Albedo feedback
Albedo feedback refers to the process by which changes in the reflectivity (albedo) of the Earth's surface influence climate change. Albedo is a measure of how much sunlight a surface reflects; for instance, Arctic ice has a high albedo, reflecting 50 to 70 percent of solar radiation, while liquid water has a significantly lower albedo, reflecting only about 6 percent. As Arctic ice melts due to rising temperatures, darker surfaces are exposed, which absorb more heat and further accelerate the melting process. This cycle is an example of a positive feedback loop, where initial changes lead to further warming and ice loss.
The implications of albedo feedback are significant for climate dynamics, particularly in polar regions where warming is occurring at an accelerated rate. Changes in albedo can lead to shifts in atmospheric greenhouse gas levels, as thawing permafrost releases methane and other gases. Additionally, the reduction in snow cover can alter local weather patterns, affecting ecosystems and human activity. Scientists warn that continued changes in albedo could push climate systems toward tipping points, making it crucial for ongoing research and mitigation efforts. The phenomenon highlights the interconnectedness of climate components and the urgency of addressing climate change globally.
Albedo feedback
Definition
Albedo (Latin for “whiteness”) is a measure of the amount of incident radiation, such as sunlight, that a surface reflects. Arctic ice has a high albedo, meaning between 50 percent and 70 percent of the light hitting it is reflected back into space. Little of the solar energy striking ice is absorbed into the Earth’s surface in the form of heat, but when the ice melts, the water only reflects about 6 percent of the radiation. When the ice melts into liquid water, surfaces darken and absorb more light, warming the planetary surface. As the ocean surface warms, more of the remaining ice melts, further increasing the amount of solar heat being absorbed. This cycle in which lower creates conditions that cause a further decrease in albedo is an example of a positive feedback loop.
Albedo, measured as the fraction of solar radiation reflected by a surface or object, is often expressed as a percentage. Snow-covered surfaces have a high albedo, the surface albedo of soils ranges from high to low, and vegetation-covered surfaces and oceans have a low albedo. The Earth’s planetary albedo varies mainly through varying cloudiness, snow, ice, leaf area, and land cover. The warming of the Arctic influences weather in the United States. Outbreaks of Arctic cold have become weaker as ice coverage erodes.
Earth’s albedo usually changes in the cryosphere (ice-covered regions), which has an albedo much greater (at around 80 percent) than the average planetary albedo (around 30 percent). In a warming climate, the shrinks, reducing the Earth’s overall albedo, as more solar radiation is absorbed to warm the Earth. Cloud cover patterns also may change, resulting in further albedo feedback. Changes in albedo have an important role in changing temperatures in any given location and, thus, the speed with which ice or melts.
Significance for Climate Change
The rate of Arctic warming at the beginning of the twenty-first century was eight times the average rate during the twentieth century. Changes in albedo are among the factors contributing to this increase. The number and extent of boreal forest fires have also grown, increasing the amount of soot in the atmosphere and decreasing Earth’s albedo. As high latitudes warm and the coverage of declines, thawing Arctic soils also may release significant amounts of and methane now trapped in permafrost.
Arctic warming has shortened the region’s snow-covered season by roughly 2.5 days per decade, increasing the amount of time during which sunlight is absorbed. The gradual darkening of Arctic surfaces produces significant changes in the total amount of solar energy the area absorbs. Scientists have estimated this increase in surface energy absorption at 3 watts per square meter per decade. With this absorption rate in areas such as the Arctic, where albedo changed markedly, the effect of this change on Earth's climate was roughly equal to the effect of doubling atmospheric CO2 levels. Moreover, the continuation of contemporary trends in shrub and tree expansion may amplify atmospheric heating by two to seven times.
Changes in albedo over a broad area, such as the Arctic, can produce a significant effect, allowing Earth to be “whipsawed” between climate states. This feedback has been called the “albedo flip” by James E. Hansen, director of the Goddard Institute for Space Studies (GISS) of the National Aeronautics and Space Administration (NASA). The flip provides a powerful trigger mechanism that can accelerate the rapid melting of ice. According to Hansen, greenhouse gas (GHG) emissions place the Earth perilously close to dramatic climate change that could run out of control, with great dangers for all life on Earth. Changes in albedo have been greatest in Earth’s polar regions, especially in the Arctic, where snow and ice are being replaced during summer (a season of long sunlight) by darker ocean or bare ground.
Changes in albedo also play a role in increasing Arctic emissions of GHGs such as methane, tropospheric ozone (O3), and nitrous oxide (N2O). Tropospheric ozone is the third most influential GHG, after CO2 and methane.
Black carbon (soot) also has a high and deserves greater attention, according to Hansen. Soot’s albedo causes massive absorption of sunlight and heat and compounds warming, especially in the Arctic. Increases in soot due in part to combustion of GHGs can play a role in accelerating climate change to tipping points, at which feedbacks take control and propel increasing levels of GHGs past a point where human control (“mitigation”) is possible.
From 2001 to 2019, there was an observable relationship between the increased albedo and the diminishing Arctic sea ice. Additionally, in 2021, some scientists predicted that an ice-free Arctic would be a reality for a few months of each year by the close of the twenty-first century, while others predicted this crisis to occur by mid-century. This prediction, based on data collected from NASA satellite instruments that monitor the Arctic sea ice, raised climate change concerns and highlighted the importance of Albedo feedback for research and prevention measures. In 2024, NASA satellite data showed that Arctic sea ice levels approached near-historic lows.
Bibliography
Alley, Richard B. The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future. Princeton, N.J.: Princeton University Press, 2000.
Glick, Daniel. “The Big Thaw.” National Geographic, 3 May 2021, www.nationalgeographic.com/environment/article/big-thaw. Accessed 10 Dec. 2024.
Chapin, F. S., et al. “Role of Land-Surface Changes in Arctic Summer Warming.” Science, vol. 310, no. 5748, 28 Oct. 2005, pp. 657–660, doi.org/10.1126/science.1117368. Accessed 10 Dec. 2024.
Federman, Adam. "The Big Thaw." Sierra, 14 Dec. 2021, www.sierraclub.org/sierra/2021-6-winter/feature/big-thaw-alaska. Accessed 10 Dec. 2024.
Foley, Jonathan A. “Tipping Points in the Tundra.” Science 310 (October 28, 2005): 627-628.
Kashiwase, Haruhiko, et al. “Evidence for Ice-Ocean Albedo Feedback in the Arctic Ocean Shifting to a Seasonal Ice Zone.” Scientific Reports, vol. 7, 2017, doi.org/10.1038/s41598-017-08467-z. Accessed 10 Dec. 2024.
Ouyang, Zutao, et al. “Albedo Changes Caused by Future Urbanization Contribute to Global Warming.” Nature Communications, vol. 13, 2022, doi.org/10.1038/s41467-022-31558-z. Accessed 10 Dec. 2024.
Perkins, Sid. “Albedo Is a Simple Concept That Plays Complicated Roles in Climate and Astronomy.”Proceedings of the National Academy of Sciences, vol. 116, no. 51, 2019, pp. 25369–25371, doi.org/10.1073/pnas.1918770116. Accessed 10 Dec. 2024.
“Positive Feedback - Arctic Albedo.” My NASA Data, National Aeronautics and Space Administration, 23 Sept. 2019, mynasadata.larc.nasa.gov/lesson-plans/positive-feedback-arctic-albedo. Accessed 10 Dec. 2024.