The Earth’s energy balance, the difference between the solar energy that arrives and the energy that the Earth radiates, has almost quadrupled in just twenty years. Recent studies indicate a significant increase in absorbed solar energy, possibly due to a cleaner atmosphere and less reflection from Earth. But is it also an explanation for the accelerated warming?
Balance between incoming and outgoing radiation
Earth’s climate is determined by a delicate balance between the amount of (short-wave) solar radiation absorbed in the atmosphere and at the surface, and the amount of thermal infrared (long-wave) radiation that Earth emits into space. A positive energy imbalance – which is what we have now – means that the Earth system is gaining energy. The result is that the planet is warming. When the Earth emits more energy than it receives, this can lead to cooling.
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The imbalance is increasing
The increase in greenhouse gases in the atmosphere traps more thermal infrared radiation, creating an imbalance. As a result, the Earth warms up and radiates even more heat in an attempt to restore balance. Recent measurements from the CERES satellite, which measures Earth’s radiation budget, show that, as expected, outgoing long-wave radiation has indeed increased due to rising temperatures.
But the increase is not as strong as that of absorbed solar radiation, especially in the past two decades, causing the energy imbalance to widen. The planet receives more energy than it radiates. The imbalance in the early 2020s is almost twice as large as that from mid-2005 to mid-2015.
Read more below the image.
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Why does the absorbed ‘irradiation’ increase so much?
This is firstly because the peak of the sun’s eleven-year cycle is approaching. The sun is therefore slightly more powerful, causing more radiation to reach the earth. But that can’t explain why our planet absorbs an extra 2.3 watts per square meter over its 510 trillion m² surface area, compared to the first decade of satellite data.
So it may also have to do with the reflectivity (albedo) of our planet that is decreasing. This may be partly because there is less ice surface, which reflects a lot of sunlight. A decrease in clouds that reflect sunlight may also be related.
This decrease in reflection can also be attributed to a global decrease in aerosols and sulfur emissions. Since 2010, emissions of aerosols, which are small particles in the atmosphere, have decreased significantly due to reduced air pollution. Since 2020, this has also been the case due to restrictions on sulfur fuels for ocean freighters.
Fewer aerosols are beneficial to human health, but now reveal the greenhouse effect that was partially hidden, leading to accelerated global warming. For a long time they reflected part of the sun’s radiation, but now this radiation reaches the earth.
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Tags: Earth absorbing solar energy impact warming Science Planet
