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 44bn tonnes of 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 US cities, 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 2-3C seems inevitable. Last year 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”.

This November, Simon Evans and Fearghal O’Nuallain will begin the first Irish circumnavigation of the globe by bicycle. Their unsupported expedition will cover over 30,000km, passing through 30 countries and some of the highest, lowest, driest, coldest, warmest and loneliest places on earth. In doing so, they will be promoting the positive contribution that cycling can make to mental health and the environment, raising €100,000 for Aware and highlighting climate change

To get a feel for what the guys will be doing here’s their flickr site and a sample of their videos:

Aswan to Alexandria from revolutioncycle on Vimeo.