Temperature

Mean Annual Temperature

About this indicator: This indicator is the average of the last ten years' annual temperature in King County as measured at the Seattle-Tacoma (SEATAC) airport compared to the historical average temperature (the average from 1949 to present). This indicator is chosen as a rough proxy to track the impact of global warming and climate change at the regional level.

Drivers/influencing factors: Many climatic factors control changes in annual temperatures. For example, cyclic and natural changes in oceanic sea surface temperatures can result in persistent weather patterns such as El Nino and La Nina that can last from months to years. In King County, La Nina weather patterns, for example, usually result in cooler and wetter than average weather conditions. In addition to natural causes of climate variability, human caused climate change caused by greenhouse gas emissions (such as carbon dioxide) are a very strong control on global and local climate. Because there is significant year to year variability in average temperature, and because this indicator is focused on measuring the human caused impact on regional climate, a 10 year average temperature is used.

Status: The year 2007 was 10th warmest year for the contiguous U.S., since national records began in 1895. Overall, six of the 10 warmest years on record for the contiguous U.S. have occurred since 1998, part of a three decade period in which mean temperatures for the contiguous U.S. have risen at a rate near 0.6ºF per decade.

At SEATAC, in 2007, the mean annual air temperature was 54.4 ºF, the average annual temperature for the last ten years was 52.3 ºF, and the long term average was 51.8 ºF. This data indicates that the trends observed at SEATAC are consistent with U.S. and national trends of a warming and changing climate system.

Mean annual temperature
2007 Findings
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