2007 second warmest year on record
With the record for 2007 now complete, it is clear that temperatures around the world are continuing their upward climb. The global average in 2007 was 14.73 degrees Celsius (58.5 degrees Fahrenheit)—the second warmest year on record, only 0.03 degrees Celsius behind the 2005 maximum. January 2007 was the hottest January ever measured, a full 0.23 degrees Celsius warmer than the previous record. August was also a record for that month and September was the second warmest September recorded. Looking at the northern hemisphere alone, 2007 temperatures averaged 15.04 degrees Celsius (59.1 degrees Fahrenheit)—easily the hottest year in the northern half of the globe since the record began in 1880, and more than a degree warmer than the 1951–80 average. Paleo-temperature records from ancient tree rings suggest that the northern hemisphere is now warmer than at any time in at least the last 1,200 years. The year 2007 fits into a pattern of steadily increasing global average temperature, with the eight warmest years on record all occurring in the last decade. According to the dataset maintained by NASA’s Goddard Institute for Space Studies, global average temperature rose from 14.02 degrees Celsius in the 1970s to 14.26 degrees in the 1980s and then to 14.40 degrees in the 1990s. In the first eight years of the twenty-first century, the world averaged 14.64 degrees Celsius. Since 1990, mean global temperature has risen by 0.33 degrees, a rate of increase faster than climate models had predicted. Although 2007 did not post a new record high, the year stands out as being extremely warm despite several natural factors that usually cool the planet. El Niño conditions in the southern Pacific tend to increase the global average temperature, and yet the second half of 2007 saw the opposite develop—a La Niña, which would usually depress global temperature. This is in stark contrast to conditions in 1998, the third warmest year, when temperatures were boosted around 0.2 degrees Celsius by the strongest El Niño of the century. In addition to the moderate La Niña, solar intensity in 2007 was slightly lower than average because the year was a minimum in the 11-year solar sunspot cycle. The combination of these factors would normally produce cooler temperatures, yet 2007 was still one of the warmest years in human history. This strongly suggests that the warming effect of increased greenhouse gas concentrations is now dwarfing other influences on the Earth’s climate.