Why do so many people commit suicide in the happy Nordic countries?

In April 2015, the United Nations released a global happiness index report. Five Nordic countries (Denmark, Finland, Iceland, Norway and Sweden) account for half of the top ten. Why are Nordic people so happy? Because unhappy people have committed suicide. This joke cannot be said to be unreasonable. The flip side of the Nordic high happiness index is extremely high suicide rates, especially in Denmark and Finland, two countries that topped the global suicide list throughout the 20th century. It was not until the 1990s that they were surpassed by former Soviet member states. For example, Greenland, with more than 80% of its land covered by ice and snow and a permanent population of just over 50,000, had 1,351 suicides between 1968 and 2002, an average of 38 per year.

The improvement of the welfare systems of the five Nordic countries is well known. Why do so many people live happy lives? One of the most likely reasons is that the long, dark winters at high latitudes put people in a worse mood than ever before. Can weather really significantly affect people's moods? Big data has given a clear answer. In 2011, researchers at Cornell University analyzed 14 million tweets and found that people did express more positive emotions as the summer solstice approached than as the winter solstice approached.

As early as the 1960s and 1970s, epidemiological surveys found that people living in high latitudes in the northern hemisphere had a higher chance of suffering from depression, which was strongly correlated with seasonal changes. Psychiatrist Rosenthal calls this phenomenon seasonal affective disorder. Rosenthal was a South African accustomed to the grassland climate of Johannesburg. After moving to the United States, he was very uncomfortable with the cold winter in New York.

The incidence of seasonal affective disorder is more significantly related to latitude. Only 1.4 percent of Florida's sunny beaches had the disease, compared with 9.9 percent on Alaska's ice and snow. Surveys in the Arctic Circle (69 degrees north latitude) show that the incidence rate in adult males is 14, while the incidence rate in females is as high as 19.