Assessing historical and projected carbon balance of Alaska: A synthesis of results and policy/management implications

Abstract

We summarize the results of a recent interagency assessment of land carbon dynamics in Alaska, in which carbon dynamics were estimated for all major terrestrial and aquatic ecosystems for the historical period (1950-2009) and a projection period (2010-2099). Between 1950 and 2009, upland and wetland (i.e., terrestrial) ecosystems of the state gained 0.4 Tg C/yr (0.1% of net primary production, NPP), resulting in a cumulative greenhouse gas radiative forcing of 1.68 × 10 W/m . The change in carbon storage is spatially variable with the region of the Northwest Boreal Landscape Conservation Cooperative (LCC) losing carbon because of fire disturbance. The combined carbon transport via various pathways through inland aquatic ecosystems of Alaska was estimated to be 41.3 Tg C/yr (17% of terrestrial NPP). During the projection period (2010-2099), carbon storage of terrestrial ecosystems of Alaska was projected to increase (22.5-70.0 Tg C/yr), primarily because of NPP increases of 10-30% associated with responses to rising atmospheric CO , increased nitrogen cycling, and longer growing seasons. Although carbon emissions to the atmosphere from wildfire and wetland CH were projected to increase for all of the climate projections, the increases in NPP more than compensated for those losses at the statewide level. Carbon dynamics of terrestrial ecosystems continue to warm the climate for four of the six future projections and cool the climate for only one of the projections. The attribution analyses we conducted indicated that the response of NPP in terrestrial ecosystems to rising atmospheric CO (~5% per 100 ppmv CO ) saturates as CO increases (between approximately +150 and +450 ppmv among projections). This response, along with the expectation that permafrost thaw would be much greater and release large quantities of permafrost carbon after 2100, suggests that projected carbon gains in terrestrial ecosystems of Alaska may not be sustained. From a national perspective, inclusion of all of Alaska in greenhouse gas inventory reports would ensure better accounting of the overall greenhouse gas balance of the nation and provide a foundation for considering mitigation activities in areas that are accessible enough to support substantive deployment.

Local-scale Arctic tundra heterogeneity affects regional-scale carbon dynamics

“…5 ). This projected increase in soil carbon storage was in line with twenty-first century simulations in northern Alaska 83 and the Pan-Arctic 4 . As compared to Pan-Arctic Permafrost Carbon Network model intercomparison 4 , TEM models consistently project higher rates of soil carbon sequestration than other models that do not include nitrogen dynamics, as net primary production is enhanced by nitrogen availability with soil warming.…”

“…As compared to Pan-Arctic Permafrost Carbon Network model intercomparison 4 , TEM models consistently project higher rates of soil carbon sequestration than other models that do not include nitrogen dynamics, as net primary production is enhanced by nitrogen availability with soil warming. Compared to simulations from a previous version of TEM that used a single parameterization to represent Arctic tundra wetlands of northern Alaska 83 , our soil carbon accumulation rates were still overestimated by as much as 75.4%. If these tundra wetland simulations 83 were implemented with at least two parameterizations (i.e., dry and wet), our findings estimate a threefold decrease in the error of prediction.…”

Cross‐scale controls on carbon emissions from boreal forest megafires

“…Using these results, we estimated a total of 94.3 ± 7.9 Tg C emitted from 2.85 Mha of burned area across the entire 2014 NWT fire complex. These C emissions offset almost 50% of mean annual NEP in terrestrial ecosystems of Canada (197 Tg C year −1 over the period 1990–2012; Chen, Hayes, & McGuire, ) and over ten times the mean annual NEP of boreal forest ecosystems of Alaska (8.3 Tg C year −1 over the period 1950–2009; McGuire et al., ).…”

Introduction to the Alaska Carbon Cycle Invited Feature

“…The synthesis of McGuire et al. () estimates that carbon storage of upland and wetland ecosystems of Alaska will increase by 22–70 Tg C/yr during the projection period, primarily because of net primary production increases of 10% to 30% associated with responses to rising atmospheric carbon dioxide, increased nitrogen cycling, and longer growing seasons. However, sensitivity analyses suggest that projected carbon sequestration in upland and wetland ecosystems of Alaska would be rather transient in nature and may not be sustained beyond the end of this century.…”

“…The approach taken in this Invited Feature is to provide analyses for Alaska of (1) the drivers (i.e., climate, fire, and permafrost dynamics) of historical ) and projected (2010-2099) carbon cycle dynamics (Pastick et al 2017), (2) the responses of historical and projected vegetation and soil organic carbon stocks and fluxes to these drivers in upland (Genet et al 2018) and (3) wetland ecosystems (Lyu et al 2018), (4) and river transport of dissolved organic and inorganic carbon, the emissions of carbon dioxide and methane from inland water surfaces, and the burial of carbon in lake sediments (Stackpoole et al 2017). Finally, the paper by McGuire et al (2018) provides an overall synthesis of historical and projected carbon balance in Alaska's landscapes and discusses carbon policy and management implications.…”