Climate change is creating “new vulnerabilities” for pandemics, according to new research.
The study, published in Science Advances, investigates nine zoonotic diseases – infections transmitted from animals to people – with high potential to cause severe public-health emergencies.
These diseases include the Zika virus, Ebola and Severe Acute Respiratory Syndrome (SARS).
Overall, the research finds that 9% of the planet’s land area is currently at “high” or “very high” risk of an outbreak of these diseases.
The study authors find that higher temperatures, increased rainfall and water scarcity are “key drivers” of disease outbreaks.
However, the paper has received a mixed reception from other scientists.
While one expert not involved in the study praises it for its novelty and rigour, another tells Carbon Brief that the research fails to capture some of the key drivers of zoonotic disease.
They tell Carbon Brief that “this idea that you can do a one-size-fits-all global risk assessment is just untrue”.
Zoonotic disease
There are more than 200 known “zoonotic diseases” – infections or diseases that are transmitted to humans from pets, livestock or wild animals.
Zoonotic diseases are spread when the pathogen that causes the disease – such as a virus, bacterium, fungus or parasite – moves from animals to humans. This can be through a bite, blood, saliva or faeces.
Lyme disease, rabies and bird flu are examples of well-known zoonotic diseases. One of the most well-known, Covid-19, is thought to have killed hundreds of thousands of people since the SARS-CoV-2 virus was first recorded in humans in 2019.
Pathogens are typically carried by animals, called hosts. For example, dogs are the main hosts of rabies.
The World Health Organization (WHO) keeps a list of “priority diseases” for research and development. These are zoonotic diseases that have the potential to cause severe public health emergencies, such as epidemics – in which there is a sharp rise in cases in a specific region – and pandemics, where a disease occurs over a very wide area and crosses borders.
The WHO updates its list regularly. It currently features the following zoonoses:
- Zika virus
- Ebola virus and Marburg virus disease
- SARS and Middle East respiratory syndrome coronavirus (MERS-CoV)
- Covid-19
- Crimean-Congo haemorrhagic fever
- Lassa fever
- Nipah disease and henipaviral diseases
- Rift Valley fever
- “Disease X” (a label created by the WHO in 2018 to represent a hypothetical, unknown pathogen that could cause a future epidemic)
The number of new zoonotic diseases is increasing rapidly.
Many different factors can influence the spread of zoonotic diseases. One of the most important is climate. Pathogens and the animals that carry them typically thrive in a warm and wet climate, so many zoonotic diseases are found in tropical regions.
The frequency of contact between humans and animals is another important factor. This means that when people live close to areas of high biodiversity, such as forests, there is a higher risk of zoonotic disease transmission.
Mapping risk
The authors of the new study collected data on “outbreaks” of the WHO priority zoonotic diseases over 1975-2020 from the Global Infectious Diseases and Epidemiology Network.
They exclude Covid-19 from their analysis, although it is a WHO priority disease, because its “overwhelming prevalence” resulted in worldwide coverage, making it difficult to identify spatial patterns.
The database defines an outbreak as two or more linked cases of the same illness, a number of cases that exceeds the expected number, or a single case of disease “caused by a pathogen that poses a significant threat to public health”, the study explains.
The authors identified 131 outbreaks of infectious diseases with epidemic and pandemic potential over 1975-2020
The authors then used satellite data to identify nine “risk factors” that can affect the transmission of zoonotic diseases:
- Annual maximum temperature
- Annual minimum temperature
- Water deficit
- Annual total rainfall
- Livestock density
- Frequency of land-use change
- Change in proximity between humans and forests
- Biodiversity loss
- Human population density
The authors used a “predictive model”, which makes use of machine-learning techniques, to combine these variables. This allows them to determine the risk of climate outbreaks from the WHO priority diseases in different regions.
Finally, the authors adjusted their results to account for a bias in how data on disease outbreaks is recorded. In developed countries and regions, diseases are more likely to be detected and recorded, while this is less likely in developing regions.
The map below shows the risk of a disease breakout across the world from the nine WHO priority zoonotic diseases. Darker colours indicate greater risk, while white indicates regions where not enough data was available.
The map shows that the southern hemisphere of the planet has a higher risk of pandemic breakout than the northern hemisphere, “with the majority of those areas located in Latin America and Oceania”. Meanwhile, very little risk is seen in Europe and North America.
The authors find that 9% of the world’s land surface, home to around 130 million people, is at “very high” or “high” risk of outbreaks of the diseases.
Lead author Dr Angela Fanelli is a researcher at the European Commission’s Joint Research Council. She tells Carbon Brief that “this study is the first to comprehensively examine the shared drivers of zoonotic diseases with epidemic and pandemic potential on a global scale”.
The authors also use data from the International Health Regulations to score countries based on their capacity to respond to zoonotic events at the animal-wildlife interface.
By integrating this data into their analysis, the authors developed an “epidemic risk index” which shows each country’s risk and capacity to respond to “zoonotic threats”. In this index, Papua New Guinea is ranked as the lowest – indicating the greatest risk of epidemics.
The full table is shown below, where a higher number indicates a greater risk of epidemics.
‘New vulnerabilities’
The authors went on to analyse the different factors that influence the risk of zoonotic breakout.
The charts below illustrate how, for most risk factors explored in the report, a higher value results in a greater risk score for zoonotic disease outbreak.
For example, the plot on the top left shows how higher maximum temperatures lead to a higher risk of disease outbreak.
The paper notes that higher temperature and annual rainfall levels “elevate the risk of disease outbreaks”. It suggests that this is because host species are better adapted to hotter, wetter conditions.
The paper also assesses water deficit, a measure that can capture the monthly differences between rainfall and potential evapotranspiration – the transfer of water from the ground into the air through a combination of evaporation and transpiration.
The authors find that “moderate water scarcity” is associated with the highest risk of outbreaks. This could be because moderate water scarcity can cause animals to group together around remaining water sources, allowing the pathogen to be transferred more easily, they suggest.
Meanwhile, they say that “excessively arid conditions” can cause the host population to die out, meaning the pathogen is unable to spread.
Fanelli tells Carbon Brief that the study highlights “several key mechanisms by which climate change could increase the risk of disease outbreaks”.
Climate change, she says, can make host populations “more susceptible to disease outbreaks” and result in water shortages that “compromise water quality, hygiene and sanitation, further increasing the risk of disease outbreaks.”
The authors warn that the changing climate is “creating new vulnerabilities” for zoonotic disease transmission as it “reshapes the geographic distribution of risk”.
The paper also finds that changes in land use can increase disease risk. When people cut down trees in areas of high biodiversity, they can suddenly come into contact with species that they do not usually interact with, providing an opportunity for pathogens to jump from humans to animals, the authors find.
Higher population densities of people or livestock are also linked to a higher risk of zoonotic diseases, because the pathogens are able to spread more easily.
Mixed reception
The study has received mixed responses from scientists not involved in the work.
Dr Ibrahima Diouf, a postdoctoral researcher on climate and health at Senegal’s Cheikh Anta Diop University, tells Carbon Brief that the research “offers a more holistic perspective” than studies that focus on a single disease and has a “sound, innovative and transparent” methodology.
He also praises the study for “bridg[ing] environmental modelling and public health planning”, and for capturing both hazard exposure and “national response capacity”. He says:
“This dual lens enables practical prioritisation of interventions. Countries like the Republic of Congo and Madagascar, which face both high risk and limited response capacity, emerge as key candidates for targeted support through regional or multilateral adaptation programmes.”
Dr Colin Carlson, an assistant professor of epidemiology at Yale School of Public Health, tells Carbon Brief that this type of work “has been done before”:
“We’ve seen a lot of these studies that look at a hundred or so outbreaks and then use machine learning – an approach that will almost always find some kind of signal – to confirm their hypothesis that environmental degradation drives disease outbreaks.”
Carlson also criticises the study’s methodology, arguing that the variables the authors chose focus on “intact tropical rainforests and other tropical ecosystems” that are “hot, wet, biodiverse [and] populated”. He continues:
“That’s where a lot of disease outbreaks are, but that’s true as much because of poverty as because of the environment, if not more.”
Carlson tells Carbon Brief that “this idea that you can do a one-size-fits-all global risk assessment is just untrue”.
He adds that the work contributes to a “narrative that spillover [of pathogens from animals to humans] is a problem of the global south – and that pandemics happen because the people living in these countries are somehow unengaged in outbreak prevention or unwilling to leave nature alone”.
In Carlson’s view, this narrative is “wrong”.
The post Climate change is creating ‘new vulnerabilities’ for disease pandemics appeared first on Carbon Brief.
Climate change is creating ‘new vulnerabilities’ for disease pandemics
Drought and heatwaves occurring together – known as “compound” events – have “surged” across the world since the early 2000s, a new study shows.
Compound drought and heat events (CDHEs) can have devastating effects, creating the ideal conditions for intense wildfires, such as Australia’s “Black Summer” of 2019-20 where bushfires burned 24m hectares and killed 33 people.
The research, published in Science Advances, finds that the increase in CDHEs is predominantly being driven by events that start with a heatwave.
The global area affected by such “heatwave-led” compound events has more than doubled between 1980-2001 and 2002-23, the study says.
The rapid increase in these events over the last 23 years cannot be explained solely by global warming, the authors note.
Since the late 1990s, feedbacks between the land and the atmosphere have become stronger, making heatwaves more likely to trigger drought conditions, they explain.
One of the study authors tells Carbon Brief that societies must pay greater attention to compound events, which can “cause severe impacts on ecosystems, agriculture and society”.
Compound events
CDHEs are extreme weather events where drought and heatwave conditions occur simultaneously – or shortly after each other – in the same region.
These events are often triggered by large-scale weather patterns, such as “blocking” highs, which can produce “prolonged” hot and dry conditions, according to the study.
Prof Sang-Wook Yeh is one of the study authors and a professor at the Ewha Womans University in South Korea. He tells Carbon Brief:
“When heatwaves and droughts occur together, the two hazards reinforce each other through land-atmosphere interactions. This amplifies surface heating and soil moisture deficits, making compound events more intense and damaging than single hazards.”
CDHEs can begin with either a heatwave or a drought.
The sequence of these extremes is important, the study says, as they have different drivers and impacts.
For example, in a CDHE where the heatwave was the precursor, increased direct sunshine causes more moisture loss from soils and plants, leading to a drought.
Conversely, in an event where the drought was the precursor, the lack of soil moisture means that less of the sun’s energy goes into evaporation and more goes into warming the Earth’s surface. This produces favourable conditions for heatwaves.
The study shows that the majority of CDHEs globally start out as a drought.
In recent years, there has been increasing focus on these events due to the devastating impact they have on agriculture, ecosystems and public health.
In Russia in the summer of 2010, a compound drought-heatwave event – and the associated wildfires – caused the death of nearly 55,000 people, the study notes.
The record-breaking Pacific north-west “heat dome” in 2021 triggered extreme drought conditions that caused “significant declines” in wheat yields, as well as in barley, canola and fruit production in British Columbia and Alberta, Canada, says the study.
Increasing events
To assess how CDHEs are changing, the researchers use daily reanalysis data to identify droughts and heatwaves events. (Reanalysis data combines past observations with climate models to create a historical climate record.) Then, using an algorithm, they analyse how these events overlap in both time and space.
The study covers the period from 1980 to 2023 and the world’s land surface, excluding polar regions where CDHEs are rare.
The research finds that the area of land affected by CDHEs has “increased substantially” since the early 2000s.
Heatwave-led events have been the main contributor to this increase, the study says, with their spatial extent rising 110% between 1980-2001 and 2002-23, compared to a 59% increase for drought-led events.
The map below shows the global distribution of CDHEs over 1980-2023. The charts show the percentage of the land surface affected by a heatwave-led CDHE (red) or a drought-led CDHE (yellow) in a given year (left) and relative increase in each CDHE type (right).
The study finds that CDHEs have occurred most frequently in northern South America, the southern US, eastern Europe, central Africa and south Asia.
Threshold passed
The authors explain that the increase in heatwave-led CDHEs is related to rising global temperatures, but that this does not tell the whole story.
In the earlier 22-year period of 1980-2001, the study finds that the spatial extent of heatwave-led CDHEs rises by 1.6% per 1C of global temperature rise. For the more-recent period of 2022-23, this increases “nearly eightfold” to 13.1%.
The change suggests that the rapid increase in the heatwave-led CDHEs occurred after the global average temperature “surpasse[d] a certain temperature threshold”, the paper says.
This threshold is an absolute global average temperature of 14.3C, the authors estimate (based on an 11-year average), which the world passed around the year 2000.
Investigating the recent surge in heatwave-leading CDHEs further, the researchers find a “regime shift” in land-atmosphere dynamics “toward a persistently intensified state after the late 1990s”.
In other words, the way that drier soils drive higher surface temperatures, and vice versa, is becoming stronger, resulting in more heatwave-led compound events.
Daily data
The research has some advantages over other previous studies, Yeh says. For instance, the new work uses daily estimations of CDHEs, compared to monthly data used in past research. This is “important for capturing the detailed occurrence” of these events, says Yeh.
He adds that another advantage of their study is that it distinguishes the sequence of droughts and heatwaves, which allows them to “better understand the differences” in the characteristics of CDHEs.
Dr Meryem Tanarhte is a climate scientist at the University Hassan II in Morocco, and Dr Ruth Cerezo Mota is a climatologist and a researcher at the National Autonomous University of Mexico. Both scientists, who were not involved in the study, agree that the daily estimations give a clearer picture of how CDHEs are changing.
Cerezo-Mota adds that another major contribution of the study is its global focus. She tells Carbon Brief that in some regions, such as Mexico and Africa, there is a lack of studies on CDHEs:
“Not because the events do not occur, but perhaps because [these regions] do not have all the data or the expertise to do so.”
However, she notes that the reanalysis data used by the study does have limitations with how it represents rainfall in some parts of the world.
Compound impacts
The study notes that if CDHEs continue to intensify – particularly events where heatwaves are the precursors – they could drive declining crop productivity, increased wildfire frequency and severe public health crises.
These impacts could be “much more rapid and severe as global warming continues”, Yeh tells Carbon Brief.
Tanarhte notes that these events can be forecasted up to 10 days ahead in many regions. Furthermore, she says, the strongest impacts can be prevented “through preparedness and adaptation”, including through “water management for agriculture, heatwave mitigation measures and wildfire mitigation”.
The study recommends reassessing current risk management strategies for these compound events. It also suggests incorporating the sequences of drought and heatwaves into compound event analysis frameworks “to enhance climate risk management”.
Cerezo-Mota says that it is clear that the world needs to be prepared for the increased occurrence of these events. She tells Carbon Brief:
“These [risk assessments and strategies] need to be carried out at the local level to understand the complexities of each region.”
The post Heatwaves driving recent ‘surge’ in compound drought and heat extremes appeared first on Carbon Brief.
Heatwaves driving recent ‘surge’ in compound drought and heat extremes
Greenhouse Gases
DeBriefed 6 March 2026: Iran energy crisis | China climate plan | Bristol’s ‘pioneering’ wind turbine
Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.
This week
Energy crisis
ENERGY SPIKE: US-Israeli attacks on Iran and subsequent counterattacks across the Middle East have sent energy prices “soaring”, according to Reuters. The newswire reported that the region “accounts for just under a third of global oil production and almost a fifth of gas”. The Guardian noted that shipping traffic through the strait of Hormuz, which normally ferries 20% of the world’s oil, “all but ground to a halt”. The Financial Times reported that attacks by Iran on Middle East energy facilities – notably in Qatar – triggered the “biggest rise in gas prices since Russia’s full-scale invasion of Ukraine”.
‘RISK’ AND ‘BENEFITS’: Bloomberg reported on increases in diesel prices in Europe and the US, speculating that rising fuel costs could be “a risk for president Donald Trump”. US gas producers are “poised to benefit from the big disruption in global supply”, according to CNBC. Indian government sources told the Economic Times that Russia is prepared to “fulfil India’s energy demands”. China Daily quoted experts who said “China’s energy security remains fundamentally unshaken”, thanks to “emergency stockpiles and a wide array of import channels”.
‘ESSENTIAL’ RENEWABLES: Energy analysts said governments should cut their fossil-fuel reliance by investing in renewables, “rather than just seeking non-Gulf oil and gas suppliers”, reported Climate Home News. This message was echoed by UK business secretary Peter Kyle, who said “doubling down on renewables” was “essential” amid “regional instability”, according to the Daily Telegraph.
China’s climate plan
PEAK COAL?: China has set out its next “five-year plan” at the annual “two sessions” meeting of the National People’s Congress, including its climate strategy out to 2030, according to the Hong Kong-based South China Morning Post. The plan called for China to cut its carbon emissions per unit of gross domestic product (GDP) by 17% from 2026 to 2030, which “may allow for continued increase in emissions given the rate of GDP growth”, reported Reuters. The newswire added that the plan also had targets to reach peak coal in the next five years and replace 30m tonnes per year of coal with renewables.
ACTIVE YET PRUDENT: Bloomberg described the new plan as “cautious”, stating that it “frustrat[es] hopes for tighter policy that would drive the nation to peak carbon emissions well before president Xi Jinping’s 2030 deadline”. Carbon Brief has just published an in-depth analysis of the plan. China Daily reported that the strategy “highlights measures to promote the climate targets of peaking carbon dioxide emissions before 2030”, which China said it would work towards “actively yet prudently”.
Around the world
- EU RULES: The European Commission has proposed new “made in Europe” rules to support domestic low-carbon industries, “against fierce competition from China”, reported Agence France-Presse. Carbon Brief examined what it means for climate efforts.
- RECORD HEAT: The US National Oceanic and Atmospheric Administration has said there is a 50-60% chance that the El Niño weather pattern could return this year, amplifying the effect of global warming and potentially driving temperatures to “record highs”, according to Euronews.
- FLAGSHIP FUND: The African Development Bank’s “flagship clean energy fund” plans to more than double its financing to $2.5bn for African renewables over the next two years, reported the Associated Press.
- NO WITHDRAWAL: Vanuatu has defied US efforts to force the Pacific-island nation to drop a UN draft resolution calling on the world to implement a landmark International Court of Justice (ICJ) ruling on climate, according to the Guardian.
98
The number of nations that submitted their national reports on tackling nature loss to the UN on time – just half of the 196 countries that are part of the UN biodiversity treaty – according to analysis by Carbon Brief.