5Dec19 SS Q39
- Option : B
- Explanation : Without the greenhouse effect, the Earth's average temperature would be around -18 or -19 degrees Celsius (0 or I degree Fahrenheit). Earth would be locked in an ice age. Because of the greenhouse effect, the Earth's actual average temperature is 14 degrees Celsius (57 degrees Fahrenheit). The gases in the atmosphere that absorb radiation are known as "greenhouse gases" (sometimes abbreviated as GHG). The most significant greenhouse gases are water vapour (H20), carbon dioxide (C02), methane (CH4) and nitrous oxide (N20), according to the Environmental Protection Agency (EPA). The Earth's climate has changed throughout history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 11,700 years ago marking the beginning of the modern climate era - and of human civilization.
