Image courtesy of Planetary Visions Ltd/Science Photo Library
Joel Kontinen
The Earth is more special than we thought.
A line that
runs through Africa, Europe, Alaska and both poles divides Earth into two
halves that reflect the same amount of light – and this newly discovered
symmetry may play a critical role in the planet’s climate.
It was
previously known that the northern and southern hemispheres have almost equal
reflectivity, or albedo, but Jianhao Zhang at the National Oceanic and Atmospheric
Administration in the US and his colleagues have now uncovered a second line of
symmetry along the 27° east and 153° west meridians.
At first,
Zhang thought it must be a coincidence. “What convinced me that the east-west
symmetry is not trivial are three features: its uniqueness, its persistence and
what we call the triple symmetry feature,” he says. “Finding one division with
equal total reflection might be expected. But finding a persistent, unique
east-west division that also balances land-ocean distribution, clear-sky
reflection and cloudy-sky reflection is much less trivial – especially given
how variable and dynamic clouds are.”
Øivind Hodnebrog
says “I was a bit sceptical of an
east-west symmetry separated at around 27 degrees east, which intuitively seems
much less obvious than a separation at the equator,
However,
Hodnebrog says he now agrees it is likely a “robust feature, and potentially
another fascinating property of the Earth”.
The
connection to ENSO may also be significant, says Hodnebrog. Unlike the
north-south symmetry, which appears to be weakening due to the effects of
climate change on sea ice and clouds, the east-west symmetry is currently
stable, though models suggest it could weaken in future. “A potential future
asymmetry could be an indication of changes in the atmospheric circulation,” he
says.
Martin Jucker at the University of New South Wales,
Sydney, says there is a high potential that the east-west symmetry is a
coincidence.
“Earth’s
weather and climate communicate easily across longitudes,” says Jucker. “This
is due to Earth’s rotation, which creates bands of circum-global easterly
and westerly winds, and atmospheric perturbations preferentially propagating in
the east-west direction as well.”
Source:
James Woodford 2026
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