Earth’s Northern Hemisphere is darkening faster than the South, scientists find

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Scientists say Earth’s northern half is darkening faster than the south, reflecting less sunlight back into space and soaking up more of the sun’s energy.

A new study based on more than two decades of satellite data shows this small but steady shift in the planet’s energy balance.

Researchers point to cleaner air, melting ice, and small but significant changes in clouds as key drivers of this change.

Shortwave and longwave radiation

Øivind Hodnebrog, a senior researcher at Norway’s Centre for International Climate Research (CICERO), said the findings indicate there has been a shift in the amount of solar radiation coming in versus heat radiated back into space.

"What we find in this paper is it's increasing more in the Northern Hemisphere than the Southern Hemisphere," he said.

At the core of the process is a balance between shortwave and longwave radiation. Shortwave radiation comes from the Sun – visible and ultraviolet light that reaches Earth’s surface. Some of it is reflected straight back into space by clouds, ice, and other bright surfaces.

"And longwave radiation is what is emitted from the Earth system, Hodnebrog said. "So by increasing absorbed solar radiation, that means a darkening of the Earth**".**

So why is the Earth growing darker from space?

Researchers said several factors are driving the change. One of the biggest is cleaner air.

Decades ago, the skies over Europe, North America, and China were filled with reflective aerosols – tiny particles that bounced sunlight back into space. As those pollutants have decreased due to increased efforts to control climate change, so has the planet’s ability to deflect the sun’s rays.

"When you remove these reflecting particles, that means that more of the sunlight is absorbed. They do not only reflect sunlight, but also affect the clouds," Hodnebrog said.

"So, when you have aerosol pollution, it makes the clouds brighter, which leads to a cooling. And again, when you clean up the aerosols, the clouds also get darker, and that’s a major effect," he added.

Cleaner air also changes how clouds form, making them slightly darker and less reflective.

Meanwhile, melting Arctic sea ice and snow are exposing darker ocean and land surfaces that soak up even more heat.

The researchers say this darkening trend may not be permanent. How it evolves will depend on future greenhouse gas emissions, aerosol pollution levels, and how the climate system responds to the extra heat.