Abstract
The snow-masking effect of vegetation exerts strong control on albedo in northern high latitude ecosystems. Large-scale changes in the distribution and stature of vegetation in this region will thus have important feedbacks to climate. The snow-albedo feedback is controlled largely by the contrast between snow-covered and snow-free albedo (Δα), which influences predictions of future warming in coupled climate models, despite being poorly constrained at seasonal and century time scales. Here, we compare satellite observations and coupled climate model representations of albedo and tree cover for the boreal and Arctic region. Our analyses reveal consistent declines in albedo with increasing tree cover, occurring south of latitudinal tree line, that are poorly represented in coupled climate models. Observed relationships between albedo and tree cover differ substantially between snow-covered and snow-free periods, and among plant functional type. Tree cover in models varies widely but surprisingly does not correlate well with model albedo. Furthermore, our results demonstrate a relationship between tree cover and snow-albedo feedback that may be used to accurately constrain high latitude albedo feedbacks in coupled climate models under current and future vegetation distributions.
Highlights
Northern high latitude ecosystems are experiencing amplified climate warming (Serreze & Barry, 2011) that will be exacerbated by a series of positive feedbacks (Chapin et al, 2005), the relative magnitudes of which remain uncertain
Maps for showing the distance of each pixel to Circumpolar Arctic Vegetation Map (CAVM) tree line were created at the resolution of each data product (e.g. Moderate Resolution Imaging Spectroradiometer (MODIS) albedo and Vegetation Continuous Fields (VCF), and each Coupled Model Intercomparison Project Phase 5 (CMIP5) model)
Satellite observations capture a gradual increase in tree cover south of latitudinal tree line (Fig. 1), accompanied by a gradual decrease in albedo in April but not July due to the snow-masking effects of vegetation
Summary
Northern high latitude ecosystems are experiencing amplified climate warming (Serreze & Barry, 2011) that will be exacerbated by a series of positive feedbacks (Chapin et al, 2005), the relative magnitudes of which remain uncertain. The decline in albedo (Da) between snow-covered and snow-free conditions represents the strength of the albedo feedback associated with changes in the length of the snow-free growing season (Qu & Hall, 2007; Fernandes et al, 2009) In climate models, this snowalbedo-feedback (SAF) can be defined as the change in albedo forced by a change in temperature (i.e. Da/DT), typically calculated at decadal timescales and large spatial scales (e.g. poleward of 30°N latitude). We test the assumption of accurate spatial characterization of boreal forest canopy biophysical properties in models by comparing satellite observations of vegetation cover and albedo with data from coupled climate models archived as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5; Taylor et al, 2012)
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