UK government targets for “sustainable aviation fuels” (SAFs) will only cut emissions from the sector to 0.8% below current levels in 2040, Carbon Brief analysis shows.
From 2025, flights taking off from the UK must use a fixed share of SAFs, which are largely made from waste products. This share will gradually rise from 2% next year to 22% in 2040.
The government says its “SAF mandate” will cut aviation emissions by 6.3m tonnes of carbon dioxide equivalent (MtCO2e) in 2040.
However, Carbon Brief analysis of government forecasts shows this being almost entirely wiped out by rising demand for air travel, meaning emissions would only fall by 0.8% overall.
The SAF mandate is the most substantial policy to date under the UK government’s “jet-zero” strategy for decarbonising air travel, which eschewed efforts to limit demand. The mandate relies heavily on fuels made from used cooking oil and other waste products, which are in limited supply.
No change
The SAF mandate will require jet fuel suppliers to ensure that an increasing share of the product they supply is “sustainable”. This is meant to encourage investment in new facilities to produce SAFs.
Fuels described as SAFs include those made from waste, such as used cooking oil, household waste and offcuts from the forestry sector.
Despite their name, SAFs produce just as many emissions as fossil fuels when burned to power planes.
However, they generally – although not always – have a lower overall “lifecycle” carbon footprint than petroleum-based jet fuel. This is due to CO2 emissions absorbed from the atmosphere when growing plants for biofuels, or emissions that are avoided by diverting waste products to be used as fuels.
These emissions savings are counted towards the UK’s aviation sector as a whole.
(The government says that, for the time being, it will not support SAFs made directly from crops, which tend to have relatively high carbon footprints due to changes in land use.)
The new UK mandate starts in 2025 with a requirement that 2% of total jet fuel demand is SAF, increasing to 10% in 2030 and 22% in 2040. The government says there is currently not enough certainty in the SAF market to set targets beyond that date.
These measures will cut overall aviation emissions by 2.7MtCO2e in 2030 and 6.3MtCO2e in 2040, according to the government.
Based on government forecasts for jet fuel use, this change will be almost totally offset by a growth in flights, leaving UK aviation emissions virtually unchanged between now and 2040.
Emissions in 2025 are expected to be 36.0MtCO2e, while 15 years later they are set to be 35.7MtCO2e, according to Carbon Brief analysis. This is a drop of just 0.3MtCO2e, or 0.8%. This is illustrated in the chart below, with the SAF mandate merely preventing an increase in emissions resulting from higher jet fuel use in 2040.
These figures are derived from the government’s “central case”, cited in its underlying analysis for the SAF mandate, which sees jet fuel use increasing from 11.5m tonnes (Mt) in 2025 to 13.3Mt in 2040. This, in turn, is based on policies in the government’s “continuation of current trends” scenario, with the SAF mandate included.
The government expects far more flights to take off from the UK in the coming years, resulting in higher jet fuel use. It has resisted pressure to curb the demand for air travel, despite warnings from experts that such actions are vital for reducing aviation emissions.
In its jet-zero strategy, the government stated that it is aiming for a “high ambition” scenario, which would see aviation emissions fall faster in the coming years. However, as it stands, it has not introduced policies to drive further emissions reductions in planes.
The SAF mandate assumes that SAFs reduce lifecycle emissions from jet fuel by 70%. Certificates will be issued to fuel suppliers for each tonne of SAF produced, using this baseline emissions reduction goal as the standard.
However, Prof Bill Rutherford, an Imperial College London biochemist who contributed to two major assessments of low-carbon aviation fuels in the UK last year, tells Carbon Brief he is sceptical about lifecycle emissions analysis that shows such high emissions benefits:
“Lifecycle analysis is a very fuzzy science…You can basically get what you want out of it.”
For example, in its analysis, the government assumes that SAFs made from used cooking oil – which are expected to make up virtually the entire UK supply in the short-term – cut lifecycle emissions by roughly 95-98% compared to conventional jet fuel.
Dr Andrea Fantuzzi, another Imperial College London chemist who also worked on the low-carbon fuel assessments with Rutherford, says such figures seem “way too high”. He estimates that the savings would be closer to 70%.
Fantuzzi adds that even this does not account for the land originally used to produce the oil, and assumes that the oil would otherwise be thrown away – rather than used to power road vehicles, for example. (For more on waste oils, see: More cooking oil.)
Additionally, Rutherford points out that the use of SAFs has no impact on non-CO2 emissions from planes, which could account for up to two-thirds of their climate impact. He concludes:
“The only way you can make aviation any more sustainable is to do less of it.”
More cooking oil
The only SAFs that are currently available in the UK are fuels made from used cooking oil and other waste oils, which are collected from restaurants and factories.
However, the SAF mandate includes a limit on the amount of waste oil-based fuels within its overall targets. This is partly to “incentivise the development of new technologies” and partly due to concerns that waste oil supplies will be insufficient.
For the first two years, these fuels will be allowed to make up 100% of UK SAFs. This then falls to 71% in 2030 and 33% in 2040. Overall, waste oil-based SAFs would account for 2% of total jet fuel use in 2025 and up to 7.8% in 2040.
Despite these limits, waste oil-based SAF use is expected to rise around 15-fold from current levels within a decade. This huge increase in demand for waste cooking oil under the SAF mandate is illustrated in the figure below.
The Aviation Environment Federation said in a statement that the amount of waste oil being allowed into UK jet fuel under the UK’s SAF mandate is “much higher than we, and many others, were expecting, and appears to be the result of airline pressure”. The looser cap on these fuels was “welcomed” by industry body Airlines UK.
It raises the question of where the UK will source the required volume of waste oil to meet SAF targets.
Studies have shown that there is nowhere near enough waste cooking oil produced domestically, within the UK, to supply jet fuel demand. “We’re not about to start eating more chips, so we will have to start importing more waste oil,” Matt Finch, UK policy manager at the NGO Transport and Environment, tells Carbon Brief.
The government itself acknowledges this, saying that production of these SAFs within the UK is likely to be constrained by the availability of waste cooking oil from 2029 onwards.
It notes that their availability will therefore be “highly dependent” on how much waste oil the UK can import.
As of 2023, waste cooking oil collected in the UK only accounted for 7% of the country’s SAF production. This share has shrunk in recent years, such that imports from other countries – particularly China – have driven most of the growth in production, as the chart below shows.
There is mounting evidence that the demand for imported cooking oil in the UK and Europe is being met with virgin palm oil that has been fraudulently passed off as waste. This would cancel out the fuel’s emissions savings, due to the land clearances for oil palm plantations.
The UK’s aviation sector will have to compete not only with other countries for a limited pool of waste cooking oil, but also with other sectors.
Most of the UK’s waste cooking oil supplies are currently used to make biofuels for trucks and other road transport. Again, diverting resources from road fuel use would undermine the emissions savings from using them in SAFs.
The government acknowledges this, noting that “the SAF mandate may divert feedstocks which would have been utilised in other sectors of the economy and this may increase emissions in other sectors”. However, it says this is justified because “there are limited alternatives to decarbonise aviation by 2050”.
One of the scenarios modelled by the government assumes that SAF targets are met, but insufficient waste cooking oil means there is not enough biodiesel for road vehicles. This reduces the cumulative emissions savings between 2025-40 from 53.9MtCO2e to 43.0MtCO2e.
New fuels
The government is also supporting new types of SAF production in the UK, including fuels made from “black bin bag waste” and residues from farming or forestry.
In the newly released documents, the government says the UK will be a “leader” and a “first mover” in these technologies, spurred on by the cap on waste oil fuels and supported by the Advanced Fuel Fund.
Unlike waste oil-based fuels, the government says there will be “sufficient” materials available to meet production demand for these advanced fuels until at least 2040. From that point onwards, it says lack of materials “may become a constraining factor”.
However, a 2023 report by the Royal Society highlighted the limited availability of some waste materials to produce SAFs. It estimated that forest offcuts, for example, would be able to provide no more than 1.7% of current jet fuel demand.
Moreover, many waste sources are already recycled or burned to generate electricity and the government has targets in place to cut household waste in the coming years. “Most waste is already used for something that’s not jet fuel, so we know supplies of waste-based SAF will be limited,” Finch tells Carbon Brief.
Finally, the government’s mandate also includes another target, within the overarching SAF goal, for scaling up the production of “power-to-liquid” fuels.
These fuels can be made using green hydrogen and carbon captured from the air. Unlike most SAFs, they could cut up to 100% of CO2 emissions compared to conventional jet fuel, but they are currently less developed than other options.
The target for power-to-liquid fuels will start in 2028 at 0.2% of total jet fuel demand, reaching 0.5% in 2030 and 3.5% in 2040.
These targets are lower than the ones introduced in the EU, which is aiming for 35% of its jet fuel to be power-to-liquid by 2050. The bloc is also targeting 70% of aviation demand to be met with SAFs by 2050, whereas the UK’s targets stop at 22% by 2040.
In its “balanced net-zero pathway” for UK aviation, government advisors the Climate Change Committee (CCC) proposed that SAFs should make up 25% of jet fuel by 2050, with one-third of this made up of power-to-liquid fuels – roughly 8% of total jet fuel. The government targets are roughly in line with this trajectory.
Thinktank Green Alliance laid out three scenarios for SAF expansion in 2022, including higher ambition goals, with power-to-liquid fuels reaching 28% and 50% of total jet fuel by 2050.
However, it noted that such a rollout could be constrained by the large amounts of additional green hydrogen and renewable power required to produce these fuels.
The report stated:
“It could be argued that aviation should not be a priority use of renewables as there are other options to cut carbon in the sector, such as managing the number of flights taken.”
The post Analysis: Benefits of UK ‘sustainable aviation fuel’ will be wiped out by rising demand appeared first on Carbon Brief.
Analysis: Benefits of UK ‘sustainable aviation fuel’ will be wiped out by rising demand
Climate Change
The Language of the Land: Revitalizing Indigenous Languages for Ecological Understanding
Indigenous languages are more than tools of communication—they are living repositories of ecological knowledge, shaped by millennia of close relationship with the land, waters, skies, and all living beings. Each word, verb, and inflection embed understandings of place, seasonality, climate cycles, and human responsibility to the natural world.
As climate change accelerates, there is a growing recognition that language revitalization is climate action. Restoring Indigenous languages is about preserving culture and restoring knowledge systems that contain detailed and relational understandings of ecological processes. These languages offer insights urgently needed to adapt to and mitigate today’s environmental crises.
How Language Encodes Ecological Knowledge
Indigenous languages often describe the world relationally, not just descriptively. Many Indigenous terms describe relationships, behaviours, and responsibilities rather than naming things in isolation.
For example:
- In the Nuu-chah-nulth language on the west coast of Vancouver Island, there are multiple verbs for water movement—words that distinguish between rippling, trickling, flooding, or rushing. Each verb carries specific environmental cues: changes in rainfall patterns, seasonal flow, or flooding risk.
- In Anishinaabemowin, “Aki” refers to Earth as an animate being, reflecting a worldview where the land is not a passive backdrop but a living relative. This linguistic structure affirms that humans are in relationship with land, not dominion over it.
- In Gwich’in, different words for caribou describe their life stages, movements, and ecological roles. These linguistic distinctions hold knowledge about migration routes, mating cycles, and the health of the land.
Such examples reveal how Indigenous languages encode local environmental indicators, climate memory, and survival strategies within everyday speech.
Language and Climate Resilience: A New Frontier
As climate change disrupts familiar patterns, Indigenous languages offer tools to interpret these changes through a culturally grounded lens. Revitalizing these languages strengthens identity and cultural continuity and equips communities with local and regional knowledge systems that can assess and respond to ecological disruption.
In many communities, land-based language camps teach youth the names of medicines, constellations, and animals, alongside the protocols and stories accompanying them. This strengthens climate resilience through:
- Intergenerational knowledge
- Cultural pride and ecological responsibility
- Reinforced relationships with land, language, and community
Colonialism, Language Loss, and Environmental Consequences
Colonial policies and practices—including residential schools, forced relocation, and assimilation—aimed to sever the ties between Indigenous Peoples and their languages. Today, many Indigenous languages in Canada are critically endangered, and with their loss comes the erosion of place-based ecological knowledge that is not documented in Western science.
As communities work to reclaim their languages, they are also reclaiming their role as land stewards, drawing on ancestral teachings that define how to live in balance with all of creation.
Revitalizing Indigenous languages is thus not only cultural preservation but also environmental justice. It challenges extractive paradigms and reasserts worldviews that prioritize reciprocity, care, and interdependence with Mother Earth.
Recommendations for Readers
- Support Language Revitalization Programs
- Contribute to immersion schools, land-based learning camps, and Indigenous language organizations. These initiatives are vital for climate and cultural resilience.
- Incorporate Indigenous Languages into Environmental Education
- If you’re an educator, integrate local Indigenous terms into your climate, geography, and ecology lessons—always with appropriate consultation and permission.
- Attend Workshops and Learn Locally
- Participate in language classes or workshops offered by nearby Indigenous Nations. Learning a few words for local species, landforms, or weather phenomena can deepen your ecological awareness.
- Explore the Language–Climate Connection
Blog by Rye Karonhiowanen Barberstock
(Image Credit: Getty images, Unsplash)
The post The Language of the Land: Revitalizing Indigenous Languages for Ecological Understanding appeared first on Indigenous Climate Hub.
The Language of the Land: Revitalizing Indigenous Languages for Ecological Understanding
火山喷发对科学家及其气候模型构成了根本性挑战。
众所周知，剧烈的火山喷发会导致地表气温突然下降，多次喷发则会在几十年乃至几个世纪的时间尺度上影响气候变率。
当火山喷发将二氧化硫注入平流层时，会形成气溶胶，从而阻挡阳光到达地球表面。
与人类对气候变化的影响不同，后者发生缓慢且可以在各种社会经济情景下被纳入气候模型进行考量。火山喷发具有突发性，这给气候预测带来了挑战。
目前科学家尚无法预测火山喷发的发生时间、地点以及二氧化硫的排放量。
那么，在进行未来气候预测时，如何考虑火山喷发对气候的影响呢？
在我们最近发表于《通讯-地球与环境》（Communications Earth & Environment）的研究中，我们表明火山喷发对全球气温预测的不确定性产生了重大影响。
我们的研究结果发现，如果将偶发的火山喷发纳入气候预测，突破《巴黎协定》所设定的1.5C升温上限的时间会略有延迟，但与此同时，未来几十年也将出现更多快速升温和降温的时期。
气候预测中的火山强迫
气候科学家将火山喷发对气候的影响——主要是通过释放出二氧化硫气体进入大气——称为“火山强迫”（volcanic forcing）。
当前的气候模型在进行未来预测时采用一个恒定的火山强迫值，该值是根据1850年至今的历史平均强迫值计算得出的。
国际耦合模式比较计划（CMIP）也是如此，这项全球模型工作为政府间气候变化专门委员会（IPCC）发布的重要评估报告提供基础数据。
然而，这种方法存在显著局限。
首先，历史平均强迫值无法表示火山爆发的偶发性。
大规模火山喷发呈零星分布——有时好多事件集中发生在某几个十年内，有时两个事件之间则可能相隔上百年。
此外，与数千年尺度的记录相比，从1850年至今的参考时期中，发生过的大规模喷发事件 ——指排放超过3太克（Tg）二氧化硫的喷发事件——相对较少。
最后，早期国际耦合模式比较计划气候模型中所使用的火山强迫重建数据并未包含排放量少于3太克二氧化硫的中小规模喷发。
这是因为这些喷发在1980年卫星时代开始之前大多未被探测到。然而，这些体量较小但发生频率更高的喷发事件，在长期火山强迫中贡献了30%至50%。
采取新方法
传统上，气候科学家认为气候预测中主要存在三种不确定性来源：内部变率、模型不确定性和情景不确定性。
其中，“内部”变率是指气候系统内部自然产生的波动，如厄尔尼诺现象；模型不确定性是指不同气候模型之间结果的差异；情景不确定性则涉及未来几十年全球可能的发展路径。
我们的研究结果表明，火山喷发应被明确视为气候预测中第四个重要的不确定性来源。
为了探究在考虑火山强迫不确定性的情况下，气候预测会发生怎样的变化，我们的研究采用了一种概率方法，这一方法建立在Bethke等人于2017年提出的研究基础之上。
为此，我们构建了“随机强迫情景”，其本质是1000种延续至本世纪末的火山活动可能时间线预测。
这些情景基于冰芯中记录的过去1.15万年火山活动历史，以及卫星观测和地质证据。每个情景都呈现了不同的喷发强度、地点、时间和频率的组合。
（在数学中，“随机”系统是指结果包含随机性或不确定性的系统，因此不可预测；这与“确定性”系统相对，后者的结果可以通过初始条件和一套规则或方程完全预测。）
随后，我们利用2015至2100年期间的随机火上强迫和历史平均火山强迫模拟气候预测，研究共享社会经济路径（SSPs）中三种不同排放情景下的升温变化：低排放情景（SSP1-1.9）、与现行气候政策相符的中等排放情景（SSP2-4.5）、非常高排放情景（SSP5-8.5）。
在这一步中，我们使用了一种称为FaIR的简化气候模型，也称“模拟器”。
通过模拟1000种不同的火山未来情况，我们发现在21世纪未来时期火山喷发所引起的气候不确定性，可能超过同期气候系统本身的内部变率。
我们还发现，到2030年代，火山喷发可能占全球气温预测总不确定性的三分之一以上。
下图中能看到这些结果。图中展示了不同来源对总不确定性的影响。火山为橙色、内部变率为深蓝色、气候模型响应为黄色，未来人类排放情景为绿色。
对1.5C临界值的意义
我们的模拟结果表明，在气候预测中纳入可能的火山活动时间线后，短期内突破《巴黎协定》设定的1.5C升温上限的概率略有下降。
根据不同的排放情景，相较于使用恒定火山强迫的预测，模拟发现超过1.5C升温上限的概率下降了4%至10%。
尽管这一结果听起来似乎令人鼓舞，但未来的火山活动并不能在长期缓和由人类引起的全球变暖。
1815年坦博拉火山的喷发事件就是一个强有力的例证。这次喷发使全球气温平均下降了约0.8C，带来了“无夏之年”，导致欧洲、北美和中国大范围的作物歉收和饥荒。
火山喷发带来的降温效应是短暂的，通常只持续几年，其并不会改变由人类排放所导致的长期变暖趋势。
我们的研究发现，即使考虑多种可能的未来火山活动，在除了最低排放路径以外的所有情景中，全球变暖仍将在几十年内超过1.5C。
即便21世纪火山活动频繁，其对全球变暖的抵消作用也仅占很小一部分——这意味着减排对于实现长期气候目标仍然至关重要。
下方图表展示了在三种排放情景下，使用随机火山强迫（实线）与恒定火山强迫（虚线）时超过1.5C的概率（上图），以及两种强迫方式之间的概率差异（下图）。
十年尺度的气温变率
我们的研究提供的另一个重要发现是：一旦将火山强迫的变率纳入考虑，将更有可能出现极端温暖和寒冷的十年期。
在中等排放情景下，我们发现出现负向十年期趋势——即全球表面温度在某个十年内平均下降——的概率增加了10%到18%。
与此同时，出现极端温暖十年期的概率也随之增加，这反映出火山强迫的变率会同时提高变暖和变冷极端事件发生的可能性。
这一结果凸显了火山喷发如何在十年时间尺度上对全球气温趋势带来显著的波动。
迈向更完善的气候预测
了解火山对气候的影响，对于全面评估农业、基础设施和能源系统在未来所面临的风险至关重要。
使用全面的地球系统模型运行数千种火山情景并不切实际，因为这需要极高的计算资源。但与此同时，当前的方法也存在上文提到的显著局限。
不过，在未来的气候模型工作中，仍有折中方案可行。
即将开展的下一阶段气候建模实验——即CMIP7情景模式比较计划——可以采用更具代表性的“平均”火山强迫基线，这一基线纳入了历史记录中常被遗漏的小型喷发事件的影响。这一偏差现已在用于下一代气候模型模拟的历史火山强迫数据集中得到纠正。
此外，建模团队还应额外运行包含高频和低频未来火山活动的情景，以全面捕捉火山不确定性对气候预测的影响范围。
虽然人类导致的温室气体排放仍是气候变化的主导因素，但若能妥善考虑火山活动的不确定性，将有助于我们获得更全面的未来气候图景及其对社会的潜在影响。
The post 嘉宾来稿：探究火山喷发如何影响气候预测 appeared first on Carbon Brief.
My heart is heavy this week. The climate crisis is causing death and destruction across the globe — floods in Texas, North Carolina, China, Columbia, and Afghanistan; extreme heat in multiple continents; senseless wars and genocides — all continue in a somber and sad death march. Authoritarianism is more deeply entrenched across the USA and the contents of the legislation passed and signed by the President just before the 4th of July will cause great harm to people I love and consider family as well as set us back decades in the fight for environmental justice and climate mitigation and adaptation.
I feel like I have been writing about hope and resistance since I started at Climate Generation almost three years ago. And I have been finding it really hard to practice what I preach, what I know, these last few weeks.
And then last night, while doom scrolling on Instagram, I saw a post from @earthlyeducation. I was reminded that we need both to envision the world we actually want to live in, and then have practical strategies to fight for it. The post was a balm for my activated brain, body, and heart. So I share, directly quoting, from their post:
1. Speak truth with love
Start with your circles. Friends, family, workmates. Share the full reality of what’s happening without sugarcoating it. This system is violent and unsustainable. The goal is to wake people up, not with fear, but with clarity and care.
2. Use your gifts for resistance
Whatever you do, you have power. Whether you make music, build things, teach, or organize behind the scenes, your skills matter. Use them to support movements, challenge the status quo, or build alternatives rooted in justice and ecology.
3. Confront power directly
Power will not give up willingly. Join movements that are resisting fossil fuels, corporate greed, and settler-colonial violence. Disrupt the smooth flow of business as usual. Show up where it hurts them most, and don’t ask for permission.
4. Divest from destruction
Move your money out of institutions funding war, fossil fuels, factory farms, and deforestation. Ethical banks and credit unions exist. Every dollar you remove is one less fuelling collapse. Starve the beast wherever you can.
5. Join or build a collective
Collective power is our only hope. Join a climate, housing, indigenous, or justice group that aligns with your values. Or start one with others who are ready. You don’t need to be perfect, just present and willing to grow.
6. Live like capitalism is ending
Radically reduce consumption. Eat more plant-based. Grow and share food. Cut ties with fast fashion and hyper-consumerism. Build your life around regeneration, repair, care and mutual support. Be a living contradiction to this system.
7. Reclaim community and connection
The system wants us isolated and distracted. Fight that by building mutual aid, sharing skills, raising kids together, and restoring kinship with the more-than-human world.
Susan Phillips
Executive Director
Photo: Fabrice Florin
The post There’s Resistance in Resilience appeared first on Climate Generation.
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