Study: The planet is getting "darker"

A study published in the journal Proceedings of the National Academy of Sciences (PNAS) shows that between 2001 and 2024, the Earth reflected less sunlight, which means that the planet has become "darker". The phenomenon is especially visible in the northern hemisphere, where the decrease in albedo - the reflectivity of the Earth's surface - has noticeable effects, informs DPA. The team led by Norman Loeb, a researcher at NASA Langley Research Center in Virginia, analyzed satellite data and discovered a previously unknown imbalance between the two hemispheres. While the southern hemisphere gains radiative energy in the upper atmosphere, there is a net loss in the north. In the past, scientists believed that this imbalance was compensated for by atmospheric and oceanic circulations, but the data show that in the last two decades this balancing mechanism has not worked fully.

• Causes: Melting ice and fewer aerosols

One of the main factors is the reduction of sea ice and snow cover in the Northern Hemisphere, which used to reflect more solar radiation. In contrast, rocks and water absorb more energy, contributing to the darkening of the planet. Another factor is related to aerosols, suspended particles that influence cloud formation and the reflection of sunlight. In the Northern Hemisphere, fine particle pollution has decreased significantly due to environmental protection measures adopted in Europe, the United States and China. The result: fewer aerosols, fewer clouds and, implicitly, lower reflectivity. In contrast, in the Southern Hemisphere, the amount of aerosols has increased, mainly due to massive vegetation fires in Australia and the eruption of the Hunga Tonga volcano in the South Pacific (2021-2022). These aerosols have contributed to the formation of clouds and the reflection of a larger part of the solar radiation.

• Impact on climate models

Although the differences seem small - a divergence of 0.34 watts per square meter per decade, at an energy input of 240-243 W/m² - scientists emphasize that the effect is statistically significant and can influence climate evolution. Until now, the role of clouds was considered crucial in maintaining a balance between the two hemispheres. But the study suggests that this symmetry of brightness is not maintained by clouds as effectively as previously thought. The researchers point out that the results can help improve climate models by more accurately understanding the interaction between aerosols, clouds and albedo. "The discovery is important for understanding how the planet absorbs and reflects solar energy, a key factor in the dynamics of climate change,” the study authors emphasized.