If you combined all of the world's urban areas into one dense nugget of urbanity, it would cover about 2 million square kilometers, or 1.3 percent of the land area of the planet. About 60 percent of that – roughly the size of California and Texas combined – is made up of pavement and rooftops.
These roads and roofs can be problematic surfaces. Often dark in color, they soak up sunlight, increasing the temperature of the building and surrounding area in what's known as the urban heat island effect. This in turn contributes to a vicious cycle: the hotter a city feels, the more we energy we tend to use to cool it down, which leads to more greenhouse gas emissions, which contribute to climate change, and so on.
But it doesn't have to be this way. Researchers from Concordia University have found [PDF] that even a slight improvement in the reflectivity of these surfaces could lead to a global reduction of billions of tons of CO2. A measly 1 percent increase in white roofs or roads rolled out across the urban world would reduce the amount of carbon dioxide released into the atmosphere by upwards of 130 billion tons over the next 50 to 100 years.
Using data from the Global Rural and Urban Mapping Project, or GRUMP (by far one of our favorite acronyms), they also calculated this same 1 percent increase would help reduce global temperatures by about 0.07 degrees Celsius.
Admittedly, improving the reflectivity of every street and building in the urban world is a massive task. But as the researchers note, roads typically have to be resurfaced every decade or so and rooftops usually need to be replaced every 20 or 30 years. If we can incrementally use lighter-colored paving on those road resurfacing projects and white paint on roofs, the impact over time could be dramatic.
Photo credit: Stefan Wermuth / Reuters