Graphics
Digital Data
2SGT, Inc., NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025 USA
3Columbia University, Center for Climate Systems Research, NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025 USA
1880-2006 (Anomalies are relative to the 1951-80 base period means.)
The NASA GISS Surface Temperature (GISTEMP) analysis provides a measure of the changing global surface temperature with monthly resolution for the period since 1880, when a reasonably global distribution of meteorological stations was established. The input data Hansen et al. use for the analysis, collected by many national meteorological services around the world, are the unadjusted data of the Global Historical Climatology Network (GHCN) (Peterson and Vose, 1997 and 1998), except that the United States Historical Climatology Network (USHCN) station records up to 1999 were replaced by a version of USHCN data with further corrections after an adjustment computed by comparing the common 1990-1999 period of the two data sets. These data were augmented by Scientific Committee on Antarctic Research (SCAR) data from Antarctic stations not present in GHCN. Documentation of the analysis is provided by Hansen et al. (1999), with several modifications described by Hansen et al. (2001). The GISS analysis is updated monthly, however CDIAC's presentation in Trends will at present be updated annually.
The NASA GISS website for the global temperature data of Hansen et al. is the most comprehensive and direct source of information for these data. Users are strongly encouraged to visit the NASA GISS website, where they may specify input for making customized maps, graphs, and subsets of the data. Here, we seek to give users a brief, high-level overview of the GISTEMP analysis in the traditional style of CDIAC's Trends publication and provide you with convenient access to the main time series graphs, data tables, and references involved. This brief summary of the methods employed by Hansen et al. in their analysis is primarily borrowed from their NASA GISS web pages.
Hansen et al. modify the GHCN/USHCN/SCAR data in two stages to get to the station data on which all their tables, graphs, and maps are based: in stage 1 they combine at each location the time records of the various sources; in stage 2 they adjust the non-rural stations in such a way that their long-term trend of annual means is as close as possible to that of the mean of the neighboring rural stations. Non-rural stations that cannot be adjusted are dropped.
The analysis includes results for a global temperature index as described by Hansen et al. (1996). The temperature index is formed by combining the meteorological station measurements over land with sea surface temperatures obtained from in situ data before 1982 (Rayner et al. 2003) and from satellite measurements thereafter (Reynolds and Smith, 1994; Smith et al. 1996). Any uses of the temperature index data, i.e., the results including sea surface temperatures, should credit Reynolds and Smith (1994) and Smith et al. (1996). (See references.)
The analysis is limited to the period since 1880 because of the poor spatial coverage of stations prior to that time and the reduced possibility of checking records against those of nearby neighbors. Meteorological station data provide a useful indication of temperature change in the Northern Hemisphere extratropics for a few decades prior to 1880, and there are a small number of station records that extend back to previous centuries. However, Hansen et al. believe that analyses for these earlier years need to be carried out on a station by station basis with an attempt to discern the method and reliability of measurements at each station, a task beyond the scope of their analysis. Global studies of still earlier times depend upon incorporation of proxy measures of temperature change. References to such studies are provided in Hansen et al. (1999).
Trends in annual mean temperature anomalies for both land and land plus ocean time series show quite a bit of variability from the beginning of the record through about 1920, but no real trend. A significant warming of about 0.3°C is observed in both series from about 1920 through the early- to mid-1940s, followed by a less dramatic cooling in both series through about the mid-1960s. From the 1970s through the present, rapid warming is observed in both series; on the order of 0.6°C. The highest global surface temperature in more than a century of instrumental data was recorded in the 2005 calendar year. However, as noted on the NASA GISS website, the error bars on the data imply that 2005 is practically in a dead heat with 1998, the warmest previous year. Hansen et al. state that the record warmth of 2005 is especially notable because global temperature did not receive any boost from a tropical El Niño that year. The prior record year, 1998, on the contrary, was lifted 0.2°C above the trend line by the strongest El Niño of the past century. 2005 was the warmest year to date in both of the global mean temperature series (0.75°C above the 1951-1980 reference period mean for land; 0.58°C above for land plus ocean). The global mean temperature for the most recent year in the record, 2006, was 0.65°C above the 1951-1980 reference period mean for land; 0.54°C above for land plus ocean. The generally accepted global mean near-surface air temperature is about 14°C. The ten warmest years of the global record (land plus ocean) have all occurred since 1990. These are, in descending order, 2005, 1998, 2002, 2003, 2006, 2004, 2001, 1997, 1995, and 1990. The average near-surface air temperature of the globe (land plus ocean) has warmed about 0.8°C since the late nineteenth century.
The northern and southern hemisphere annual trends series show some general similarities, e.g., little sign of trends before about 1920, an increasing trend ending with a peak in the early 1940s, some cooling from the 1940s through the mid-1970s, followed by strong warming thereafter, with the highest temperatures occurring after 1990. The overall trend for the northern hemisphere is somewhat higher than that of the southern hemisphere, and while the northern hemisphere's highest temperature occurred in 2005, 2002 is still the warmest year recorded for the southern hemisphere. The relatively cool years of the early 1990s (mainly 1992 and 1993) are believed to have resulted from the effects of the dust veil produced by the eruption of Mt. Pinatubo (Parker et al. 1996).
Hansen et al. have also calculated temperature anomaly series for three latitude bands (90°N to 23.6°N; 23.6°N to 23.6°S; 23.6°S to 90°S) that cover 30%, 40%, and 30% of the globe, respectively. These series reveal that the northern latitudes have warmed much more than either the low or southern latitudes.
Summaries of global surface temperature trends, including discussions, graphs, and maps are available directly from the GISS webpages for 2006, 2005, 2004, 2003, 2002, and 2001,
(Note: All of the references included below are not cited in the above text. Additional references are included because they are described on the GISS website as being related to the overall global temperature research of Hansen et al.)
