Snow cover (CLIM 008) - Assessment published Sep 2008

Justification for indicator selection

Snow covers more than 33 % of the land surface north of the equator from November to April. It reaches a maximum of about 45.2 million km² in January, and a minimum of about 1.9 million km² in August (Clark et al., 1999).
Snow cover is an important feedback mechanism of the climate system. The extent of snow cover depends on the climate, for example on temperature and precipitation, and on solar radiation. But it also influences the climate and climate-related systems because of its high reflectivity, insulating properties, effects on water resources and ecosystems, and cooling of the atmosphere. Thus a decrease in snow cover reduces the reflection of solar radiation, contributing to accelerated climate change. Changes in the extent, duration, thickness and properties of snow cover can affect water availability for domestic use, navigation and power generation. Changes in snow cover affect human well-being through influences on agriculture, infrastructure, the livelihoods of indigenous Arctic people, environmental hazards and winter recreation. Snow-cover retreat can reduce problems of winter road and rail maintenance, affecting the exploitation and transport of oil and gas in cold regions (UNEP, 2007; ACIA, 2004).
Shallow snow cover at low elevations in temperate regions is the most sensitive to temperature fluctuations and hence most likely to decline with increasing temperature (IPCC, 2007a, b).
For several of these impacts, adaptation can reduce the negative effects of snow-cover change. Some adaptation options, such as artificial snowmaking in the Alps to maintain tourism as a main source of income, have to be balanced against their negative implications for mitigation, due to increased energy use and greenhouse gas emissions.

Scientific references:

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