Human activities since the Industrial Revolution have increased atmospheric greenhouse gas levels, trapping heat in the Earth’s atmosphere and leading to warming. Continued increases in the levels of human-caused greenhouse gases, such as carbon dioxide, methane and nitrous oxide, are expected to lead to continued global warming and regional climate change.

The earth’s average surface temperature has risen about 2.0 degrees Fahrenheit since the late nineteenth century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere. Most of the warming has occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since 2001. Temperature data in northwestern Washington State indicate a warming trend is present for this region as well.

With an increase in air temperature, there are likely to be changes in precipitation patterns as well as in the amount of precipitable atmospheric water. Areas that historically received precipitation in the form of snowfall will see rainfall instead, leading to a reduced snowpack area and changes to the local and regional hydrology. Many climate models project increased winter precipitation and decreased summer precipitation throughout the Pacific Northwest with the potential for more extreme precipitation events, although there is more uncertainty and variability than in the temperature projections.

Sources: NOAA, NASA/GISS (2017;

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