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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.

The post Guest post: Investigating how volcanic eruptions can affect climate projections appeared first on Carbon Brief.

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Energy transition policymaking must evolve to fit an age of rupture

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Andreas Sieber is head of political strategy at 350.0g. Cat Abreu is director of the International Climate Politics Hub.

From the US abduction of Venezuela’s president at the start of this year to the Iran war which rumbles on, disruption is the new normal for global geopolitics, more often than not linked to conflict over supplies of oil and gas. 

Events so far in 2026 – driven largely by the desire of the Trump administration to grab control of fossil fuels around the world – show that the climate community’s approach to energy diplomacy will have to evolve if we are to operate effectively and push for climate action in such a volatile landscape.

Today’s climate and energy governance must be able to cope with trade wars, genocide, fascism, spiralling inequality and challenges to multilateralism. The increasingly dominant paradigms of economic competitiveness, energy security and green industrialisation can help drive the transition but they also challenge our collective mission to deliver an equitable green shift.

US-China rivalry dominates

Longer-term geopolitical trends that are seeing power move from West to East and North to South have fuelled a US–China “superpower rivalry”, which is pulling the global economy apart and reining in trade.

A key question will be how the fracture “lines” are drawn: by the US and China, or also by other countries or blocs? Many governments will try to remain “in the middle” between the two giants to capture economic gains from both sides. Yet despite the language of “strategic autonomy”, Washington and Beijing may be in a position to force choices via market access, export controls and sanctions.

    At first glance, this may not seem particularly relevant for climate and energy politics. But Huawei’s exclusion from 5G operations across the political West and India following the so-called Clean Network Campaign by the US government serves as a warning of what could happen to climate green tech.

    And the recent debate to cut out Chinese inverters from European markets follows the same pattern – US security forces perceive a risk and start encouraging their allies to drop Chinese technology.

    The new drivers: competition and security

    Despite this fracturing geopolitical and economic context, energy transition is still happening. To ensure it is effective and equitable, we need to understand what is driving it and how to adapt climate politics so that it better responds to these drivers.

    Put simply, China is supplying the world with low-cost renewables (roughly 60% of critical wind and 80% of solar components), batteries, EVs and other key elements. Other countries now also want their piece of the green tech pie and are forming industrial policies to get it.

    It is this new competitiveness-driven logic that will shape the quest for decarbonisation, which has shifted from cooperating around the cost of tackling climate change to rivalry for the benefits of climate action.

    Over 90% of new renewables projects are now cheaper than fossil alternatives. Gas-fired power is 3–4 times more expensive than solar and wind. In 2015, most decarbonisation policies were “traditional” emissions-cutting strategies like carbon pricing or net zero dates, whereas green industrial policies now underpin the majority.

    Iran war could boost fossil fuel phase-out push, says Colombian minister

    Meanwhile, security has become a central driver of energy politics. We are living through the second major fossil fuel crisis in just four years. Elevated oil and gas prices will impose up to $1 trillion in additional costs on the global economy by the end of the year if disruption continues in the Strait of Hormuz. Fossil fuel supply chains have exposed countries to conflict, coercion and brutal price shocks.

    Fossil fuel volatility destabilises whole economies – higher fuel costs drive up food prices, increase political instability, and push millions into poverty and hunger. This incentivises governments to shield themselves from global shocks, especially in countries that are net fossil fuel importers and home to roughly three-quarters of the world’s population. 

    Yet security fears can cut both ways. The same instability that makes fossil fuel dependence untenable is also sharpening concern over China’s dominance of critical clean technologies and supply chains.

    Equity, cooperation and the opportunity for change

    Developing countries benefit from the rapid uptake of renewables enabled by low-cost Chinese technologies. But significant fiscal space and public investment is needed for the electricity grids and infrastructure required to fully unleash the energy transition, as well as for green industrialisation to diversify revenue streams.

    Despite this, industrial-scale domestic production and ownership often remain out of reach for too many countries that lack the fiscal space to allow green supply chains to flourish and compete with their traditional industrial base. But more just and diversified green tech supply chains could be achieved with concomitant support.

    Can giant batteries unlock Africa’s green industrial future?

    For the first time in decades, the international order is being substantially reshaped. If within this context, decarbonisation is increasingly driven by green industrial policy, energy security and competitiveness, the climate policy community must better anticipate where these debates are moving. We must speak the same language, and enter the forums where decisions are made, including security, trade and bilateral or trilateral spaces.

    We should build on an enlightened self interest recognising that cooperation remains essential and beneficial. This includes using the UN climate process differently: less as an ever-expanding negotiation machine, and more as a space for norm-setting, political alignment and deal-making. In an age of fragmentation, effective cooperation must not only be framed as necessary but thought of as a strategically compelling source of resilience and shared advantage.

    The post Energy transition policymaking must evolve to fit an age of rupture appeared first on Climate Home News.

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    Extreme heat costing India’s poorest workers 2% of GDP, survey finds

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    Low-income Indian workers, many of them migrants from rural areas hit by climate change, are paying for worsening extreme heat through lost working days and health complications, with the cost equivalent to 2% of national GDP per year, new research shows.

    The International Institute of Environment and Development (IIED), a London-based think-tank, worked with local organisations to survey around 540 households of informal workers in three Indian cities: Ajmer, Delhi and Agra. Most had migrated from rural areas to find work in industries such as construction, brick-making, garment manufacturing and food packaging.

    The survey found them struggling through long working days with little access to shade, cooling, rest or water, as well as few toilets for women. And even when they go home, many live in makeshift shelters or airless cramped rooms with barely a single fan, bringing almost no respite.

    Outdoor workers are losing about 24 days of work a year due to heat, costing them nearly a tenth of their annual earnings, while indoor workers sacrifice roughly 15 days. On top of losing income, they are also bearing the cost of health problems like heat exhaustion, psychological stress and kidney damage brought on by repeated dehydration.

    If the survey’s findings are extrapolated to a national level, the IIED researchers estimate that the decline in productivity and effects of kidney disease combined add up to lost wages of $78 billion each year.

      Vishram Meena, 45, from Alwar in Rajasthan, has worked on construction sites in Ajmer for more than a decade, toiling for 10 to 12 hours a day carrying materials and mixing cement in the full sun.

      In May 2024, on one of the hottest days, he collapsed after feeling dizzy and suffering a nosebleed. His wife and colleagues managed to get him to hospital where he was diagnosed with heat stroke. He has since returned to the same building work because the family needs the money.

      “I went back because what else could I do? We are not machines. We are human beings. The heat is killing us slowly,” he was quoted as saying in a report on the survey’s findings.

      “Victorian-era” conditions

      Ritu Bharadwaj, IIED’s director of climate resilience, finance and loss and damage, described some of the stories from workers about their experiences of extreme heat as “genuinely horrifying”.

      Kusum, a tailor at a garment manufacturing and export unit in Kapashera, Delhi, recounted how the machines for ironing finished garments are in the same tiny room where workers are making the clothes, with steam and hot air building up through her shift.

      Fans are too far apart to move the air and nothing has changed in over a decade, she said, adding that “in summer, the unit feels like a furnace”.

      “These are Victorian-era working conditions and they’re completely unacceptable in the 21st century,” said Bharadwaj. She called for stepped-up social protection from the government to pay people for days they are unable work due to heat, as well as micro-insurance schemes with payouts triggered by temperature measurements.   

      This money would help families buy food and pay medical bills when their income dips if they fall ill or cannot work their usual hours due to soaring temperatures.

      Climate change-driven heatwaves hit Delhi’s Red Fort market traders

      The aim of the IIED study, Bharadwaj added, is to get policy-makers’ attention by showing the scale of damage extreme heat is doing to India’s GDP in an economy whose growth relies on service-led industries. “If the workers within them start falling sick, you know it’s the economic growth which is going to get impacted,” she told a webinar to present the research.

      “Whether [policymakers] care about the workers or not, at least they would care about the GDP, and therefore then invest in their care,” she explained.

      Labour code leaves out heat

      However, Bharadwaj noted that a 2026 reform to India’s labour law bringing a range of regulations together in one code does not include heat-related protections for workers and only applies to businesses above a certain size. She urged the government to introduce a temperature threshold above which all workers would be able to stop their activities.

      IIED and its partners have also carried out a similar study in Bangladesh which will be published later this month, showing that extreme heat is costing its workforce the equivalent of nearly 1.4% of GDP.

      Shakirul Islam, chairperson of the Ovibashi Karmi Unnayan Program (OKUP) in Bangladesh, said the government had introduced stricter safety policies for garment-making companies after the Rana Plaza complex collapsed in 2013. But, he said, these rules are rarely followed by manufacturers, especially at the level of smaller subcontractors.

      The workers’ welfare centres that do exist are open mainly during work hours so they are difficult to visit. Some companies also make saline water available for heat stress, which is no good for those with high blood pressure, he noted.

      For Indian women workers, a just transition means surviving climate impacts with dignity

      Archana Shukla Mukherjee, CEO of India’s Change Alliance, which also partnered with IIED on the survey, said it was time to hold both the government and businesses accountable for finding solutions to the intensifying problem of extreme heat’s effects on workers.

      She said that employee state insurance schemes should identify heat stroke as an occupational disease while companies along the whole supply chain should start putting in place heat protection measures, including for informal workers and migrants.

      If the tools and mechanisms available to help workers do not reach the most vulnerable and marginalised people, “then I think we are not doing something right,” she said.

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      Top maritime court rejects bid to halt UN deep-sea mining inquiry

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      A United Nations investigation into deep-sea mining firms will continue after the world’s top maritime court rejected their bid to suspend the inquiry triggered by a US-backed push to extract critical minerals from the ocean floor.

      In two orders issued on Saturday, the International Tribunal for the Law of the Sea (ITLOS) declined to halt an inquiry launched by the International Seabed Authority (ISA) into whether permit holders, including Tonga Offshore Mining Ltd (TOML) and Nauru Ocean Resources Inc (NORI), have breached their obligations under UN exploration contracts.

      The two companies are subsidiaries of Canadian firm The Metals Company (TMC), which earlier this year sought permits from the United States to commercially mine the deep seabed in an area already covered by its UN exploration licences, bypassing the ISA’s regulatory process.

      The inquiry was opened after TMC’s move raised questions over whether its subsidiaries had complied with their contractual obligations to the ISA, which regulates mining in international waters under the UN Convention on the Law of the Sea. TOML and NORI sued the ISA last June for allegedly targeting them “in breach of due process” and without “good faith”.

        While allowing the inquiry to proceed, the court ordered the ISA to ensure the companies receive due process. Judges said the regulator must explain the factual and legal basis of its inquiry, clarify the procedures being followed and provide TOML and NORI with a meaningful opportunity to respond.

        The companies seeks to mine an area called the Clarion-Clipperton Zone, which holds vast reserves of critical minerals like nickel, manganese and rare earths but is also home to a little-studied deep ocean ecosystem with thousands of unnamed species.

        In response to the court’s ruling, the ISA welcomed the decision, saying the inquiry “remains in effect” and would continue “with due regard to all applicable legal requirements”.

        Last week, during an annual meeting of its member governments, ISA secretary-general Leticia Carvalho said the resources in the ocean floor are “the common heritage of humankind” and upheld the agency’s role as “more important than ever”.

        TMC also welcomed the court decision in a statement and claimed that judges ruled to “protect the rights of TMC subsidiaries”.

        “Contractors like NORI and TOML, who have together spent hundreds of millions of dollars on the promise of a fair regulatory framework, should be informed of the factual and legal basis of any non-compliance inquiries, understand the procedure being applied, and receive a meaningful opportunity to respond,” said Gerard Barron, CEO of The Metals Company.

        Iridogorgia and bamboo coral pictured around the Johnston Atoll Unit of the Pacific Remote Islands Marine National Monument (Photo: NOAA Office of Ocean Exploration and Research)

        Environmental groups said the ruling allows scrutiny of the companies’ actions to continue.

        Louisa Casson, deep-sea mining campaigner with Greenpeace, said the “entire litigation has been an egregious waste of time and money”, which was part of the industry’s “textbook distraction tactic” meant to delay the consequences of the inquiry.

        “If the inquiry confirms that TMC’s subsidiaries are breaching their contracts, governments must send the strongest possible signal that complicity in unlawful deep sea mining will not be tolerated,” she said.

        While investigation is still ongoing, NORI’s contract is set to expire this week and is up for review. Governments asked the ISA to report back and make “make appropriate recommendations” by the next ISA assembly, its main decision-making body set to take place next week from July 27 to 31.

        The court ordered both the ISA and TMC to submit a report on how they complied with the ruling by August 31, and called on both to “cooperate and refrain from any action that might lead to
        aggravating the dispute”.

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        Top maritime court rejects bid to halt UN deep-sea mining inquiry

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