Question

state the ways by which carbon dioxide present in the air is removed

Answer 1

Carbon Sequestration is one of the best methods to remove carbon dioxide from air.
Oxygen from the atmosphere is combined with carbohydrates to liberate the stored energy. Water and carbon dioxide are byproducts. Notice that photosynthesis and respiration are essentially the opposite of one another. Photosynthesis removes CO2 from the atmosphere and replaces it with O2.

Answer 2

Carbon dioxide (CO2) is the 5th most abundant gas in the atmosphere and, together with water vapor, probably the best known of the greenhouse gases.

Most everyone agrees that human activities are causing the atmospheric concentration of carbon dioxide to slowly increase. We'll look at some of the experimental evidence in a moment.

Not everyone agrees however about the effect that increasing amounts of CO2 will have on the earth's energy budget and climate. The worry is that increasing greenhouse gas concentrations will strengthen the greenhouse effect and will cause the earth's surface to warm.

It is important to remember that the greenhouse effect isn't all bad, it has a beneficial side. You might refer to this as the natural greenhouse effect (i.e. one that has not been affected or influenced by human activities)

If the earth's atmosphere did not contain any greenhouse gases, the global annual average surface temperature would be about 0o F. That's cold enough and that's the average, there would be many locations much colder than that. The presence of greenhouse gases raises this average temperature to about 60o F and makes the earth a much more habitable place. So some warming is a good thing.

The concern is that increasing atmospheric greenhouse gas concentrations might cause some additional warming (and we rely on computer models to predict or estimate how much warming there will be). This alone might not sound like a bad thing. However even a small change in average temperature might melt polar ice and cause a rise in sea level which, at the very least, might pose an environmental threat to coastal areas. Warming might change weather patterns and bring more precipitation to some areas and prolonged drought to