Global warming linked to the world’s biggest oil and gas companies made all “major” 21st century heatwaves more intense and frequent.
This is according to new research, published in Nature, which uses “extreme event attribution” to assess the impact of climate change on all 21st-century heatwaves that were classified as “major disasters”.
The authors find one-quarter of the 213 heatwaves would have been “virtually impossible” without human-caused global warming.
They add that the effect of climate change on heatwave frequency and intensity is becoming more pronounced as the planet warms.
The study estimates the emissions stemming from the operations and production of more than 100 “carbon majors”, such as ExxonMobil, BP, Saudi Aramco and Shell.
The fossil fuels produced by these companies account for 60% of all human-caused CO2 emissions over 1850-2023, the study says.
The authors find that heatwaves recorded over 2000-23 were made, on average, 1.7C hotter due to climate change, with half of this increase due to the emissions originating from carbon majors.
This study “could be used to support future climate lawsuits and aid diplomatic negotiation”, according to a scientist not involved in the research.
Worsening heatwaves
As the planet warms, heatwaves are becoming more intense and frequent, driving economic losses, ecosystem damage and a rise in heath-related deaths.
The EM-DAT database catalogues all “major disasters” that have been reported since the year 1900 – defined as events that cause at least 10 fatalities, affect at least 100 people, or result in the declaration of state of emergency or a call for international assistance.
Between 2000 and 2023, the database lists more than 200 heatwaves. These are shown on the map below, where darker pink indicates a greater number of heatwaves. Countries with no reported heatwaves are shown in grey.
The study authors acknowledge that heatwave reporting is “highly uneven”, with only nine of the heatwaves reported in the database since the year 2000 in Africa, Latin America or the Caribbean. (This is largely because extreme heat events in these regions are not routinely monitored.)
They then carried an attribution analysis on each heatwave to identify whether it was made more likely or intense due to human-caused climate change.
The chart below shows how climate changes increased the intensity and frequency of the 78 heatwaves assessed over 2000-09 (left), 54 heatwaves assessed over 2010-19 (middle) and 81 heatwaves assessed over 2020-23 (right).
The authors find that climate change increased the intensity and probability of all 213 heatwaves in the study. They add that the influence of climate change on heatwaves is strengthening over time.
In each panel, the bars show the percentage of heatwaves in that time period that were made 0.25-1.0C (yellow), 1.0-2.0C (orange) or 2.0-3.0C (red) hotter due to climate change.
The position of bars indicate the change in likelihood of the heatwaves. This ranges from those made 1-10 times more likely due to climate change (left-most bar in each panel) to those made more than 11,000 times more likely (right-most bar in each panel).
Heatwaves recorded over 2000-09 were, on average, 20 times more likely due to climate change, according to the authors. Meanwhile, those recorded over 2010-19 were about 200 times more likely.
Similarly, 2000-09 heatwaves were 1.4C hotter due to human-caused climate change on average, according to the study, while 2010-19 heatwaves were made 1.7C hotter.
The study finds that human-caused climate change made 55 heatwaves at least 10,000 times more likely. According to the authors, this is “equivalent to saying that they would have been virtually impossible” without the influence of human activity.
Carbon majors
To assess the contribution to heatwaves by oil and gas companies’ products, the authors use a database of carbon dioxide and methane emissions from 180 carbon majors over 1854-2023. This includes direct emissions from the companies, as well as the emissions released when the oil and gas they produced is used by others.
The 180 carbon majors in the database represent 60% of all human-caused CO2 emissions, including land use, over 1850-2023, according to the study. The paper adds that 14 companies, including ExxonMobil, BP, Saudi Aramco and Shell, are responsible for almost half of these emissions.
Using the Earth system model OSCAR, the authors estimate that global average surface temperatures increased by 1.3C between the 1850-1900 average and the year 2023.
They find that 0.7C of this increase was linked to the carbon majors, with 0.3C due to the emissions of the 14 largest.
The chart below, taken from an accompanying Nature “news and views” article, shows the contribution of oil and gas companies’ products to increasing global average surface temperatures over 1950-2023, compared to the 1850-1900 average.
Each colour indicates a carbon major, while grey indicates other sources of temperature increase, such as land-use change.
Heatwaves recorded over 2000-23 were, on average, 1.7C hotter due to climate change, according to the study. The authors find that emissions originating from carbon majors and their products contributed about half of the increase in intensity of heatwaves seen since pre-industrial times.
The authors then break down the contribution of emissions from each carbon major on each heatwave in their analysis.
For example, they find that the emissions linked to Saudi Aramco made 51 heatwaves at least 10,000 times more likely. They add that on average, emissions tied to the company made the 213 heatwaves 0.04C hotter.
Legal action
Attribution studies already play an important role in courts by providing evidence that helps judges to determine liability.
Dr Rupert Stuart-Smith is a research associate in climate science and the law at the University of Oxford’s Sustainable Law Programme. He was not involved in the study, but has published separate work showing that the emissions linked to each of the six largest corporate emitters cause one heat-related death in Zurich alone, every summer.
Stuart-Smith tells Carbon Brief that the new paper is a “high-quality analysis and a meaningful step forward for the field of climate change attribution”. He adds:
“With more and more lawsuits aiming to hold high-emitting companies responsible for their contributions to climate change impacts or compel state and corporate actors to reduce their emissions and prevent rising climate harms, work like this provides the basis for well-informed judicial decision-making.”
Dr Yann Quilcaille is a researcher at ETH Zürich and lead author of the study. He stresses the importance of attribution research for court cases, telling Carbon Brief that he hopes his work “can be used by legal practitioners”.
However, he also says that his role as a scientist is not to assign “responsibility” for climate change, but to “provide information to governments for decision making and to courts for litigation”.
Earlier this year, Dr Christopher Callahan, the principal investigator of the IU Climate & Society Lab, published a study with Prof Justin Makin, an associate professor in the department of geography at the University of Dartmouth, which links trillions of dollars in economic losses to the extreme heat caused by emissions tied to oil and gas companies.
Mankin tells Carbon Brief that the new paper is “very closely” linked to his research.
Callahan says the new paper is “an important contribution to an emerging literature that illustrates how individual emitters can be linked to the change risk of extreme climate conditions and human impacts”.
He explains that “this kind of evidence will be important in courtrooms – holding emitters legally accountable requires demonstrating a causal nexus between that emitter and a particularised harm suffered by a plaintiff”.
Attribution
The cutting-edge field of extreme weather attribution seeks to establish the role that human-caused warming played in these events. Attribution studies have been carried out on hundreds of heatwaves all around the world, as shown in Carbon Brief’s interactive map.
The new paper uses one of the earliest and most commonly used methods of attribution, called “probabilistic attribution”.
Specifically, it uses the method set out by the World Weather Attribution initiative for its “rapid attribution” analyses.
The authors first chose a temperature “threshold” to define their heatwave.
They then used a global climate model to simulate two worlds – one mirroring the world as it was during the heatwave and the other using the climate of 1850-1900. This second scenario is used to represent the climate in a world without human-caused climate change.
The authors run their models thousands of times in each scenario. As the world’s climate is inherently chaotic, each model “run” – individual simulations of how the climate progresses over many years – produces a slightly different progression of temperatures. This means that some runs simulate the heatwave, while others do not.
The authors count how many times the threshold temperature was in each model run. They then compared the likelihood of crossing the threshold temperature in the world with – and a world without – climate change.
For example, they find that the 2021 Pacific north-west heatwave was made 3.1C hotter due to human caused climate change and more than 10,000 times more likely.
(A study by the WWA at the time of the heatwave found that the heatwave was made 150 times more likely. The discrepancy is due to differences in the definition of the event, as well as its “very unlikely nature” according to the study authors.)
Dr Frederieke Otto is a professor at Imperial College London and founder of the WWA initiative. She tells Carbon Brief that the new study is “very similar to some other recent studies on impacts, based on the hazard attribution method used by WWA”, but says that “this is the most high profile and wide-reaching one”.
Otto adds:
“I do hope that many more impact attribution studies will follow, based on our or other extreme event attribution studies. We need more research on this.”
The post Study links world’s top oil and gas firms to 200 ‘more intense’ heatwaves appeared first on Carbon Brief.
Study links world’s top oil and gas firms to 200 ‘more intense’ heatwaves
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.
Latest climate research
- Sea levels are already “much higher than assumed” in most assessments of the threat posed by sea-level rise, due to “inadequate” modelling assumptions |