Most schoolkids have seen simple scientific experiments at school demonstrating that light coloured surfaces reflect light and heat whilst dark surfaces absorb it and get hotter. So would painting our roofs in our major cities white, actually help reduce the temperature of our major cities in summer and reduce some of the effects of global warming? The answer seems to be a straight forward "Yes".
Experiments carried out in California for example demonstrated that some houses with their roofs painted white, lowered the internal temperature so much that they were able to turn off the air conditioning. This not only reduced the residents power bills but also of course lowered their carbon foot prints and as we know, small carbon footprints are very sexy nowadays.
Our larger towns and cities are usualy a few degrees hotter than the surrounding country side during both summer and winter and major cities in the lower lattitudes can become insufferably hot during summer heatwaves. This can result in a high death toll for vulnerable groups such as the elderly and those with heart conditions as they discovered in Paris in the summer of 2003. It makes sense therfore, to do anything we can to reduce this danger and if it saves lives, global emissions, energy and expense in one fell swoop then this idea probably has legs.
It is estimated that if the 100 largest cities in the world replaced their dark roofs and their asphalt-based roads with concrete or other light-colored material, it could offset 44 metric gigatons (billion tons) of greenhouse gases. This is more greenhouse gas than the entire human population emits in a year. According to an article in the Los Angeles Times, this could also offset the growth in carbon diooxide emissions for the next ten years.
The physicist Hashem Akbari, says that it takes about 10 square meters of white roof to offset 1 metric ton of carbon dioxide. and in warm climates, white roofs have the additional benefit of lowering the cost of air conditioning by up to 20% in hot months, By these means, cities could be cooler in summer and suffer less smog. It was these costs that prompted the state of California to require in 2005 that flat-roofed commercial buildings must have white roofs. In 2009, California will require that new and retrofitted residential and commercial buildings with both flat and sloped roofs, must be installed with heat-reflective roofing. These requirements are now part of California´s energy-efficient building code.
It would seem that this is a fairly low tech fix for several of our problems both local and global and if these ideas catch on in the worlds larger cities, their may still be hope for those glaciers and ice sheets at the Poles and the wildlife that depends upon it including millions of lives in coastal areas threatened by sea-level rises. For once we seem to have a problem for which Politicians do have some expertise, for after all, who better when it comes to whitewash. My message to our PM is therefore, cut the crap and grab a brush.
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