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Climate Change

The Earth has always changed through time. These changes are based on complex, nested oscillating climatic cycles that occur on decadal, century, and millennium time scales. Climatic cycles are driven by a variety of factors including changes in the Earth’s orbit, ocean currents, volcanic eruptions, and the amount of energy released from the sun. Paleoecological and paleoclimatic studies, and paleoclimatic models reveal that climateshifts are common, with events such as ice ages and long warming periods (Cook et al. 2007; Kiehl and Sheilds 2005) .

Presently, there is evidence that human activities have altered natural climatic cycles (IPCC Web site). Over the past several hundred years, the composition of the atmosphere has been altered by the burning of fossil fuels (e.g., coal and oil) and deforestation (removal of trees that trap or sequester carbon). The net result is that heat-trapping concentrations of “greenhouse gas” have increased significantly. Greenhouse gases prevent heat from escaping the Earth’s atmosphere, creating the greenhouse analogy. The major greenhouse gas being contributed to the atmospshere by human activities is carbon dioxide, or CO₂.

Concentrations of CO₂ in the atmosphere are regulated naturally by numerous processes collectively known as the “carbon cycle” (fig. 1).

Figure 1—The global carbon cycle (billion metric tons carbon).

The movement (“flux”) of carbon between the atmosphere and the land and oceans is dominated by plant photosynthesis. Although natural processes such as photosynthesis can absorb some of anthropogenic CO₂ emissions produced each year, much more carbon is being added than can be “sequestered” by natural processes. Presently, the Earth’s imbalance between emissions and sequestration has resulted in an increase in CO₂ in the atmosphere every year. Simply put, natural processes cannot use up the extra carbon that is being produced by human activities, and CO₂ is accumulating in the Earth’s atmosphere (fig. 2).

Figure 2—Trends in atmospheric concentrations and anthropogenic emissions of carbon dioxide.

Given the natural variability of the Earth’s climate, it is difficult to determine the extent of change that green house gas buildup and land use change (e.g., deforestation) can cause. In computer-based models, rising concentrations of green house gases generally produce an increase in the average temperature of the Earth (fig. 3). Rising temperatures may, in turn, produce changes in weather, sea levels, and other changes. Collectively, these changes are commonly referred to as “climate change.”

Figure 3—Trends in average global temperatures.

Climate change has the potential to significantly affect western wildland resources and many ecosystem services. The climate of the Earth is changing and will continue to change for many decades in unique ways predicted in response to the buildup of green green house gases in the atmosphere.

The “fingerprint” of climate change as a result of green house gases buildup has been known for some time:

• More warming
  • at the earth’s poles than at the equator
  • over land than over the sea
  • in the winter than in the summer
  • at night than in daytime
  • in the lower atmosphere (troposphere) while cooling in the upper atmosphere (stratosphere)
• Less rain in the subtropics and more in high latitudes
• Increasing climate variability producing more intense and variable events such as large storms and longer more intense droughts.

Climate change has already been measured in many places around the globe, and these changes, as well as predicted future changes, differ considerably from place to place. Therefore each region of the West will experience site-specific changes in temperature and precipitation. Because the nature of wildlands in these regions also differ, management actions will differ widely to account for those differing climate changes and effects.

 

Threat Interactions

The interaction with other threats and climate change are complex and highly significant. We know from paleoecological studies that past climatic shifts can reorganize landscapes, and species populations will adjust or change in response to shifts in climate. Climate change also alters disturbance processes such as fires, floods, and insect and disease infestations. These secondary effects can reset the sucessional stage and initiate major ecological change. Land-use change is also an important contributor to climate change, especially deforestation. Climate change will also influence land-use change as people may migrate to more livable areas.

 

WWETAC Projects and Workshops

Rapid Threat Assessment of Climate Change Effects on Western Bark Beetles
Climate Change and Forest Diseases in the West - An Information Synthesis
Climate Change Effects in the Pacific Northwest on the Future Dynamics of the Gypsy Moth
Westwide Climate Change Initiative
Forests, Insectsand Pathogens, and Climate Change - Workshop
Exploring Quantitative Approaches for Vegetation Management and Forest Planning Under a Changing Climate—Workshop