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The American West is getting warmer

Rapid warming in the US West has been observed in all seasons over the past few decades, but particularly in spring (see more on Montana and the spring in Washington).  Studies examining some of these trends—warming in winter throughout the region, and in both winter and spring in California — have shown them to exceed the maximum believed possible due to natural variability.  This goes beyond saying that the trends are statistically significant; it implies that they are caused in part, and in some cases caused mainly, by humans. Recent warming has been linked to earlier snowmelt, pine bark beetle outbreaks and an increase in wildfires.

The figures at the bottom show spring and summer temperature increases for five western states.  The data for these and more states are publicly available through a National Climatic Data Center (NCDC) website, following the "Statewide" menu option, and choosing the seasonal options. Complete records are available from 1895 through 2009.

The trend analysis shown is based on statewide monthly average temperatures calculated by the NCDC from weather station records that have been quality-controlled and adjusted for possible confounding factors, such as instrument changes, station relocations, observer practice changes and urbanization. A simple linear trend was fitted by ordinary least squares to the annual series of each season, starting from the year 1950 and extending to the end of the available records (September 2009).

 

Degrees F increase per decade in…

 

Spring

Summer

Washington

0.48

0.37

Oregon

0.43

0.36

Idaho

0.69

0.41

California

0.49

0.34

Nevada

0.55

0.37

Table: Observed rate of temperature increases during 1950-2008 (degrees F per decade).1

References
  1. National Climatic Data Center, “NCDC: US Climate at a Glance,” August 7, 2009.

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Heavy Precipitation, A City View A local look at the trend of heavy precipitation since 1950 in 100+ cities across the country.

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