2009 State of the Climate Report Released in BAMS
The State of the Climate Report is a yearly supplement to the Bulletin of the American Meteorological Society (BAMS) that summarizes the global and regional climate for each calendar year. The 2009 report was released in July (Arndt et al., 2010). This note highlights some of the main points in the report.
Globally, the 2009 average temperature was 0.46°C above the 1961-1990 mean, according to the NOAA/NCDC data set. The 2000s now rank as the warmest decade on record (compared back to the 1850s). The 2009 average precipitation was also above the 1961-1990 mean, according to three independent data sources.
For the US, 2009 was relatively cool when compared to the decade of the 2000s. The nationally averaged temperature was 11.7°C (53.1°F), the second coolest year since 2000 (2008 was slightly cooler). Still, 2009 was 0.1°C above the long-term average (1895-2009), and the average temperature for the 2000-2009 decade was 0.7°C above the 1901-2000 average. The 2009 US average precipitation was 64 mm (2.52”) above 1895-2009 average (740 mm; 29.13”). The 2000-2009 decade as a whole was also relatively wet and averaged 18 mm (0.71”) above the 1901-2000 average. Despite the wetter than average decade, some areas of the US experienced severe drought. The report tracks drought in the past 110 years, as defined by the Palmer Drought Severity Index, and ranked 2000-2009 as the decade with the third greatest drought, for the country as a whole, in the entire record.
Annual average temperature is useful in comparing one year to another, but it can mask important seasonal variations. The year of 2009 featured a swinging back and forth of temperature anomalies that was likely caused by natural variability. M. Hoerling and the NOAA Climate Scene Investigation (CSI) team discuss this idea in a small insert on pages S140-S141. They hypothesize that the transition between La Nina-like conditions (late 2008 through March 2009) and a moderate El Nino (developed in July 2009 and strengthened in October through the end of 2009) was partially responsible for large switches in temperature anomalies across the country. Using an ensemble of runs from global climate models (GCMs) that were only forced by the global sea surface temperatures (SSTs), a large amount of the seasonal variability is replicated. For example, in WA, the cool January-February-March 2009 (JFM) anomalies were replicated by the model simulation though not to the same strength. The July-August-September (JAS) warm anomalies in WA were also represented in the models, meaning that the some of the seasonal variability may have been a result of ocean variability.
Reference:
Arndt, D.S., M. O. Baringer, and M. R. Johnson, Eds., 2010: State of the Climate in 2009. Bull. Amer. Meteor. Soc., 91 (7), S1-S224.