Why surface temperature matters
Conditions in 2014
Overall, the globally averaged annual temperature over land was 0.37-0.44° Celsius (0.70° -0.79° F) above the 1981-2010 average, ranking it as the warmest year in some datasets and fourth-warmest in others. Land surfaces over Eurasia and western North America were particularly warm in 2014, and the frequency of warm temperature extremes was above average for all regions apart from North America.
The only land areas with widespread temperatures below the 1981-2010 average were the eastern half of the contiguous United States, central and southern Canada, and parts of central Asia. Eastern North America, including the eastern U.S., was relatively cool for the majority of 2014, with some sharp cold air outbreaks early in the year.
In 2014, the globally averaged sea surface temperature was 0.21-0.27°C (0.34°-0.49°F) above the 1981-2010 average--the highest on record according to all datasets. Even though conditions across the tropical Pacific Ocean were ENSO-neutral to marginal, sea surface temperatures averaged across the larger Pacific basin were much warmer than average in 2014. Every major ocean basin had at least one region with temperatures more than 1°C warmer than average during 2014. Some areas across the Atlantic, South Pacific, and northwestern Pacific Oceans experienced below-average temperatures.
Change over time
The natural variability of climate, including El Niño and La Niña cycles and the warm and cool phases of the Pacific Decadal Oscillation, causes surface temperature to rise and fall from year to year and even decade to decade. This “short-term” variability is overwhelmed, however, by what is happening over longer timescales; from the perspective of a century or longer, all both land and ocean have warmed.
To calculate global average temperature, four independent teams accessed air temperatures from weather stations on land and sea surface temperatures collected by ships and buoys. Each team used their own methods to analyze and merge the land and ocean datasets to estimate annual temperature for the whole globe. Though their methods differ, all four analyses are in close agreement about the long-term increase in global temperature.
ReferencesSánchez-Lugo, A., P. Berrisford and C. Morice, 2015: Surface Temperature [in “State of the Climate in 2014”]. Bulletin of the American Meteorological Society, 96 (7), S9-S14.