The correct answer is option-1: Earth is tilted towards the sun in the Northern Hemisphere.

The tilt of the Earth`s axis is responsible for the changing seasons. During winter, the hemisphere tilted away from the sun receives less direct sunlight, which leads to colder temperatures. In the Northern Hemisphere, winter occurs when it is tilted away from the sun, while in the Southern Hemisphere, winter occurs when it is tilted towards the sun.

Option-2 is incorrect as the amount of sunlight received is not the cause of the severity of winters in the Southern Hemisphere. Option-3 is also incorrect as iceberg activity does not directly influence the severity of winters. Option-4 does not have any direct relation to the severity of winters.