We’re going dark. The Earth is reflecting less light than it used to, especially the Northern Hemisphere. While climate change is to blame, the reverse is also true: the planet being darker — and absorbing light instead of reflecting it — is in turn worsening climate change. But scientists are still unsure exactly how the change in Earth’s reflectivity will affect our planet’s future.
A light problem
Climate change is darkening the Earth, according to a study published in the journal PNAS. Data from NASA’s Clouds and the Earth’s Radiant Energy System (CERES) satellites found that the planet is reflecting much less light into space than it did two decades ago. In addition, while both sides of the planet should be receiving and reflecting equal amounts of sunlight, Earth’s Northern Hemisphere (NH) is reflecting less than the Southern Hemisphere (SH), thus retaining more heat and appearing dimmer.
This affects the Earth’s radiation budget, which is the “amount of light the planet absorbs and re-emits into space as outgoing longwave radiation,” said Popular Mechanics. Any imbalance between the NH and SH is typically “offset by the oceanic currents that transport energy from the southern hemisphere to the northern hemisphere.” But this research suggests that “surface changes have tipped the balance so much that ocean currents haven’t been making up the difference for the past two decades.”
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Along with the NH dimming and warming more than the SH, the “NH tropics are getting wetter, which suggests changes in large-scale atmospheric circulation are occurring,” said the study.
A dim future
The reason for this phenomenon, like most environmental problems, is climate change. Melting Arctic ice and reduced snow cover are actively dimming the glow of the planet. The NH “used to be so snowy that all that white was bouncing tons of light back into space,” said Vice. Temperatures have increased, melting the snow cover and “exposing these darker surfaces that absorb more sunlight instead of reflecting it,” said the BBC.
Changes in cloud formation have also contributed to the dimming Earth. Low-lying clouds “decreased in recent decades,” said Popular Mechanics. Ironically, this may be because we have been polluting less than we used to. In the NH, “stricter environmental regulations have reduced aerosol pollution, which previously reflected sunlight,” said the BBC. So, while the air has been cleaner, it has also incurred an unintended consequence. On the SH, “aerosol levels are increasing due to events like bushfires and volcanic eruptions, which reflect more sunlight.”
In a positive feedback loop, the Earth’s darkening is “accelerating the effects of climate change, and an asymmetric hemispheric darkening could produce its own complex impacts, including disruptive shifts in precipitation,” said 404 Media. Researchers are “watching for signs that the symmetry might reemerge in the future, or if asymmetry is perhaps the new normal.”
“All of this means that our planet isn’t just growing darker to outside observers,” said Vice. “Darkness is a symptom of a planet that is getting hotter. So hot that it’s essentially causing a planet-wide brownout.”
