TORONTO -- Earth鈥檚 bright blue glow is dimming, according to a new study, and it may be due to climate change.
With warming oceans potentially fuelling less cloud cover, the planet is simply reflecting less light back into space. And if the trend continues, it could contribute to the overall warming of the planet.
A new study published in at the end of August looked at decades of data on something called the 鈥渆arthshine鈥� 鈥� the level of light reflected off of Earth that illuminates the dark face of the Moon 鈥� in order to judge whether there鈥檚 been a drop in Earth鈥檚 terrestrial albedo.
Albedo is a thermodynamics term that measures, essentially, the whiteness of a surface and thus how much solar energy it can reflect or absorb. A value of zero means a black so dark it absorbs all incoming energy, while a value of one means the surface is a 鈥減erfect reflector.鈥�
For instance, according to the National Snow and Ice Data Center, bare sea ice has a higher albedo than open water, at around 0.07 versus 0.06, which means that sea ice absorbs less solar energy.
In this new study, researchers found that the Earth is now reflecting 鈥渁bout half a watt less light per square meter than it was 20 years ago,鈥�
The Earth generally reflects around 30 per cent of the sunlight that shines on us, but this is a 0.5 per cent decrease in the Earth鈥檚 reflectance. It may sound small, but it is 鈥渃limatologically significant,鈥� according to the study.
In the mid-1990s, the Big Bear Solar Observatory (BBSO) in southern California, began to take measurements of the Earth鈥檚 albedo using observations of the Moon. The largest chunk of data looked at in this study is from 1998 to 2017.
鈥淭he albedo drop was such a surprise to us when we analyzed the last three years of data after 17 years of nearly flat albedo,鈥� said Philip Goode, a researcher at New Jersey Institute of Technology and the lead author of the new study, in the release.
Researchers found that when recent data was added to this legacy data, the dimming trend was clear.
And most of the dimming has occurred in the last three years of earthshine data.
So why is this happening, and what does it mean?
Researchers found that there was no correlation between changes in the brightness of the Sun itself and changes in Earth鈥檚 albedo, which means that whatever is dimming the Earth is occurring here at home.
When researchers cross-referenced their data with satellite measurements taken as part of NASA鈥檚 Clouds and the Earth鈥檚 Radiant Energy System (CERES) project, they noticed that there was a reduction in low-lying clouds over the eastern Pacific Ocean in recent years, clouds that regularly reflect a lot of sunlight.
The affected area is the same region where a climatic condition called the Pacific Decadal Oscillation (PDO) has led to increases in sea surface temperatures. And while the PDO is a naturally occurring phenomenon, scientists have noted that it has become less predictable due to global warming.
If the Earth is dimming, that means it is also absorbing more solar energy than before, something that could have serious implications in the future.
鈥淚t鈥檚 actually quite concerning,鈥� Edward Schwieterman, a planetary scientist at the University of California at Riverside, said in the release. Schwieterman was not involved in the new study.
He explained that scientists had hoped that as the Earth warmed, it might lead to more clouds and a higher albedo that could help balance the Earth鈥檚 warming.
鈥淏ut this shows the opposite is true.鈥�
