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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).

Chart: Annual mean contribution of uncertainties
Annual average contribution to the total uncertainty in global average surface temperature from volcanic eruptions, internal variability, climate model response and human emissions scenarios from 2020 to 2100. Credit: Amended from Chim et al. (2025).

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).

Charts: Probability of exceeding 1.5C
The top chart (a) shows the probability of scenarios exceeding 1.5C using stochastic volcanic forcing (solid lines) and 1850-2014 mean historically-averaged forcing (dotted lines) for SSP1-1.9 (very low emissions), SSP2-4.5 (approximate current policies) and SSP5-8.5 (very high emissions) scenarios. The lower chart (b) shows the difference in probability in exceeding 1.5C between the simulations and historically-averaged forcing and stochastic volcanic forcing. Credit: Chim et al. (2025)

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.

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Carbon Brief Quiz 2026: Picture Round 1 and 2

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All answers will need to be submitted via the Google form by the end of the half-time break

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Landmark deal to share Chile’s lithium windfall fractures Indigenous communities

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Rudecindo Espíndola’s family has been growing corn, figs and other crops for generations in the Soncor Valley in northern Chile, an oasis of green orchards in one of the driest places on Earth the Atacama desert.

Perched nearly 2,500 metres above sea level, his village, Toconao, means “lost corner” in the Kunza language of the Indigenous people who have lived and farmed the land in this remote spot for millennia.

“Our deep connection to this place is based on what we have inherited from our ancestors: our culture, our language,” said Espíndola, a member of a local research team that found evidence that people have inhabited the desert for more than 12,000 years.

This distant outpost is at the heart of the global rush for lithium, a silvery-white metal used to make batteries for electric vehicles (EV) and renewable energy storage that are vital to the world’s clean energy transition. The Atacama salt flat is home to about 25% of the world’s known lithium reserves, turning Chile into the world’s second-largest lithium producer after Australia.

For decades, the Atacama’s Indigenous Lickanantay people have protested against the expansion of the lithium industry, warning that the large evaporation ponds used to extract lithium from the brine beneath the salt flats are depleting scarce and sacred water supplies and destroying fragile desert ecosystems.

Espíndola joined the protests, fearing that competition for water could pose an existential threat to his community.

But last year, he was among dozens of Indigenous representatives who sat across the table from executives representing two Chilean mining giants to hammer out a governance model that gives Indigenous communities living close to lithium sites a bigger say over operations, and a greater share of the economic benefits.

A man wearing a black T-shirt and a hat stands in front of a tree
Rudecindo Espíndola stands in a green oasis near the village of Toconao in the Atacama desert (Photo: Francisco Parra)

A pioneering deal

The agreement is part of a landmark deal between state-owned copper miner Codelco and lithium producer the Sociedad Química y Minera de Chile (SQM) to extract lithium from the salt flats until 2060 through a joint venture called NovaAndino Litio.

The governance model that promises people living in Toconao and other villages around the salt flats millions of dollars in benefits and greater environmental oversight is the first of its kind in mineral-rich Chile, and has been hailed by industry experts as the start of a potential model for more responsible mining for energy transition metals.

NovaAndino told Climate Home News the negotiations with local communities represented an “unprecedented process that has allowed us to incorporate the territory’s vision early in the project’s design” and creates “a system of permanent engagement” with local communities.

The company added it will contribute to sustainable development in the area and help “the safeguarding of [the Lickanantay people’s] culture and environmental values”.

    For mining companies, such agreements could help reduce social conflicts and protests, which have delayed and stalled extraction in other parts of South America’s lithium-rich region, known as the lithium triangle.

    “Argentina and Bolivia could learn a lot from what we’re doing [here],” said Rodrigo Guerrero, a researcher at the Santiago-based Espacio Público think-tank, adding that adopting participatory frameworks early on could prevent them from “going through the entire cycle of disputes” that Chile has experienced.

    Justice at last?

    As part of the governance deal, NovaAndino has pledged to adopt technologies that will reduce water use and mitigate the environmental impacts of lithium extraction.

    It has also committed to hold more than 100 annual meetings with community representatives to build a “good faith” relationship, and an Indigenous Advisory Council will meet twice a year with the company’s sustainability committee to discuss its environmental strategy, company sources said. The meetings are due to begin next month.

    To oversee the agreement’s implementation, an assembly – composed of representatives from all 25 signatory communities – will track the project’s progress. In addition, NovaAndino will hold one-on-one meetings with each community to address issues such as the hiring of local people and the protection of Indigenous employees.

    A flamingo at the Chaxa Lagoon in the Atacama salt flat (Photo: REUTERS/Cristian Rudolffi)

    Espíndola said the deal, while far from perfect, was an important step forward.

    “Previously, Indigenous participation was ambiguous. Now we talk about participation at [every] hierarchical level of this process, a very strong empowerment for Indigenous communities,” said Espíndola, adding that it did not give local communities everything they had asked for. For instance, they will not hold veto power over NovaAndino’s decisions or have a formal shareholder role.

    But after years of conflict with mining companies, a form of “participatory justice is being done”, he said.

    Not everyone is convinced that the accord, pushed by Chile’s former leftist government, marks progress, however.

    “Not in our name”

    The negotiations have caused deep divisions among the Lickanantay, some of whom say greater engagement with mining companies will not stop irreparable damage to the salt flats on which their traditional way of life depends. Others fear the promise of more money will further erode community bonds.

    In January 2024, Indigenous communities from five villages closest to the mining operations, including Toconao, blocked the main access roads to the lithium extraction sites. They said the Council of Atacameño Peoples, which represents 18 Lickanantay communities and was leading discussions with the company, no longer spoke for them.

    Official transcripts of consultations on the extension of the lithium contracts and how to share the promised benefits reveal deep divisions. Tensions peaked when communities around the mining operations clashed over how to distribute the multimillion-dollar windfall, with villages closest to the mining sites demanding the largest share.

    Eventually, separate deals establishing a new governance framework over mining activities were reached between Codelco and SQM with 25 local communities, including a specific agreement for the five villages closest to the extraction sites.

    Codelco’s chairman Maximo Pacheco (Photo: REUTERS/Rodrigo Garrido)

    The division caused by the separate deal for the five villages “will cause historic damage” to the unity of the Atacama desert’s Indigenous peoples, said Hugo Flores, president of the Council of Atacameño Associations, a separate group representing farmers, herders and local workers who oppose the mining expansion.

    Sonia Ramos, 83, a renowned Lickanantay healer and well-known anti-mining activist, lamented the fracturing of social bonds over money, and for the sake of meeting government objectives.

    “There is fragmentation among the communities themselves. Everything has transformed into disequilibrium,” said the 83-year-old.

    “[NovaAndino] supposedly has economic significance for the country, but for us, it is the opposite,” she said.

    The company told Climate Home News it has “acted consistently” to promote “transparent, voluntary, and good-faith dialogue with the communities in the territory, recognising their diversity and autonomy, and always respecting their timelines and forms of participation”.

    A one-off deal or a model for others?

    The NovaAndino joint venture is a pillar of Chile’s strategy to double lithium production by 2031 and consolidate the copper-producing nation’s role in the clean energy transition as demand for battery minerals accelerates.

    Chile’s new far-right president, José Antonio Kast, who was sworn in last week, promised to respect the lithium contracts signed by his predecessor’s administration – including the governance model.

    Still, some experts say the splits over the new model highlight the need for legislation that mandates direct engagement and minimum community benefits for all large mining projects.

    “In the past, this has lent itself to clientelism, communities who negotiate best or arrive first get the better deal,” said Pedro Zapata, a programme officer in Chile for the Natural Resource Governance Institute.

    “This can be to the detriment of other communities with less strength. We cannot have first- and second-class citizens subject to the same industry,” he added.

    The government is already negotiating two more public-private partnerships to extract lithium with mining giant Rio Tinto, which it said would include a framework to engage with Indigenous communities and share some of the revenues. The details will need to be negotiated between local people, the government and the company.

    Sharing the benefits of mining

    Under the deal in the Atacama, NovaAndino will run SQM’s current lithium concessions until they expire in 2030 before seeking new permits to expand mining in the region under a vast project known as “Salar Futuro” – a process which will require further mandatory consultations with communities.

    Besides the participatory mechanism, the new agreement promises more money than ever before for salt flat communities.

    A stone arch welcomes visitors to the village of Peine, one of the closest settlements to lithium mining sites in the Atacama salt flat (Photo: REUTERS/Cristian Rudolffi)

    Depending on the global price of lithium and their proximity to the mining operations, Indigenous communities could collectively receive roughly $30 million annually in funding – about double what SQM currently disburses under existing contracts.

    When taking into account the company’s payments to local and regional authorities, contributions could reach $150 million annually, according to the government.

    To access these resources, each community will need to submit a pipeline of projects they would like funding for under a complex arrangement that includes five separate financial streams:

    • A general investment fund will distribute funding based on each village’s size and proximity to the mining sites
    • A development fund will support projects specifically in the five communities closest to the extraction sites
    • Contributions to farmers and livestock associations
    • Contributions to local governments
    • A groundbreaking “intergenerational fund” held in trust for the Lickanantay until 2060

    For many isolated communities in the Atacama desert, financial contributions from mining firms have funded essential public services, such as healthcare and facilities like football pitches and swimming pools.

    In the past, communities have used some of the benefits they received from mining to build their own environmental monitoring units, hiring teams of hydrogeologists and lawyers to scrutinise miners’ activities.

    Espíndola said the new model could pave the way for more ambitious development projects such as water treatment plants and community solar energy projects.

    A man in a white shirt and glasses stands in front of a stone wall
    Sergio Cubillos, president of the Peine community, was one of the Indigenous representatives in the negotiations with Codelco and SQM (Photo credit: Formando Rutas/ Daniela Carvajal)

    Competition for water

    The depletion of water resources is one of local people’s biggest environmental concerns.

    To extract lithium from the salt flats, miners pump lithium-rich brine accumulated over millions of years in underground reservoirs into gigantic pools, where the water is left to evaporate under the sun and leaves behind lithium carbonate.

    One study has shown that the practice is causing the salt flat to sink by up to two centimetres a year. SQM recently said its current operations consume approximately 11,500 to 12,500 litres of industrial freshwater for every metric ton of lithium produced.

    NovaAndino has committed to significantly reduce the company’s water use by returning at least 30% of the water it extracts from the brine and eliminating the use of all freshwater in its operations within five years of obtaining an environmental permit.

      Cristina Dorador, a microbiologist at the University of Antofagasta, told Climate Home News that reinjecting the water underground is untested at a large scale and could impact the chemical composition of the salt flats.

      Continuing to extract lithium from the flats until 2060 could be the “final blow” for this fragile ecosystem, she said.

      Asked to comment on such concerns, NovaAndino said any new technology will be “subject to the highest regulatory standards”, and pledged to ensure transparency through “an updated monitoring system with the participation of Indigenous communities”.

      High price for hard-won gains

      For the five communities living on the doorstep of the lithium pools, one of the biggest gains is being granted physical access to the mining sites to monitor the lithium extraction and its impact on the salt flats.

      That is a first and will strengthen communities’ ability to call out environmental harms, said Sergio Cubillos, the community president of Peine, the village closest to the evaporation ponds. It could also give them the means to seek remediation through the courts if necessary, Espíndola said.

      Gaining such rights represents long-overdue progress, Cubillos said, but it has come at a high price for the Lickanantay people.

      “Communities receiving money today is what has ultimately led to this division, because we haven’t been able to figure out what we want, how we want it, and how we envision our future as a people,” he said.

      Main image: A truck loads concentrated brine at SQM’s lithium mine at the Atacama salt flat in Chile (Photo: REUTERS/Ivan Alvarado)

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      Roadmap launched to restart deadlocked UN plastics treaty talks

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      Diplomats will hold a series of informal meetings this year in a bid to revive stalled talks over a global treaty to curb plastic pollution, before aiming to reconvene for the next round of official negotiations at the end of 2026 or early 2027.

      Hoping to find a long-awaited breakthrough in the deeply divided UN process, the chair of the talks, Chilean ambassador Julio Cordano, released a roadmap on Monday to inject momentum into the discussions after negotiations collapsed at a chaotic session in Geneva last August.

      Cordano wrote in a letter that countries would meet in Nairobi from June 30 to July 3 for informal discussions to review all the components of the negotiations, including thorny issues such as efforts to limit soaring plastic production.

        The gathering should result in the drafting of a new document laying the foundations of a future treaty text with options on elements with divergent views, but “no surprises” such as new ideas or compromise proposals. This plan aims to address the fact that countries left Geneva without a draft text to work on – something Cordano called a “significant limitation” in his letter.

        “Predictable pathway”

        The meeting in the Kenyan capital will follow a series of virtual consultations every four to six weeks, where heads of country delegations will exchange views on specific topics. A second in-person meeting aimed at finding solutions might take place in early October, depending on the availability of funding.

        Cordano said the roadmap should offer “a predictable pathway” in the lead-up to the next formal negotiating session, which is expected to take place over 10 days at the end of 2026 or early 2027. A host country has yet to be selected, but Climate Home News understands that Brazil, Azerbaijan or Kenya – the home of the UN Environment Programme – have been put forward as options.

        Countries have twice failed to agree on a global plastics treaty at what were meant to be final rounds of negotiations in December 2024 and August 2025.

        Divisions on plastic production

        One of the most divisive elements of the discussions remains what the pact should do about plastic production, which, according to the UN, is set to triple by 2060 without intervention.

        A majority, which includes most European, Latin American, African and Pacific island nations, wants to limit the manufacturing of plastic to “sustainable levels”. But large fossil fuel and petrochemical producers, led by Saudi Arabia, the United States, Russia and India, say the treaty should only focus on managing plastic waste.

        As nearly all plastic is made from planet-heating oil, gas and coal, the sector’s trajectory will have a significant impact on global efforts to reduce greenhouse gas emissions.

        Countries still far apart

        After an eight-month hiatus, informal discussions restarted in early March at an informal meeting of about 20 countries hosted by Japan.

        A participant told Climate Home News that, while the gathering had been helpful to test ideas, progress remained “challenging”, with national stances largely unchanged.

        The source added that countries would need to achieve a significant shift in positions in the coming months to make reconvening formal negotiations worthwhile.

        Deep divisions persist as plastics treaty talks restart at informal meeting

        Jacob Kean-Hammerson, global plastics policy lead at Greenpeace USA, said the new roadmap offers an opportunity for countries to “defend and protect the most critical provisions on the table”.

        He said that the document expected after the Nairobi meeting “must include and revisit proposals backed by a large number of countries, especially on plastic production, that have previously been disregarded”.

        “These measures are essential to addressing the crisis at its source and must be reinstated as a key part of the negotiations,” he added.

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        Roadmap launched to restart deadlocked UN plastics treaty talks

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