Global dimming

Gocart sulfate optical thickness

Julsrud 2022 dimming

SulufrDioxide2017

Bellouin 2019 smoke albedo effects

Aerosol dimming

Global dimming is a phenomenon that refers to the gradual reduction in the amount of global direct irradiance at the Earth's surface, observed since the beginning of systematic measurements in the 1950s. The effect varies by location but is estimated to have led to a dimming of approximately 4% between 1960 and 1990. Global dimming is thought to be caused by an increase in particulates such as sulfate aerosols in the atmosphere due to human action.

Causes

The primary cause of global dimming is believed to be the increase in particulate pollutants such as sulfate aerosols, black carbon, and other air pollution particles that reflect sunlight back into space before it reaches the Earth's surface. These particles, or aerosols, can also affect the properties of clouds. Aerosols and other particulates absorb some of the outgoing long-wave radiation and reflect sunlight, which can lead to cooling of the surface. The main sources of these aerosols are the burning of fossil fuels, biomass burning, and industrial processes.

Effects

Global dimming has several implications for the Earth's climate and ecosystems. By reducing the amount of solar radiation reaching the surface, it can lead to cooler surface temperatures in some regions and can affect weather patterns. For example, it has been linked to reduced evaporation and may have contributed to the reduction in rainfall observed in some parts of the world during the late 20th century. This can have significant impacts on water resources and agriculture, potentially leading to crop failures and famine.

Moreover, global dimming can mask the full effect of global warming caused by increased levels of greenhouse gases in the atmosphere. The cooling effect of dimming may have offset some of the warming, leading to an underestimation of the impact of greenhouse gases on climate change.

Mitigation and Reversal

Efforts to reduce air pollution have led to a partial reversal of global dimming since the 1990s. For instance, the introduction of cleaner technologies and stricter environmental regulations in many countries has reduced the emissions of particulate pollutants. This has led to what is sometimes referred to as "global brightening," where the amount of solar radiation reaching the Earth's surface is increasing again.

However, while improvements in air quality are beneficial for human health and the environment, they may also lead to an acceleration in the rate of global warming by reducing the masking effect of global dimming.

Research and Monitoring

Ongoing research and monitoring are crucial to understanding the complex interactions between global dimming, global warming, and the Earth's climate system. Scientists use a variety of tools, including satellite observations, ground-based measurements, and climate models, to study these phenomena and predict their future impacts.

Conclusion

Global dimming is a significant but often overlooked aspect of climate change. While efforts to reduce air pollution are crucial, they also highlight the need for comprehensive strategies to address the broader challenges of climate change, including reducing greenhouse gas emissions and adapting to the changing climate.