Nocturnal landscape of Kuala Lumpur, Malaysia, during Eid al-Fit, the
Muslim festival marking the end of the fast of Ramadan, on 17th July 2015. At the
bottom right corner, streets with white- and blue-rich lights where celebrations are
taking place.
Photo by Airam Rodríguez.

By Francisco Ramírez, Yago Cordón, Diego García, Airam Rodríguez, Marta Coll, Lloyd S. Davis, Andre Chiaradia, and Josep L. Carrasco.

Read the full paper here.

We, humans, have modified the Earth in many different ways, with far-reaching consequences for a vast array of life, including us. We can see one of the most striking human fingerprints on Earth from space: how artificial lights have transformed the nightscape. This is called light pollution. Understanding how we contribute to light pollution is essential for evaluating impacts and for implementing possible means of mitigation. That is what we have done in this study, based on the longest and widest information on night light intensity from satellite imagery.

Humanity’s scheduled routines and gregarious nature may increase light pollution. This is particularly true when considering macro-cultural events and festivities that involve large human aggregations, nocturnal activities, and the use of artificial lights: Christmas, Ramadan, Diwali or Chinese New Year celebrations, among others. Here, we provide the first evidence showing that these super-polluter events enhance urban light pollution globally. We show that the display of Christmas lights between Christmas and Epiphany Day celebrations (December-January) coincides with the annual peak in urban night-time light intensity in Christian countries. Night celebrations during Ramadan (from May to July) and Diwali (from May to July) also fits with annual night light peaks in Muslim and Hindu countries. In China and Vietnam, annual peaks of urban light intensity match the Chinese and Vietnamese (Tê’t) New Year celebrations (January-February).

Artificial lighting and light pollution has dramatically increased over recent decades. The continued economic development and growth in the human population will only worsen the impacts on natural systems, even beyond urban areas. Our findings highlight the need for continuous monitoring of light pollution associated with human celebrations, and also for global policies directed towards the sustainable use of artificial lights to reduce light pollution and mitigate deleterious effects.