Dan Kulpinski

Two recent reports put 2007 as either the second-warmest year in the last century, or the fifth-warmest. Either way, 2007 was part of a trend of warm years — a trend that has seen the rate of warming triple in recent decades.

The studies were done separately by NASA and the National Oceanic and Atmospheric Administration (NOAA). Each reviewed the same data for land and ocean surface temperatures worldwide. NASA concluded that 2007 was tied for the second-warmest year; NOAA put it at the fifth-warmest.

The two agencies analyzed the data slightly differently. NOAA spokesman John Leslie explained to me via e-mail that the main difference is how the agencies treat areas on the globe that lack temperature recording stations, such as part of the Arctic region. NASA estimates a value for any point on the globe that is within 1200 km of a temperature recording station; NOAA does not. NASA says that temperature anomalies and trends are highly correlated over large geographical distances. (See reference) I believe the differences between the two agencies’ measurements are small.

Because the top five warmest years are within 9/100 of a degree of each other (per NOAA’s data table “Global Top 10 Warm Years“), where 2007 falls on this list is inconsequential. What is important, however, is that nine of the 10 warmest years on record occurred in the last 11 years — and that the rate of temperature increase per decade has tripled during the last 25 to 30 years. (In NOAA’s words, “During the past century, global surface temperatures have increased at a rate near 0.05°C/decade (0.09°F/decade), but this trend has increased to a rate of approximately 0.15°C/decade (0.27°F/decade) during the past 25 to 30 years.” [from the Climate of 2007 Annual Report])

At this rate, the average global temperature will rise one degree F about every 40 years.

The Intergovernmental Panel on Climate Change predicts a slightly faster rate for the next two decades of about .36 degree F per decade, which would raise temps by one degree F in 30 years.

In terms of land temperatures alone, 2007 was the warmest year since record-keeping began in 1880.

Other interesting tidbits from the reports:

• The 15 named tropical storms in the Atlantic Basin last year were four more than the long-term average. Two Category 5 hurricanes, Dean and Felix, hit Mexico and Nicaragua, respectively. It was the first time two Category 5 hurricanes
  made landfall in the Atlantic Basin in the same season.
• Warming was greatest in the Arctic and neighboring regions at high latitudes.
• The average temperature for the contiguous United States in 2007 was the 10th-highest on record, at 54.2 degrees F. This was 1.4 degrees F above the 20th-century mean.
• Temps in the contiguous United States have risen at a rate of nearly 0.6 degrees F per decade during the last three decades.

Temperature Anomalies: This graph from the National Climatic Data Center shows temperature anomalies through 2007. It portrays how much colder or warmer each year was, compared to the average temperature for the 20th century.