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Earth is reflecting less solar radiation and scientists are intrigued, but most of all they have reason to be concerned

A part of the short wave radiation with which the Sun bathes the Earth without rest is not absorbed by our planet; reflects and returns to space. Scientists have known for decades that this delicate balance between absorbed and reflected energy has a perceptible impact on the Earth’s climate, which, however, is also influenced by many other factors.

But this is not the only thing they know about this phenomenon. They also know quite well the mechanism that explains how the solar radiation that falls on the surface of our planet behaves. Broadly speaking, when short-wave solar radiation passes through the Earth’s atmosphere a part of its energy is absorbed by the molecules of the gases that constitute it, such as ozone or water vapor, and also by the particles in suspension. And another part is reflected by the clouds.

Scientists have known for decades that this delicate balance between absorbed and reflected solar radiation has a perceptible impact on Earth’s climate.

Despite this weakening, a good part of the solar radiation continues its journey to the earth’s surface, and when it reaches its destination, regardless of whether it affects a body of water or continental terrain, it experiences the same phenomenon that we have just described: a part of its energy is absorbed, and the other part is reflected and returns to space in the form of long wave radiation. Interestingly, this reflected radiation contributes to the warming of the Earth’s atmosphere.

In 1998, researchers at the Big Bear Solar Observatory, in California (United States), began using advanced photometric techniques to continuously measure the solar radiation that falls on the Earth’s surface, and they continued to do so until 2017. When they concluded the experiment they dedicated themselves to process and interpret all information They had collected during these 19 years, and came to a surprising conclusion: during this period the Earth reflected less and less solar radiation. And therefore absorbed more.

This is what scientists know, and what they do not know

Estimating to what extent the terrestrial climate conditions the balance that exists between absorbed solar radiation and that reflected by our planet is not trivial. In fact, this is the great challenge that scientists face due to how difficult it is to isolate this parameter from all other factors They also leave their mark on the Earth’s climate. However, the measurements that these researchers have obtained during this solar radiation monitoring experiment have allowed them to draw some interesting conclusions.

One of the most surprising is that, apparently, there is no correlation between solar activity and the amount of radiation that our planet absorbs and reflects. This simply means that the fact that the Sun is in a period of low activity does not imply that the amount of short-wave radiation that our planet is absorbing is less than during a phase of high solar activity. In a way, this behavior is unintuitive, which has caused these researchers to be intrigued and strive to better understand this curious mechanism.

Each of the square meters of surface of our planet absorbs an average of 0.5 watts of additional solar energy

However, this is not the only unknown that this experiment has brought to the table. The measurements that these scientists have collected reflect that during the almost two decades that this experiment has lasted, each one of the square meters of surface of our planet absorbs an average of 0.5 watts of additional solar power.

And, curiously, at the moment these researchers do not know if it is a trend that it will be sustained over time, or if, on the contrary, it is a punctual phenomenon that will end up fading. A better understanding of this mechanism is crucial to trying to mitigate global warming as much as possible, so it is clear that there is still a lot of scientific work to do. And a lot to learn.

Cover image | POT

More information | American Geophysical Union