Environment Magazine

Causes and Effects of Global Dimming

Posted on the 14 May 2013 by Rinkesh @ThinkDevGrow

What is Global Dimming?

Global dimming is defined as the decrease in the amounts of solar radiation reaching the surface of the Earth. The by-product of fossil fuels are tiny particles or pollutants which absorb solar energy and reflect back sunlight into the space. This phenomenon was first recognized in the year 1950. Scientists believe that since 1950, the sun’s energy reaching Earth has dropped by 9% in Antarctica, 10% in the USA, 16% in parts of Europe and 30% in Russia – putting the overall average drop to be at an enormous 22%. This causes high risk to our environment.

The critical issue of Global Dimming was first raised through a documentary called Horizon by BBC on 15 January 2005.

Sunset Global Dimming

Various regions observe different levels of global dimming. Till now, the Southern Hemisphere has seen very small amounts of global dimming while Northern Hemisphere has witnessed more significant reductions, to the tune of 4-8%.  Regions such as parts of Europe and North America has observed partial recovery from dimming while parts of China and India have experienced increase in global dimming.

Causes of Global Dimming

Earlier it was thought that changes in the sun’s luminosity cause global dimming but later it was realized that this was very small to explain the enormity of global dimming.

Aerosols have been found to be the major cause of global dimming. The burning of fossil fuels by industry and internal combustion engines emits by-products such as sulfur dioxide, soot and ash.  These together form particulate pollution—primarily called aerosols. Aerosols acts as precursor to global dimming in the following two ways:

  • These particle matters enter the atmosphere and directly absorb solar energy and reflect radiation back into the space, before it reaches the planet’s surface.
  • Water droplets containing these air-borne particles form polluted clouds. These polluted clouds have heavier and larger number of droplets. These changed properties of the cloud – such clouds are called ‘brown clouds’ – makes them more reflective.

Vapors emitted from the planes flying high in the sky called contrails are another cause of heat reflection and related global dimming.

Both global dimming and global warming have been happening all over the world and together they have caused severe changes in the rainfall patterns. It is also believed that it was global dimming behind the 1984 Saharan drought that killed millions of people in sub-Saharan Africa. Scientists believe that despite the cooling effect created by global dimming, the earth’s temperature has increased by more than 1 deg. in last century.  If global dimming wouldn’t have happened, the temperature of this planet would be much higher and could have posed a serious effect o the lives of humans, plants and animals.

Due to increase in the burning of fossil fuels and pollution from various other sources, the heat is getting trapped into the earth’s atmosphere. This heat has resulted in a marginal increase in earth’s temperature. This is due to the fact that warming from greenhouse gases is getting offset by cooling effect from global dimming.

Effects of Global Dimming

Global dimming has devastating effects on the earth’s environment and living beings. The pollutants causing global dimming also leads to acid rain, smog and respiratory diseases in humans.

Due to reflection of solar energy and global dimming, the water in the northern hemisphere has become colder. This leads to slower evaporation and generation of lesser water droplets. This further causes reduction in the amount of rain reaching certain parts of the globe, resulting in drought and famine situations.  This has tragic consequences like miserable lives and deaths due starvation.  It has now been determined that the drought and famine of The Sahel which has killed thousands of innocent people in sub-Saharan Africa during 1970s, was largely due to global dimming.  A growing concern is the impact of global dimming on Asian monsoons which cause 50% of the world’s annual rainfall. If this happens, then half of the world’s population will be starving.

Global dimming is also believed to cause heat waves and runaway fires. Also, decrease in sunlight or solar radiation will negatively impact process of photosynthesis in plants.

Global dimming is thought to be counteracting the actual effect of carbon emissions on global warming. So, if efforts are made to reduce particulate emission causing global dimming, it will enhance global warming and increase the global temperatures to more than double. This will make planet Earth, almost uninhabitable. To prevent this situation, it is important that emission of both greenhouse gases and particulate matter should be reduced simultaneously. This will balance out both the phenomena.

Global Dimming and Global Warming

Global warming and global dimming are opposite phenomena.

Global warming is defined as the increase in the atmospheric temperature. This largely caused by greenhouse gases (GHGs). Greenhouse gases produced from the burning of fossil fuels traps the infrared radiations. This heats up the earth’s atmosphere.

absence of sun

Global dimming is the exact opposite. Fine particles such as aerosols, also produced as the by-product of fossil fuels burning, reflect away sunlight. This decreases the amount of solar radiation entering our planet. It produces a cooling effect.

Though both are opposite phenomena with contrasting effects but both are destructive to the planet. It is due to both global warming and global dimming that earth’s temperature has increased less than what it should have been. Without global dimming, this planet would have turned to be too hot for all of us to survive. Both of them are dangerous and can prove fatal for our environment and need to be solved together. Solving each problem at a time could create conditions that may be harmful and may prove fatal for all of us.

Image credit: nonotmebob , 42809384@N08

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