Albedo and global warming

The most significant projected impact on albedo is through future global warming. With the exception of Antarctic sea-ice, recently increasing by 1% a year, nearly all the ice on the planet is melting. As the white surfaces decrease in area, less energy is reflected into space, and the Earth will warm up even more.

The loss of Arctic ice is of particular concern. The ice is disappearing quite fast; not only is albedo decreasing, but the loss triggers a positive feedback. By exposing the ocean surface to sunlight, the water warms up. This melts the ice from underneath, while man-made CO2 in the atmosphere warms the surface. Humidity also increases; water vapor is a powerful greenhouse gas.  More ice therefore melts, which exposes more water, which melts more ice from underneath…

This loop fuels itself, the effect getting more and more pronounced. This is a good example of a positive feedback. Increased water vapor also has another effect, which is to increase the amount of cloud. As mentioned already, clouds can increase albedo (a negative feedback), but also warming (a positive feedback).

Urban heat island effect

Because of the effects of albedo, highly developed areas such as urban cities can experience higher average temperatures than surrounding suburban or rural areas, a phenomenon known as the “urban heat island effect.” The higher average temperatures can be attributed to less vegetation, higher population densities, and more infra structure with darker surfaces (asphalt roads, brick buildings, etc.) that generate, reflect, and trap heat during hot summer months. Research has found that in some urban cities, the average air temperature can be as much as 22°F hotter in the evenings than surrounding areas. People who live in urban cities may be at greater risk for heat-related illnesses. 

What is the urban heat island effect?

The term “heat island” describes built up areas that are hotter than nearby rural areas. The annual mean air temperature of a city with 1 million people or more can be 1–3°C warmer than its surroundings. In the evening, the difference can be as high as 12°C. Heat islands can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness and mortality, and water quality.

Increasing the albedo of surfaces in cities will reduce the heat island effect, resulting in significant, cost, comfort and health benefits.

To prevent the urban island effect with Albedo

COOL ROOF

A cool roof is one that has been designed to reflect more sunlight and absorb less heat than a standard roof. Cool roofs can be made of a highly reflective type of paint, a sheet covering, or highly reflective tiles or shingles. Nearly any type of building can benefit from a cool roof, but consider the climate and other factors before deciding to install one.

Just as wearing light-colored clothing can help keep you cool on a sunny day, cool roofs material that is designed to reflect more sunlight and absorb less heat than a standard roof. Cool roofs can be made of a highly reflective type of paint, a sheet covering, or highly reflective tiles or shingles. Standard or dark roofs can reach temperatures of 150°F or more in the summer sun. A cool roof under the same conditions could stay more than 50°F cooler and save energy and money by using less air conditioning.

On a global scale, with urban areas comprising about 1 percent of the Earth’s land surface and roofs and paved surfaces comprising about 25 percent and 35 percent of a typical urban area, respectively, lightening their color would have the same cooling effect as keeping 44 gigitons of carbon dioxide out of the atmosphere.

By changing the albedo of roofs and pavement in the urban world, it is believed we could offset the expected heat increase due to projected growth in greenhouse emissions over the next 11 years.