Researchers have discovered that the Earth is becoming darker. Climate change may be to blame. The oceans are heating up faster, and they seem to produce fewer bright clouds. This means that less sunlight is reflected into space, which in turn warms the planet.
By observing the moonshine, researchers measured Earth's reflectance and albedo. The study used data spanning nearly 20 years, from 1998 to 2017.
These measurements revealed that Earth now reflects about half a Watt less light per square meter than 1998. This is equivalent to a 0.5% decrease in Earth’s reflectance. Our planet is able to reflect around 30 percent of the sun's rays.
Philip Goode, a theoretical physicist from the New Jersey Institute of Technology, says that the albedo drop was so surprising after 17 years of almost flat albedo.
The amount of sunlight hitting Earth and its reflectiveness affect the brightness of Earth. The study revealed that the two factors did not work together, and something is causing Earth's dimming, particularly in recent years.
The research team looked at satellite measurements and concluded that the main contributor to the decrease in Earth's brightness is a decrease in bright, reflective, low lying clouds over eastern Pacific Ocean.
It's all likely to be related to climate change. The ocean surface temperatures are rising in the same places as the brightest clouds are falling, possibly due to the reverse of a climatic condition called Pacific Decadal Oscillation.
In their published paper, researchers write that "[Earth’s albedo] plays an important role in the earth’s climate because, in the broadest terms, climate changes are caused by the simultaneous evolutions of the solar intensity, Earth's temperature, and greenhouse insulation."
The Big Bear Solar Observatory in California collected Earthshine data over 1,500 nights. The phenomenon of Earthshine, which has been documented intermittently for close to 100 years, was first described in 16th-century Leonardo da Vinci's book.
Researchers need large amounts of data to make conclusions as the Earth spins. Because clouds, water, ice and forests all reflect sunlight differently, researchers must have access to large numbers of data. The readings can also be affected by human pollution.
Researchers now call for greater detail in the next few years. Although it was hoped that a warmer planet would result in a higher albedo and thus less warming, the contrary appears to be true.
Researchers conclude that stringent data quality standards were used to generate monthly as well as annual means. These vary on the monthly, annual and decadal levels with the net being a gradual decrease over the past two decades that accelerated in recent years.
Geophysical Research Letters published the research.
