Evaluating biases in simulated snow albedo feedback in two generations of climate models

Abstract

This study presents a comprehensive evaluation of snow albedo feedback (SAF) in two generations of climate models (Coupled Model Intercomparison Project versions 3 (CMIP3) and 5 (CMIP5)). A comparison of the models is performed against a multiobservation‐based reference data set (mOBS) derived from the seasonal cycle of albedo, snow cover, and temperature. The observed total SAF shows low uncertainty and is generally well simulated by the CMIP3 and CMIP5 ensemble mean, except for a low (high) bias over the Arctic (northern boreal forest). Most CMIP5 models overestimate the snow cover component of SAF (SNC) and underestimate the temperature sensitivity component (TEM). The high bias in SNC is due to simulated snow albedos 4–5% brighter than observed driving unrealistically large albedo contrasts. However, overall representation of surface albedo—and mean climate—has improved, as fewer CMIP5 models exhibit large cold temperature, or high snow, biases. The low bias in TEM is related to overly persistent snow albedo during spring, particularly over southern Eurasia and North America. There is large observational uncertainty in the reference data set mOBS that is traced primarily to the different snow cover products, with a secondary contribution from the albedo products and a small contribution from the temperature products. The conclusion is that the model mean tends to simulate the multiobservation mean very closely; however, this masks considerable spread in both models and observations. There is clear motivation for producing improved submonthly snow cover products for the purpose of model evaluation.

Spring snow albedo feedback over northern Eurasia: Comparing in situ measurements with reanalysis products

“…Snow albedo feedback (SAF) and its impact on climate have been studied for several decades (Wexler et al, 1953;Budyko, 1967;Schneider and Dickinson, 1974;Lian and Cess, 1977). It received further attention in the wake of anthropogenic global warming accompanied by the reduction of snow and ice cover over the Northern Hemisphere (NH) (Bony et al, 2006;Hall, 2007, 2014;Fernandes et al, 2009;Flanner et al, 2011;Fletcher et al, 2015;Thackeray and Fletcher, 2016).…”

“…Several studies investigated spring NH extratropical SAF based on satellite, reanalysis and model data sets (Fernandes et al, 2009;Fletcher et al, 2012Fletcher et al, , 2015Qu and Hall, 2014). Satellite-based estimates of SAF vary within ±10 % depending on the analysed data set.…”

“…Fletcher et al (2015) investigated Coupled Model Intercomparison Project 3 and 5 (CMIP3/CMIP5) ensembles to estimate the SAF for an assortment of global climate models (GCMs). The authors found a SAF ensemble model mean of −1.2 % K −1 for the NH extratropics, which is in fair agreement with MODIS values but is higher compared to ISCCP-and AVHHR-based estimates.…”

“…The authors found a SAF ensemble model mean of −1.2 % K −1 for the NH extratropics, which is in fair agreement with MODIS values but is higher compared to ISCCP-and AVHHR-based estimates. Within this comparison Fletcher et al (2015) also investigated SAF computations based on ERA-Interim (Dee et al, 2011), Modern-Era Retrospective Analysis for Research and Applications (MERRA) (Rienecker et al, 2011) and NCEP-2 (Kanamitsu et al, 2002) reanalyses, thus providing the most up-to-date assessment of SAF in reanalysis data sets. While MERRA data resulted in a slightly weaker SAF of −1.17 % K −1 compared to ERAInterim (−1.23 % K −1 ), both reanalyses show similar SAF values compared to MODIS.…”

Simulation of black carbon in snow and its climate impact in the Canadian Global Climate Model

“…Fletcher et al (2015) showed that climate models generally reproduce observation-based estimates of snow-albedo feedbacks well but tend to underestimate the temperature sensitive component of the total snow-albedo feedback. This implies that where snow persists, its albedo does not reduce fast enough when the temperature warms, including warming from absorption of solar radiation by BC in snow.…”