Tag Archives: Environment

Why is the sky dull when a storm is coming on?

The light of day is almost all due to the Sun. The stars are shining, of course, as they do all the time, but they are so far away that the light of all of them put together counts for nothing compared to the light of the Sun; nor does the light of the Moon count for anything when it happens to be up during the day. Thus we may say that the light of the day is due to direct sunlight and to skylight, which is sunlight reflected from the sky – that is to say, from the air.

When a storm is coming on, clouds gather, and these clouds are thick and dense, so that they cut off the light of the sky, and so we say that the sky is dull. If we went up in a balloon above the clouds, we should find ourselves in brilliant sunshine, even when it was almost as dark as night to the people of the Earth below.

More reading:
Thunderstorm (Wikipedia)

Why the composition of atmosphere is so specific and steady with 21% oxygen and 78% nitrogen?

Nobody knows for sure, but you should surely thank your luck for the kind of air mixture you have been provided with by natural processes that took place long in the past.

Consider this: If the abundance of oxygen was any greater, all life would be at risk. The probability of forest fire increases by 70 percent for each 1 percent rise in oxygen concentration above the present level. If it formed 25% of the air instead of 21% now, oxygen would leave all land vegetation in raging conflagration. Everything from the driest Arctic tundra to the wettest tropical rain forest would burst into flame. And if the level of nitrogen, which is largely responsible for air pressure, were to fall to 75% from its present level of 78%, our planet would enter ice-age – possibly permanent.

It seems that the present equilibrium between blow hot and blow cold is nothing less than a miracle.

Additional reading:
Atmosphere of Earth (Wikipedia)

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Why do clouds float in the sky even though they have tons of water in them?

Clouds are the visible part of a continuous cycle in which water evaporates into the air, condenses and returns to Earth mostly as rain. The cycle starts when the Sun warms the Earth, which in turn, warms pockets of moist air. When an air pocket heats up, its molecules bounce around more actively and begin to take up more space. As a result, the air expands and becomes less dense. The surrounding heavier air then pushes its way underneath the warm pocket, which rises like a hot-sir balloon.

Only when the water condenses does it become visible, and when enough droplets condense, they form a cloud. Clouds can grow to vast proportions if enough air is heated. A thunderhead can tower up to 12 kilometers high, and half a million tons of water can be released in a single downpour. Clouds stay aloft because the droplets are so tiny that they remain suspended on air currents. Each mist particle is minuscule – only one millionth the mass of a final raindrop. They do not have any appreciable fall velocity and most of them continue to float with the surrounding air. Sometimes the larger particles drop out of the cloud, only to evaporate and be swept up again. At other times they leave the sides of the cloud to be replaced by water vapor from below, which condenses as tiny droplets. So there is no perceptible change in the cloud’s shape as well as size. The mass of water the cloud holds also remains more or less the same.

What makes this great mass float in the air is its relative lightness compared to the mass of air in which it resides. Take an example of a small cloud at an altitude of some 3,000 meters. Assume that it occupies a volume of 1 cubic kilometer and there is a 1 gram droplet per cubic meter. The total mass of these water particles would be about 1,000 tons, whereas the mass of the air in that same cubic kilometer would not be less than 1,00,000 tons. The heavier air keeps the cloud buoyant.

Additional reading:
Cloud (Wikipedia)

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To what extent the sea level would rise if all the icecaps in the world melt due to Greenhouse Effect and the global warming?

No one knows for sure, but some estimates have been made and they are largely focused on Antarctica. The Arctic on the other end is not a major cause of worry, because there is no icecap as such and its ice floats on the Arctic Ocean. If it is melted, the sea levels would not be affected. In the case of Antarctica, the largest ice-covered landmass with about 90% of the world’s ice, the results for the mankind would be disastrous. This frozen continent’s ice has an average thickness of 2,133 meters. If all of it melts, sea levels around the world are likely to go up by about 61 meters. Then, of course, there is Greenland which would add another 7 meters or so to the sea levels. The levels could go further up by 2 meters as the mountain ranges like the Andes, Himalayas, and Alps are striped bare.