Earth, like all planets in the solar system, reflects a portion of the sun’s light. A portion that scientists say is getting smaller and smaller. Our planet is getting darker. And this phenomenon is a cause for concern. Because it could increase global warming.
We see the moon at night because it reflects sunlight. The same is true of the other planets in the solar system and Earth is no exception as it, too, reflects sunlight. Astronomers call this reflectivity albedo. To measure it, of course, you have to get high up. That’s what an international team of researchers just did and the results they have delivered are not reassuring.
A reduction in Earth’s albedo
Over the past 20 years, measurements have shown a reduction in Earth’s albedo that scientists call significant. Our planet now reflects half a watt less light per square meter than it did 20 years ago. This corresponds to a 0.5% reduction in albedo.
But what could be the cause of this phenomenon? First, of course, there is the possibility that the brightness of our sun has changed. However, over the past 20 years, astronomers have been unable to find any such correlation. So they had to look elsewhere. One explanation, they say, is the decrease in cloud cover in the eastern Pacific.
Measurements taken as part of the Ceres (Clouds and Earth’s Radiative System) project confirm this. There are fewer and fewer bright, reflective low clouds over the region. This is likely the result of human-induced global warming, which is raising ocean surface temperatures.
Scientists had hoped that global warming would lead to an increase in cloud development and an increase in albedo. This would have helped limit global warming by reflecting a little more energy from the sun into space. However, these results show the opposite.
On our planet, different surfaces – clouds, water, ice, deserts, land, forests – reflect sunlight differently. This can slow or accelerate ongoing global warming.
Snow and ice at the poles alone reflect up to 85% of the sunlight that reaches the Earth which helps maintain acceptable temperatures on the surface of our planet. But in recent decades, this snow and ice have melted as a result of human-induced global warming, especially in the Arctic Ocean. Temperatures there are rising two to three times faster than elsewhere in the world. The natural cycle has always existed, but the ice is now melting earlier. Each year, the ice sheet shrinks a little more causing the ocean to become darker. A darker ocean reflects much less light which increases the temperature of the planet.
A dangerous feedback loop occurs
As the Earth gradually loses some of its reflectivity, a dangerous feedback loop occurs. Global warming melts the ice, causing more darker surfaces that absorb, rather than reflect, sunlight which amplifies the warming. Worse, as the ocean itself warms, it releases carbon dioxide (CO2) and water vapor, two greenhouse gases that also contribute to further warming.
As the ice sheet melts, darker land emerges. Worse, sea levels rise. Higher and warmer water temperatures accelerate ice melting even more. Another feedback loop activated to the detriment of our climate.
But by reducing greenhouse gas emissions, we can still reduce temperatures, which will help bring back snow and restore ice at the poles, and in fact, restore the albedo of our planet. “The longer we wait, the harder it will be. That will take several years. But it is still possible,” says Don Perovich, a geophysicist at Dartmouth College, in a series of short films about the climate emergency.