Once covering a larger area, visitors now walk a path to Exit Glacier showing how it has receded in the last 60 years at Kenai Fjords National Park. In the lower right corner of the image you can see where the glacier terminated in 1951. Photo by NPS.
In 1824 it was discovered that certain gases will trap heat within the Earth's atmosphere. This has been called the Greenhouse Effect
as the process reminded people of the way the glass of a greenhouse will seal the warm air inside. Though it comprises less than 0.04% of the atmosphere, carbon dioxide (CO2
) is the principle greenhouse gas. Without it, the average temperature of the planet would be well below freezing, but with that small fraction the Earth's average temperature is about 60° F. So it is no surprise that adding more CO2
to the atmosphere can further warm the planet. This is the basic premise of global warming
, which increases the temperature of the land, sea, and atmosphere. It is more accurately called global climate change
, since there are many complicated factors involved.
Global temperature is the master driver affecting climate and everything else that climate affects. Other climate drivers are important to consider:
Temperature - The effects of temperature includes not only the annual average, but also the daily high and low temperatures, the onset warm spring temperatures and the delay of the first frost, and the extremes of hot and cold.
Sea Level Rise - Melting polar ice and the expansion of seawater as it is heated cause the sea level to rise like a bathtub being overfilled.
Evaporation and Precipitation - Where there is heat, there is increased evaporation. This in turn changes precipitation patterns. Moisture laden clouds create their own climate influence. Many locations will get more rainfall, but storms will be shunted away from other areas causing drought.
Snowfall and Snowcover - Just like rainfall, snowfall requires heat to create evaporation and jumpstart the water cycle. But increased temperature can also limit snowfall, drive the snowline further up the mountain, or melt it rapidly once it falls. Changes in snowcover are especially important as the snow reflects more solar radiation and tends to keep the land cool; reduced snowcover can lead to a feedback effect (where changes tend to drive further changes and the effects are compounded).
Sea Ice and Glaciers - Like snowcover, ice on the land cools the planet by reflecting more solar energy back into the atmosphere instead of being absorbed and emitted as heat by the land or sea.
Streamflow - Glaciers, snowpack, and rainfall produce water that flows through streams, lakes and rivers. These waterways are critical to life, and complete the planet's water cycle. Climate change will affect streams differently, but increased variability is suspected along with a shift in the timing of peak flows.
Growing Season - With changes in temperature, precipitation, and moisture for plants will come a change in growing season. In many cases, growing season will shift earlier in the spring.
Extreme Events and Storminess - Often it is not the average weather that matters, but the extremes. Record warm days, cold snaps, and the intensity and frequency of storms often dictate plant life, wildlife, and human civilization. Though it is difficult to predict, many climate models forecast greater swings in the weather.
Each natural and human system is based upon a certain climate. Alpine tundra is defined by a very short growing season, cool summers, winter snow cover, and sufficient summer water availability. Likewise, the state of Minnesota's character is based on a climate that provides numerous lakes for fishing and recreation, supports corn, pea, and spring wheat agriculture, and offers adequate snowfall for winter sports. Many national parks and other protected areas were set up to safeguard a wide range of plant and animal life assuming a certain set of climate conditions. As the climate drivers change, the natural ecosystem and human use of that landscape are bound to change. Even subtle shifts in climate can create substantial changes—earlier snowmelt, a slight increase in summer temperatures, and a slight decrease in rainfall can combine to change the intensity of forest fires, or render forests more susceptible to pests and diseases. With climate change, nature will begin to rearrange itself, and our ability to protect and manage national parks will be challenged.
Scientists are understanding more about the changes to climate drivers, and now focus their attention on the subsequent impacts to natural and cultural resources. The U.S. Fish & Wildlife Service has collected a list of Possible Impacts on Fish and Wildlife in the United States
and the U.S. Forest Service has published two atlases on the potential redistribution of Trees and Birds
due to global climate change.
Regional Climate Effects
Bioregions are areas that tend to have the same suite of climate effects, for example the western mountains will be significantly impacted by decreased snowpack, while the Atlantic coast is vulnerable to sea level rise. We group these climate effects into bioregional overviews to more easily understand the impact climate change will have. The National Park Service and U.S. Fish & Wildlife Service have developed 11 regional "talking point" documents to help staff, collaborators, and the public understand the consequences of climate change.