Last updated August 25, 2025

Global Dimming: A Dangerous Respite in the Climate Crisis

A poorly understood atmospheric phenomenon

Global dimming is a little-known climatic phenomenon among the general public, yet it is crucial for understanding the climate crisis. Global dimming is the gradual reduction in the amount of solar radiation reaching the Earth's surface, observed between the 1950s and 1990s. This phenomenon is caused by aerosols and particles from the combustion of coal, oil, and gas. These particles scatter and reflect solar radiation, thus reducing the incident flux \(\Phi\) measured in \(\mathrm{W/m^2}\).

An effect that masks warming

The screening effect of aerosols temporarily offset some of the warming due to greenhouse gases. Estimates suggest that, without this dimming, the increase in average temperature would already have exceeded \(+1.5^\circ\mathrm{C}\). However, the gradual reduction of atmospheric pollutants, particularly in Europe and North America, has led since the 1990s to a reversal of the phenomenon called "brightening."

Comparative impact of global dimming and global warming
Phenomenon	Radiative forcing (W/m²)	Main effect	Recent evolution
Greenhouse gases (CO₂, CH₄, N₂O)	+3.0 ± 0.3	Global warming	Continuous increase
Aerosols (direct effect)	-0.5 ± 0.4	Surface cooling	Stable or slight decrease
Aerosols (indirect effect on clouds)	-0.7 ± 0.7	Increased cloud albedo	Variable by region
Global dimming (total)	-1.2 ± 0.8	Reduction in surface sunlight	Decreasing in some regions

Source: IPCC, AR6 Report, Working Group I and Nature, Vol 597, pages 31-35 (2021).

Hydrological and agricultural consequences

The decrease in solar radiation has had notable effects on the water cycle. Studies have shown a weakening of the Asian monsoon and a reduction in evapotranspiration. In agriculture, this decrease in photosynthesis has sometimes reduced yields, although the complexity of climate systems makes correlations difficult to isolate.

Comparison of impacts related to global dimming
Aspect	Observed effect	Mechanism	Comment
Average temperature	Apparent reduction in warming	Scattering and reflection of solar radiation by aerosols	Can mask the true intensity of radiative forcing due to CO₂
Precipitation	Regional changes in rainfall cycles	Increased formation of condensation nuclei and altered cloud dynamics	Promotes droughts in some areas and intense rains elsewhere
Air quality	Health degradation	Presence of sulfated aerosols and fine particles	Increases respiratory and cardiovascular risks for populations
Future climate	Delayed warming effect	Temporary masking of heat accumulation by greenhouse gases	Rapid cleaning of the atmosphere could cause a sudden temperature rise

The paradox of global dimming

Understanding global dimming is crucial for developing effective climate strategies. A too rapid reduction in aerosol emissions without parallel control of greenhouse gases could lead to a dangerous "climate rebound" with a sudden acceleration of warming.

Global dimming represents a complex climate paradox: a phenomenon harmful to health and ecosystems that temporarily masks the true extent of global warming. Its understanding is essential to anticipate future climate developments and to develop coherent environmental policies. As we strive to improve air quality, we must simultaneously intensify our efforts to reduce greenhouse gas emissions, or risk seeing the climate crisis accelerate abruptly.