June 15, 2010
Each month NOAA’s National Climatic Data Center (NCDC) releases two assessments, one national and one global, of the previous month’s climate. These reports include information on the temperature and precipitation levels experienced nationally and globally, providing useful information about these important climate variables in historical perspective. The reports also chronicle any significant weather and climate-related events that occurred during the month. This trusted source of information is used globally by industry and business, government agencies, academia, and members of the public to help inform decision making.
The global report is a monthly snapshot of the climate system around the globe that informs the public of the current state of the global climate and helps planners, academics and sector users factor the climate’s current state and recent trends into their decision making. The report details the average global land temperature, the average global ocean temperature, and the combined average of the two. Instead of using raw temperatures, the report presents temperature anomalies, which means the difference from average temperatures for any given area over a period of time. Using anomalies allows for a more accurate understanding of temperature trends over space and time, even with some fluctuations in data availability (see additional information below).
This figure depicts the global surface temperature anomalies for the month of May from 1880 to 2010.
This figure depicts the global surface temperature anomalies for the period of time from January to May 2010. The temperature is compared to the average global temperature from 1971-2000.
Animation of year-to-date average global temperatures for each of the last 20 years (since 1990).
Animation (Credit: NOAA)
Each of the 10 warmest average global temperatures recorded since 1880 have occurred in the last fifteen years. The warmest year-to-date on record, through May, was 1998, and 2010 is warmer so far (note: although 1998 was the warmest year through May, a late-year warm surge in 2005 made that year the warmest total year). Analysis by the National Climatic Data Center reveals that May of 2010 was the warmest global average for that month on record, and is also the warmest year-to-date from January to May. This animated graph plots the year-to-date average global temperature for each of the last 20 years (since 1990). The 2010 value, complete only through May, is shown in red at the end of the animation.
Temperature anomaly refers to the difference from average. The global temperature is calculated using anomalies because they give a more accurate picture of temperature change. If calculating an average temperature for a region, factors like station location or elevation affect the data, but when looking at the difference from the average for that same location, those factors are less critical. For example, while the actual temperature on a hilltop will be different than in a nearby valley on a given day or month, stations in both places will show a similar trend in temperature when you calculate the change in temperature compared to average for that station.
Using anomalies also helps minimize problems when stations are added to or removed from the monitoring network. The above diagram helps show how even if one station were removed from the record or did not report data for some period of time, the average anomaly would not change significantly, whereas the overall average temperature could change significantly depending on which station dropped out of the record.
Red dots show how a typical month's worth of data arrives at NCDC.
Animation (Credit: NOAA)
NOAA's NCDC is the world's largest active archive of weather data. It houses data archives dating back to 1880 from all over the world. Each month, countries from all over the world send their land-based meteorological surface observations, meaning temperature and precipitation measurements, to NCDC to be added to the global record.
This information is sent through the World Meteorological Organization's (WMO) Global Telecommunication System (GTS)—a coordinated system for the rapid collection, exchange and distribution of observation data from more than 200 countries around the world. The data are sent in a format called "CLIMAT messages" (pronounced "cleem-mat"), which are a summary of monthly weather data for a specific station. The CLIMAT message contains information of average pressure at station level, average air temperature, maximum air temperature, minimum air temperature, average vapor pressure, total precipitation, and total sunshine for a particular month.
These messages are typically sent to NCDC by the 8th of every month. NCDC uses the data to produce numerous climate publications, such as the monthly global state of the climate report. In the image, the red dots on the animation above show how a typical month's worth of data arrives at NCDC, in a day-by-day, country-by-country fashion. Please refer to the WMO for detailed information about CLIMAT messages or the GTS.
State of the Climate Report The full monthly state of the climate report is available online.
Historical global temperature information, by month, season and continent.
Historical temperature and precipitation data for the United States.