A perspective from NOAA and NASA scientists published online on January 29, 2014 in Nature Climate Change addresses a key question surrounding proposals to engineer the Earth’s climate to increase the planet’s reflection of sunlight to counteract climate warming: Could we measure manmade increases in reflectivity?
“Satellite observations would permit us to detect and measure large human- created increases in the earth’s reflectivity, but the natural variability of the earth’s reflectivity overwhelms increases that could result from some proposed experiments, and would render them undetectable,” said Dian J. Seidel, Ph.D., NOAA senior scientist and lead author. “Although this is only one of many questions and concerns about climate engineering, without the ability to measure the effects, it would be difficult to manage such activities.”
Climate engineering, also called geo-engineering, refers to deliberate, large-scale manipulation of the Earth’s climate intended to counteract human-caused climate change. One class of climate engineering proposals involves trying to increase the reflectivity of the Earth, and some of the proposed methods involve modifying stratus clouds in the marine environment, injecting reflective particles into the stratosphere, and changing agricultural plantings or the material used on roof surfaces to be more reflective.
This animation shows variations in Earth's reflection of sunlight, called albedo, from month to month, based on NASA satellite measurements over a 12-year period.
While there is a growing body of literature addressing the scientific, technical, environmental, ethical and legal issues raised by climate engineering, the NOAA-led research is one of the first studies to address the difficulty of detecting and quantifying the effects of short-term climate engineering experiments or sustained implementation.
Detection of engineered increases in the earth’s reflection of sunlight would require both the continuation of a long-term, high quality record of observations of light from the sun and light reflected by Earth, as well as an engineered signal large enough to exceed the background variability of the Earth’s sunlight reflection. The perspective article shows, for example, that a three-month experiment in the equatorial zone would need to cause an increase in sunlight reflection that is three times as large as what occurred when Mount Pinatubo erupted in 1991 to exceed the background variability and be detected.
To read the perspective in Nature Climate Change, “Detection limits of albedo changes induced by climate engineering,” click here.
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