Recent climate warming has already aff ected Denali’s ecosystems in ways that are readily apparent, such as reduced snowfall in spring, earlier snowmelt, earlier green-up, shorter seasons of river and lake ice, and thawing of permanent snowfi elds. Other impacts are dramatic but less easily noticed—thawing of permafrost, changes in habitat suitability, changes in breeding times, vegetation shifts, and changes in landscape processes that infl uence wildlife distribution and habitat use.
Denali’s subarctic ecosystems are extremely sensitive to natural climate variability and to long-term natural or anthropogenic climate change. All places at high latitudes are experiencing some of the planet’s most rapid and severe climate changes. According to the 2007 Intergovernmental Panel on Climate Change (IPCC) report, average arctic temperatures have increased over the past 100 years at a rate that is nearly twice the average for the rest of the world.
Natural Influences on Denali’s Climate
Denali’s climate varies greatly across its 6 million acres. The Alaska Range divides the park into two distinct climate regimes--the transitional maritime climate, south of the Range, that is infl uenced by the ocean, and the drier continental climate, north of the mountain barrier, that is farther from ocean infl uences. Complex climate patterns exist in the park because of gradients of elevation and latitude, and eff ects of local topography. Short-term climate variability is subject to seasonal variations, annual variations (El Niño), decadal events (Pacific Decadal Oscillation), and other large-scale patterns.
Trends in Precipitation and Temperature
Park weather records dating back to 1925 indicate that annual average temperatures and precipitation amounts have increased. Evaporation has increased with higher temperatures leading to a net drying. In recent years, the number of snow-free days has increased and the growing season (defi ned by active plant growth) has lengthened. Over the past few decades, warming around the state of Alaska has averaged 4°F (2°C). Winter in Alaska’s Interior (including Denali) has experienced the largest warming (about 7°F (4°C)).
Monitoring Climate Change in Denali
Denali provides a special opportunity to study a large, intact, and naturally-functioning ecosystem. Understanding climate patterns and the ability to detect changes and their cause play a critical role in conserving unimpaired the park’s natural resources. As part of the National Park Service’s Inventory and Monitoring program, protocols are being developed for monitoring ecosystem components aff ected by climate change. Major objectives for climate monitoring are to identify long and shortterm trends, provide reliable climate data to other researchers, and contribute to larger-scale climate monitoring and modeling efforts.
Researchers and park scientists use climate data to correlate climate patterns with a wide variety of research findings. Two examples of possible correlations are:
•Reduced numbers of stream macro-invertebrates after deep snow winters (snowmelt may flush them)
•Reduced numbers of red-backed voles in some habitats in dry summers (voles may be elsewhere seeking water)
Integrating Observations of Climate Change
To assess climate change and its impact on park resources, Denali resource staff are consistently monitoring these components of environmental change and will integrate long-term observations.
Changes in Snow Cover
Very important in Denali’s winter landscape is the creation of a snow cover. Snow cover protects and insulates the ground and low-lying plants, reduces desiccation, and maintains ground temperatures that are warmer than air temperatures. Snow thickness and duration of snow cover aff ect wildlife population densities, herd movements, vegetation succession, soil temperature regimes, and hydrologic systems. Snow depth is monitored through surveys at several Denali locations.