Enhanced terrestrial carbon uptake in the Northern High Latitudes in the 21st century from the Coupled Carbon Cycle Climate Model Intercomparison Project model projections

Abstract

The ongoing and projected warming in the northern high latitudes (NHL; poleward of 601N) may lead to dramatic changes in the terrestrial carbon cycle. On the one hand, warming and increasing atmospheric CO 2 concentration stimulate vegetation productivity, taking up CO 2 . On the other hand, warming accelerates the decomposition of soil organic matter (SOM), releasing carbon into the atmosphere. Here, the NHL terrestrial carbon storage is investigated based on 10 models from the Coupled Carbon Cycle Climate Model Intercomparison Project. Our analysis suggests that the NHL will be a carbon sink of 0.3 AE 0.3 Pg C yr À1 by 2100. The cumulative land organic carbon storage is modeled to increase by 38 AE 20 Pg C over 1901 levels, of which 17 AE 8 Pg C comes from vegetation (43%) and 21 AE 16 Pg C from the soil (8%). Both CO 2 fertilization and warming enhance vegetation growth in the NHL. Although the intense warming there enhances SOM decomposition, soil organic carbon (SOC) storage continues to increase in the 21st century. This is because higher vegetation productivity leads to more turnover (litterfall) into the soil, a process that has received relatively little attention. However, the projected growth rate of SOC begins to level off after 2060 when SOM decomposition accelerates at high temperature and then catches up with the increasing input from vegetation turnover. Such competing mechanisms may lead to a switch of the NHL SOC pool from a sink to a source after 2100 under more intense warming, but large uncertainty exists due to our incomplete understanding of processes such as the strength of the CO 2 fertilization effect, permafrost, and the role of soil moisture. Unlike the CO 2 fertilization effect that enhances vegetation productivity across the world, global warming increases the productivity at high latitudes but tends to reduce it in the tropics and mid-latitudes. These effects are further enhanced as a result of positive carbon cycle-climate feedbacks due to additional CO 2 and warming.

Tundra in the Rain: Differential Vegetation Responses to Three Years of Experimentally Doubled Summer Precipitation in Siberian Shrub and Swedish Bog Tundra

“…Climatic changes, which are currently increasing decomposition rates of old carbon, threaten to change the tundra from a carbon sink into a source (Dorrepaal et al 2009). In contrast, enhanced vegetation productivity in response to climatic changes may increase net storage of carbon in these systems in the near future (Qian et al 2010). Hence, climatic changes alleviating growth-limiting factors of tundra vegetation have a potential to feed back to the global carbon cycle.…”

“…In addition to low temperature and low nutrient availability (Chapin et al 1995;Shaver et al 2001;Aerts et al 2006;Elmendorf et al 2012), water shortage is frequently listed as one of the growth-limiting factors for tundra vegetation (e.g. Bliss et al 1994;Ostendorf and Reynolds 1998;Press et al 1998a;Hodkinson et al 1999;Kade et al 2005;Qian et al 2010). However, the notion that growth of tundra vegetation is water limited is largely based on observational evidence: the best-developed arctic plant communities are often found at sites where snowmelt water or seasonal streambeds keep the soil moist (Bliss et al 1984(Bliss et al , 1994Kade et al 2005).…”

Increased nitrous oxide emissions from Arctic peatlands after permafrost thaw

“…Recent reports indicate a browning trend for the Arctic (31), seemingly reversing the enhanced plant growth referred to as Arctic greening predicted by the majority of carbon models (32). Arctic browning, triggered by factors such as winter warming, extreme weather events, tundra fires, and thermokarst development (31), may be an important driver promoting Arctic N 2 O emissions in the future.…”

Attribution of divergent northern vegetation growth responses to lengthening non-frozen seasons using satellite optical-NIR and microwave remote sensing

“…The FT metrics were compared against atmosphere CO 2 seasonal shape metrics defined from HNL monitoring stations represented by the NOAA ESRL GLOBALVIEW-CO 2 record (GLOBALVIEW-CO 2 2011). Because seasonal CO 2 cycles are strongly influenced by regional differences between ecosystem net carbon uptake (NPP) and carbon release from soil heterotrophic respiration, biomass burning, and anthropogenic emissions (Patra et al 2005;Qian, Joseph, and Zeng 2010;Randerson et al 1997;Sitch et al 2007), it is necessary to address issues on the sparseness and temporal discontinuity in CO 2 observations when defining atmospheric CO 2 seasonal shape metrics (Vadrevu and Choi 2011;Xueref-Remy et al 2010). Since the GLOBALVIEW-CO 2 record is derived from the integration of surface, tower, and aircraft measurements by an atmospheric transport model (Masarie and Tans 1995), this record is considered suitable for representing aggregated HNL atmospheric CO 2 variability (Higuchi et al 2003;Murayama, Taguchi, and Higuchi 2004).…”

“…Recent environmental changes attributed to HNL warming include earlier and longer potential growing seasons (Nemani et al 2003;Kim et al 2012), vegetation greening Bunn and Goetz 2006;Hudson and Henry 2009) and productivity increases ), a northward shift in vegetation biomes , and tundra shrub expansion (McManus et al 2012;Tape et al 2012). HNL vegetation growth is primarily constrained by seasonal cold temperatures (Nemani et al 2003;Friedlingstein et al 2006;Qian, Joseph, and Zeng 2010), but recent reports indicate that widespread drought and wildfire disturbances exacerbated by continued warming have resulted in the frequent occurrences of tree mortality and declines in boreal productivity (Girardin and Mudelsee 2008;Goetz et al 2005;Peng et al 2011). Spatially extensive patterns of drought-induced vegetation growth decline have also been reported across the HNL domain (Goetz et al 2012;Kim et al 2012;Schaphoff et al 2006;Zhang et al 2008), including interior Alaska (Baird, Verbyla, and Hollingsworth 2012;Verbyla 2008), Canada (Ma et al 2012;Peng et al 2011), and Eurasia (Park and Sohn 2010;Piao et al 2011).…”