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Paint it white

Global warming may seem like an overwhelmingly complex problem to tackle. But one scientist thinks the answer is brilliantly simple: a lot of white paint. David Adam reports.

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Hashem Akbari has a vision of a shiny, happy world. He sees polished roads and cities that gleam in the sunlight. Rooftops are bright and pavements light. Akbari wants to turn our cities into a giant mirror and he needs your help. And paint, lots of it.

Akbari is no architect and his grand plan is no conceptual art project. Based at the prestigious Lawrence Berkeley National Laboratory in California, Akbari is a scientist who has come up with a new way to fight global warming. It could be the easiest solution you've never heard of.

His big idea is based on principles as old as the whitewashed villages that scatter the hills of southern Europe and North Africa. Turn enough of the world's black urban landscape white, he says, and it would reflect enough sunlight to delay global warming, and grant us some precious breathing space in the global struggle to control carbon emissions.

Akbari is poised to launch a campaign to paint the world white. He wants dozens of the world's largest cities to unite in an effort to replace the dark-coloured materials used to cover roads and roofs with something a little more reflective.

It sounds simple, but the effect could be dramatic. Study after study has shown that buildings with white roofs stay cooler during the summer. The change reduces the way heat accumulates in built-up areas -- known as the urban heat island effect -- and allows people who live and work inside to switch off power-hungry air-conditioning units.

Aware of the benefit, California has forced warehouses and other commercial premises with flat roofs to make them white since 2005, and, if such an effort could be extended, the results could make a big difference.

Together, roads and roofs are reckoned to cover more than half the available surfaces in urban areas, which have spread over some 2.4% of the earth's land area. A mass movement to change their colour, Akbari calculates, would increase the amount of sunlight bounced off our planet by 0.03%. And, he says, that would cool the earth enough to cancel out the warming caused by 44 billion tonnes of carbon dioxide (CO2) pollution.

If you think that sounds like a lot, then you're right. It would wipe out the expected rise in global emissions over the next decade. It won't solve the problem of climate change, Akbari says, but could be a simple and effective weapon to delay its impact -- just so long as people start doing it in earnest. "Roofs are going to have to be changed one by one, and to make that effort at a very local level, we need to have an organisation in place to make it happen," he says. Groups in several cities in the United States, including Houston, Chicago and Salt Lake City, are on board with his plan, and he is talking to others.

The idea is a form of geo-engineering, a broad term used to cover all schemes that tackle the symptoms of climate change -- namely catastrophic temperature rise, without addressing the root cause, our spiralling greenhouse-gas emissions. And if altering all of the world's roofs and roads sounds extreme, then take a look at some ideas from the other end of the geo-engineering scale: giant mirrors in space, shiny balloons to float above the clouds and millions of fake plastic trees to suck carbon from the air.

An increasing number of climate scientists argue that the world has little choice but to investigate such drastic options. Carbon emissions since 2000 have risen faster than anyone thought possible, mainly driven by the coal-fuelled boom in China, and a global temperature rise of 2º to 3° Celsius seems inevitable. Last September, a special edition of a Royal Society journal, dedicated to geo-engineering said the geo-engineering schemes "may be risky, but the time may well come when they are accepted as less risky than doing nothing".

Akbari says his plan is more workable than other geo-engineering ideas. The science is simple. Sunlight reflected from a surface does not contribute to the greenhouse effect, which drives global warming. That problem comes when dark surfaces soak up sunlight and send it back up as thermal energy, at just the right wavelength to rebound off CO2 in the sky.

The problem with shiny cities, according to Kevin Anderson of the Tyndall Centre for Climate Change Research at Manchester University, is more simple science. "It won't tackle global warming because carbon emissions are still rising," he says. Like all geo-engineering schemes, it will need to be kept up indefinitely, Anderson says, and does not address the growing acidification of the oceans, caused as extra CO2 dissolves. The cooling effect and energy savings in cities would be welcome though, he adds.

Akbari says his idea is not intended to replace efforts to cut carbon emissions, but to work alongside them. "We can give the atmosphere time to breathe," he says. "I just don't see a downside to this idea. It benefits everybody and you don't have to have hard negotiations to make it happen."

Dark roofs reflect about 10% to 20% of sunlight, while white surfaces tend to send back at least half. In technical terms, the percentage of light reflected by a surface is called its albedo -- so a perfectly reflective surface has an albedo of 1. Coloured paints have an albedo of 0.1 to 0.3, and white paints an albedo of 0.5 to 0.9. Asphalt road surfaces have albedos as low as 0.05, so they absorb up to 95% of the sun's energy. Concrete has an albedo of up to 0.3, tar and gravel just 0.1. Akbari's mission is to get individuals, local authorities, builders and communities to think about albedo alongside cost, colour and design when it comes to repairs, maintenance and new construction.

"This is not just a question of painting things white,” he says. “Roofs and roads are routinely repaired and replaced and, when it comes to householders changing their roofs, we want them to look at reflective options. That's the time to target people." He says an "aggressive" programme could convert all cities within 10 to 20 years.

It is fairly easy to persuade, or require, the owners of buildings to select white materials for flat roofs, because the colour is only noticed by passing air travellers. But sloping roofs, found on most houses, are a different issue because they are visible from the ground. As pretty as snow-coated Alpine villages may look, skiers wear powerful sunglasses for a reason. Streets of white-roofed houses would dazzle in the sun. The same is true of road surfaces -- too light a colour and too much light reflects as glare into the eyes of motorists.

No problem, Akbari says: reflective materials need not be white. Light colours such as grey are good, too. And there are other ways to increase the albedo of materials. Pigments that bounce back infrared light can raise the reflectivity of dark surfaces by 40% without any obvious change in colour. They are not as effective as white, which bounces back visible wavelengths of light too, but they are much better than conventional materials.

The Public Works Research Institute in Japan has experimented with paints with such pigments applied to conventional asphalt surfaces. They made a road that reflects 86% of infrared light, which helps keep the surface cool, yet reflects just 23% of visible light, to keep down glare. The researchers were nervous that the extra infrared bouncing off the shiny road could cook pedestrians, but volunteers recruited in summertime to "stand on the paint-coated pavement and conventional pavement" said they actually preferred the painted version. This could be because the coated road kept their feet cool, the researchers said.

There are other benefits, too. Computer simulations of Los Angeles show that resurfacing about two-thirds of roads and rooftops with reflective surfaces, as well as planting more trees, could cool the city by 2º to 3º Celsius. That would reduce the city’s smog as much as a total ban on cars and trucks, and cooler roofs also could save a fortune in electricity bills. On hot days in North America, up to 40% of all electricity can be consumed by air-conditioners, and each temperature degree by a city such as Los Angeles warms is reckoned to see the air-con turned up enough to need another 500 megawatts of power -- the output of a decent sized nuclear power station. Akbari estimates that widespread use of cooler rooftops could slash US$1 billion from electricity bills in the United States alone.

That may be very well for places such as California, with its 300 days of sunshine a year, but what about gloomy northern Europe and the United Kingdom, with a measly 100 sunny days? The effect would not be as great, admits Surabi Menon, who works with Akbari at Lawrence Berkeley, but she says anywhere that needs air-conditioning, or has cities warmer than the outer rural areas, would benefit. Akbari says his estimates of the global cooling potential of reflective cities are based on a global average, so the cloudier places will be made up for by the sunnier spots. "It's absolutely worth doing in the UK," he says. And, he adds, he might just have found a way to pay for it.

Each 10 square metres of urban surface changed from dark to white, he says, has the same cooling effect as preventing the release of a tonne of carbon dioxide. So why not include such resurfacing in carbon-offset schemes? Just as money from green consumers and firms anxious about their carbon footprint is used to fund projects that plant trees, fit green light bulbs and develop renewable energy, in exchange for carbon credits, so it could pay people across the world to paint, coat and resurface.

At today's carbon prices, changing the colour of an average roof could net the householder more than US$200, and Akbari's global scheme could together generate more than US$700 million. "We want to target 30 to 40 cities initially, but within a few years we hope it will mushroom around the world," he says. Go on, paint your town white.


www.guardian.co.uk


Copyright Guardian News and Media Limited 2009

 Homepage photo by peamasher

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评论 comments

Default avatar
匿名 | Anonymous

碳排放的增长

文中说,“自2000年以来,碳排放主要是中国燃煤的急速发展所致”,我对此表示怀疑,随着中国的强大,似乎任何全球问题都与中国纠缠在一起,难道其他发达国家就不应负责吗?

The growth of carbon emissions

This article states that "Carbon emissions since 2000 have risen faster than anyone thought possible, mainly driven by the coal-fuelled boom in China". I am suspicious of this statements. It seems that ever since China has been getting stronger, all global problems are tangled up with China. Surely other developed countries are responsible too?

Translated by Jing Jiang

Default avatar
匿名 | Anonymous

团结力量大

如果世界各大城市能够联合起来采取行动,把路面和屋顶的颜色改变一下的想法还是不错的。而且,全球变暖的问题没有一招制敌的办法,但全球共同努力就一定能解决问题。

Unity is strength

If all the cities of the world could unite together and take action, I think the idea of changing the colour of the road surfaces and roofs is a good one. What is more, there is no direct method to handle the global warming issue, but united global efforts could definitely provide a solution.
(Translated by Tian Liang)

Default avatar
匿名 | Anonymous

谁应当对二氧化碳排放负责

你好,比起中国,别的发达国家当然应当对排放更多二氧化碳负责,特别是如果你考虑到每个人的排放量。但是,这儿陈述的观点是这种增长是由中国煤炭燃料的激增驱使的,这是个事实。是否你认为这个评论在这篇文章中有没有体现重要性是另一个问题。Stephane.

本篇评论由陈丽英翻译。

Reply to comment 1

Hi,

Other developed countries are of course "responsible" for releasing more carbon dioxide than China, especially if you consider emissions per individual.

However, the point of the statement here was that the growth is driven by the coal fuelled boom in China, which is simply true.

Whether you consider this remark has its place in the article is another question...

Sincerely yours,

Stephane

Default avatar
匿名 | Anonymous

科技创造未来

暂且不论作者在气候变暖的原因上的无知(“自2000年以来,碳排放的增速超乎任何人的想像,主要是中国燃煤的急速发展所致”),因为这位所谓的科学家好像没有看过IPCC2007年发布的第四次评估报告。
他提出的点子恰恰印证了科技应对气候变化的重要途径之一,虽然他的科学研究听上去很滑稽。
科技应对气候变化是不争的事实。2007年5月18日,全球能源技术战略计划(Global Energy Technology Strategy Program,GTSP) 发布了题为《全球能源技术战略:应对气候变化》(Global EnergyTechnology Strategy:Addressing Climate Change)的研究报告。认为技术是应对气候变化的长期战略中最重要的部分。发展与提高能源技术,每年可将应对全球变暖的成本降低近万亿美元。2007年《中国应对气候变化科技专项行动》中列出的控制GHG排放和减缓气候变化的技术开发主要就集中在节能和提高能效技术;可再生能源和新能源技术;煤的清洁高效开发利用技术;油气资源和煤层气勘探和清洁高效开发利用技术;先进核能技术;二氧化碳捕集与封存技术;生物固碳技术和其他固碳工程技术;农业和土地利用方式控制温室气体排放技术等。
因此,不妨在研究机构之外,发动全球公民以朴素的减排GHG的热情,投身到创造性的科技研发中去,如同英国的《专利法》催生了工业革命一样,让全球公民(不仅仅是科学家)一起来推动科技创新下GHG减排的目标和愿望。
评论人是华东政法大学国际法学博士研究生李威.

Technology creates the future

Let us disregard, for the time being, the author’s ignorance about the cause of climate change (“that since 2000, the growing speed of carbon’s release has been beyond everyone’s imagination, which is mainly caused by the coal fuelled boom in China”) because it seems that this so-called scientist hasn't read the fourth evaluation report issued by IPC in 2007. Comical as his scientific research sounds, the point he raises confirms one of the important ways that technology copes with climate change. It is an indisputable fact that technology copes with climate change. On 18th May 2007, the Global Energy Technology Strategy Program (GTSP) issued a research report titled "Global Energy Technology Strategy: Addressing Climate Change". It was thought that technology was the most important measure in coping with the long-term strategy of climate change. Developing and improving energy technology can lower the cost of coping with global warming by about a trillion dollars per year. In 2007, “China’s Scientific and Technological Actions On Climate Change” listed that scientific and technological developments to control the release of GHG and slow down climate change should mainly be focused on: the technology of energy saving and increasing energy efficiency; renewable energy and new energy technology; developing and making use of technologies for the efficient use of clean coal; exploring hydrocarbon resources and coal bed methane and exploiting them cleanly and efficiently; advanced nuclear energy technology; the technology for catching and sealing carbon; biologically fixing carbon; controlling the release of greenhouse gases during the processes of farming and land management. Therefore, as well as scientific institutions, it is worth harnessing the enthusiasm felt by global citizens and incorporating it into creative scientific research related to reducing GHG releases.

Just as the English Patent Law caused the Industrial Revolution, let us allow global citizens (and not just scientists) to act together in pushing forward the goals and wishes of reducing GHG releases using scientific creativity. This comment is made by Li Wei, a doctoral candidate majoring in international law in East China University of Political Science and Law.

Translated by Anna Chen

Default avatar
匿名 | Anonymous

纯属开玩笑

你是在开玩笑,还是在瞎胡闹?
有不同的声音是好事,但是哗众取宠的声音没有任何意义。

Sheer nonsense

Is the author joking, or fooling around? It's good to hear a different voice, but not the likes of this one - which is sounding merely to attract others' attention. (translated by Yang bin)

Default avatar
匿名 | Anonymous

GHG的减排需要全民行动

现实的情况是,技术的提高、效率的提高并没有减缓GHG的排放,原因是人口和消费的增长抵消了技术提高所带来的减排效果。而对于人口和消费的减少,需要全民的参与。

Reducing GHG emissions requires action from the entire population

The reality of the situation is that improving technology and raising efficiency aren't slowing down GHG emissions. The reason is because growing population and consumption are counteracting whatever emission reduction results are brought by technology. With regard to reducing population and consumption, the entire population must participate. (Translated by David Vance Wagner)

Default avatar
匿名 | Anonymous

涂成白色的原理

在这简要地解释一下为什么涂白漆可以有助地球降温1)约有一半的太阳光都是可见光2)50%的光都是热3)可见光的频率决定它无法被大气吸收4)一些来自太阳的热可以直接被大气吸收(温室气体可以令到大气升温)5)来自太阳的热也会使地球表面升温并且这些热在被温室气体吸收后再次反射到大气层中6)吸收可见光往往难以被大气吸收,其中一部分还会经大气反射回去7)没有被大气反射的可见光要不经地球表面被反射回去(如雪地)或者被地球表面吸收(沥青地的停车场/马路)。这些被吸收了的光使得深色的地表升温。而这些热之后又会再次被反射至大气层并为温室气体所吸收从而使得造成大气温度变高。8)把屋顶和其他表面涂成白色的话,就可以把约50%来自太阳的可见光能量反射回去,就既避免使大气升温又可以反射回宇宙来这点说来这是一个相当可观的量。9)当把足够多的屋顶都涂成白色之后,房屋和大气都会变凉爽起来。空凋也因为变得凉快而能够更好地工作,也许到那时候我们已经不再需要空凋了?
(由diaoshuhuan翻译)

White paint: an explanation

A quick explanation of why white paint works to cool the planet:

1) Around 50 percent of sunlight is visible light.

2) Around 50 percent of sunlight is heat.

3) Visible light is a frequency of light not absorbed by the atmosphere.

4) Some heat from the sun is absorbed by the atmosphere directly (greenhouse gases which make the atmosphere warmer).

5) Heat from the sun also warms the surface of the planet and this heat is then radiated back into the atmosphere again being absorbed by greenhouse gases.

6) Visible light is poorly absorbed by the atmosphere, some of it gets reflected back by the atmosphere.

7) The visible light that doesn't get reflected back by the atmosphere is either reflected by the surface (eg a snow field) or absorbed by the surface (an asphalt car park/ road). This absorbed light heats the dark surface. this heat is then radiated into the atmosphere and is absorbed by greenhouses gases making the atmosphere warmer.

8) By painting your roof white and other surface you reflect around 50 percent of the visible energy from the sun, a significant amount of this is reflected back into space without heating the atmosphere.

9) By painting enough roofs you make buildings cooler and cool the atmosphere. Air conditioning works easier to cool houses because they are cooler, perhaps you wouldn't even need air conditioning?

Default avatar
匿名 | Anonymous

可以考虑

看来我们不仅要把建筑物,道路刷成白色,用的东西甚至衣服也要穿成白色才行啊。只是到那时候,光看着就够冷的了。有一个问题,白色很容易脏。

It could be taken into account

It seems that we should not only paint the buildings and roads white, but things we have been used even clothes also should be white color. It would then be cold just simply by looking at them. And another problem is that white is apt to get dirty.

Default avatar
匿名 | Anonymous

热反射涂料

非常有趣的文章。有没有数据表明,与花园屋顶相比,白色屋顶既能吸热又能抵消二氧化碳的排放?热反射涂料将能反射足够多的日光和减缓全球变暖的步伐。它在全球与碳排量作斗争中为我们争取一些宝贵的喘气时间。

heat reflective paint

Very interesting article. Is there data on how white roofs compare to, say, rooftop gardens, which can both absorb heat and offset carbon dioxide emissions? heat reflective paint would reflect enough sunlight to delay global warming, and grant us some precious breathing space in the global struggle to control carbon emissions.