October 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).
Each of the 10 warmest average global temperatures recorded since 1880 have occurred in the last thirteen years. The warmest year-to-date on record, through September, was 1998 (note: although 1998 was the warmest year through September, a late-year surge in 2005 made that year the warmest total year). Analysis by the National Climatic Data Center reveals that, averaged globally, 2010 had the eighth-warmest September on record, and is virtually tied with 1998 for the warmest from January through September.
High Resolution (Credit: NOAA)
This graph plots the year-to-date average global land and ocean temperature. The 2010 value, complete only through September, is shown in bright red. On the graph, "ONI" stands for Oceanic Niño Index, which is one way of measuring whether El Niño or La Niña is occurring. Each of the three warmest years on record (2005, 1998, and [so far] 2010) began with a positive ONI, which is associated with El Nino and warmer than normal conditions across much of the equatorial Pacific Ocean. However, each of these years eventually transitioned into negative ONI values at some time in the year, which - after some lag - tends to depress global average temperatures slightly below the long-term trend (see below).
Temperature Anomolies, September 2010
High Resolution (Credit: NOAA)
La Nina is the name given to processes associated with cooler-than-normal sea surface temperatures (SSTs) in the eastern and central equatorial Pacific Ocean. You can see the "footprint" of La Nina on this month's global surface temperature map as a large blue (cooler-than-normal) collection of dots in the Pacific Ocean. La Nina is the "flip side" of the more-famous El Nino phenomenon, which features warm SSTs in the same region. La Nina is important for a number of reasons: its far-reaching "teleconnections" can influence seasonal weather patterns as far away as the US and Asia. Indeed, depending on the time of year and the strength of La Nina, long-term outlooks like those provided by NOAA's Climate Prediction Center may consider La Nina as a major influence. In the context of global temperatures, La Nina tends to have a cooling effect. This is mainly because of the simple reason that La Nina is associated with a very large footprint of cooler waters that feeds into the larger global average.
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.
High resolution (Credit: NOAA)
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.
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.
Red dots show how a typical month's worth of data arrives at NCDC.
Animation (Credit: NOAA)
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.