Navigating Earth’s Unbalanced Reflection: A Study of Satellite Data
NASA’s last 24 years of satellite data reveal an “unequivocal” trend: the earth has lost its balance, and now the northern hemisphere reflects less light than the southern hemisphere .
How is that? Until a few years ago, our planet maintained an almost perfect symmetry regarding its albedo : its reflectivity from the perspective of an observer in the earth’s orbit.
Despite its obvious differences (the north dominated by terrestrial masses and the south by oceans ), both hemispheres reflected practically the same amount of sunlight to outer space. Now that doesn’t happen anymore. The northern hemisphere is absorbing more solar energy than the southern hemisphere, breaking the balance that had been maintained for a long time.
In figures. The new study, published in the Proceedings of the National Academy of Sciences, quantifies this divergence at 0.34 W/m² per decade . It is a statistically significant value that points to a deep change in the energy engine of our planet.
And why? The study, led by Norman Loeb from the NASA Langley Research Center , points to a combination of factors. The first one, somewhat paradoxical, is that the main engine of the growing asymmetry is aerosols , the tiny particles suspended in the atmosphere against which we have been fighting for some time.
Thanks to environmental protection measures , fine particle pollution has decreased significantly in Europe , the United States , and China in recent years. Less contamination means cleaner air, and therefore fewer particles that reflect sunlight. The result is that more radiation reaches the surface and is absorbed.
In the southern hemisphere , the situation has occurred just the opposite. Mass events, such as the Australian wildfires of 2019-2020 or the eruption of the Hunga Tonga volcano in 2022, injected enormous amounts of aerosols into the atmosphere, temporarily increasing its reflectivity.
There is something else. To the aerosols, we must also add changes in the albedo of the surface itself. The northern hemisphere is losing snow and sea ice rapidly due to global warming. If white and bright surfaces (which reflect light) are replaced by water and dark terrain (which absorb light), the hemisphere becomes increasingly darkened.
Clouds are missing. What has most bewildered scientists is the role of clouds . For a long time, it was theorized that clouds would act as a natural compensatory mechanism for this phenomenon. If a hemisphere darkened due to external factors, atmospheric circulation would adjust cloudiness to reflect more light and restore balance.
However, the data shows that this is not what is happening. The study concludes that the contribution of clouds to the difference in reflectivity between hemispheres is surprisingly small. The reason is complex: it seems that the changes in the clouds of the tropics are being canceled out by the changes at higher latitudes, questioning one of the foundational hypotheses on the self-regulation of the earth’s climate.
A problem. That one hemisphere absorbs more heat than the other is not simply an academic curiosity. The Earth’s energy balance is the engine that drives both atmospheric and oceanic circulation; in essence, it influences our climate and weather patterns . This imbalance is already having critical consequences.
The northern hemisphere not only heats up faster than the south, but it is also witnessing an increase in rainfall in tropical latitudes. If the intertropical convergence zone , a significant rain belt, moves northward, the repercussions will be severe for billions of people.
Image | NASA, GOES
In Xataka | The rains are not always good news. In the Arctic, for example, they begin to become alarming.