On July 11, 1987, the world is thought to have welcomed its 5-billionth person. Thirty-six years later, our population has reached 8 billion and is still rising. World Population Day, established by the UN, is a day to reflect on how much life Earth can sustain, and how our lives impact our environment.

Pictured here is Hong Kong, a city recognized as one of the world's most densely populated areas, with approximately 17,582 people per square mile. Though Hong Kong has a low birth rate, the density remains high as people live longer thanks to improvements in healthcare, a contributing factor to population increases worldwide. While this colorful night scene might appear glamorous, it is also an example of light pollution, which can disrupt ecosystems and affect our health—one of humanity's many impacts on the world around us.