The Earth is reflecting less and less sunlight
Renaud de RICHTER
The Earth is reflecting less and less sunlight, study reveals
Science X 30/09/2025The Earth became darker from 2001 to 2024, meaning it reflects less sunlight, a research team reports in the journal Proceedings of the National Academy of Sciences.
The development is more pronounced in the northern hemisphere than in the southern half of the planet, the study published on Monday revealed.
A team led by Norman Loeb from NASA's Langley Research Center in Hampton in the U.S. state of Virginia discovered this previously unknown inequality between the northern and southern hemispheres after analyzing satellite data.
In general, the southern hemisphere gains radiative energy at the top of the atmosphere on average, while there is a net loss in the northern hemisphere, the research group wrote.
However, earlier studies indicated that this imbalance is offset by atmospheric and oceanic circulations that transport energy across the equator from the southern to the northern hemisphere.
Decline in surface albedo in the northern hemisphere
The current study now shows that atmospheric and oceanic circulations have not been able to fully compensate for the differences over the past two decades.
With an average energy intake from solar radiation of 240 to 243 watts per square meter, a divergence of 0.34 watts per square meter per decade is not very much. Nevertheless, the value is statistically significant, the team wrote.
The differing developments in the northern and southern hemispheres are attributed to changes in water vapor and clouds in the atmosphere, as well as changes in the albedo, the reflectivity of surfaces, at the Earth's surface.
For example, ice and snow reflect more solar radiation than rock or water. According to the study, the decrease in sea ice concentration and snow cover in the northern hemisphere has contributed to the darkening.
Zonal mean anomalies in (A) aerosol–radiation
interaction IRF and (B)–SW cloud radiative response for 2001 to 2024.
Credit: Proceedings of the National Academy of Sciences (2025). DOI: 10.1073/pnas.2511595122
Bushfires in Australia and volcanic eruption in South Pacific
In addition to these factors, the interaction between radiation and aerosols—tiny suspended particles—makes the largest contribution to the difference.
These particles act as condensation nuclei for cloud formation, which in turn promotes the reflection of solar radiation.
The researchers explained the observed trend by stating that in the northern hemisphere, fine particulate pollution has significantly decreased due to environmental protection measures, such as in Europe, the United States and China.
In contrast, in the southern hemisphere, bushfires in Australia and the eruption of the Hunga Tonga volcano in the southern Pacific in 2021 and 2022 have led to a larger amount of aerosols.
Findings important for climate change models
Scientists had previously assumed that differences in darkening between the two hemispheres would also be compensated by changes in cloud cover.
However, the study suggests that the role of clouds in maintaining hemispheric symmetry might be limited. Understanding these relationships is also important for improving climate models, the researchers emphasized.
More information: Norman G. Loeb et al, Emerging hemispheric asymmetry of Earth's radiation, Proceedings of the National Academy of Sciences (2025). DOI: 10.1073/pnas.2511595122