Northern boreal and arctic ecosystems are purported to be a considerable land sink for atmospheric CO2 [Euskirchen et al., 2006; McGuire et al., 2009], though sensitivity of the regional carbon cycle to a warming climate is uncertain [McGuire et al., 2009; Hayes et al., 2011]. The high latitudes have experienced generally greater warming than other global areas in recent decades [Serreze and Francis, 2006]. A lengthening growing season has been linked to vegetation greening and enhanced productivity in the northern latitudes [e.g., Nemani et al., 2003; Chen et al., 2006; Beck and Goetz, 2011]. However, increasing vegetation water stress and enhanced autumn respiration may be offsetting the potential benefits of longer growing seasons and decreasing regional carbon sequestration [Angert et al., 2005; Piao et al., 2008; Zhang et al., 2008]. Boreal forests have had more frequent and widespread wildfire and insect disturbances [Bond-Lamberty et al., 2007; Kurz et al., 2008], which may alter vegetation composition and function and associated growth and respiration processes [Amiro et al., 2010; Coursolle et al., 2012]. Moreover, a large portion of soil organic carbon stored in northern boreal forest and tundra areas is potentially vulnerable to soil warming and likely more frequent burning due to climate warming [Turetsky et al., 2010; Mack et al., 2011].
 A diverse response of northern ecosystems to regional warming and drought has been reported from limited field experiments [e.g., Chen et al., 2006; Welp et al., 2007; Schwalm et al., 2010; Yi et al., 2010b; Peng et al., 2011], while extension of these findings to the larger pan-boreal/Arctic region is constrained by the limited extent of these studies and a sparse regional measurement network. A recent decline in northern ecosystem productivity, especially in the boreal forest, has been reported from satellite measurement records [e.g., Angert et al., 2005; Goetz et al., 2007; Beck and Goetz, 2011]. However, many of these studies are based on satellite-derived vegetation “greenness” indices (VIs) including the EVI (Enhanced Vegetation Index) and NDVI (Normalized Difference Vegetation Index) that do not distinguish underlying gross primary productivity (GPP) and respiration processes or their environmental drivers. Meanwhile, the impact of wildfire on the northern carbon cycle is increasing, while the associated effects on regional vegetation and soil carbon recovery have not been investigated using ecosystem models until recently [Balshi et al., 2007; Yi et al., 2010a]. Therefore, regional applications of ecosystem models are desirable to clarify recent impacts from climate variability and disturbance on the northern carbon cycle.
 Satellite remote sensing offers a diverse set of land parameter retrievals that can serve as critical inputs to regional ecosystem models for estimating land-atmosphere carbon fluxes and associated climate impacts to the terrestrial carbon budget [e.g., Nemani et al., 2003; Potter et al., 2003; Zhang et al., 2008; Kimball et al., 2009]. The Moderate Resolution Imaging Spectroradiometer (MODIS) provides continuous, well calibrated, and relatively long-term global records that are sensitive to photosynthetic canopy cover [Running et al., 2004]; global monitoring from these sensors can also detect abrupt disturbance-related vegetation changes [Mildrexler et al., 2007; Giglio et al., 2010]. Satellite microwave sensors provide synergistic information on land surface moisture and temperature variations owing to strong microwave sensitivity to associated changes in land surface dielectric properties and emissivity [Ulaby et al., 1982]. Land surface retrievals at longer microwave wavelengths also have reduced sensitivity to solar illumination effects, clouds, and atmospheric aerosol contamination relative to optical sensors; these properties have been exploited for determining daily landscape freeze/thaw (FT) status and nonfrozen season variability, which provides an effective surrogate for frozen temperature constraints to vegetation productivity and the potential growing season in boreal/Arctic regions [Kimball et al., 2004; Kim et al., 2012]. The planned NASA Soil Moisture Active Passive (SMAP) mission will provide global measurements of surface soil moisture and FT status, with improved spatial resolution (<10 km) and enhanced L-band microwave sensitivity to soil processes relative to current satellite microwave sensors [Entekhabi et al., 2010]. The SMAP land parameter retrievals will inform higher level land model simulations including a planned level 4 carbon (L4_C) product that will provide regular global estimates of terrestrial carbon fluxes and underlying environmental drivers [Kimball et al., 2012]. These new measurements and geophysical products are intended to improve understanding of processes linking terrestrial water, energy, and carbon cycles, quantify the net carbon flux in boreal landscapes, and reduce uncertainties regarding the purported missing carbon sink on land [Entekhabi et al., 2010].
 In this study, we applied a terrestrial carbon flux (TCF) model partially driven by satellite-derived FPAR (Fraction of Photosynthetically Active Radiation absorbed by vegetation), FT, and burned area inputs to estimate daily GPP, net ecosystem CO2 exchange (NEE), and surface (<10 cm depth) soil organic carbon (SOC) stocks over all northern vegetated land areas. The TCF model used for this study is similar to the L4_C algorithm being developed for the SMAP mission. Our primary objectives were to use the TCF projections to examine how recent climate variability and fire disturbance have affected northern GPP and NEE carbon sink activity during the 11 year satellite record (2000–2010). We hypothesized that potential productivity gains from regional warming still outweigh productivity losses caused by recent drought stress and wildfire disturbance in the northern latitudes, while prediction of NEE is more uncertain due to similar, compensating GPP and ecosystem respiration (Reco) responses to these factors. These results were also used to test the initial algorithm and model performance for the planned SMAP L4_C product.
 The following sections include descriptions of the TCF model equations and methods used for the model simulations, validation and uncertainty assessment (section 2); presentation of model validation results relative to independent GPP and NEE estimates from northern tower eddy covariance CO2 flux measurement sites and SOC data from soil inventory records (section 3.1); model assessment of regional drought and fire impacts on the northern carbon cycle (section 3.2); discussion of model and observation uncertainties (section 4); and the implications of the study results for informing development of similar carbon model simulations for the SMAP mission (section 5).