‘Earthshine’ levels show the planet is dimming

‘Earthshine’ levels show the planet is dimming

Subject – Science and Tech

Context – Over the past two decades, scientists have been studying earthshine levels, something that Leonardo da Vinci also researched.

Concept –

• Earthshine is apparent when you can faintly see the entire moon when the moon is actually only in its crescent phase. This dim illumination of the moon happens when light reflects off of the Earth.
• Leonardo da Vinci was one of the first people to explain that sunlight bounces off the Earth, reflecting light onto the moon. Almost 600 years later, scientists still use this principle to study climate change.

• The scientists measured the brightness of the Earth for 20 years by observing the amount of earthshine that reached the moon.
• They found that, in the last two decades, the Earth is becoming dimmer. Our planet is not reflecting as much of the sun’s light as it used to. Overall, the reduction was about half of a watt of light, which is a lot and is important.

• The Earth’s energy balance depends on clouds reflecting some of the sun’s energy reflected back into space. Overall, the Earth reflects about 30% of the sun’s light. The more sunlight that reaches the Earth, the more warming we are expected to see.
• The research showed that low, bright clouds, which are the best for reflecting rays, have been disappearing in parts of the world.
• The findings from the research noted that low, bright clouds off the west coasts of North and South America are much less abundant now than 20 years ago. This is also a region where the ocean has substantially warmed. The scientists think the reduction of these clouds is likely climate-related.
• Many studies point to a long-term decline in sea ice (especially in the Arctic), ice on land, and tiny pollutants called aerosols — all of which scatter sunlight back into space to cool Earth.
• A key term in this research is “albedo.” This refers to how much light the Earth’s surface reflects back out. Without those critical clouds, the albedo, or shininess, of the Earth is lower. This means that more heat is reaching the Earth.
• With ice cover declining, Earth is absorbing more radiation. The extra radiation absorbed by Earth in recent decades goes toward warming the oceans and melting more ice, which can contribute to even more warming via a vicious feedback loop.
• The scientists noted that much of the dimming of our planet occurred in the past 3 to 5 years of their study, which was a surprise after nearly 17 years of only minor dimming. Also, it’s worth noting that the study showed that there was no significant change in the energy output of the sun during the time they were conducting measurements and observations, so they have concluded that the change in brightness is due to events occurring on our Earth.
• From 1998 to 2017, Earth’s reflectance declined about 0.5 percent.
• That means the decline in Earth’s reflectance has, over that 20-year period, almost doubled the warming effect our planet experienced.