During the past century,the temperature of the Earth has increased by $......$. (in $^{\circ}C$)

The current average temperature of the Earth is $...i...$. If the greenhouse effect were absent,the temperature of the Earth would have been $...ii...$.

Which of the following is not a greenhouse gas?

What is the effect of greenhouse gases?

What will be the environmental consequence of a $25\%$ increase of $CO_2$ level in our atmosphere?

Gases referred to as 'greenhouse gases' are