The year 2005 was likely the hottest year in more than a century. According to a study by the NASA Goddard Institute for Space Studies (GISS) examining temperatures around the world, 2005 was either the warmest or tied for the warmest ever recorded. According to the GISS team, global warming is now 0.6°C (about 1°F) over the past 30 years, and 0.8°C (about 1.4°F) over the past 100 years.
The GISS team measured temperatures using records from land-based weather stations, and ship and satellite measurements of sea-surface temperature. This image shows temperature anomalies relative to the 1951-1980 mean. Areas of white indicate no deviation from the mean. Colors ranging from yellow to red indicate warmer-than-average anomalies, and colors ranging from green to purple indicate cooler-than-average anomalies. Most of the map shows warm colors, and temperatures are particularly warm in the Arctic and in south-central Africa. The high-resolution image shows both the temperature map and a line graph of global temperatures from 1880 to 2005.
All measurements have a range of uncertainty, including estimates of global temperature. The “real” average global temperature may be a little above or below the reported value. The range of uncertainty for 2005 temperatures overlaps with that of 1998, which means the two years are vying closely for the position of “warmest year on record.” Other research groups observing climate change place 1998 at the top of the temperature record, and the GISS team describes 2005 as “practically in a dead heat with 1998.”
Although these years were very close in temperature, they reached the top of the charts by different means. In 1998, the strongest El Niño in a century occurred. El Niños result in unusually warm temperatures in the eastern Pacific Ocean, and this warmth is significant enough to elevate overall global temperatures. No El Niño occurred in 2005, however, which means that 2005 reached the same record-high temperature as 1998 without the aid of an El Niño.
In early 2006, James Hansen, director of NASA GISS, pointed out that five of the warmest years over the last century were in the previous eight years: 1998, 2002, 2003, 2004, and 2005. Moreover, the GISS team states, “It is no longer correct to say that ‘most global warming occurred before 1940,’ ” an argument sometimes made by those who are skeptical of the link between human-produced greenhouse gases and global warming. Instead, the GISS team says, global warming over the last century up until 1975 was slow, with large fluctuations. Since 1975, there has been a “rapid warming of almost 0.2°C per decade.”