Scientists in the late 1980s noticed that less of the sun’s brightness was reaching Earth’s surface. The phenomenon became known as “global dimming.” Now, it’s in reverse, meaning the planet is becoming less dark. The researchers came up with two theories regarding what is driving the shifts in brightness: natural variations in cloud cover or human-caused air pollution. A new study points to the latter.
Based on the long-term Potsdam radiation time series, the study shows that variations in the sunlight’s intensity over decades are caused by ultra-fine, human-made dirt particles in the atmosphere. The Potsdam record is one of the world’s longest and best-maintained continuous solar radiation measurements on the Earth’s surface.
Lead author Martin Wild, a professor at ETH Zurich, said in a press release:
Although we’d already assumed as much, we’d been unable to prove it directly until now. [We looked at] one of the longest and best‐maintained records of sunlight measured at Potsdam, Germany. The record covered the period from 1947 to 2017.
The team filtered out the impacts of clouds and analyzed brightness on cloudy and sunny days to prove it. Like this, they could determine that overall patterns in brightness and dimming remained consistent even without cloud cover.
The authors wrote:
This implies that aerosol pollutants play a crucial role in these variations and point to a discernible human influence on the vital level of sunlight required for sustainable living conditions.
The findings and historical records match up. For example, in the Soviet Union, the sky dimmed almost 30% between the 1950s and 1980s, around the same time industrialization rose. Then, as the most harmful aerosols were banned, the region began to brighten.
The same thing happened in North America and Europe. In the 1990s, both continents enacted clean air legislation, and the regions brightened. Meanwhile, India and China have seen further dimming, coinciding with their pollution increases from rapid industrialization.
Air pollution dims sunlight because the particles reflect and absorb solar radiation, stopping it from even reaching the Earth’s surface. The effect can profoundly impact planetary systems – like altering the water cycle by impacting evaporation, and ultimately precipitation. The study noted that less water evaporated, and rain fell during the period of widespread planetary darkening.
Furthermore, it governs the temperature and masks the impacts of the climate crisis. When there’s less sunlight, the planet is cooler. But as we improve air quality, the already warming planet will become even hotter.
Wild said:
GLACIAL RETREAT accelerated when the atmosphere began brightening again.
The situation has led some scientists to suggest solar geoengineering to artificially dim the planet and tackle the climate crisis. However, others warn the move is far too risky as it could have disastrous unintended consequences. For example, a separate study found that dimming can inhibit tree growth. If trees grow slower with less sunlight, it could jeopardize one of Earth’s most important carbon sinks.
This means that as things get better with the world transitioning to clean energy, it may actually get worse at first before truly getting better.
