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बेसिक इंग्लिश का दूसरा सत्र (कक्षा प्रारंभ : 22 अक्तूबर, शाम 3:30 से 5:30)
Global dimming
Apr 29, 2015


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.

Scientists are now worried that dimming, by shielding the oceans from the full power of the Sun, may be disrupting the pattern of the world's rainfall. There are suggestions that dimming was behind the droughts in sub-Saharan Africa which claimed hundreds of thousands of lives in the 1970s and 1980s. There are disturbing hints the same thing may be happening today in Asia, home to half the world's population.

But perhaps the most alarming aspect of global dimming is that it may have led scientists to underestimate the true power of the greenhouse effect. They know how much extra energy is being trapped in the Earth's atmosphere by the extra carbon dioxide (CO2) we have placed there. What has been surprising is that this extra energy has so far resulted in a temperature rise of just 0.6°C.

This has led many scientists to conclude that the present-day climate is less sensitive to the effects of carbon dioxide than it was, say, during the ice age, when a similar rise in CO2 led to a temperature rise of 6°C. But it now appears the warming from greenhouse gases has been offset by a strong cooling effect from dimming - in effect two of our pollutants have been cancelling each other out. This means that the climate may in fact be more sensitive to the greenhouse effect than thought.

Causes of Global Dimming

Dimming appears to be caused by:
♦ Air pollution.
♦ Burning coal, oil and wood,
♦ Vapors emitted from the planes flying high in the sky called contrails are another cause of heat reflection and related global dimming.

This visible air pollution reflects sunlight back into space, preventing it reaching the surface. But the pollution also changes the optical properties of clouds. Because the particles seed the formation of water droplets, polluted clouds contain a larger number of droplets than unpolluted clouds. Recent research shows that this makes them more reflective than they would otherwise be, again reflecting the Sun's rays back into space.

Effect of Global Dimming

  • Global dimming is thought to have had a number of substantial impacts. For example, there is evidence to suggest it has masked part of the historical warming caused by greenhouse gases. Indeed, areas that have undergone brightening have seen rapid warming.

  • 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.

  • 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.

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