Clouds have been undergoing a significant change in recent years, becoming darker and reflecting less sunlight due to a decrease in sulphate air pollution. This shift in cloud properties has led to additional warming beyond what is caused by greenhouse gases, according to researchers at the University of Exeter in the UK.
Peter Cox, a climate scientist at the University of Exeter, highlights that two-thirds of the global warming since 2001 can be attributed to the reduction in sulphur dioxide (SO2) emissions rather than an increase in carbon dioxide (CO2) levels. While rising CO2 levels trap radiant heat and contribute to the greenhouse effect, the planet’s albedo, or reflectivity, also plays a crucial role in regulating its temperature.
Since 2001, satellite instruments known as CERES have been monitoring the balance of reflected sunlight versus absorbed sunlight. These measurements have revealed a decline in the planet’s albedo, indicating that it is becoming darker and, consequently, experiencing additional warming. The main factor behind this decline in albedo appears to be the darkening of clouds, as observed in the analysis of CERES data from 2001 to 2019 by Cox and Margaux Marchant.
Sulphate pollution from industrial activities and ships has historically increased the reflectivity of clouds by enhancing the density of droplets. However, recent efforts to reduce sulphate emissions, particularly by transitioning away from high-sulphur fuels like coal, have resulted in a decline in cloud brightness. Marchant and Cox’s analysis suggests a correlation between the decrease in cloud brightness and regions with reduced SO2 pollution levels.
This finding is significant because it indicates that the recent acceleration in global warming may be primarily driven by the decrease in air pollution rather than a feedback loop caused by rising CO2 levels. Laura Wilcox, a climate scientist at the University of Reading, acknowledges the limitations of the datasets used in the study but agrees that the reduction in air pollution is likely a temporary driver of global warming.
While ongoing research is still needed to fully understand the complex dynamics of cloud properties and their impact on climate change, the evidence suggests that addressing air pollution can have a positive effect on mitigating global warming. The findings offer hope that efforts to reduce sulphate emissions and improve air quality can help counteract the effects of climate change in the long run.
