09 Feb 2018

Global Dimming

Posted in Miscellaneous By attemptnwin On February 9, 2018

Global dimming is the process which causes reduction of heat reaching the earth. Global warming is caused by greenhouse gases produced by fossil fuels. Burning of fossil fuels produce some by-products also that lead to global dimming. Such by-products like Sulphur dioxide, soot, ash etc are the root cause of global dimming. Global dimming is exactly opposite to global warming.

What causes global dimming?

Formation of cloud happens when air-borne particles like pollen seed water droplets in atmosphere. Polluted air forms clouds with bigger droplets compared to unpolluted air. The presence of clouds with bigger droplets leads to more reflection leading most of the Sun’s energy and heat getting reflected back into space. This results in global dimming.

What are the impacts of global dimming?

Global dimming came to notice in 1950. Since then, it is estimated that Sun’s energy reaching earth has dropped by around 1% in Antarctica, 10% in US, 16% in Europe, and about 30% in Russia. The average reduction is estimated to be in the range of 22%. Global dimming can lead to severe environmental risks. After 2005, northern hemisphere has witnessed significant reductions to the tune of around 8%. The condition in parts of Europe and North America has improved. But the condition in parts of China and India has deteriorated.

What is the role of aerosols in global dimming?

Burning of fossil fuels by vehicles and industry releases the bye products like Sulphur dioxide, soot, ash etc . They constitute pollutant particles termed aerosols. These aerosols contribute to global dimming in two ways.
1. Aerosols entered in the atmosphere directly absorbs Sun’s energy and reflect radiation back into space.
2. They form water droplets leading to formation of clouds with bigger droplets called brown clouds.

Apart from the by-products released from earth, vapours emitted by planes flying high in the sky (contrails) also support reflection of light and energy.

What are the side effects of global dimming?

Due to global dimming, water in the norther hemisphere has become colder leading to slower evaporation and generation of less water droplets. This affects the quantum of rain reaching certain parts of the globe finally leading to drought and famine. Global dimming also causes heat waves and runway fires.

Sulphur dioxide, soot, ash etc present in aerosols sometimes lead to acid rain, smog, and respiratory diseases in humans.

Global warming is caused by trapping of infrared radiations by certain gases and leads to warming while effect while global dimming results in cooling effect. The solution for controlling both effects is same; reduce emission of greenhouse gases and aerosols by judicious use of fossil fuels.