Cold and Health

Abstract

In temperate climates, winter is the coldest season of the year (Fig. 10.1). In the winter solstice that starts on December 21, in the Northern Hemisphere, the days are the shortest and the nights are the longest, with the days getting increasingly longer until the advent of the spring equinox between March 20 and 22, when day and night are equal. The inclination of the Earth’s axis relative to its orbital plane plays a big role in the weather. Earth is inclined at an angle of 23.44° with respect to the orbital plane. Movement of the Earth in its orbit causes different latitudes on Earth to be directly exposed to the Sun. In fact, this change affects the occurrence of seasons. During the winter in the Northern Hemisphere, the Southern Hemisphere is directly inclined toward the Sun, and therefore the temperature is higher than in the Northern Hemisphere. In contrast, winter in the Southern Hemisphere occurs when the Northern Hemisphere is tilted more toward the Sun. The Sun in winter in both hemispheres is found at a lower altitude. This causes the sunlight to fall at a diagonal angle. Thus, in winter, the same amount of solar radiation is spread over a larger area. In addition, the light must pass through more atmosphere, allowing the atmosphere to lose more heat. Meteorologists often define winter as a period that consists of three calendar months with the lowest average temperatures. It corresponds to the months of December, January, and February in the Northern Hemisphere and June, July, and August in the Southern Hemisphere (Tiina et al. 2020; Patz et al. 2000).