The Alaska Land Carbon Assessment: Baseline and Projected Future Carbon Storage and Greenhouse-gas Fluxes in Ecosystems of Alaska

Monday, December 14, 2015 - 11:20
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The Alaska Land Carbon Assessment was conducted to inform mitigation and adaptation policies and land management decisions at sub-regional, regional, and national scales. Ecosystem carbon balance of Alaska was estimated for two time periods, a historical period (1950-2009) and a projected period (2010-2099) by synthesizing results for upland, wetland, and inland aquatic ecosystems. The total area of Alaska considered in this assessment was 1,474,844 km2, which is composed of 84 percent uplands, 12 percent wetlands, and 4 percent inland waters. Between 1950 and 2009 the upland and wetland ecosystems of the state sequestered an average of 4.4 TgC/yr, which is almost 2 percent of net primary production (NPP) by upland and wetland ecosystems. However, this sequestration is spatially variable with the northern boreal sub-region losing C because of fire disturbance and other sub-regions gaining carbon. For inland aquatic ecosystems, there was a net combined carbon flux through various pathways of 41.2 TgC/yr, or about 17 percent of upland and wetland NPP. The greenhouse gas forcing potential of upland and wetland ecosystems of Alaska was approximately neutral during the historical period, but the state as a whole could be a source for greenhouse gas forcing to the climate system from methane emissions from lake ecosystems, which were not considered in the assessment. During the projected period (2010-2099), carbon sequestration of upland and wetland ecosystems of Alaska would increase substantially (18.2 to 34.4 TgC/yr) primarily because of an increase in NPP of 8 to 19 percent associated with responses to rising atmospheric CO2, increased nitrogen cycling, and longer growing seasons. Although C emissions to the atmosphere from wildfire increase substantially for all of the projected climates, the increases in NPP more than compensate for those losses. The analysis indicates that upland and wetland ecosystems would be sinks for greenhouse gases for all scenarios during the projected period. However, as in the case of the analysis of the historical period, there is an uncertainty as whether the state could be a net source for GHG if emissions of CH4from lakes in Alaska were considered.