Why is the Earth reflecting less light in recent years?

The Earth has been “losing its luster” for a few years.

This means that our planet is reflecting, or returning, less light from the Sun to space, according to a new study published in the Geophysical Research Letters magazine, of the Geophysical Union of the United States, in September.

The authors of the research, from the USA and Spain, reached this conclusion after analyzing data on the amount of light that the Earth reflects on the Moon, gathered over the past 17 years by satellites and the Big Bear Solar Observatory in California.

Scientists still hope to identify with precise the causes of the reduction of the Earth’s brightness, but they already present some hypotheses.

Find out what they are and the consequences that this phenomenon can cause on the planet.

How light is reflected

As is already known about light in general, light surfaces reflect, and dark ones absorb it. The same thing happens with the light from the Sun and the Earth.

The dark parts of the planet absorb the light and heat of our star, the Sun. poles and clouds, reflect and return light to space.

The amount of light from the Sun that the Earth reflects is known as albedo and, on average, is composed of about 30% of all sunlight received.

“Changes in ice cover, cloud cover, Earth cover (such as forests or farmland) and air contamination have subtle effects on the global albedo”, explains the NASA Earth Observatory, the American space agency on its website.

During the last two decades, the albedo has been reduced. “The Earth now reflects about half a watt less light per square meter than it did 20 years ago. That’s the equivalent of a 0.5% reduction in the Earth’s reflectance.” said the US Geophysical Union.

This reduction was mainly concentrated in the last three years. “The drop in albedo was a surprise to us when we looked at the last three years of data, after 17 years of nearly stable albedo,” said Philip Goode, a researcher at the Institute of New Jersey Technology, USA, and lead author of the study, referring to the reflected light data from the Earth from 1998 to 1998.

But what is this reduction due to?

Possible causes

The authors of the study did not detect changes in the sun’s brightness in the last few years three years, therefore, the decrease in reflected light is not related to the Sun, but to factors linked to the Earth.

The cause detected by scientists on Earth was a “substantial” variation in the amount of clouds in certain areas of the Pacific Ocean, told BBC News Mundo Enric Pallé, one of the authors of the study and a researcher at the Instituto de Astrophysics de Canary Islands and the Department of Astrophysics at the University La Laguna in Spain.

There are fewer clouds – so fewer white surfaces. the bright ones that reflect light in the Western Pacific Ocean—compared to the western coasts of North and South America, according to NASA’s Cloud and Earth Radiant Energy System.

This reduction in clouds is due to an increase in sea temperature, “with likely connections to global climate change,” the US Geophysical Union said in a statement in September.

But Pallé said BBC News Mundo (the BBC’s Spanish-language news service) who does not know “if it would be so easy to attribute (the increase in sea temperature) to climate change, because the climate system is very complex” and because the albedo has only been measured in the last 17 years, while “natural processes have longer cycles”.

“In other words, I think it is likely due to climate change, but I believe it is premature to state this for now. It could be that there are natural cycles of cloudiness that could be modifying the albedo”, highlighted Pallé.

“Within the global warming trend, there are episodes of increases and decreases (in temperature), so who you know we’re seeing something episodic,” the researcher added. clouds is closely linked to atmospheric temperature and wind patterns, which are affected by global warming and natural variability.”

“(But) the record of 20 Earth’s brightness years is not really long enough to separate these two effects,” Nielsen-Gammon, who did not participate in the research, also stated.

To determine exactly what is due to variation in albedo, “we have to keep measuring how it’s going to change in the next few years, measure it long enough to see r if we can really associate this with climate change and be sure that it is not a natural variation”, highlighted Pallé.


While they investigate the Because of the reduction in Earth’s brightness, scientists know that the light and heat from the Sun that the Earth fails to reflect into space remains on the planet, in the oceans and in the atmosphere. Therefore, it can influence temperature.

“If the amount of light that the Earth reflects changes over days or decades, there will be an influence on climate change, because it will let in more or less energy from the sun “, Pallé told BBC Mundo.

“What is clear is that albedo has always been considered in climate studies as something constant, but it is not. ability to predict climate change between now and 20, 20 or 20 years”, added the scientist.

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