Scientists from Connecticut University, Cornell University and NASA Space Flight Center performed the major research of the night-time lighting of Earth as of today. Having analyzed the NASA Black Marble satellite images for nine years (from 2014 to 2022), they developed a detailed map of changes of the night-time lighting of our planet.
Up until now, it was believed that during the night Earth gradually brightens up: the cities are growing, the infrastructure enhances, energy consumption is growing. However, new data invert such perception. The night-time life of Earth turned out to be not just steadily brightening up, but pulsating demonstrating frequent and multidirectional changes. On average, every land area where the changes were registered went through approximately 6-7 changes during the period of nine years – i.e., several times grew brighter, and then grew darker.
To understand these dynamics, the researchers applied the continuous change tracking algorithm. They analyzed over one million of satellite images cleared from interference such as clouds, snow and moonlight, and covered about 15 mln km² – about 10% of land excluding uncouth deserts and polar zones. Every pixel of the image (approximately 500 meters on the equator) was checked for abrupt and gradual changes of brightness. The methodology allowed not only to register the fact of changes, but also to identify their dates, intensity and type: sudden event (e.g., construction or blackout) or long-time trend (like gradual growing of suburbs).
The results showed that the aggregate area of abrupt changes of lighting was over 2 mln km², and gradual changes – over 19 mln km². This is 5.5 times more than the entire illuminated territory of the planet in 2014. And the changes were both ways: the increase in brightness (brightening up) provided for radiation increment equivalent to 34% of 2014 level, and the obscuration compensated for 18%. It means that the broad picture became brighter, but due to on-going and not unidirectional changes. In certain places the light is turned on, and in others – turned off, and this process is picking up momentum.
The scientists identified several main reasons. In Asia, especially in China and India, bright flashes are associated with urbanization, the construction of plants and rural electrification. On the contrary, in Europe structured obscuration is visible, for example, in France the light dimmed by 33%, in the UK – by 22%. This results from the deliberate energy saving policy, transition to light-emitting diodes and struggle against light pollution. In the USA the picture varies: the coastline gets brighter due to the growth of cities, and old industrial regions in the Midwest get darker.
Overall, in 2014 – 2022, the global trend towards increase in brightness was accompanied by simultaneous growth of obscuration intensity. Both multidirectional trends were growing simultaneously resembling the accelerated heartbeat of the planet: the light “waves” became steeper, and the “cavities” — deeper. Due to this, the scientists propose to view the night-time satellite data as a “sociological electrocardiogram”. For example, the global decrease in brightness in early 2020 ideally matched with the lockdowns due to COVID-19.
Thus, decrypting the night-time pulsating of Earth, the scientists can in real time mode monitor not only the growth of the cities, but also economic crises and the consequences of conflicts.
