The greenhouse effect is caused by certain gases in the Earth`s atmosphere trapping heat from the sun, which leads to an increase in the planet`s overall temperature. This is why option 2, "temperature of earth is increasing," is the correct answer. Greenhouse gases such as carbon dioxide and methane accumulate in the atmosphere and prevent some of the heat from escaping back into space. As a result, the Earth`s surface becomes warmer over time. This phenomenon is known as global warming. It is important to note that while some regions may experience temporary drops in temperature due to various weather patterns, the overall trend is an increase in the Earth`s temperature due to the greenhouse effect.