Volcanic eruptions pose a fundamental challenge for scientists and their climate models.
It is well known that explosive eruptions can cause sudden cooling at the Earth’s surface and that multiple eruptions shape climate variability over decades and centuries.
When sulphur dioxide is injected into the stratosphere during an eruption, it forms aerosols that block sunlight from reaching the Earth’s surface.
Unlike human influences on climate change, which occur slowly and can be accounted for in climate models under a range of socioeconomic scenarios, the sporadic nature of volcanic eruptions poses a challenge for climate projections.
Scientists cannot currently forecast the occurrence of volcanic eruptions – including when and where they will occur and how much sulphur they will emit.
How, then, to account for the climate impact of volcanic eruptions when projecting into the future?
In a recent study, published in Communications Earth & Environment, we show that volcanic eruptions make a substantial contribution to the uncertainty in projections of global temperatures.
Our findings suggest that, when sporadic volcanic eruptions are included in climate projections, breaching of the Paris Agreement’s 1.5C warming limit is slightly delayed – but we will also see more decades with rapid rates of warming and cooling.
Volcanic forcing in climate projections
Climate scientists refer to the influence volcanic eruptions have on the climate – largely through the release of sulphur dioxide gas into the atmosphere – as “volcanic forcing”.
Current climate models apply a constant volcanic forcing value when running future projections. This value is calculated based on the historical average of forcings from 1850 to the present day.
This is the case with the Coupled Model Intercomparison Project (CMIP), the international modelling effort that feeds into the influential assessment reports from the Intergovernmental Panel on Climate Change (IPCC).
However, this approach has significant limitations.
For starters, historically averaged forcing does not capture the episodic nature of eruptions.
Large-magnitude volcanic eruptions happen sporadically – sometimes clustering within decades and other times leaving century-long gaps between events.
Meanwhile, the reference period of 1850 to the present day has seen a relatively low frequency of large-magnitude eruptions that emitted more than 3 teragrams (Tg) of sulphur dioxide (SO2), when compared to multimillennial records.
Finally, volcanic forcing reconstructions used in earlier generations of CMIP climate models did not include small-to-moderate magnitude eruptions that emitted less than 3Tg of SO2.
This is because these eruptions went largely undetected before the satellite era began in 1980. Nonetheless, these smaller, but more frequent, eruptions contribute to 30-50% of long-term volcanic forcing.
Taking a new approach
Traditionally, climate scientists have recognised three main sources of uncertainty in climate projections: internal variability, model uncertainty and scenario uncertainty.
Here, “internal” variability refers to natural fluctuations that are generated within the climate system, such as by El Niño; model uncertainty refers to the differences in the results between multiple climate models; and scenario uncertainty refers to the different ways that the world could develop over the decades to come.
Our results show that volcanic eruptions should be specifically considered as a fourth significant source of uncertainty in climate projections.
To explore how climate projections change when accounting for volcanic forcing uncertainty, our study uses a probabilistic approach that builds on a 2017 methodology developed by Bethke et al.
To do this, we develop “stochastic forcing scenarios” – essentially, 1,000 different plausible timelines of volcanic activity extending to the end of the century.
These scenarios draw from past volcanic activity recorded in ice cores going back 11,500 years, along with satellite measurements and geological evidence. Each scenario represents different combinations of eruption magnitudes, location, timing and frequency.
(In mathematics, “stochastic” systems involve randomness or uncertainty of outcome, making them unpredictable. This is in contrast to “deterministic” systems, which are characterised by having outcomes that are completely predictable based on initial conditions and a set of rules or equations.)
We then simulate climate projections using both stochastic and historically-averaged volcanic forcing between 2015 and 2100, exploring temperature rise under three different emissions scenarios drawn from the Shared Socioeconomic Pathways (SSPs). These are a low-emission scenario (SSP1-1.9), an intermediate scenario that is in line with current climate policies(SSP2-4.5) and a very-high emissions scenario (SSP5-8.5).
For this step, we use a simple climate model, or “emulator”, called FaIR.
By simulating 1,000 different volcanic futures, we find that the climate uncertainty caused by future 21st century eruptions could exceed the internal variability of the climate system itself over the same period.
We also find that volcanic eruptions could account for more than one-third of total uncertainty in global temperature projections until the 2030s.
You can see these results in the plot below. It shows the contribution to the total uncertainty from the different sources. The colours represent volcanoes (orange), internal variability (dark blue), climate model response (yellow) and scenarios of future human emissions (green).
What this means for the 1.5C threshold
Our simulations demonstrate that incorporating possible timelines of volcanic activity slightly reduces the probability of crossing the Paris Agreement’s aspirational 1.5C temperature limit in the near term.
We find that – depending on the emissions scenario – the probability of exceeding 1.5C decreases by 4-10%, compared to projections using constant volcanic forcing.
While this might sound encouraging, future volcanic activity does not provide any long-term mitigation of human-caused warming.
The eruption of Mount Tambora in 1815 offers a dramatic illustration of this point. While the event cooled global temperatures by an average of 0.8C, it led to a “year without a summer” and caused crop failures and widespread famine across Europe, North America and China.
Eruptions produce temporary cooling lasting just a few years. They do not alter the underlying warming trend driven by human emissions.
Our study finds that, taking into account a range of future volcanic activity, global warming will still exceed 1.5C within decades under all but the very lowest emissions scenarios.
A high level of volcanic activity over the 21st century would help offset just a small fraction of global warming – meaning that emission reduction remains essential for meeting long-term climate goals.
The charts below show the probability of scenarios exceeding 1.5C using stochastic volcanic forcing (solid lines) and constant volcanic forcing (dashed lines) under three emissions scenarios (top) and the difference in probability between the two forcing approaches (bottom).
Decadal-scale temperature variability
Another important insight from our research is that extreme warm and cold decades become more likely once the variability of volcanic forcing is accounted for.
We find that the chance of a negative decadal trend – a decade where global surface temperature cools on average – increases by 10-18% under the intermediate emissions scenario.
We also find a corresponding increase in the probability of extremely warm decades, reflecting how volcanic forcing variability enhances the likelihood of both cooling and warming extremes.
This underscores how volcanic eruptions could introduce significant variability into the global temperature trends over decadal timescales.
Toward better climate projections
Understanding volcanic effects on the climate is essential for comprehensively assessing future risks to agriculture, infrastructure and energy systems.
Running thousands of volcanic scenarios with full-scale Earth system models is not practical as it requires too much computing power. On the other hand, current approaches have significant limitations, as described above.
However, there is a middle ground for future climate modelling efforts.
The next phase of future climate modelling experiments – the Scenario Model Intercomparison Project for CMIP7 – can use a more representative “average” volcanic forcing baseline that incorporates the effects of small eruptions often missed in historical records. This bias has now been addressed in the historical volcanic forcing dataset that will underpin the next generation of climate model simulations.
Additionally, modelling teams should run additional scenarios with high and low future volcanic activity to capture the range of volcanic uncertainty on climate projections.
While human-caused greenhouse gas emissions remain the dominant driver of climate change, properly accounting for volcanic uncertainty provides a more complete picture of possible climate futures and their implications for society.
The post Guest post: Investigating how volcanic eruptions can affect climate projections appeared first on Carbon Brief.
Guest post: Investigating how volcanic eruptions can affect climate projections
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 | Nature
- Accelerating human-caused global warming could see the Paris Agreement’s 1.5C limit crossed before 2030 | Geophysical Research Letters covered by Carbon Brief
- Future “super El Niño events” could “significantly lower” solar power generation due to a reduction in solar irradiance in key regions, such as California and east China | Communications Earth & Environment
(For more, see Carbon Brief’s in-depth daily summaries of the top climate news stories on Monday, Tuesday, Wednesday, Thursday and Friday.)
Captured
UK greenhouse gas emissions in 2025 fell to 54% below 1990 levels, the baseline year for its legally binding climate goals, according to new Carbon Brief analysis. Over the same period, data from the World Bank shows that the UK’s economy has expanded by 95%, meaning that emissions have been decoupling from growth.
Spotlight
Bristol’s ‘pioneering’ community wind turbine
Following the recent launch of