Variations in Sunlight Have More to Do With Pollution Than Clouds, Says Study 21 FEBRUARY 2021 The amount of sunlight reaching Earth's surface has been fluctuating for decades now, and a new study supports the idea that human activity is to blame. In the late 1980s, researchers first noticed a steady decline or 'dimming' in Earth's brightness in various parts of the world, including a near 30 percent drop in sunlight since the 1950s over a particular region in the Soviet Union.
Just a few decades later, after the most harmful aerosols were banned and the Soviet Union dissolved, the trend suddenly switched from a "global dimming" effect to a brightening one.