Climate Change Basics
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Climate Change Basics 


The results of climate change will significantly affect Washington’s forests in a number of ways.  It is commonly understood that forests play a key role in efforts to address global climate change. The choices made by DNR will have significant affects on the efficacy of both climate change mitigation and adaptation efforts. A basic understanding of climate change and its expected impacts on Washington’s forests is essential to understanding the agency’s existing and planned efforts.

What is “climate change?”
The United State Environmental Protection Agency defines climate change as “any significant change in measures of climate (such as temperature, precipitation, or wind) lasting for an extended period (decades or longer).  Climate change can result from:

  • Natural factors, such as changes in the sun’s intensity or slow changes in the Earth’s orbit around the sun;
  • Natural processes within the climate system (e.g. changes in ocean circulation);
  • Human activities that change the atmosphere’s composition (e.g. through burning of fossil fuels) and land surface (e.g. deforestation, reforestation, urbanization, desertification, etc.).

Human caused climate changes are the result of activities, as mentioned above, that release greenhouse gases (GHG’s). Common greenhouse gases include: carbon dioxide, methane, nitrous oxide and others.  Greenhouse gases have always been present in the earth’s atmosphere.  The industrial revolution and other human activities, however, have resulted in the increased release of these gases into the atmosphere.  Over the 21st century, atmospheric CO2 levels had increased by 35% compared to pre-industrial levels. If humans continue to emit greenhouse gases along the same trend line that we have over the 20th century, we may see increases of 2.0°F to 11.5°F (1.1°C to 6.4°C) by 2100 : global warming.

Global warming is linked, but not identical to climate change.  EPA defines global warming as “an average increase in the temperature of the atmosphere near the Earth’s surface and in the troposphere, which can contribute to changes in global climate patterns.  Global warming can occur from a variety of causes, both natural and human induced. In common usage, ‘global warming’ often refers to the warming that can occur as a result of increased emissions of greenhouse gases from human activities.”  See the diagram below.

Color illustration of climate change componentsSource: U.S. Strategic Plan for the Climate Change Science Program (2003).

Climate Change and Washington’s Forest Ecosystems
According to the University of Washington’s Climate Impacts Group, forests in the Pacific Northwest can expect impacts from a changing global environment in the following areas key to both ecosystem and economic services provided by the forests: Douglas fir productivity and water limitation, Conifer species ranges, Fire area burned, and mountain pine beetle outbreaks (CIG, 2009). These changes will significantly affect Washington’s economy and environment.

Douglas Fir Productivity and Water Limitation
It is projected that the area of severely water limited forests in Washington will increase by 32% in the 2020’s and an additional 12% in the 2040’s and 2080’s (Litell, et. al., 2009). For douglas fir, an important species for the state’s timber industry, growth rates are largely determined by water availability. As we see significant increases in water limited forests in the coming years, we need to expect declines in Douglas Fir vitality and the economic impacts that will result.

Conifer Species Ranges
Because of increases in temperature and water limitation, existing conifer species ranges are expected to see significant shifts.  UW’s Climate Impacts Group projects that by the 2060’s, approximately “32% of the area currently classified as appropriate for Douglas-fir would be outside the identified climatic envelope and 55% would be in the 50-75% range of marginal climatic agreement models” (range modeling was based on IPCC scenarios). Changes in the Columbia Basin and eastern Cascades are expected to be even more severe as early as the 2040s.

Fire area burned
As decreases in summer precipitation are coupled with increases in summer temperatures, significant increases are expected in both numbers of fires and area burned by fires. 

Mountain pine beetle outbreaks
It is expected that mountain pine beetle outbreaks will continue to be a concern as our environment continues to see changes in our climatic conditions.  Decreases in summer precipitation will increase trees’ vulnerability to pest pressures.  Outbreaks are expected to reach higher elevations than they currently do, as we see continued changes in temperatures.

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Michal Rechner
Aquatic Resources Assistant Division Manager

Dan Siemann
Executive Policy Advisor for Climate Adaptation & Energy


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