# Albedo

Albedo (al-bee-doh) is a measure of how much light that hits a surface is reflected without being absorbed.  Something that appears white reflects most of the light that hits it and has a high albedo, while something that looks dark absorbs most of the light that hits it, indicating a low albedo.

Why do I care? Albedo is another name for reflectivity. The albedo of a surface determines how much sunlight will be absorbed and warm the surface compared to another surface that reflects most of the light and does not change temperature.

Figure A. A high albedo surface reflects 80% of incoming radiation. The low albedo surface reflects only 10% of incoming radiation.

The amount of energy that is reflected by a surface is determined by the reflectivity of that surface, called the albedo.  A high albedo means the surface reflects the majority of the radiation that hits it and absorbs the rest.  A low albedo means a surface reflects a small amount of the incoming radiation and absorbs the rest.  For instance, fresh snow reflects up to 95% of the incoming radiation.  Therefore, fresh snow has a high albedo of .95.  By contrast, water reflects about 10% of the incoming radiation, resulting in a low albedo of .10.  Since 30% of the sun’s energy is reflected by the entire earth, the earth has an average albedo of .30.  Generally, dark surfaces have a low albedo and light surfaces have a high albedo.  For example, in summer the black asphalt road is scorching hot. This is because much of the heat is absorbed by the asphalt allowing the asphalt to burn your feet as you walk on it. When it’s hot outside, lighter clothing keeps you cooler because it reflects most of the sunlight that hits it, keeping you cool. Keep in mind that it is still possible to get sunburnt while wearing a light colored shirt with no sunscreen underneath. Although much of the incoming radiation is reflected, there is still quite a bit that is absorbed by the shirt.

How does this relate to public health?

Figure B: Urban Heat Island Effect (Image from EPA).

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.”1 The higher average temperatures can be attributed to less vegetation, higher population densities, and more infrastructure 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.2,3 People who live in urban cities may be at greater risk for heat-related illnesses.

The state of North Carolina, however, has much more rural land mass and less densely populated urban areas than other states, making it less susceptible to the urban heat island effect.4,5

Figure C: Various land uses have different impacts on daily temperature. (Image from EPA).

In fact, research suggests that in North Carolina, heat-related illnesses are more likely to occur in rural areas than in urban areas.6 Albedo is also related to sea level rise. The oceans’ dark surfaces facilitate the absorption of heat from the sun, melting large masses of ice in the ocean.7 As glaciers and ice caps in the ocean melt, sea level rise coupled with more frequent storm surges, may result in more frequent and intense flooding.8 These extreme weather events can reduce the availability of drinkable water, compromise the integrity of public health infrastructure, and cause direct death or injury in coastal communities.9,10

Figure D. Albedo and land cover. (Image from EPA).

1Buechley RW, Van Bruggen J, Truppi LE. 1972. Heat island equals death island? Environmental Research. Mar;5(1):85–92.

2Portier CJ, et al. 2010. A human health perspective on climate change: a report outlining the research needs on the human health effects of climate change. Research Triangle Park, NC: Environmental Health Perspectives/National Institute of Environmental Health Sciences. doi:10.1289/ehp.1002272 <www.niehs.nih.gov/climatereport> Accessed November 17, 2012.

3Environmental Protection Agency, State and Local Climate and Energy Program. Heat island effect. October 19, 2012. <http://www.epa.gov/hiri/> Accessed November 17, 2012.

4Reid CE, O'Neill MS, Gronlund CJ, Brines SJ, Brown DG, Diez-Roux AV, Schwartz J. 2009. Mapping community determinants of heat vulnerability. Environmental Health Perspectives. Nov;117(11):1730-1736.

5UNC Institute for the Environment, The University of North Carolina at Chapel Hill. 2009. Climate change committee report 2009. <http://www.ie.unc.edu/PDF/Climate_Change_Report.pdf> Accessed November 17, 2012.

6Fuhrmann, C.M., Kovach, M.M., and C.E. Konrad II: Heat-related illness in North Carolina: Who’s at Risk? Annual Education Conference of the North Carolina Public Health Association, New Bern, NC, September 20, 2013. <http://www.sercc.com/sercc_projects> Accessed December 22, 2012.

7The Climate Institute. Oceans and sea level rise. (n.d.) <http://www.climate.org/topics/sea-level/index.html> Accessed November 17, 2012.

8Tebaldi, C., Strauss, B. H., & Zervas, C. E. (2012). Modelling sea level rise impacts on storm surges along US coasts. Environmental Research Letters, 7(1):014032.

9Environmental Protection Agency. Climate change: Human impacts and adaptation. June 14, 2012. <http://www.epa.gov/climatechange/impacts-adaptation/coasts.html#impactssea> Accessed November 17, 2012.

10English, PB; et al. 2009. Environmental health indicators of climate change for the United States: Findings from the State Environmental Health Indicator Collaborative. Environmental Health Perspectives. Nov;117(11):1673-1681.