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Our Earth was Dark – The sinking albedo has reduced the Earth’s brightness by 0.5 percent in the last 20 years

Enigmatic effect: Seen from space, the Earth glows less brightly than it did 20 years ago. On average, it reflects about 0.5 percent less sunlight, as revealed by astronomical measurements of the Earth’s luminosity and satellite data. Researchers suspect that the possible cause of this reduced albedo may be the warming of the oceans and the consequent thinning of low, low-hanging ocean clouds. However, it is not clear whether this is natural or anthropological.

The short wave that returns to Earth blows back 30 percent of the sunlight into space. This light makes our planet appear slightly blue and white from space. Its brightness The brightness of the earth Mainly depends on the cloud cover of the planet and the snow and ice cover. Because of the greater terrain in the Northern Hemisphere, these factors vary greatly during the seasons, so the terrain albedo is higher in the northern winter than in the summer.

Earth’s brightness: The light reflected from the earth illuminates the side of the moon facing us. span class = “img-copyright”> © NASA

For the light and albedo view of the earth

However, these weather and seasonal fluctuations obscure the long-term trend as the measurements of Philip Goode and his team at the New Jersey Institute of Technology now reveal. For their study, they evaluated data from the Big Bear Solar Laboratory in California, which has been measuring the brightness of the moon since 1998 before and after the new moon. In addition, they used measurement data from the CERES instrument of the Aqua- and Terra Earth observation satellites, which have been measuring the reflection of the Earth’s surface since 2000.

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To record the impact of solar radiation, the researchers selected a period of more than 20 years for their estimates. “During its eleven-year cycle, the Sun is 0.1 percent brighter than the minimum at its maximum activity,” Goode and his colleagues explain. It affects the brightness of the Earth’s luminosity and is included in the analyzes.

0.5 percent black in 20 years

Surprising result: Earth has been dark for the last two decades. Today it emits an average of 0.5 percent less light back into space than it did 20 years ago. “According to geological data, the Earth’s albedo dropped by 0.5 watts per square meter at this time,” the scientists said. Satellite data represent an even bigger decrease of 1.6 watts per square meter.

“This fall of Albedo was a surprise to us,” Goode says. “Mutual geothermal contradictions are surprisingly compatible with CERES. Both show declines, especially in recent years, although they cover slightly different parts of the Earth,” the researchers explain.

Decreasing sea clouds

But what causes the darkness of the earth to darken? It would be reasonable to assume that solar radiation changed at this time. However, comparisons with solar data show no correlation between solar activity, the number of sunspots, or radiation with the trends of the Earth’s origin. “Our data show no evidence that solar activity has directly or indirectly influenced the Earth’s reflection over the past two decades,” Goode and his colleagues write.

Instead, researchers suspect terrestrial causes for our planet’s albedo decline, including ice caps, but also long-term changes in ocean temperatures. Previous studies have shown that low, bright ocean clouds in temperate regions reflect 30 to 60 percent of short-wave solar radiation back into space. These sea clouds play an important role in climate control and landscape albedo.

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Is it natural fluctuations or the effect of climate change?

But as the CERES data show, these clouds in particular have thinned in recent years. Due to rising sea temperatures in the eastern Pacific, cloud cover, especially along the west coast of North and South America, has reduced the albedo levels of these areas. “However, so far, it is not clear whether these changes are caused by internal variation in climate or whether they are part of a reaction to external influences,” State Coote and his team said.

In theory, both climate change and natural climate change, such as the Pacific Decimal Fluctuation (PDO), could be responsible for global warming and the retreat of sea clouds – or both. Resulting in 2019 Sample simulationRising CO2 values ​​and associated climate change are leading to strong thinning of ocean clouds.

Impact on the climate

If the Earth’s albedo falls further, this will have consequences for the Earth’s climate anyway. This is because if less sunlight is thrown back into space, there will be more energy in the Earth’s system – and thus heat. So, if the albedo is actually caused by melting ice, low ocean clouds and other effects for a long time, it could further intensify the heat of the climate.

“It’s very worrying,” comments Edward Sweeterman, an uneducated geographer at the University of California, Riverside. For a long time it was believed that a warmer Earth would have more bright clouds, thus more albedo – thus a certain compensation for human warming. “But these results suggest that the opposite may be the case,” says Schweiterman. (Geophysical Research Letters, 2021; doi: 10.1029 / 2021GL094888)

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Quell: American Geophysical Union