The Department of Energy will paint the roofs white on its buildings to save energy and fight global warming. Secretary of Energy Steven Chu ordered DOE offices to â¿¿implement cool roof technologiesâ¿ (paint their roofs white or use reflective coatings) and he encouraged the heads of other federal agencies to give similar orders for their buildings. White roofs absorb less heat and reflect more sunlight back into space, thus keeping both the buildings themselves and the air around them cooler. â¿¿Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change,â¿ said Chu, a Nobel laureate and former director of Lawrence Berkeley National Laboratory. Researchers at Lawrence Berkeley Lab said in a recent report that the â¿¿cool roofâ¿ idea, which has been around for years, can not only affect buildings themselves, but also can cool the entire earth. Black roofs not only make the buildings below them hotter and less comfortable (requiring more energy for air conditioning), they also radiate heat into the air above the buildings, which is picked up by the wind and heats up the atmosphere through the so-called greenhouse effect. Visible light passes easily through the atmosphere to strike the earth, including the roofs of buildings, but the air is much more opaque to infrared light (heat) emitted by hot ground and hot roofs, so that heat is trapped close to the surface. Lab researchers led by Surabi Menon and Hashem Akbari said increasing the reflectivity of roofs and pavements could eliminate 57 gigatons of carbon dioxide from the atmosphere -- twice the amount of carbon dioxide emitted worldwide in 2006. Though that would be a one-time reduction, it could slow down global warming due to other pollution that wasnâ¿¿t eliminated as quickly.