2005 Hottest Year on Record

Joseph Florence

The year 2005 was the hottest on record. The average global surface temperature of 14.77 degrees Celsius (58.6 degrees Fahrenheit) was the highest since recordkeeping began in 1880. January, April, September, and October of 2005 were the hottest of those months on record, while March, June, and November were the second warmest ever.

In fact, the six hottest years on record have all occurred in the last eight years. After 2005, 1998 was the second warmest, with an average global temperature of 14.71 degrees Celsius. But there was an important difference between 1998 and 2005: the strongest El Niño of the past 100 years lifted the average 1998 temperature 0.2 degrees Celsius, whereas the record warmth last year was not buoyed by such an effect.

These readings, which come from the series maintained by NASA’s Goddard Institute for Space Studies, continue a trend of rising global temperatures. During the past century, temperatures rose 0.8 degrees Celsius (1.44 degrees Fahrenheit), 0.6 degrees of which occurred during the last three decades, a rate unprecedented in the last millennium. The average temperature of 14.02 degrees Celsius in the 1970s rose to 14.26 degrees in the 1980s. In the 1990s it reached 14.40 degrees Celsius. And during the first six years of this new decade, global temperature has averaged 14.62 degrees Celsius.

Rising temperatures are due primarily to the buildup of greenhouse gases in the atmosphere, particularly carbon dioxide (CO2) from the burning of fossil fuels. Once released into the atmosphere, CO2 traps heat that would otherwise escape back into space. Emissions of CO2 have been rising since the start of the Industrial Revolution in 1760, causing temperatures to climb.