"The reflectance of the Earth is a fundamental climate parameter that we measured from Big Bear Solar Observatory between 1998 and 2017 by observing the earthshine using modern photometric techniques to precisely determine daily, monthly, seasonal, yearly, and decadal changes in terrestrial albedo from earthshine," wrote the researchers in their paper. "We measure a gradual, but climatologically significant ~0.5 W/m2 decline in the global albedo over the two decades of data."
The Earth's reflectance is an essential determinant of the earth's climate, since, changes in climate arise from the simultaneous evolution of the solar intensity, the Earth's albedo, and greenhouse insulation.
To come to their conclusion, scientists looked at data from Big Bear Solar Observatory in Southern California and evaluated how earthshine fluctuates since 1998. They then combined that data with observations from NASA’s Clouds and the Earth's Radiant Energy (CERES) project, which had been active since 1997, and with instruments from a couple of NASA and National Oceanic and Atmospheric Administration (NOAA) satellites.
It should be noted that most of the changes in reflectance took place in the last year indicating that the effects of climate change are growing exponentially. The researchers attribute this development mainly to a change in clouds.
Clouds are notoriously hard to study as scientists don't fully understand their relationship with Earth elements. However, in this study, the researchers attribute the decline in reflectance to the clouds over the Pacific ocean.
Clouds are known to reflect about half the sunlight that hits them, while snow and ice that fall down from clouds reflect most of the light they receive. What do these new findings mean for our planet and climate change? It's too early for the scientists to draw up conclusions, but we can imagine that any change caused by global warming would give cause for worry.