For decades, the amount of sunlight penetrating the atmosphere and reaching the planet's surface has fluctuated. A study suggests that it may be due to anthropogenic activity.
Researchers first noticed the consistent decline or dimming in the planet's brightness in different parts of the world in the late 1980s. This includes an almost 30% drop in sunlight in the 1950s in some regions in the Soviet Union.
Some decades later, the Soviet Union banned harmful aerosols and flipped the switch from a 'global dimming' effect to brightening.
What is Global Dimming?
Simply put, global dimming is the steady reduction of global direct irradiance at the surface of the planet. It has been an observed phenomenon subject to systematic measurements since the 1950s.
Coined by English scientists Gerry Stanhill, he compared sunlight records in Israel from the 50s to current reports. Stanhill reports a 22% drop in sunlight, a 10% decline in the US, a 16% reduction in some parts of the British Isles, and 30% in the Soviet Union.
Global dimming has a reverse effect on global warming due to reducing solar heat reaching the Earth's surface. However, the effects of global dimming vary depending on the location.
Some areas report a decline of 4-8% sunlight reduction in Europe and North America in 1961-1990, leading to spatial recovery or global brightening.
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Pollution and Global Dimming
Aerosols are one of the prime culprits behind the global dimming phenomenon. Fine particulates have been long suspected of creating hazes in the atmosphere that block sunlight from entering the atmosphere.
Research shows that this form of pollution reflects virtually all forms of radiation it encounters in the atmosphere while reflecting or absorbing light.
Whether or not fine particles are solely responsible for decades worth of global dimming remains debated in the scientific community, with many arguing that natural variability such as cloud absorption of sunlight is a bigger factor that contributes to the amount of light on the planet's surface than pollution.
However, a new study published in the Geophysical Research Letters on February 1st analyzed variations in sunlight under both clear and cloudy conditions in Central Europe, which shows that man-made pollution is, in fact, the key culprit behind global dimming.
Martin Wild, the lead author from the Institute of Atmospheric and Climate Science, Switzerland, says that despite analyzing clear skies, findings reveal that strong dimming and brightening trends show anthropogenic activity as the main causes.
The authors of the study write, "our analysis shows that strong decadal variations not only appear when clouds are considered but also remain evident under cloud-free conditions when cloud effects are eliminated."
Wild explains how aerosols are substantial modifiers in global dimming and brightening trends, "Although we'd already assumed as much, we'd been unable to prove directly until now."
Concurring on the study, reports of heavy mining practices in the Arctic linked to regional dimming in the 1970s strengthen Wild and his team's findings.
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