If you are serious about climate change you might want to change the colour of your car. In fact, you might want to change the colour of quite a few things, including the tiles on the roof of your house.
Unseen impact of colour
In all the lines devoted to climate change, we often fail to factor in the contribution colour makes to heating up the planet. Let me suggest a simple demonstration. Put your hand on the roof of a black car in a supermarket car park on a sunny day in summer and you won’t need a thermometer to tell you it is extremely hot. Put your hand on a white car, or even a pale-coloured one, and you will be able to tell the difference immediately.
Black absorbs all the visible rays of light and radiates it back into the atmosphere as heat. One car is not going to mitigate the 1.5˚C increase in global temperature below which the climate scientists tell us we need to stay if we are to save the planet. But were we to change everything black in the man-made environment we could make a serious contribution.
My own house is roofed in black glazed pantiles, as are many buildings in East Anglia. Yet more are roofed in dark grey slates, all of which heat up quickly and intensely in sunlight radiating heat back into the surrounding air.
The greater the proportion of black in a colour the more visible rays of light are absorbed and the more heat is radiated back. There is some difference in the nature of the material used but the general principle is true. It’s called the albedo effect.
Cultural wisdom of colour
Other cultures recognise this and have acted accordingly. In the city of Jodhpur in India the houses are painted pale blue – it is known as The Blue City. The houses of the Pueblos Blancos of southern Spain are painted white to reflect sunlight. The house builders in these places have known for hundreds of years that the paler the colour, the less heat is absorbed and the cooler the internal environment.
There is currently an architectural vogue for cladding new houses in black – not a very ecological solution at a time when we are trying to lower global temperatures. The black, clap-boarded barns they emulate are visually attractive and there was originally a good reason for painting them with black tar – a by-product of coal-fired power stations sold cheaply to farmers – as it is a good timber preservative.
Prior to the industrial revolution barns were painted in other colours but now black has become entrenched in the minds of planners and conservation officers as part of our vernacular architecture. Time to re-examine a practice that has been around for less than 250 years?
Rethinking road colours
Tar has a lot to answer for when it comes to contributing to climate change. Most roads in the world are black, surfaced in bitumen. There are millions of miles of them, together with car parks and people’s front gardens. Asphalt is cheap to make and easy to lay and maintain, so the incentive to change it is low.
Airport runways, however, are made of pale grey concrete, partly because when aircraft wheels hit the ground at 150mph the surface needs to be extremely hard and partly because in hot weather black asphalt softens and, in very high temperatures, melts and becomes sticky.
But long-lasting though asphalt is, roads have to be resurfaced at some point and this will be our opportunity to change the colour and the degree of heat that is radiated back into the atmosphere. Recycled concrete chips mixed with asphalt is one solution to toning down the colour of roads.
Cities have long been known to be warmer than surrounding countryside, called the ‘urban heat island’ effect. This is in part due to dark-coloured roads and roofs. To combat this, Los Angeles, where temperatures hover in the high 30s in summer, has been trialling painting roads with a special white, reflective asphalt coating since 2015. The aim of the city’s mayor is to have 300km of roads painted by 2028. The hope is to decrease air temperature by 3C. This would lessen the burden on the energy grid with buildings needing less intensive air-conditioning.
Transportation and colour influence
The transport industry has long known about the cooling power of white. The roofs of planes were painted white to reflect the heat of the sun and make the interiors comfortable for passengers, as were the roofs of Pullman cars on the railways. The default colour for Ford Transit vans, when they first appeared, was white. You paid more for other colours because they heated up more quickly and needed more powerful fans to keep the drivers cool.
While on the subject of roads and cars and their contribution to global warming let’s not forget vehicle tyres. These are made of black rubber. Over the life of a tyre the rubber is worn away and deposited on roads, so even if roads were changed from black to pale grey, say, a layer of black is daily deposited on their surface, adding, however minimally, to its light absorbing capacity. Maybe we need to wean ourselves off our acceptance of black tyres as the only option.
Another ubiquitous form of deposit is black carbon (think soot). Particulates come from many sources: from cooking fires and our beloved wood burning stoves, to diesel emissions. The black smut landing on pristine white snow in the arctic is hastening the melting of the ice cap and we are unwittingly contributing to this.
We all need to look at black in our environment – it’s certainly not the new green. While it’s unlikely you’re going to rush to get your roof painted white, you can make a difference by thinking twice about investing in a wood-burning stove or choosing the colour of your next car.