Abstract
Long-term measurements of ecological effects of warming are often not statistically significant because of annual variability or signal noise. These are reduced in indicators that filter or reduce the noise around the signal and allow effects of climate warming to emerge. In this way, certain indicators act as medium pass filters integrating the signal over years-to-decades. In the Alaskan Arctic, the 25-year record of warming of air temperature revealed no significant trend, yet environmental and ecological changes prove that warming is affecting the ecosystem. The useful indicators are deep permafrost temperatures, vegetation and shrub biomass, satellite measures of canopy reflectance (NDVI), and chemical measures of soil weathering. In contrast, the 18-year record in the Greenland Arctic revealed an extremely high summer air-warming of 1.3 °C/decade; the cover of some plant species increased while the cover of others decreased. Useful indicators of change are NDVI and the active layer thickness.
Highlights
Long-term measurements of ecological effects of warming are often not statistically significant because of annual variability or signal noise
Keywords Alaska Toolik Á Climate change Á Ecological effects Á Greenland Zackenberg Á Medium pass filter Á Vegetation to changes in ecological processes, such as plant growth, which can result in changes in the state of ecosystem components such as plant biomass or changes in ecosystem structure (Chapin et al 2000; Sturm et al 2001; Epstein et al 2004)
An overall warming trend does occur in northern Alaska where air temperatures at Barrow, the only permanent town, have warmed *3.1 °C in the last 65 years
Summary
Long-term measurements of ecological effects of warming are often not statistically significant because of annual variability or signal noise These are reduced in indicators that filter or reduce the noise around the signal and allow effects of climate warming to emerge. In spite of the large number of environmental and ecological measurements made over recent decades, it has proven difficult to discover statistically significant trends in these measurements This difficulty is caused by the high annual and seasonal variability of warming in the air temperature and the complexity of biological interactions. Climate warming in the Arctic, substantial over recent decades and well-documented in IPCC reports (IPCC 2001, 2013), is reflected in changes in a wide range of environmental and ecological measures. The Long Term Ecological Research (LTER) and related projects at this site have
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