Wind in the trees: how urban green canopies offset the need for AC

As poet Mary Oliver writes in her verse When I am Among the Trees: “I would almost say that they save me, and daily”. If that was resonant some two decades ago, it will reverberate even more now among the millions of Londoners and other European city dwellers seeking shelter from the summer heat in recent months.

Unprecedented high temperatures have caused severe difficulties in cities and large towns in south-west France, Croatia, Italy and Spain this summer, with records being broken according to the United Nations. This poses a threat that goes beyond discomfort: the UN blames extreme temperatures for around 489,000 heat-related deaths annually between 2000 and 2019, of which more than a third (36 per cent) were in Europe.

When temperatures feel like 90°F or higher, the body faces serious health risks such as heat stroke and seizures and heart complications, while heavy sweating may compromise kidney function by reducing blood circulation to these organs. For pregnant women, exposure to extreme heat poses additional dangers to their unborn children.

While the debate over mitigating climate change is covered widely elsewhere, the immediate issue for city residents is how to adapt to temperatures that make normal life hard. The easy solution is air conditioning, which is much more common in Asia and North America than it is in Europe.

But greater provision of AC would be a double-edged sword as the devices suck up electricity, requiring greater production of energy from fossil fuels and thus adding to the generation of harmful greenhouse gases. Cooling is already responsible for around one-tenth of global electricity consumption, according to the International Energy Agency.

In any event, air conditioning only helps people when they are inside buildings with that facility and does not help those who need or want to be outside. The provision of AC is inherently inequitable as less developed countries where more activity, such as farming and trading, takes place in the open have a much lower share of AC provision.

The urban challenge is exacerbated by the fact that temperatures are higher within cities than outside because of a number of factors that create the so-called “urban heat island” effect. This phenomenon is caused by the dark-coloured, human-made materials such as bitumen used on roads and in buildings absorbing and storing heat during the day, which is then released at night, helping to keep temperatures uncomfortably hot during the nighttime hours. So as ever, cities are both the cause and victim of the problem.

Under the spreading chestnut tree

If AC is an ill wind for climate change, then Mary Oliver may have been right in identifying trees as our saviour. They provide shade but also mitigate against negative climate impacts. They provide critical climate benefits by absorbing atmospheric carbon dioxide through photosynthesis and storing it in wood and soil. Research has found that tree bark surfaces too play an important role, by removing methane gas from the atmosphere.

This particularly relevant in London, which boasts 10,000 plane trees which have a particularly strong appetite for pollution. Planes contribute to better urban air quality through their natural filtration systems, capturing pollutants and taking in carbon dioxide to create cleaner environments. The foliage and bark function as organic air purifiers, collecting dust particles and toxic gases from the atmosphere.

Research has found that London's urban forest annually eliminates between 850 and 2,000 tonnes of PM10 particles — the kind that pose health risks to people. The trees to regularly drop their pollution-saturated outer bark, essentially self-cleaning their filtration system. An investigation by MIT in the US together with the Dubai Future Foundation that has been picked up in the Financial Times, found that urban trees can be significantly cooler than nearby city surfaces — up to 15 degrees C during peak heat periods. However, plant cooling effectiveness varies dramatically: low-growing vegetation like shrubs and grass offer little temperature reduction, while trees with thick, full canopies provide much better cooling in most areas.

London may be an accidental beneficiary here. As I wrote on a sister blog to this, with 21 per cent canopy cover London meets the UN definition of a forest area “land spanning more than 0.5 hectares with trees higher than 5 metres and a canopy cover of more than 10 per cent”. But London is a sea of construction cranes and other major cities are building like crazy so the challenge is permanent.

In his book, The Hidden Life of Trees, Peter Wohlleben makes a convincing case based on scientific evidence that trees operate like human households, with parent trees maintaining communication and providing assistance during their development of their “offspring” and “neighbours”. They distribute resources to weaker or ailing members and establish an environment that buffers the entire community against temperature extremes.

A halo of protection that trees offer city dwellers. Photo by author

These cooperative relationships enable trees within family units or communities to thrive and achieve remarkable longevity. Isolated trees, however, face significant hardships comparable to homeless youth, typically experiencing much shorter lifespans than their socially connected counterparts.

This might seem a swerve into the arena of animism and arboreal imaginaries, but believing that trees have agency, memory and social networks but help think us more carefully about protecting assets that in turn can help us at these climactic times. Growing and preserving city woodlands is essential not only for tackling climate change and protecting wildlife, but also for building vibrant, healthy places where people want to live. Caring for the trees we already have should be considered just as vital as planting new ones.

Reaping what sow: urban gardens and inequality

Gardens hold a strong place in British culture dating from the innovation of landscape gardening that was professionalised in the 1500s and became as essential part of the aristocratic way of life. But as society became urbanised, access to pieces of green land for enjoyment and cultivation became an important and often contested issue.

The Industrial Revolution saw hundreds of thousands of people move from rural areas into rapidly expanding conurbations such as London, Manchester, Birmingham and Glasgow. London’s population more than doubled over five decades from 1.14 million in 1811 to 2.81 million in 1881. This led to intense concentration of workers and their families in cramped conditions.

Even then, social reformers could see the negative impacts of lack of access to green space. One consequence was the creation of Victoria Park, Tower Hamlets, opened in 1845 for the benefit of the East End working class. Another was the launch of the garden city movement by Ebeneezer Howard who laid out a vision of an urban environment with green spaces for all that led to the creation of Letchworth and Welwyn garden cities and Hampstead Garden Suburb.

Ebenezer Howard's vision of green urban paradise

Of course, not everyone has access to a garden. While official statistics show that eight of 10 Londoners do, that falls to 65 per cent for those living in flats, whether on social estates, new-build condominium skyscrapers or simply those living in first- and second-floor flats in old Victorian houses.

Many cities also have allotments, a piece of ground that is split into smaller plots which people or families can rent to grow their own gardens. While the main focus is on growing vegetables and other food crops, you might also find decorative plants and flowers mixed in.

They became a focus on wartime time public policy during the 1914-1918 and 1939-1945 conflicts and lately there has been rising acknowledgment that urban areas need to tackle food security problems and climate issues by developing greater independence in meeting their own needs.

According to the National Allotment Society, there are over 740 allotment sites with 40,000 plus (and increasing) individual plots in London. But a report a coupe of decades ago a study commissioned by the London Assembly found that although demand for allotments had reached record levels throughout London, the stress from intensive urban development was continuing to reduce the available allotment space even further.

Community gardens

Gardening has thus gotten entwined with issues such as socio-spatial and racial urban inequality. Those without access to a garden in a city are more likely to come have lower incomes and to come from a diverse background. But while initiatives such as Victoria Park and the garden cities came from “above”, today’s response to the need for access to gardens comes from the communities themselves.

A recent impressive exhibition, Unearthed, at the British Library in London (which closed on 10 August, sorry), featured the Coco Collective, a grass-roots gardening organisation with two Afro-diaspora led community gardens in Lewisham, south London.

Through a series of personal video interviews, it investigates the connections between cultivating food and wellness activities. It views gardens as means to reclaim territory and foster community bonds, and analyses how colonial history has influenced plant cultivation while emphasising the value of honouring traditional wisdom. As one gardener says: “I’m looking after this plant and the plants is looking after me.” Another points out that it strengthens the connection between city-dwellers and nature: “We plant the seeds together and recap what we’ve sown.”

Research in the American city of Washington, DC, which has a very pronounced divides between well-structured residential areas and unstructured poor neighbourhoods, has looked at local initiatives to create access for local residents while at the same producing food for this predominantly Black community. The researcher identified self-reliance as a way of people to better themselves and better their communities.

But it is a constant struggle. The exhibition looks at the history of Tolmers Square near Euston station whose vacant land was used by protestors who established a village until they were evicted and land given over for property development.

A more upbeat lesson from history comes from the Meanwhile Gardens in Paddington. The gardens were established on previously unused land located in a working-class and immigrant neighbourhood that was historically known as north Paddington but is now Kensal Town.

A local activist successfully lobbied Westminster City Council to explore using the area for community gardening. During the legal proceedings to determine the outcome, the council granted a Meanwhile Permit that temporarily prohibited any activities on the property. Ultimately, the community won the legal battle, and the gardens live on under the “meanwhile” name.

A successful fight for a community garden

But some threats are more invisible. One of the responses to mounting concerns over climate change and its impact on food systems food system on sustainability is the idea of localised urban food systems. Just as allotments played that role during wartime, London innovators are now using vertical gardens to grow food for restaurants that reduces their need to bring supplied in from further afield.

For example, in London's Clapham area, an innovative underground farm operates 100 feet beneath street level in a disused air raid shelter, supplying fresh produce to local grocery stores. This venture replaces natural sunlight with LED lighting systems to cultivate various greens and herbs like coriander and sweet pea shoots. The operation represents a sustainable farming approach aimed at transforming traditional food production methods.

Gardening extends far beyond being merely a popular recreational activity — it gives people the ability to transform their lives. The practice of gardening links us to our heritage, anchors us in the current moment and can inspire a different attitude to both community and food.

While gardens are often seen within the context of the grand landscapes of aristocratic estates, gardening has always been and continues to be practiced by people from every social background and circumstance, where growing salad vegetables in one’s garden or allotment can be an act of rebellion as well as self-sufficiency.

Fairness in transport is more than just fares: it is a political choice

The tricky process of organising how people get around cities ultimately comes down to allocating scarce resources: land for the transport network and space on the road or within the vehicle. This will lead to some sort of rationing which is why many interventions lead to a cry of “unfair”.

Whether the intervention is keeping old, polluting vehicles off the road, charging for road use, allowing (genuinely) safe cycle lanes or restricting the times when older people can use the bus for free will annoy some people while leading others to see the restriction as a fair decision in a crowded but democratic city.

Even a decision such as London Mayor Sadiq Khan’s decision to freeze some bus and tube fares for six of the last 10 years means finding money from some taxpayers or other budgets. And the impact of all these moves is accentuated by a consensus against embarking on more road building with London that might — at least temporarily — open up space for motorists.

These are ultimately political decisions so the final arbiter will or should be the ballot box, but it raises questions about what people see as fair and whether perceptions that a government is punishing certain groups or stepping beyond its powers undermines their strategy.

With this in mind, academics at the London School of Economics looked at policies aimed at making London more environmentally sustainable from a transport perspective. In particular it used a representative survey of Londoners, citizens’ juries with nine participants and a behavioural experiment with 19 car drivers to explore how much car use is enough and how to fairly share driving privileges as part of transport planning.

The headline finding was that the survey of some 1,200 people found firm opinions about who should bear greater responsibility for cutting local transport emissions. Almost six out of 10 respondents (57 per cent) believed that wealthy Londoners with access to quality public transport should take on the primary responsibility, while fewer than 15 per cent thought older residents who travel less frequently should be held accountable.

Asked who should get an exemption from having to reduce their emissions as much as others, the same majority (57%) would exempt the disabled with half would do so for older people, those without any alternative to a car, and carers. Fewer than one in 17 would give an exemption for wealthy residents and people with excellent public transport (surprisingly high unless that reflected that same group within the survey).

The idea of giving everyone a "budget" for how much they can drive (like having a limit on car trips) was generally well-received. People found it easier to understand big environmental goals when they were broken down into personal budgets. But this is linked to the idea of how much use of these scarce resources – road space and clean air – is sufficient for each group to have.

Fairness matters

So, what does this tell us about fairness? Most importantly, fairness matters: people care deeply about equity when it comes to transport policies. When policies seem fair, people are more willing to accept changes. Fairness served as a valuable focal point that guided discussions and deliberations between members of the citizens' jury, they found. People want transport to be fair, but making it work in practice requires careful attention to how policies are designed and explained.

While that research looked at car travel, private transport makes up a third of daily trips in London with the rest split roughly evenly between public transport and walking and cycling. In 2024 Transport for London rolled out “Equity in Motion”, its strategy to ensure the city’s public transport system is more equitable, secure, welcoming, and accessible for all residents and visitors. Many initiatives in its first year were aimed at helping the elderly and infirm including more step-free access and ramps, priority seating and moves to reduce the number of slips and falls.

Swiss Cottage is not accessible to mobility impaired Londoners due to about 60 steps between platform and street level

But as well as accessibility, the strategy acknowledges goals of making transport more available — mapping with the idea of sufficiency in the LSE research — more affordable (such as fare caps) and a more “available” way to travel such as making it comfortable and not overcrowded.

There are clearly different meanings of fairness: the study of people’s views on car use and budgets is about distributional fairness of scarce resource. TfL is looking to ensure that everyone has a fair opportunity to participate and are treated fairly (i.e., are not excluded).

While some decisions such as ensuring step-free access comes down to money, given TfL’s status as a public sector body this comes down to political decisions as do interventions such as low-traffic neighbourhoods, extensive cycling networks, clean air zones, car-free city blocks, increased parking costs, congestion charging, reduced speed limits and pedestrian-friendly enhancements. TfL warns that while many of the initiatives are funded, others can only be guaranteed if its financial future is secured.

Ultimately, fairness is a philosophical concept. Within the transport arena it has been argued that providing a fair system is less about ensuring efficiency and operational excellence and more about providing as many as possible with adequate transportation and so mitigating social inequalities in cities such as London. While that is an admirable goal, making it happen will still come back to political choices.