Urban planning can mean climate action

With more emphasis than ever on planting trees and parkland to make metropolitan areas more liveable, Martin Guttridge Hewitt explores guidance to help local authorities bring nature into the concrete jungle, and the biotech tackling air pollution and heat islands.

By 2014, 54% of the world had moved to a city. By 2050, that figure will stand at 70%. To accommodate the shift, our built environment is predicted to have expanded by two-thirds once this decade is done compared with the last, setting pace for the next 20 years. 

This raises some profound concerns among those fighting to bring emissions down, improve air quality and mitigate the worst threats of climate change. Construction and building materials alone account for 13% of total global carbon emissions each year. Depressingly, that figure is rising. Meanwhile, the prioritisation of biodiversity through the 30×30 target – which calls for 30% of the Earth’s landmass to be protected from development by 2030 – further draws attention to the uneasy balance between growth and ecology. 

City planning also faces another challenge. While new places must be built in climate-positive ways, falling livability scores and health risks linked to environmental factors in urban areas that already exist also need to be addressed. So-called ‘greening’ – creating parkland, designating nature reserves, introducing vegetation – is often seen as the solution. But while these practices have a proven impact on wellbeing and health, as a means of tackling pollution things aren’t so simple. Those who think planting en masse is the best idea are barking up the wrong tree. 

Mike Henderson has worked in ‘greening’ for 21 years. During that time, he’s led on green infrastructure strategy for the London 2012 Olympic Games and post-Olympic Legacy Communities Scheme, delivered support to the Greater London Authority to refresh the All London Green Grid, and spearheaded Green Infrastructure Guidance for London’s boroughs. As Director for Regenerative Cities at Ramboll, he runs a team focused on ‘developing places that go beyond net zero to deliver self-reinforcing ecological, built and social systems’. Suffice to say, he’s clear on what won’t work. 

green-leafed tree at daytime

‘With regards to air pollution, the most important action we must prioritise is to remove the pollutant in the first place; that is, reduce vehicle emissions. And it’s worth noting that not all greening is equal. For example, some plant species are more resilient to urban conditions, better at redirecting air flow and encouraging pollutant deposition than others,’ Henderson explains. ‘We know that by appropriate selection and arrangement of green infrastructure, people’s exposure to pollution can be reduced. 

‘[But] the Government’s Air Quality Expert Group reported where vegetation acts as a barrier close to a pollution source, concentrations immediately behind the barrier are halved, whereas on the source-side of that barrier, concentrations increase,’ he continues. ‘We need to be careful with ‘canyoning’, whether with buildings or trees and vegetation, whereby pollution and particulate matter get trapped and can funnel air pollution through cities.’ 

Henderson says research into more advanced ‘nature-based solutions’ to air pollution is underway, for example paint that ‘eats’ particulate matter or building materials containing microbes. However, much of this is in the early stages, and development is likely to be resource-heavy, reinforcing the idea that reduction must be the primary goal. 

Nevertheless, he points out that guidance on the use of green infrastructure to bring traffic-related emissions down, produced by the Mayor of London, is very useful. Similar information is found in the Association of Directors of Environment, Economy, Planning & Transport’s (ADEPT) Value of Trees Toolkit, a free resource developed with the Rees Jeffreys Road Fund. And for those looking to better understand ideal built-to-natural environment ratios, the gold standard comes from Natural England and Defra’s biodiversity net gain metric, compliance with which will soon be mandatory for all new developments. 

If greening has a complex relationship with air pollution, its effect on ‘urban heat islands’ is easier to understand. In 2022, UK cities were an average of 1.2C warmer than nearby rural areas, rising to 1.5C for Europe. Research conducted by Mark Nieuwenhuijsen, Director of Urban Planning, Environment and Health Initiative at ISGlobal, shows the impact on residents is huge. Using data from 93 European cities – a combined population of 57m – the study found around 6,700 premature deaths could be attributed to heightened urban temperatures. That’s 4.3% of total summertime mortality in the region. 

‘Previous studies have shown that when ambient temperatures get out of an optimal range – become too hot or too cold – we see more people dying,’ Nieuwenhuijsen replies when we ask how his latest work began, explaining that reducing asphalt and road use in cities, which also tackles air pollution at source, is key to bringing thermometers down. ‘85% or so of the petrol in cars is emitted as heat, only 15% is used to move the car. Time to change. Replacing asphalt with trees and other greenery would be excellent to change an environment currently detrimental to health into something health-promoting with less air pollution, noise, and lower temperatures. 

alone bare tree planted on sidewalk

‘The more distributed trees are throughout the city the more benefits are expected in terms of cooling. But this is also important for equity issues, whereby a good distribution [of trees] through a city [means] everyone can benefit, rich and poor,’ he continues. This echoes a report by the University of Leeds and United Bank of Carbon suggesting that socioeconomic factors surrounding the location of green space do not impact frequency of use. As such, introducing more parkland can help address health inequalities between low and high income demographics, of which air quality is already a major contributor.

While words like ‘greening’ are usually associated with planting trees and protecting natural assets, in Germany another type of organism is yielding impressive results in terms of air quality when combined with cutting edge technology. Established in 2014, it took six years of development before Green City Solutions unveiled its first product –  the CityTree.

This Internet of Things device essentially acts as an outdoor filter. Moss modules on the exterior, controlled by computer algorithms, are capable of removing 82% of fine dust from the atmosphere. This is also cooled, by up to 2.5C. The result is enough clean air for 10,000 people per hour. And as this is connected, the kit adds to existing smart city infrastructure. 

Raised in a family whose business has been selling plants since the late-1800s, horticulturist, co-founder and CEO of Green City Solutions, Peter Sänger, tells us the company has worked with a range of local authorities. Reeling off a list of locations, these range from the firm’s hometown, Berlin, to Amsterdam, Paris, Brussels and Vienna. In the UK, Hereford already has a functioning CityTree, with projects in London boroughs such as Fulham and Hammersmith underway. 

‘We should think not about a standalone CityTree, but a network of biotech solutions,’ says Sänger, explaining two other products play a key part in this vision. One, CityBreeze, offers the same air filtration, while providing display advertising opportunities by splitting surface area between moss wall and a 75 inch LCD screen, helping secure revenue for authorities while they tackle heat and pollution. 

The WallBreeze, currently in development, has the potential to significantly scale up this impact. This modular moss filter can be attached to any wall, transforming existing and new building facades without expensive retrofitting, up to an area between 100 and 200m2. Through ongoing consultation with university departments and property developers, it is hoped that maximum size will eventually increase significantly. 

‘The comparison to trees is obvious, and often used, but we think that’s an unfair advantage on our side. Moss can be actively ventilated, regulated, it is a machine-like organism. That’s why it is so important. A tree is a natural thing, and hard to predict the impact,’ Sänger continues, revealing that the CityTree uses 10% of the energy a conventional filter would. 

‘We can see here in our cities that trees are suffering from droughts, soil degradation, things like this. And the effectiveness of a tree planted one or two years ago is quite small, maybe insignificant. That’s why we try to bridge this ecologically friendly, natural feeling with technical, measurable impact,’ he adds. 

Thanks to complex algorithms working behind the scenes, a CityTree can also be adjusted and fine-tuned, so maximum output can occur as local emissions peak. Unlike a tree, which can require 10 years of plantation growth before it is ready to be introduced to a city, the moss modules are good to go within 12 to 14 weeks, and recycled at the end of their life span, helping Green City Solutions with its own zero waste aims.

All of which means significant value for money, not least when smart functionality is taken into account. A city tree can form a WiFi hotspot, reducing the need to spend on this separately. And, with the equivalent environmental impact of up to 67 natural trees, the five-digit price tag – variable depending on location and order size –  looks even more affordable. Ultimately, though, even this reflects an outmoded view. In reality, inaction on emissions, pollution and other environmental issues becomes less cost-effective by the day. And that’s before we consider the huge long-term, baked-in price tag of failing to invest now.


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