show the ratio of temperature-related deaths to Covid-driven deaths over the full study period (left), heatwave period (middle) and cold period (right). Numbers below zero, shown in grey, indicate that Covid-related deaths are higher than temperature-related deaths. Numbers above zero, shown in blue and purple, indicate that temperature-related deaths are higher.
During heatwaves, heat-related deaths far exceed deaths due to Covid-19 in almost all the regions studied. The study finds that the ratio of temperature to Covid-related deaths was highest in London at 2.7, where temperatures tend to be higher.
(This is likely due, in part, to the urban heat island effect – in which a combination of factors, such as buildings, reduced vegetation and high domestic energy use, cause urban areas to become hotter than more rural regions.)
This finding shows that “that even during the Covid-19 pandemic, heatwaves posed a serious threat to public health”, the study says.
Meanwhile, during cold snaps – when both cold-related mortality and deaths due to Covid spiked – Covid-related mortality was higher. The ratio ranges from 0.4 in east of England to 0.8 in south-west England.
The authors suggest that this is mainly due to “large surges in Covid-19 mortality following the first emergence of the coronavirus and the domination of the Alpha variant, both of which occurred in winter”.
The authors then performed the same heatwave and cold snap calculations for the decade preceding the pandemic, to provide a 2010-19 pre-Covid baseline.
The maps below show the ratio of average annual deaths per 100,000 people during the Covid study period to that during the preceding decade, during heatwaves (left) and cold snaps (right). Lighter green indicates that mortality rates in the Covid and pre-Covid periods were similar, while darker colours indicate that deaths during the Covid study period were higher.
The authors find that during pre-Covid heatwave days, heat-related deaths ranged from six to 14 people per 100,000. They add that during the Covid-19 study period, deaths due to heat and Covid-19 together range from 19 to 24 deaths per 100,000 people.
The authors assume that mortality broadly links to regional demand on health services. As such, they estimate that demand on regional health services was between 1.6 (London) and 3.2 (north-west England) times higher during the pandemic than in the previous decade.
By carrying out the same analysis, the authors find that during cold snaps, demand on health services was between 2.0 (south-west England) and 3.4 (east of England) times higher during Covid than in the previous decade.
The paper highlights “the deadly consequences of an already overwhelmed NHS severely stretched to function through the compound crises of extreme weather and Covid-19”, the authors say, adding:
“If health services are already operating at capacity because of one crisis, the additional health burden from another crisis can break the system entirely, endangering the lives of many people.”
Dr Kristina Dahl is senior climate scientist at the Union of Concerned Scientists. In 2020, she was a co-author on a comment paper in Nature Climate Change on the compound risks of climate change and the Covid pandemic.
Dahl tells Carbon Brief that the results of this study highlight the need for “amplified public messaging to increase awareness of temperature-related risks”, for “stronger policies and protections around extreme weather”, and to “more adequately prepare public health systems for the co-occurrence of hazards”.
Co-occurring hazards
Despite the study treating temperature- and Covid-related deaths as independent, Lo tells Carbon Brief that “there is certainly a two-way interaction” between the two.
She explains that “a lot of vulnerabilities to temperatures and Covid-10 are shared”, noting that elderly people and those with pre-existing conditions are vulnerable to both extreme temperatures and viruses. This means that one could exacerbate the other, she warns.
She adds that many measures taken to reduce the spread of Covid may have contributed to a rise in temperature-related death. For example, closing social spaces, such as swimming pools and air-conditioned buildings, meant that many people “didn’t have as much of an escape” from the high temperatures in their homes, she says.
Dr Colin Carlson is an assistant research professor at Georgetown University’s centre for global health, science and security and another co-author on the Nature Climate Change comment paper.
Carlson, who studies the relationship between global climate change, biodiversity loss and emerging infectious diseases, tells Carbon Brief that “for the last two decades, we’ve been operating in a very limited framework with how we think about climate change and infectious disease”.
He adds that “going forward, every pandemic will probably be a ‘syndemic’ with a few climate change-related components”.
Lo notes that while this study focuses on the relationship between Covid-19 and extreme temperatures, it speaks to a larger point about the link between climate-related extremes and other hazards, as co-occurring crises can threaten healthcare and other key systems.
Similarly, Dahl warns:
“As climate-related extremes become more frequent, the likelihood that they will intersect with other crises – whether related to public health, social or political unrest, or other environmental problems – will increase.”
The post Dual impact of extreme heat and Covid-19 had ‘deadly consequences’ for UK appeared first on Carbon Brief.
Dual impact of extreme heat and Covid-19 had ‘deadly consequences’ for UK
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.
Two to tango: How governments can unlock private investment for national climate goals
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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