The year 2014 was Earth's warmest in 134 years of records, according to an analysis of surface temperature measurements by scientists at NASA's Goddard Institute for Space Studies (GISS). In a separate, independent analysis, scientists at the National Oceanic and Atmospheric Administration (NOAA) also found 2014 to be the warmest on record. With the exception of 1998, the 10 warmest years in the instrumental record (dating to 1880) have all occurred since 2000.
The top map depicts global temperature anomalies in 2014. It doesn't show absolute temperatures, but rather how much warmer or cooler Earth was compared with a baseline average from 1951 to 1980. The GISS team assembles its analysis with publicly available data from roughly 6,300 meteorological stations around the world; ship- and buoy-based observations of sea surface temperature; and Antarctic research station measurements. Such raw data are analyzed using an algorithm that takes into account the varied spacing of temperature stations around the globe and urban heating effects that could skew the calculation.
Since 1880, Earth's average surface temperature has warmed by about 0.8 degrees Celsius (1.4 degrees Fahrenheit), a trend largely driven by the increase in carbon dioxide and other human emissions into the atmosphere, according to NASA. Most of that warming occurred in the past three or four decades, which is reflected in the bottom NASA GISS map.
NOAA scientists used much of the same raw temperature data as NASA, but they employ a different baseline period and their own methods to estimate global temperatures. And yet NASA and NOAA”as well as the Japan Meteorological Agency and the Met Office Hadley Centre in the United Kingdom”all come up with similar records despite different approaches. The line plot at left shows yearly temperature anomalies from 1880 to 2014 as recorded by the four institutions. Though there are minor variations from year to year, all four records show peaks and valleys in sync with each other. All show rapid warming in the past few decades, and all show the last decade as the warmest.