What is Global Dimming ?

Global Dimming v/s Global Warming

Global Dimming is something people are totally unaware of. But it is something that needs an equal attention just as much as Global Warming (Read more about Global Warming and reasons leading to Global warming).

Global dimming is the slow and gradual reduction in the amount of direct global irradiance that is reaching the earth’s surface. In simple terms Global dimming refers to the reduction in direct sunlight reaching the surface of earth due to air pollution. It is a phenomenon that has been observed since the 1950s which has been concluded thus through systematic measurements. The causal effects have mostly been location based but it is observed as a worldwide phenomenon. But the observations have shown that there has been a reduction of around almost 4% in the thirty years from 1960 – 1990. This trend that was observed was slightly perturbed by the eruption of Mount Pinatubo volcano in the year 1991 which reversed this.

As goes by the word of ‘dimming’ it means something completely opposite of ‘warming’. It is the phenomenon responsible for letting the temperatures still being in control even when Global Warming has taken its own toll on the climatic phenomenon all over the world. Global Dimming is the answer to all the questions about the freaks of nature and the entire unnatural phenomenon that we might observe in our weather. Global dimming is exactly the opposite of Global Warming. Global dimming has influenced and interfered with the hydrological cycle causing total disruption in the normal functioning of this system. It has led to reduction in evaporation which has consequently affected the amount of precipitation in many areas. This has caused cooling effect which has counteracted upon the heightened effects of global warming caused by greenhouse gases (Read more about Greenhouse Gases and their sources).

The very reason that Global Dimming is the other side of the coin for Global Warming is that the factors which cause global warming are responsible for causing global dimming as well. Aerosols that lead to trapping of the greenhouse gases and then making the atmosphere warmer also makes the incoming solar radiations reflect back into the atmosphere and thus reducing the solar radiation lessen reaching the earth surface. It is thought that the particulate materials like sulfate aerosols that are produced by the anthropogenic reasons are the factors leading to cause global dimming. Had it not been because of global dimming being able to exist on earth for global warming would have been impossible.

Causes and Effects of Global Dimming

Global Dimming is believed to have been caused due to the increased presence of aerosol particles which has increased in the atmosphere due to the incautious anthropogenic actions.

The cycle of Global Dimming starts as the aerosols and other Suspended Particulate Matter (SPM) absorb the solar irradiation & energy and reflect this sunlight back into outer space again.
This way the direct solar irradiance is hindered to enter the earth’s atmosphere. These ‘SPMs’ sometimes become nuclei for cloud droplets in which water in the clouds then coalesce around these particles. With the increasing pollution in the world this particulate matter is prevailing more in the atmosphere. These are creating more clouds which consist of a larger number of smaller droplets. This causes the same amount of water to be distributed among more number of particulate materials. These smaller droplets are more reflective in nature. They reflect back the incoming solar radiation into space and lesser amount is able to reach the Earth’s surface thus.

Even in the lower atmosphere this process takes place causing reflections and consequently smaller droplets invariably to reduce the amount of rainfall.Clouds act as an intercept for trapping the heat that is radiated from the earth and also the incoming solar radiation.This effect is complex which is variable as per the location, time as well as the altitude. As during the daytime the incoming solar radiation is intercepted more there is a predominance of this phenomenon during this time causing relative cooling.

Whereas, at night the re-radiation of heat from the earth’s surface getting trapped helps in maintaining the heat balance which might have fallen drastically without it.

Throughout this whole discussion it might be obvious that global dimming is the solution to global warming. But think again! The particulate matter that is causing global dimming is inversely responsible for global warming as well. The only solution to both is the reduction of aerosol particles itself and thus gaining back the originality of the climatic system and restoring is to its previous form.

Read More:
Social effects of Global warming
Environmental impact of Climate Change

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