Artificial Light Brightens Earth by 16% in Eight Years

Key facts

• Artificial nighttime lights have brightened Earth by 16% between 2014 and 2022.
• Nearly 80% of Americans cannot see the Milky Way due to light pollution.
• The United States recorded the highest total luminosity in 2022.
• Nights in Europe dramatically darkened in 2022 due to the Russia-Ukraine conflict.
• The study analyzed a decade of daily NASA satellite imagery.
• Light pollution is categorized into glare, skyglow, light trespass, and clutter.

The Expanding Footprint of Artificial Nighttime Light

The Earth's night sky is steadily growing brighter, not from celestial bodies, but from the pervasive spread of artificial illumination. While essential for modern life, this widespread outdoor lighting has fundamentally altered natural darkness, impacting both human and animal well-being and diminishing our view of the cosmos. A comprehensive new study, utilizing satellite imagery, indicates that artificial nighttime lights have increased Earth's overall luminosity by a striking 16% between 2014 and 2022. Researchers at the University of Connecticut have observed a gradual brightening of nights across the globe. However, this trend is not uniform, with regional variations influenced by factors such as conflict and natural disasters. The study's findings challenge a long-held assumption that the planet's illumination solely correlates with population and economic growth. "For decades, we've held a simplified view that the Earth at night is just getting steadily brighter as human population and economies grow," stated Zhe Zhu, the study's senior author and director of the University of Connecticut's Global Environmental Remote Sensing Laboratory. "The planet's lighting footprint is constantly expanding, contracting and shifting," he added, underscoring the dynamic nature of this phenomenon.

America's Obscured Skies

In 2022, the United States registered the highest total luminosity among all nations, followed by China, India, Canada, and Brazil. This intense illumination has profound consequences for astronomical observation and our connection to the night sky. In the U.S., where nearly 80% of the population resides in urban areas, the sheer brightness of artificial light sources effectively blots out the natural beauty of the stars. As a result, only the most luminous celestial objects—the brightest stars, planets, and other prominent astronomical features—remain visible to the naked eye. This phenomenon is a primary concern for organizations like DarkSky International, a non-profit dedicated to preserving the integrity of night skies worldwide. The study's methodology involved analyzing a decade's worth of daily satellite imagery from NASA, comparing data from 2012 with that of 2023 to map shifts in human nighttime activity and its luminous impact.

Regional Variations and Conflict's Dimming Effect

While the overall trend points to a brighter planet, the research also identified specific regions where artificial light levels have notably decreased. A significant instance of this dimming was observed in Europe during 2022, directly linked to the Russia-Ukraine conflict. The ensuing regional energy crisis led to a dramatic reduction in nighttime lighting across many European areas. This observation highlights how geopolitical events and their economic repercussions can directly influence the extent of light pollution. The study's findings underscore that the expansion and contraction of human nighttime activity are not merely driven by development but can also be shaped by unforeseen global circumstances. These localized decreases serve as a counterpoint to the global increase, illustrating the complex and varied impacts of artificial lighting on different parts of the world.

Understanding the Spectrum of Light Pollution

The study, published in the journal Nature, provides a detailed understanding of the various forms that light pollution takes. These include glare, which is defined as intense, uncomfortable light that directly impairs vision. Skyglow refers to the general brightening of the night sky caused by light scattering in the atmosphere from human-made sources. Furthermore, light trespass describes unwanted artificial light that encroaches upon another's property or space, such as streetlights illuminating a private bedroom. Clutter involves excessively bright lights that cause visual discomfort, commonly seen in poorly aimed spotlights or overly intense streetlights. These categories collectively describe the multifaceted ways in which artificial lighting degrades the natural night environment. The intensity of sky brightness is often quantified using the Bortle scale, which ranges from Class 1 (darkest) to Class 9 (highest light pollution), providing a standardized measure for assessing the impact on astronomical visibility.

Implications for Health and Environment

The persistent increase in artificial light at night carries significant implications beyond the simple obscuring of stars. For decades, scientists have raised concerns about the disruption of natural light-dark cycles, which are fundamental to the biological rhythms of both humans and wildlife. This disruption can affect sleep patterns, hormone production, and overall health in humans, while for animals, it can interfere with navigation, foraging, reproduction, and predator-prey dynamics. The study's findings reinforce the need for a more nuanced approach to outdoor lighting. While necessary for safety and commerce, excessive or poorly designed lighting contributes to a growing environmental problem. The expansion of urban and suburban areas, characterized by abundant artificial illumination, is a primary driver of this trend. Addressing light pollution requires a concerted effort to implement smarter lighting strategies, including reducing unnecessary illumination, directing light downwards, and using warmer color temperatures where appropriate. These measures can help mitigate the negative effects on the environment and restore the visibility of the night sky.

The bottom line

• Artificial light pollution has increased Earth's brightness by 16% from 2014 to 2022.
• Nearly 80% of Americans can no longer see the Milky Way due to light pollution.
• The United States had the highest total luminosity in 2022, followed by China and India.
• The Russia-Ukraine conflict caused a significant dimming of European nights in 2022.
• Light pollution is categorized into glare, skyglow, light trespass, and clutter.
• The study utilized NASA satellite imagery to track changes in nighttime illumination over a decade.