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Why is the Earth's 'shine' lower in recent years?

Why is the Earth’s ‘shine’ lower in recent years?

The Earth has been “brightening” less in recent years.

For a few years, the Earth was “losing its luster”.

In other words, our planet is reflecting – or returning – less light from the Sun back into space, according to a new study published in the journal Science. Geophysical Research Letters, of the American Geophysical Union (AGU), Sept.

The research authors, from the United States and Spain, came to this conclusion after analyzing data fromThe amount of light that the Earth reflects on the moon, collected over the past 20 years by satellites and by the Big Bear Solar Observatory in California.

Scientists still hope to determine the reasons for the decrease in the brightness of the Earth, but they already have some hypotheses.

Here we tell you what it is and what consequences this phenomenon can have on the planet.

What is “whiteness”

As is already known about light in general, it is reflected by light surfaces and absorbed by dark surfaces.

The same thing happens with sunlight and the earth.

sea ​​ice layers

The optical parts of the Earth, such as the poles, reflect light from the Sun.

The dark parts of the planet absorb light and heat from our star; While the luminous parts, such as the icy surfaces of the poles and clouds, reflect them back into space.

It is known how much light from the Sun is reflected back into space by the Earth “Whiteness” On average, it processes about 30% of the sunlight received.

“Changes in ice cover, cloud cover, air pollution, or land cover (such as forests or farmland, for example) have minor effects on global albedo,” NASA Earth Observatory explains on its website.

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During the past two decades, This reflex or albedo is reduced.

“The Earth now reflects about half a watt of light per square meter than it did 20 years ago. This equates to a 0.5% reduction in Earth’s reflectance,” says AGU.

This limit the reaction Mainly focused in the past three years.

Philip Good, a researcher at the New Jersey Institute of Technology in the US, and lead author of the study citing Earth-light data from 1998 to 2017.

But what is the reason for this reduction?

Possible reasons

The study authors have not detected changes in the brightness of the Sun in the past three years, so the decrease in Earth’s reflectance is not related to the star, but rather to the causes of the planet.

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Scientists have detected a decrease in clouds in the eastern Pacific Ocean.

The reason scientists discovered here on Earth was a “fundamental” difference in the amount of clouds in certain regions of the Pacific, said Enrique Bali, one of the study’s authors and a researcher at the Institute of Canaries (IAC). ) and from the Department of Astrophysics at the University of La Laguna in Spain to BBC Mundo.

Now there are fewer clouds – and therefore fewer bright white surfaces that reflect light – in the eastern Pacific, off the western coasts of North and South America, according to data from NASA’s Earth and Cloud Radiant Energy System (CERES).

The Clouds Union said in a statement in September that the decrease in clouds was due to rising sea temperatures “with a possible link to global climate change.”

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But Balleh told BBC Mundo he didn’t know “whether it is very easy to attribute (rising sea temperature) to climate change because the climate system is so complex” and because they have only measured albedo in the past 20 years, while “natural processes have cycles.” longer.”

“In other words, I think it’s likely due to climate change, but I think it’s still too early to set it. There may be natural cycles of clouds that might change albedo,” Ballet said.

“Under the global warming trend, there are periods of highs and lows (in temperatures), so we may be seeing something episodic,” the researcher added.

“Cloud cover is closely related to atmospheric temperature and wind patterns, which are influenced by global warming and natural variability,” climate scientist John Nielsen-Gammon, professor in the Department of Atmospheric Sciences at Texas A&M University, told BBC Mundo.

“[But]the 20-year record of Earth’s brightness is not long enough to separate these two effects,” said Nielsen-Gammon, who was not involved in the study.


Scientists calculated albedo by measuring the sunlight that the Earth reflected from the moon.

To determine exactly what caused the difference in albedo, “we have to continue to measure how this factor will change in the coming years, and measure long enough to see if we can really relate it to for climate change Or to make sure that this is not a natural variation,” Ballet said.


While investigating the causes of the decrease in the brightness of the Earth, scientists know that the light and heat from the sun that the Earth ceases to reflect in space remains on the planet, in the oceans and in the atmosphere, therefore, It can affect the temperature.

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“If the amount of light reflected by the Earth changes over the course of days or decades, it will have an impact on climate change, because it will let in more or less energy from the sun,” Ballet told BBC Mundo.

“What is clear is that albedo has always been seen in climate studies as something constant, but it is not and we have to continue to measure it because It will greatly affect our ability to predict climate change 20, 30 or 50 years from now.”

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