Night-time warming and the greenhouse effect

Studies of temperature data collected mainly from rural stations in North America, China, the Commonwealth of Independent States, Australia, Sudan, Japan, Denmark, Northern Finland, several Pacific Islands, Pakistan, South Africa and Europe suggest that the reported warming of the Northern Hemisphere since WWII is principally a result of an increase in night-time temperatures. The average monthly maximum and minimum temperatures, as well as the mean diurnal temperature range (DTR), were calculated for various regions from data supplied by 1000 stations from 1951 to 1990. Average and minimum temperatures generally rose during the analysed interval and the rise in night-time temperatures was more pronounced than the increase in daily maximum temperatures. As a result, the mean DTR decreased almost everywhere. The most probable causes of the rise in night-time temperatures are: an increase in cloudiness owing to natural changes in the circulation patterns of oceans and the atmosphere; increased cloud cover density caused by industrial pollution; urban heat islands, generated by cities, which are strongest during the night; irrigation which keeps the surface warmer at night and cooler by day; and anthropogenic greenhouse gases. 18 refs., 3 figs