Researchers at the Lawrence Berkeley National Laboratory conducted an economic analysis of the costs and benefits of white, black and green roofs and found that white roofs are far superior in fighting climate change than the other two. While roofs painted black absorb heat and contribute to the urban heat island effect, white roofs reflect the sunlight back into the atmosphere and help cool down its lower parts. The study advises those concerned with global climate change to choose white roofs, adding to a host of other studies in the past decade that have allowed the white roof movement” to gain momentum across the United States. However, things are not as simple as they seem.
A series of climate simulations carried out by Mark Z. Jacobson and Ten Hoeve of Stanford University showed some unexpected results. Despite their beneficial effects on the lower parts of the atmosphere, white roofs decrease the temperature difference half a mile above ground-a difference which drives cloud formation and less clouds means more sunlight reaching the Earth’s surface. This, among other issues like the impact on fossil fuel consumption and summer cooling vs. winter heating gains, is still subject of scientific debates. Meanwhile, it should also be noted that vegetated roofs offer built-in storm water management mechanisms in addition to some cooling benefits.