Abstract
Abstract. The 20th century seasonal Northern Hemisphere (NH) land snow cover as simulated by available CMIP5 model output is compared to observations. On average, the models reproduce the observed snow cover extent very well, but the significant trend towards a reduced spring snow cover extent over the 1979–2005 period is underestimated (observed: (−3.4 ± 1.1)% per decade; simulated: (−1.0 ± 0.3)% per decade). We show that this is linked to the simulated Northern Hemisphere extratropical spring land warming trend over the same period, which is also underestimated, although the models, on average, correctly capture the observed global warming trend. There is a good linear correlation between the extent of hemispheric seasonal spring snow cover and boreal large-scale spring surface air temperature in the models, supported by available observations. This relationship also persists in the future and is independent of the particular anthropogenic climate forcing scenario. Similarly, the simulated linear relationship between the hemispheric seasonal spring snow cover extent and global mean annual mean surface air temperature is stable in time. However, the slope of this relationship is underestimated at present (observed: (−11.8 ± 2.7)% °C−1; simulated: (−5.1 ± 3.0)% °C−1) because the trend towards lower snow cover extent is underestimated, while the recent global warming trend is correctly represented.
Highlights
With a maximum extent of about 45 × 106 km2, seasonal snow cover, essentially located in the Northern Hemisphere (NH) land areas, is the largest component of the terrestrial cryosphere (e.g. Lemke et al, 2007)
We provide a short assessment of the simulated present-day snow cover, including its current trends, and analyze the dominant factors determining the future evolution of Northern Hemisphere spring snow cover as simulated by the CMIP5 models
The weaker average performance of the climate models in the southern realm of the seasonal snow area is due to incorrect timing of the snow onset and melt, and possibly to an incorrect representation of the annual maximum snow cover fraction. This latter error might be due to the way snow cover extent is diagnosed here: for any given month, snow cover is diagnosed to be complete (100 %) if the snow mass exceeds a threshold of 5 kg m−2, and 0 if the snow mass is below this threshold
Summary
With a maximum extent of about 45 × 106 km, seasonal snow cover, essentially located in the Northern Hemisphere (NH) land areas, is the largest component of the terrestrial cryosphere (e.g. Lemke et al, 2007). With a maximum extent of about 45 × 106 km, seasonal snow cover, essentially located in the Northern Hemisphere (NH) land areas, is the largest component of the terrestrial cryosphere Snow cover has important effects on climate. The most obvious effect is due to its high albedo. Alexander et al, 2010) This gives rise to the well-known snow-albedo feedback which (i) is thought to be one important reason for the polar amplification of ongoing and projected climate change Due to its low heat conductivity, snow effectively insulates the underlying soil, with important effects on deep soil temperatures and permafrost extent (Zhang, 2005; Lawrence and Slater, 2010; Gouttevin et al, 2012)
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