Earth is divided into two halves: the Northern and Southern Hemispheres. Both reflect equal amounts of sunlight (albedo) even though they have different landmasses and weather patterns, especially cloud distribution. Why this is so is an ongoing mystery waiting to be solved.
To add to the puzzle, Jianhao Zhang at the National Oceanic and Atmospheric Administration in the US and his colleagues have discovered another line of symmetry that splits the planet into an Eastern Hemisphere and a Western Hemisphere. And these two halves also reflect the same amount of sunlight as each other. The discovery could mean that some current climate models may be missing an important feature.
Decoding satellite data
As they explain in a paper published in Nature, the team analyzed 25 years of data (2001–2025) from NASA’s CERES satellites. These measure the amount of solar energy reflected back into space. They also used advanced computer coding to break down the albedo into different categories, such as how much reflected light comes from ice-free oceans and how much from landmasses.
The researchers checked these categories against eight top climate models to see if they could replicate real-world data. Then they digitally sliced Earth into different sections by longitude to see how the reflected light changes as you move across the globe.
When they did this, they found a previously unnoticed line of symmetry along the 27° East and 153° West meridians, running through Europe and Africa, which divides the planet into two equally reflective halves.
However, unlike the north-south symmetry where the two halves have different amounts of land and ocean, the east-west halves contain nearly identical fractions of ice-free ocean and show similar patterns in cloud cover and the amount of sunlight reflected by cloud-free skies. “This E–W all-sky hemispheric symmetry coincides with near symmetries in ocean fraction, CRE and clear-sky reflection, together yielding a triple symmetry distinct from the N–S albedo symmetry,” wrote the team in their paper.
The study authors also found that the east-west line of symmetry shifts slightly from year to year and that it’s linked to the El Niño-Southern Oscillation cycle. This suggests the symmetry is connected to changing global weather patterns.
Upgrading climate models
This balancing act matters because the planet’s overall reflectivity impacts global warming. The albedo reflects about 29% of incoming solar radiation back into space. However, many current models do not reproduce the observed east-west symmetry, the team found. They suggest future models should be upgraded to accurately capture this feature and potentially improve predictions.
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Publication details
Jianhao Zhang et al, Earth’s east–west albedo symmetry, Nature (2026). DOI: 10.1038/s41586-026-10624-2
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