Winter
The Earth tilts at an angle of 23.44 degrees relative to its orbital plane. This specific tilt causes different latitudes to face the Sun directly as our planet moves through its yearly orbit. When winter arrives in the Northern Hemisphere, that half turns away from the Sun. Conversely, the Southern Hemisphere faces the Sun more directly during this time and experiences warmer temperatures. The winter Sun maintains a lower maximum altitude in the sky compared to the summer Sun. Sunlight hits the Earth at an oblique angle during these months. A lower amount of solar radiation strikes each unit of surface area. Light must travel a longer distance through the atmosphere before reaching the ground. This allows the atmosphere to dissipate more heat. Changes in the Earth's distance from the Sun due to elliptical orbits have negligible effects on temperature variations.
Winnipeg, Canada, records January highs and lows that differ sharply from Vancouver, located on the west coast. Both cities sit at 49 degrees North latitude yet experience vastly different weather patterns. Marine winds from the Pacific moderate temperatures in Vancouver while landlocked conditions create extreme cold in Winnipeg. Meteorologists define winter as the three calendar months with the lowest average temperatures. In the Northern Hemisphere this covers December, January, and February. The Southern Hemisphere observes June, July, and August as their coldest months. Ancient Indo-European cultures divided the year into just two seasons: winter and summer. The Julian calendar used in ancient Rome marked winter beginning on the 10th of November. Midwinter occurred on the 25th of December when the solstice fell. Christian Anglo-Saxon calendars started winter on the 7th of November and ended it on the 6th of February. Bede described an older system where winter began at the full moon during Winterfylleth in October. Martinmas on the 11th of November signaled the start of winter for many Germanic regions. Celtic nations celebrated Samhain on the 1st of November as the beginning of the season. Norsemen opened winter with Winter Nights between 9 and the 15th of October. Chinese astronomy marks Lìdōng around the 7th of November as the commencement of winter.
The snowshoe hare changes its fur color to white to match the surrounding snow. This camouflage allows the animal to retain cryptic coloration throughout the year. Gophers, frogs, snakes, bats, and bears enter a state of reduced metabolic activity known as hibernation. Squirrels, beavers, skunks, badgers, and raccoons store food instead of sleeping through the cold. Rock ptarmigans, Arctic foxes, weasels, white-tailed jackrabbits, and mountain hares all grow white coats. Mice and voles live under the insulating layer of snow. Annual plants may never survive the harsh conditions but some require winter cold to complete their life cycle. Perennial trees let their upper parts go dormant while roots stay protected by snow. The flowering plum blooms in time for Chinese New Year as an exception to typical blooming patterns. Trappers sought heavier winter coats from fur-coated mammals because they were more profitable during these months.
The Great Frost of 1683 froze the River Thames all the way up to London Bridge. Ice reached about two feet thick in London and three feet thick in Somerset. The sea froze out around the coast of the southern North Sea causing severe shipping problems. The Irish famine of 1740, 1741 claimed at least 300,000 lives following one of the most severe winters on record. Mount Tambora erupted in Indonesia in April 1815 creating the Year Without a Summer. Frost formed in May in New England killing newly planted crops. Snow fell in New York and Maine in June while ice formed in lakes and rivers in July. Agricultural crops failed across much of the Northern Hemisphere resulting in food shortages. The Little Ice Age began between 1310 and 1330 with many severe winters and cold wet summers. This period lasted until about 1900 and caused great hardship globally. The persistently cold weather contributed to the Great Famine of 1315, 1317. Malnutrition weakened immunity leading up to the Black Death which struck between 1348 and 1350.
Slipping on icy surfaces causes common winter injuries throughout temperate zones. Shivering leads to uncoordinated movements and can result in death from hypothermia. Freezing skin causes frostbite leading to loss of feeling and damaged tissue. Trench foot results in numbness causing damaged tissue and potential gangrene. Capillary damage in digits creates chilblains as another form of cold injury. Rates of influenza increase significantly during the winter months. COVID-19 transmission also rises when temperatures drop. Respiratory diseases show higher outbreak frequencies in colder seasons. Humans compromise their body's ability to maintain core heat during extreme cold. Surface heat regulation fails under prolonged exposure to freezing conditions.
Common questions
What causes winter to occur in the Northern Hemisphere?
Winter occurs when the Earth tilts 23.44 degrees relative to its orbital plane and turns away from the Sun. This tilt causes sunlight to hit the surface at an oblique angle, reducing solar radiation per unit area.
When does winter begin according to the Julian calendar used in ancient Rome?
The Julian calendar marked winter beginning on the 10th of November. Midwinter occurred on the 25th of December when the solstice fell within that system.
Which animals enter hibernation during winter months?
Gophers, frogs, snakes, bats, and bears enter a state of reduced metabolic activity known as hibernation. Snowshoe hares change their fur color to white to match surrounding snow for camouflage.
How did the Great Frost of 1683 affect London and the River Thames?
The Great Frost of 1683 froze the River Thames all the way up to London Bridge with ice reaching about two feet thick in London. The sea froze out around the coast of the southern North Sea causing severe shipping problems.
What health risks are associated with extreme cold exposure?
Freezing skin causes frostbite leading to loss of feeling and damaged tissue while trench foot results in numbness causing potential gangrene. Shivering leads to uncoordinated movements and can result in death from hypothermia.