Today's Edition
WASHINGTON (dpa)
The Earth became darker from 2001 to 2024, meaning it reflects less sunlight, a research team reported in the journal Proceedings of the National Academy of Sciences (PNAS).
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 US state of Virginia discovered this previously unknown inequality between the northern and southern hemispheres after analysing 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.
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 metre, a divergence of 0.34 watts per square metre 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 vapour and clouds in the atmosphere, as well as changes in the albedo, or the reflectivity of surfaces, at the Earth's surface.
