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Increasing reflectivity
What is the idea?
Dr Hashem Akbari, a physicist from the Lawrence Berkley National Laboratory in California, believes that by making urban areas more reflective, greenhouse gases can be offset.
Rooftops and pavements could be painted paler colours to reflect, rather than absorb, more of the sun's energy.
Since 2005, the State of California has required that flat commercial structures have white roofs.
In 2009 new and retrofitted residential and commercial buildings, with both flat and sloped roofs, will have to install heat-reflecting roofing, as part of an energy-efficient building code.
44 metric gigatones
Estimate of the amount of greenhouse gases that could be offset by switching roofs and pavements of 100 of the largest cities in the world to more reflective materials.
This amount is greater than current annual global emissions.
Dr Hashem Akbari, together with his colleagues Surabi Menon and Arthur Rosenfeld, a member of the California Energy Commission, wrote a paper 'Global Cooling: Increasing Worldwide Urban Albedos to Offset CO2'
The paper was published in the journal Climatic Change.
Dr Hashem Akbari argues that while this idea would not address the causes of climate change - rising carbon emissions - it would delay its effects.
Experts are also researching the potential of increasing reflectivity of other land areas.
Food scientists claim planet could be cooled by up to 2°C simply by planting crops specially bred to reflect more sunlight. Andy Ridgewell led a team of scientists at the University of Bristol to calculate how different varieties of crops would affect global temperatures.
Could new varieties of wheat and barley save the planet from climate change?
The Guardian, 15 January 2009
Others have suggested we could cover the deserts or polar ice caps with reflective blankets. This idea has been successful on a small scale at European ski resorts.
Geoengineers wrap up Greenland's glaciers in a blanket Discovery Channel 13 February 2009