Cities are an often overlooked as being a major contributor to climate change. Yet their diversity has made it hard to assess how far they can cut their emissions.
Moreover, efforts to tackle their emissions, such as those from urban transport, often come with trade-offs in terms of costs and co-benefits from cleaner air or health.
In our new study, published in Nature Sustainability, we conducted a comprehensive analysis of transport policies in 120 cities, spanning five continents.
We found that the cities could cut carbon dioxide (CO2) emissions by a combined 22%, without cutting residents’ quality of life measured via an aggregate, monetised metric.
In individual cities, we found that a combination of policies, such as fuel taxes, public transport improvement and urban planning, could reduce transport CO2 by up to 31%.
Cities in climate policies
Cities bear a major responsibility for climate change, as they account for 70% of global emissions.
They can also play a key role in implementing climate action at the local level. Many cities have set ambitious climate goals, with members of the Global Covenant of Mayors city network, for instance, aiming to reduce their emissions by 66% by 2050.
Urban transport, in particular, is an important sector, representing 8% of global emissions alone. This also tends to be an area where cities have the ability to act.
Yet, quantifying the aggregated potential of cities to mitigate transport emissions has proven challenging. Indeed, the impacts of city-level policies depend on the unique characteristics of each city, such as urban spatial organisation and existing infrastructure.
On the other hand, detailed city models applied to case-study cities are difficult to generalise, since the scientific literature is fragmented and biased toward larger cities and developed countries.
Exploring strategies
Using an urban simulation model, we estimated the aggregate potential for 120 cities on five different continents to reduce their urban transport emissions.
We also considered the impact of such climate actions on inhabitants’ quality of life, through housing and transport prices, local taxes and health co-benefits related to transportation. This included those related to cleaner air, reduced noise, reduced traffic accidents and increased physical activity due to active transportation modes.
The 120 cities are home to 525 million inhabitants, or about 20% of the total global population that lives in cities larger than 300,000 people.
To calibrate the model on each city, we relied on spatially explicit socio-economic data that we collected through web-scraping of local websites, as well as data on local transportation systems that was provided by Open Street Map, Google Maps and Baidu Maps.
Our study explores four main types of complementary strategies that could help reduce transport-related emissions in cities: taxation of polluting vehicles; incentives to use vehicles that consume less fossil fuel; investment in public transport; and urban planning policies that restrict urban sprawl.
For each of these strategies, we examined examples of public policies that can be implemented at local level. For example, to improve public transport, one possibility is to set up a bus rapid transit system on dedicated lanes.
Other examples include that urban planning can involve limiting new construction away from public transport stations. Polluting vehicles can be taxed by raising fuel prices or by introducing local congestion charges.
Finally, the use of more efficient vehicles, such as electric cars, can be encouraged by a combination of subsidies and bans on the most polluting vehicles in urban centres.
Comparing local policies
Our findings suggest that a combination of these policies could reduce overall transportation GHG emissions by up to 31% in 15 years, across the 120 cities studied.
Policies implemented individually could mitigate emissions by 4% to 12%, depending on the policy considered.
These results are in line with the scientific and “grey” literature on the topic, which has shown that urban transport emissions could be mitigated by 20% to 25% through a combination of urban planning and technological solutions.
The impact of a given policy varies according to the city in which it is implemented. For example, in the majority of South American cities studied, the introduction of new public transport lines would be particularly beneficial, our results suggest.
Given the relatively high population density and underdeveloped public transport systems in these cities, our simulations indicate that the implementation of new public transport lines could potentially reduce emissions by up to 21% and 26% in Brazilian cities such as Goiânia and Belém, respectively.
In Europe, taxing fuel prices appears to be more effective, primarily due to the generally well-developed public transport networks available in European cities. For instance, a fuel tax would lead to a 7.5% reduction in transport-related emissions in Barcelona, we found, while the impact would be only 0.6% in Atlanta (USA), where alternatives to private cars are less readily accessible.
Simultaneous implementation of multiple policies can have a particularly significant impact, our results show. Combining taxes on polluting vehicles with public transport development could result in substantial emission reductions, as could promoting public transport alongside measures to control urban sprawl and increase population density near railway stations.
For instance, in Lille (France), implementing policies to control urban sprawl, tax polluting vehicles and develop public transport concurrently would potentially reduce transport-related emissions by almost 24%, compared to reductions of 9%, 4%, and 7%, respectively, if each policy was implemented individually.
An example of the differing impact of public transport development on CO2 emissions after 15 years can be seen in the map below, with purple circles showing cities that could achieve a more than 10% saving, blue showing 5-10%, green 1-5% and yellow less than 1%.
Variation in transport-related CO2 emissions
Inhabitants’ quality of life
Assuming that these policies are fully financed locally by a tax, our study also estimates their impact on the material conditions of residents and on their health.
We analysed the impacts of urban transport emission reduction policies on a range of factors linked to quality of life. In terms of income, for example, building locally financed public transit lines increases local taxes, while taxing polluting vehicles reduces them. We also looked at transportation costs, average housing prices, air quality, noise pollution, road accidents and the health benefits associated with “active” mobility (walking or cycling instead of driving).
Depending on the city, these impacts can be positive or negative overall. A fuel tax or the opening of new public transport lines would be expected to improve air quality, reduce noise pollution and the number of road accidents. More efficient vehicles improve air quality and reduce the household transport budget – even if their impact in terms of road accidents remains unchanged.
On the other hand, urban planning that limits urban sprawl can contribute to higher housing prices and the introduction of public transport lines can sometimes prove extremely costly.
To facilitate comparison, we expressed these variations in monetary terms, creating a composite indicator of welfare that encompasses all dimensions of residents’ quality of life mentioned earlier, as shown in the figure below.
Our study reveals that, in all cities examined, there are policy combinations that can effectively reduce emissions while improving overall well-being.
Most importantly, if, in each of the 120 cities of our sample, instead of applying all the policies that we considered, we choose to apply only policy combinations which do not reduce our monetised measure of welfare, we find that we can reach in total a 22% reduction in urban transportation GHG emissions in 15 years.
This means that most of the emission reductions that we simulate in our study can be reached without affecting residents’ quality of life in any of the cities that we considered.
While 22% is not sufficient, in itself, to reach carbon neutrality, we only analysed four simple and generic policies. Specifically designed and optimised policy portfolios for each city could reach larger emission reductions.
Climate governance and research
As numerous protests worldwide have demonstrated, public policies aimed at reducing emissions must also positively impact residents’ quality of life to gain acceptance.
In all the cities that we studied, we found that it is possible to combine reduction of GHG emissions and the enhancement of quality of life, through well-adapted policy choices.
In order to achieve this, the set of policies needs to be tailored to each city’s specificities, however, with strategies which cannot necessarily be directly transposed from one city to another. In our city sample, the emission reduction that can be reached – even with a generic policy toolkit – is also significant.
Cities are frequently overlooked in international climate discussions, in part because of the diversity of their characteristics. This diversity does make it difficult to assess the potential of urban policies to contribute to global climate goals.
With the recent increases in local urban data becoming available, however, our study shows that it is now possible to explicitly model and assess the consequences of climate strategies over a wide range of cities.
Important research gaps still remain. We could not, for instance, include any African cities in our sample due to challenges accessing reliable and comparable data. If current trends in data availability continue, this and other issues could be solved over the coming years.
The post Guest post: How 120 of the world’s major cities could cut transport CO2 by 22% appeared first on Carbon Brief.
Guest post: How 120 of the world’s major cities could cut transport CO2 by 22%
Climate Change
Australia’s climate credibility tested at Pacific Pre-COP talks, as High Court fossil fuel ruling puts government on notice
NADI, FIJI Thursday 8 October 2026 — As the Pacific Pre-COP talks wrap up and Australia prepares to take the reins of COP31 Negotiations in Türkiye next month, Greenpeace Australia Pacific says the government is on notice over fossil fuel expansion and exports, and must accelerate action to align with a 1.5°C pathway.
Following yesterday’s landmark High Court ruling that the climate impacts of coal and gas exports must be considered by New South Wales planning authorities, Greenpeace Australia Pacific is calling on the Albanese government to find the “courage, leadership and grit” to chart a new course away from fossil fuels.
High res images and video from yesterday’s ‘Keep 1.5C Alive’ flotilla in Nadi can be found here
Speaking from Nadi, Shiva Gounden, Head of Pacific at Greenpeace Australia Pacific, said:
“The outcomes of this week’s talks are a drop in the ocean given the scale of need, and urgency of the crisis our communities are facing. It is like taking a glass of water to a burning house if we do not urgently act to address the root cause of the existential threat facing Tuvalu, Fiji and all Pacific countries: fossil fuel expansion.
“The Electrification Pledge must end fossil fuel dependence, not be an end in itself — its ultimate success depends on ensuring electricity comes from renewable sources that displace fossil fuels and align with a 1.5°C pathway. It must be underpinned by justice and backed by finance flowing from polluters to communities.
“Limiting global warming to 1.5°C is a non-negotiable survival line for humanity and Australia must act. The landmark climate advisory ruling from the ICJ is clear — 1.5°C is the moral, the scientific and the legal limit. Continuing down the fossil fuel path, and failing to align efforts with limiting warming to 1.5°C, is a breach of our international legal obligations, and risks making Australia liable for future reparations from climate-vulnerable nations.”
Also in Nadi, Dr Simon Bradshaw, COP31 Lead and climate expert at Greenpeace Australia Pacific, said: “The Pacific was never going to be a mere backdrop for Australia in its role as incoming chair of the COP31 climate talks, but where its credibility and commitment to climate leadership would be tested.
“Here we see communities fighting for their survival and doing everything possible to hold the line on returning warming to 1.5°C. When governments profess to take their concerns seriously, only to then throw more fuel on the fire, the pain and sadness is visceral.
“This week the High Court of Australia recognised what the Federal Government refuses to — that Australia is responsible for the climate damage of our fossil fuel exports and if governments don’t act, the courts will intervene. The message is simple: this is not someone else’s problem, it is ours.
“We must now follow other countries in developing a national roadmap away from fossil fuels that ensures a managed wind-down of fossil fuel production, including exports, in line with our legal obligation to help return warming to 1.5°C.”
ENDS
Media contact: Kate O’Callaghan in Nadi on +61 406 231 892 (Whatsapp/Signal)
A Dutch NGO has filed the first climate complaint under the European Union’s trade rules, arguing that New Zealand violated the environmental provisions of its free trade agreement with the bloc by weakening its climate regulations.
The case will test whether binding climate provisions in the EU’s free trade deals can be enforced to hold governments accountable to their climate obligations, experts told Climate Home News.
The EU-New Zealand free trade agreement, which came into force in 2024, was the first in the world to include legally-binding climate provisions and possible sanctions for violating them, as the EU seeks to use its trade partnerships to advance greater environmental protection.
Under the deal, both parties committed not to weaken their environmental law to promote trade or investment and to “refrain from any action or omission that materially defeats the object and purpose of the Paris Agreement”.
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At the time the agreement was signed, EU Commission President Ursula von der Leyen said the agreement included “unprecedented social and climate commitments”. But experts warned it was unclear how the Paris Agreement provisions would be enforced.
The EU included a similar “trade and sustainable development” clause in 14 other bilateral trade deals in recent years, with several others, including with China, awaiting ratification or being negotiated.
Climate activists at the Dutch NGO Both ENDS argue that the New Zealand government breached these terms by reopening its waters to offshore oil and gas exploration, releasing a climate plan that barely requires any emissions reductions, and passing a law that prevents corporations from getting sued over climate damages.
“Here, we have a so-called gold standard for free trade agreements with sustainability provisions but we have a trading partner that is doing exactly the opposite: regressing, as all the evidence points to, away from the Paris Agreement,” said Marius Troost, a senior policy advisor at Both ENDS.
Can the EU enforce its climate trading rules?
The Dutch environmental group filed the complaint under the EU Commission’s Single Entry Point, a mechanism that allows civil society to request enforcement of the bloc’s trade commitments.
The EU-New Zealand trade deal includes the possibility of suspending beneficial trading arrangements between the two parties in response to serious violations of its climate provisions. This, Troost said, is a “unique” tool to enforce both parties’ obligations under the deal.
“This is an opportunity for the EU and New Zealand to show that they are actually serious about these commitments,” he told Climate Home News.
A spokesperson for New Zealand’s Ministry of Foreign Affairs and Trade denied any violations of the agreement and said the government hadn’t received formal notice of the complaint. The country, they said, “takes its commitments under the NZ-EU Free Trade Agreement seriously, including the agreement’s environment and climate-related provisions”.
An EU Commission spokesperson said it will start a preliminary assessment of the complaint and engage with NGO Both ENDS. “Sustainability is a central pillar of the EU-New Zealand relationship,” they added.
The EU is New Zealand’s second-largest trading partner after China, with about 14% of the country’s exports going to the European market. Agricultural products like meat, diary, fruit and vegetables are the country’s biggest exports to Europe.
New Zealand is ‘having its cake and eating it’
Eliza Prestidge-Oldfield, a senior legal researcher at the New Zealand-based Environmental Law Initiative, which is supporting Both ENDS’s claim, told Climate Home News that if the EU upholds the complaint, both parties would begin a negotiation process.
“The idea is to try and resolve this positively with the New Zealand government acknowledging areas where it needs to change its actions in order to comply with the agreement, and get that change in place as soon as possible,” she said.
But New Zealand’s right-wing coalition government said it won’t take any directives from foreign actors regarding its policies. Trade minister Todd McClay told local media that it was “not for overseas countries, organisations or lobby groups to tell New Zealand how to meet its obligations”.
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Prestidge-Oldfield argued the complaint isn’t about “Europe telling anyone what to do at all”, but rather stressing the conditions under which they are willing to import goods from New Zealand. “The New Zealand government is trying to have its cake and eat it too,” she said.
If New Zealand refuses to adjust its policies in line with the agreement, the complaint will be assessed by an independent panel, which can require the country to make changes. If those changes are not implemented, the panel could decide that New Zealand should lose its preferential EU market access.
A negotiated resolution is more likely, however, with no prior labour-related complaints to the EU having ever reached the panel stage.
Alexander Gillespie, a law professor at the University of Waikato in New Zealand, said sanctions would be a “last resort”. “This is a test case, which will generate considerable attention – as it is not just about climate change, but how free trade and environmental sustainability have been woven together,” he said in a statement.
Trade deals as tool for climate accountability
Experts said the case could set a precedent for how trade deals can be used to hold governments accountable on climate action. The EU has enacted similar “trade and sustainable development” clauses in its trade agreements with Canada, Japan and South Korea.
While still pending ratification, the EU’s 2024 trade agreement with Mercosur – which encompasses Argentina, Brazil, Paraguay and Uruguay – also includes climate provisions, including a commitment to “effectively implement” the Paris Agreement and promote low-carbon trade.
In addition, legal researcher Prestidge-Oldfield noted that last year’s landmark advisory opinion on climate change by the International Court of Justice (ICJ) laid out stronger climate obligations for developed countries like New Zealand and could strengthen allegations of violations of the terms of the trade deal.
“It will be an interesting area to watch how the EU free trade agreement is interpreted in the light of this advisory opinion,” she said.
The post New Zealand accused of breaching EU trade deal over climate rollbacks appeared first on Climate Home News.
New Zealand accused of breaching EU trade deal over climate rollbacks