Satellite imagery reveals increasing volatility in human night-time activity | Nature

## Summary
Driven by this volatility, the cumulative area of total ALAN change comprised 2.05 million km 2 of abrupt changes and 19.04 million km 2 of gradual changes. By adapting a continuous change detection algorithm 4 , 5 ( Methods ), we quantified the timing (day-of-year and year), intensity (area-averaged radiance change), type (abrupt or gradual), and direction (brightening or dimming) of ALAN changes for every 15-arc-second pixel (about 500 m at the equator) across the primary inhabited landmasses of Earth (70° N–60° S) from 2014 to 2022. More revealing of the true dynamics is the total cumulative ALAN change area (or gross area change) during 2014–2022 (Extended Data Table 3 ), which sums the area changed each year, thereby accounting for pixels that underwent several changes (for example, a brightening followed by a dimming, or multiple abrupt events). Full size image a , b , Maps show the average number of years (per 15-arc-second pixels within 0.5° × 0.5° grid cells) experiencing abrupt ALAN change ( a ) and gradual ALAN change ( b ). c , Donut charts showing the estimated proportions of causal drivers associated with the brightening and dimming for both abrupt and gradual changes.

## Article Content
Download PDF
Subjects
Environmental impact
Interdisciplinary studies
Optical sensors
Abstract
Artificial light at night (ALAN) marks the global impact of humanity
1
,
2
. Yet, our understanding of its true ebb and flow has been limited, often based on temporally aggregated satellite data that obscure finer dynamics. Here, using daily night-time satellite imagery
3
and a continuous change detection approach
4
,
5
, we created global maps of high-frequency ALAN dynamics (2014–2022). Our findings challenge the prevailing perspective that changes in light radiance are largely gradual and unidirectional. Instead, the nightlights of Earth are surprisingly dynamic, characterized by frequent and coexisting brightening and dimming. On average, each location experiencing change underwent 6.6 distinct shifts over the 9 years. Driven by this volatility, the cumulative area of total ALAN change comprised 2.05 million km
2
of abrupt changes and 19.04 million km
2
of gradual changes. Brightening contributed a radiance increase equivalent to 34% of the 2014 global baseline, whereas dimming offset this by 18%. Notably, both brightening and dimming have markedly intensified over the past decade. This evidence of increasing volatility in human night-time activity provides an important dynamic dimension for understanding urban evolution, energy transitions, policy impacts and ecological consequences of rapidly changing illuminated nights.
Main
The illuminated Earth, viewed from space at night, is a powerful testament to human presence, revealing a ‘Black Marble’ increasingly delineated by the light of human settlements, industries and energy infrastructures. Artificial light at night (ALAN) extends visibility beyond daylight hours, enabling round-the-clock movement, gathering and continuation of daily life. Yet, ALAN is far more than a visual spectacle: it is a direct, measurable signal of human activity, reflecting how we build and power our settlements, the dynamics of our economies and our responses to both crises and opportunities
6
. The variability of ALAN mirrors the pace and nature of human activity, manifesting as either abrupt events, such as new constructions or disasters, or gradual trends driven by long-term economic or demographic forces. Understanding the direction, location and intensity of these changes is, therefore, important for assessing the full scope of global change and its impact on human infrastructure and energy transitions
7
. We define brightening and dimming as sustained increases and decreases in radiance (excluding transient noise), respectively, driven by either abrupt events or gradual trends, as shown in Extended Data Fig.
5
.
For decades, global assessment of ALAN trends has centred on a narrative of continuous and widespread brightening, with dimming viewed as a localized exception. This perspective stems largely from temporally aggregated night-time light (NTL) satellite observations
8
,
9
. Annual and multi-year composites, such as those produced from earlier Defense Meteorological Satellite Program Operational Linescan System (DMSP-OLS)
10
and later from Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band (DNB) data
11
,
12
, have been instrumental in mapping long-term ALAN trends
2
, documenting the expansion of urban extent
13
and estimating the light pollution effects
1
. Monthly VIIRS DNB products subsequently improved temporal granularity, enabling analyses of intra-annual variability
14
, such as seasonal impacts
15
and epidemiological dynamics
16
. However, despite these strengths, temporal aggregation inherently masks short-term fluctuations and the bidirectional changes arising from the coexistence of brightening and dimming.
In reality, human activities and the resulting changes in ALAN are not uniform, linear or steady processes. They operate across a spectrum of timescales, ranging from gradual shifts such as suburban expansions or LED adoptions to discrete, abrupt events such as industrial constructions, changes in municipal lighting codes, power outages triggered by disasters and the disruptions of infrastructure or destructions of buildings due to armed conflicts
17
,
18
,
19
,
20
. Focusing only on the net change derived from temporal composites masks the specific timing and impacts of these incidents. This oversight limits our ability to truly link cause and effect, assess policy effectiveness with precision, and understand the full ecological implications of a rapidly changing nocturnal environment.
More recently, advances in NASA’s daily Atmospheric- and Lunar-BRDF (bidirectional reflectance distribution function)-corrected Black Marble NTL product
3
have provided an unprecedented opportunity to quantitatively characterize the finer daily night-time light dynamics of Earth. Unlike earlier nightlight products that primarily served visualization or coarse trend analysis, Black Marble applies comprehensive corrections for atmospheric conditions, terrain and l

---

## Expert Analysis

### Merits
- This evidence of increasing volatility in human night-time activity provides an important dynamic dimension for understanding urban evolution, energy transitions, policy impacts and ecological consequences of rapidly changing illuminated nights.
- Understanding the direction, location and intensity of these changes is, therefore, important for assessing the full scope of global change and its impact on human infrastructure and energy transitions 7 .
- Unlike earlier nightlight products that primarily served visualization or coarse trend analysis, Black Marble applies comprehensive corrections for atmospheric conditions, terrain and lunar illumination to improve radiometric stability, and at the same time provides information on the contaminated pixels, such as clouds and snow 21 .
- This study presents the first comprehensive global analysis of ALAN change dynamics derived from daily Black Marble NTL data.

### Areas for Consideration
- Our findings challenge the prevailing perspective that changes in light radiance are largely gradual and unidirectional.

### Implications
- Download PDF Subjects Environmental impact Interdisciplinary studies Optical sensors Abstract Artificial light at night (ALAN) marks the global impact of humanity 1 , 2 .
- Here, using daily night-time satellite imagery 3 and a continuous change detection approach 4 , 5 , we created global maps of high-frequency ALAN dynamics (2014–2022).
- On average, each location experiencing change underwent 6.6 distinct shifts over the 9 years.
- Driven by this volatility, the cumulative area of total ALAN change comprised 2.05 million km 2 of abrupt changes and 19.04 million km 2 of gradual changes.

### Expert Commentary
This article covers changes, change, alan topics. Notable strengths include discussion of changes. Areas of concern are also raised. Readability: Flesch-Kincaid grade 0.0. Word count: 2273.