Contrasting trends in light pollution across Europe based on satellite observed night time lights

Abstract

Since the 1970s nighttime satellite images of the Earth from space have provided a striking illustration of the extent of artificial light. Meanwhile, growing awareness of adverse impacts of artificial light at night on scientific astronomy, human health, ecological processes and aesthetic enjoyment of the night sky has led to recognition of light pollution as a significant global environmental issue. Links between economic activity, population growth and artificial light are well documented in rapidly developing regions. Applying a novel method to analysis of satellite images of European nighttime lights over 15 years, we show that while the continental trend is towards increasing brightness, some economically developed regions show more complex patterns with large areas decreasing in observed brightness over this period. This highlights that opportunities exist to constrain and even reduce the environmental impact of artificial light pollution while delivering cost and energy-saving benefits.

Figure 1. 15-year changes in nighttime brightness in South-West England.

Highlighted regions: (a) Annual trend in brightness for areas associated with the china-clay (kaolin) industry, (blue line); total china clay production (black line). (b) Annual trend in brightness for the urban region of Torbay (blue); total power load on municipal street lighting in Torbay (black). (c) Annual trend in brightness for Wytch Farm onshore oil field (blue); total oil production from the field (black). Map generated using ESRI ArcMap 9.2.

Figure 2

(a) Intercalibrated mean brightness for Europe 2005–2010. (b) 10-year change in brightness, calculated as the difference in mean values for the periods 2005–2010 and 1995–2000. Grey areas are saturated throughout the time period, so trends cannot be detected. (c) Proportions of the total land surface area for which artificial light was detected to increase (orange) and decrease (blue) by more than 3 DN units in constituent countries of Europe. *Data south of 65 degrees latitude only. Map generated using ESRI ArcMap 9.2.

Figure 3. Selected areas of maps shown in Figure 2, showing contrasts in trends in detected nighttime light between different countries.

(a) Belgium shows decreases in nighttime brightness along the motorway network, while neighbouring regions of France have increased substantially in brightness. (b) Slovakia shows marked decreases in brightness, with the exception of Bratslava and towns in the west of the country. In contrast, neighbouring regions of Poland have become substantially brighter. Map generated using ESRI ArcMap 9.2.