Emerging role of wetland methane emissions in driving 21st century climate change

Abstract

Wetland methane (CH 4 ) emissions are the largest natural source in the global CH 4 budget, contributing to roughly one third of total natural and anthropogenic emissions. As the second most important anthropogenic greenhouse gas in the atmosphere after CO 2 , CH 4 is strongly associated with climate feedbacks. However, due to the paucity of data, wetland CH 4 feedbacks were not fully assessed in the Intergovernmental Panel on Climate Change Fifth Assessment Report. The degree to which future expansion of wetlands and CH 4 emissions will evolve and consequently drive climate feedbacks is thus a question of major concern. Here we present an ensemble estimate of wetland CH 4 emissions driven by 38 general circulation models for the 21st century. We find that climate changeinduced increases in boreal wetland extent and temperature-driven increases in tropical CH 4 T errestrial wetlands are among the largest biogenic sources of methane contributing to growing atmospheric CH 4 concentrations (1) and are, in turn, highly sensitive to climate change (2). However, radiative feedbacks from wetland CH 4 emissions were not considered in the Coupled Model Intercomparison Project Phase 5 (CMIP5), and Integrated Assessment Models (IAM) assumed anthropogenic sources to be the only driver responsible for the increase of atmospheric CH 4 burden since the 1750s (3). The role of wetland CH 4 emissions, however, may play an increasingly larger role in future atmospheric growth of methane because of the large stocks of mineral and organic carbon stored under anaerobic conditions in both boreal and tropical regions. Paleoclimatological and contemporary observations of the climate sensitivity of wetland methane emissions suggest the potential for a large feedback (4), but there remains large uncertainty in quantifying the actual range of the response (5, 6).Increasing air temperature is linked to the thawing of permafrost and to increased rates of soil microbial activity (7), which directly lead to greater CH 4 production in soils due to thaw-induced change in surface wetland areas (8). In the tropics, wetland areal extent is also influenced by precipitation, which affects the area of surface inundation, water table depth, and soil moisture that, in turn, promote methanogenesis. Elevated CO 2 concentrations can increase ecosystem water use efficiency and thus soil moisture, and also increase soil carbon substrate availability for microbial activities (9). Tropical wetlands, for which a decline in inundation was observed in recent decades (10), are already exposed to increasing frequencies in extreme climate events, e.g., heat waves, floods, and droughts, and changes in rainfall distribution (11) and variability in methane emissions (12). Meanwhile, northern highlatitude ecosystems are experiencing a more rapid temperature increase than elsewhere globally and with increased rates of soil respiration (13), yet, locally at least, no response in methane emissions (14). Despite the importance of these feedbacks noted by the Intergovernmen...

Methane Feedbacks to the Global Climate System in a Warmer World

“…However, these estimates do not include water level changes or direct temperature effects, which have a slight negative and a slight positive effect, respectively. A recent model ensemble that incorporates temperature effects predicted a similar range of wetland CH 4 emissions by 2100 (338 ± 28 Tg CH 4 yr −1 , RCP8.5) but a larger percentage increase relative to the ensemble's current predicted level of CH 4 emissions from wetlands (80–113%) (Zhang et al, ). We indicate an immediate feedback response from wetlands as rising precipitation increases wetland areas and the area of individual water bodies, which may already be occurring in the tropics (Nisbet et al, ), but this will be balanced between drought and increased water saturation (O'Connor et al, ).…”

A Biogeochemical Compromise: The High Methane Cost of Sequestering Carbon in Restored Wetlands

“…· m À2 · year À1 ), are net GHG sinks (Figure 1). Zhang et al, 2017). · m À2 · year À1 ) and 2017 (À229.7 ± 321.2 g CO 2 eq.…”

“…Previous work has pointed out that over multicentury to geologic timescales, wetlands commonly exhibit net negative radiative forcing (cooling), due to the short lifetime and dissipating effect of atmospheric CH 4 (Frolking & Roulet, 2007;Frolking et al, 2006;Mitsch et al, 2013). This long-term climate benefit notwithstanding, mounting evidence points to the urgency of climate change mitigation to prevent runaway land-atmospheric feedbacks (Arneth et al, 2010;Z. This long-term climate benefit notwithstanding, mounting evidence points to the urgency of climate change mitigation to prevent runaway land-atmospheric feedbacks (Arneth et al, 2010;Z.…”

The effects of management on long‐term carbon stability in a southeastern U.S. forest matrix under extreme fire weather

“…Further, the belowground dynamics in the carbon-rich soils of wetland forests can potentially release large amounts of sequestered carbon in the form of CH 4 with increases in temperature and changes in soil moisture, resulting in significant feedbacks to climate (Zhang et al 2017). This is a process not described by LANDIS-II or any of its extensions.…”