Cooling down cities could make a big difference to global warming

Image: russavia via Flickr.

Cities may only occupy about 2 per cent of the world’s habitable land, but they are big drivers of global climate change. That's because they're usually hotter than rural areas; a phenomenon which is known as the “urban heat island" effect. 

Cities are hotter for a number of reasons. Traffic pollution creates a greenhouse effect that keeps heat in at night. The lack of trees, meanwhile, means cities lose their ability to absorb heat and convert it into nutrients. Paving and tarmac quickly release the heat they retain back into the air, and rainwater has to be drained away in sewer systems, which deprives the area of the cooling effect of rain-soaked soil.

Then there are people. They both generate body heat and heat buildings to keep themselves warm – or use air-conditioning to cool them down. Aircon means they are transferring warmer air into the streets outside, so it adds to the city’s warmth just as much as heating systems would. 

As cities expand in size and more people live in them, these warming factors have gradually been exacerbated. In the south of England, the difference between rural areas and London is as much as 6°C. In Glasgow, where the population has been on the decline until recently, the difference can still be as much as 8°C.

In hotter parts of the world, the situation is reaching breaking point. Colombo in Sri Lanka has seen people migrating away in substantial numbers to live in cooler areas. The searing heat in Phoenix, Arizona, may prevent the city from continued expansion. Even in more temperate cities like London or Paris, unexpected heatwaves can kill hundreds and even thousands of people.

Phoenix, Arizona. Image: DPPed  at WIkimedia Commons.

The global warming debate

Discussions about global warming tend to overlook the contribution of urban growth to the problem, and instead concentrate on what is happening to the temperature across the world.

Policy developers aiming to fight global warming overlook the fact that by focusing on ways to make cities cooler, they might contribute in a big way to the solution – perhaps much more so than by focusing on global carbon-reduction agreements that either fail or end up badly watered down. Given the forecasts for climate change out to 2050, this it's beginning to look like policymakers have missed a trick when it comes to cities.

The good news is that cities have been living with the effects of local warming for decades. By observing different cities around the world, we can see what needs to happen – the problem lies in getting those cities that do less to focus on doing more.

One size doesn’t fit all

The solutions in hotter and cooler climates are different. Research in warm, humid Colombo shows excessive amounts of solar radiation. But because of the availability of abundant water from year-round rainfall and a large amount of urban vegetation, there is much less temperature difference between the city centre and rural surroundings. This suggests that were this not in place, the migration problem could be even worse.

The research found that you a big difference can be made to the climate in tropical cities, whether humid or arid, through shade.

Colombo, Sri Lanka would be far warmer were it not for all the tree cover. Image: Diana Montero Melis.

This is not about shading buildings per se (nor is this desirable) but to encourage an urban geometry that makes the spaces between buildings naturally shaded without compromising buildings' ability to draw in the sunlight as and when required.

Achieving this when the tropical sun is so high in the sky means that you have to use an intelligent combination of building heights and geometry together with elements such as canopies, awnings and urban vegetation.

With care and attention to detail, built-up areas can combine good shading with generous urban vegetation to cool neighbourhoods to temperatures that are even below those of rural areas. This is good news given the continued acceleration of urban growth in many tropical cities and rising concentrations of people. And even a couple of degrees' difference can make a city unbearable in an area that is already hot.

London and New York are a good examples of what cities in cooler areas can do to make a difference. Their heat island policies include things like planning requirements to plant trees, reduce paved areas in parking lots and reduce traffic. But these sorts of policies are still quite rare across the board, and you rarely see similar policies in hotter climes. Singapore is one of very few tropical cities that prioritise traffic control, for example.

Finally a word on colder cities such as Glasgow, where I am based and have been involved in work aiming to cool down the city. This may not seem very necessary when the temperature is not particularly high, but we need to bear in mind that it is likely to get hotter in the coming decades. For example our simulations suggest that if you increase tree cover by 20 per cent, you could eliminate a third to half of the expected urban heat increase by 2050. This sort of intervention is well worth considering.

This article was originally published on The Conversation. Read the original article.

Rohinton Emmanuel is a Professor of Sustainable Design & Construction at Glasgow Caledonian University.

 
 
 
 

It’s not all cool bridges and very real concerns: In defence of Teesside

Just one of the many interesting bridges you’ll find in Teesside. Image: Stephen Jorgensen-Murray.

The latest entry in our ‘In Defence Of’ series...

I have to start this with a disclaimer: I’m not writing this from anywhere in Teesside. I’m writing this from Germany, where I live and work. Some of you may remember being told by Norman Tebbit, that instead of complaining that we can’t find jobs, we should get on our bikes (or, more recently, by IDS to get on a bus), and I did. I’m paid well here, to do a job that doesn’t really exist in Teesside. And yet, every time I go home to visit my family, I almost wish I’d stayed.

This isn’t going to be a very straightforward take – I’m hoping to pay my respects to Stockton, Middlesbrough and Hartlepool as well as my native Billingham – but Teesside isn’t a very straightforward place. What county is it in? Cleveland, Stockton-on-Tees, Durham or North Yorkshire depending on how old you are and where you’re standing. I always had great fun ordering online and trying to guess which of the unfamiliar options on the dropdown menu would get my parcel to me.

But regardless of where you draw the lines, Teesside is still there.

Our accent is similarly hard to pin down: Geordie, Mackem, Yorkshire, even Scouse, depending on who’s imitating us. I’ve been pegged as Irish, American and South African by determined people in the past. Our slang is stolen from Scotland, Northumberland, Newcastle and Yorkshire, and, not satisfied, some words are purely our own. Hoy, shan, howay, dinner nanny. We have as many words for classless people as the Romans did for murder.

But regardless of how it sounds to you, Teesside still talks.


On a map of the UK, Teesside sits as an isolated blob of civilisation between the Dales and the sea. Half-urban, half-rural, half-seaside, half-inland, half industrial estate and half nature reserve. A Labour heartland with a Tory mayor. Places that sprang up fully formed in the ICI rush of the 1950s, but that still have Viking place names.

We’ve been portrayed in fiction by Richard Milward, in song by Maximo Park, in statistics by Lady Florence Bell and in cinema by Sir Ridley Scott (our chemical works and power plants inspired the look of Blade Runner). More recently, we’re being portrayed in documentary in The Mighty Redcar, and in the media as an area of left-behind, white working class racists who all voted Leave. But while most of the area is whiter than the average, Middlesbrough mirrors the UK average for racial diversity and has been assigned to resettle more refugees than any other town in the UK – and more than its cut-back council can look after.

And when you look at the numbers, the proportion of the population of Teesside who voted to leave the EU is much less than many other areas. (And yes, of course I voted Remain from my now slightly more precarious home in Frankfurt, joining 100,000 other Teesside Remainers.)

We’re pitied for the loss of the Teesside steelworks and derided for blaming the EU for it (when of course it was our own government’s sabotaging of EU attempts to block Chinese steel dumping that drove that knife in). Even the people who profess to be on our side take our angry, uneducated racism as fact, baking it into the premises of their arguments, which consist of addressing our “racist but real concerns”, and how to reach us.

But whether you understand us or not, whether you miss the point or not, we’ll continue to exist, long after we’ve been forgotten again.

Billingham town centre. One of the first pedestrianised town centres in the UK. Image: Stephen Jorgensen-Murray.

Still, while we’re in the spotlight, why not see what we have to offer? Come to see our rather wonderful collection of interesting bridges. See where the first public steam train ran, from Stockton to Darlington. Visit Mima, the modern art gallery in Middlesbrough and the 1960s utopia of Billingham’s pedestrianised town centre. Feel slightly uncomfortable around all the things that are named for Captain Cook (though the replica of the Endeavour at Stockton riverside is impressive regardless on your thoughts on its captain – and it’s the best you’ll see until they work out whether they’ve found the real one yet). Wander Middlesbrough’s thriving student/hipster district on Linthorpe RoadD – despite being a punchline during my youth, Teesside University has become a respected institution. Visit Billingham’s Folklore Festival in August, where as schoolchildren we’d watch troupes of folk dancers from across the world open-mouthed, and get their autographs afterwards as though they were celebrities.

Fried chicken, white sauce and cheese make the Teesside parmo. Perfect. Image: Stephen Jorgensen-Murray.

Try a parmo. Try the Billingham Catholic Club’s real ale, and stay for the bingo, which is called by a man with the most acrobatic mental arithmetic skills I’ve ever seen. Try a lemon top ice cream from Pacitto’s in Redcar and wonder why no one else has ever done this before. Lemon sorbet and vanilla ice cream! Together at last!

While you’re at the beach, take a ride on the Saltburn Cliff Lift, the oldest operating water-balance cliff lift in the UK. Pretend Saltburn is sort of in Teesside while you’re enjoying the view. Look out on beaches black with sea coal, washed up from undersea seams and nearby coal mines. Visit the golf course by Seaton Carew to catch a glimpse of a curlew or two, and watch the young seagulls pick up golf balls to crack them open by dropping them from a great height. Visit Seal Sands, whose owners can be observed lazing on the estuary banks whenever the tide is out. Or visit Saltholme, the RSPB nature reserve, where you can see avocets, Britain’s weirdest-looking and most beloved seabird.

Nature coexists with industry on Teesside. Image: Stephen Jorgensen-Murray.

Go white water rafting, bell boating or paddleboarding at the Tees Barrage, where there are so many seals that they’ve had to put up guards to keep them out of the way. The Tees used to be too polluted even to support salmon and trout, and now we have too many of one of Britain’s largest native mammals. The return of the seals to the Tees was the first documented case of seals returning to an industrial area. You’d be surprised at how well nature can thrive in the shadow of industry, colonising the quiet fields and marshy ponds on private land that are never disturbed, haunted by sika deer and shelducks, redshanks, knots, stonechats.

Teesside has plenty to offer. What it doesn’t have is the jobs to keep its younger generations from having to get on their bikes and leave. We aren’t aliens, or Jacob Rees-Mogg’s army of goblin henchbrexiteers. We’re just like you, but with more seals and fewer employment opportunities.