Climate-CH<sub>4</sub> feedback from wetlands and its interaction with the climate-CO<sub>2</sub> feedback

Abstract

The existence of a feedback between climate and methane (CH₄) emissions from wetlands has previously been hypothesized, but both its sign and amplitude remain unknown. Moreover, this feedback could interact with the climate-CO₂ cycle feedback, which has not yet been accounted for at the global scale. These interactions relate to (i) the effect of atmospheric CO₂ on methanogenic substrates by virtue of its fertilizing effect on plant productivity and (ii) the fact that a climate perturbation due to CO₂ (respectively CH₄) radiative forcing has an effect on wetland CH₄ emissions (respectively CO₂ fluxes at the surface/atmosphere interface). <br><br> We present a theoretical analysis of these interactions, which makes it possible to express the magnitude of the feedback for CO₂ and CH₄ alone, the additional gain due to interactions between these two feedbacks and the effects of these feedbacks on the difference in atmospheric CH₄ and CO₂ between 2100 and pre-industrial time (respectively ΔCH₄ and &Delta;CO₂). These gains are expressed as functions of different sensitivity terms, which we estimate based on prior studies and from experiments performed with the global terrestrial vegetation model ORCHIDEE. <br><br> Despite high uncertainties on the sensitivity of wetland CH₄ emissions to climate, we found that the absolute value of the gain of the climate-CH₄ feedback from wetlands is relatively low (<30% of climate-CO₂ feedback gain), with either negative or positive sign within the range of estimates. Whereas the interactions between the two feedbacks have low influence on &Delta;CO₂, the &Delta;CH₄ could increase by 475 to 1400 ppb based on the sign of the C-CH₄ feedback gain. <br><br> Our study suggests that it is necessary to better constrain the evolution of wetland area and the substrate for methanogenesis under future climate change, as these are the dominant sources of uncertainty in our model

Source attribution of the changes in atmospheric methane for 2006–2008

“…The simulated space-time distribution of saturated soils is evaluated globally (Ringeval et al, 2011a) against inundated area derived from a suite of satellite observations from multiple sensors of Prigent et al (2001Prigent et al ( , 2007. As explained in Ringeval et al (2011b), we use Prigent et al (2001) satellite data to represent wetland areas and compute anomalies from the saturated area given by TOPMODEL, relatively to the 1993-2000 climatology given by the satellite data. Moreover, in the present work, for boreal ecosystems, resulting wetlands are further filtered using soil organic carbon data as done by Wania et al (2010) to diagnose the presence of peatlands.…”

“…Wetland CH 4 emissions are computed using the global vegetation model ORCHIDEE, which simulates land energy budgets, hydrology and carbon cycling (Krinner et al, 2005), and which has been further developed to compute CH 4 emissions from natural wetlands (Ringeval et al, 2010(Ringeval et al, , 2011b. CH 4 emissions are computed monthly for each 1 • × 1 • model grid cell as the product of an emitting water saturated area by a flux density for the period 1990-2008 (see Appendix).…”

“…In this paper, we investigate the changes in atmospheric CH 4 for 2006-2008 using the results of two atmospheric inversion models (Bousquet et al, 2006;Pison et al, 2009) and of a recent ecosystem model for CH 4 wetland emissions (Ringeval et al, 2011b).…”

Present state of global wetland extent and wetland methane modelling: methodology of a model inter-comparison project (WETCHIMP)

“…As in Ringeval et al (2011) the wetland extent is corrected to subtract the systematic biases of the model by normalizing the mean yearly wetland extent to the GIEMS data (i.e. both the seasonal and year to year variability come from TOP-MODEL).…”

WETCHIMP-WSL: intercomparison of wetland methane emissions models over West Siberia

“…Globally, wetlands are the largest natural source of CH 4 emissions to the atmosphere (IPCC, 2013). Because wetland CH 4 emissions are highly sensitive to soil temperature and moisture conditions (Saarnio et al, 1997;Friborg et al, 2003;Christensen et al, 2003;Moore et al, 2011;Glagolev et al, 2011;Sabrekov et al, 2014), there is concern that they will provide positive feedback to future climate warming (Gedney et al, 2004;Eliseev et al, 2008;Ringeval et al, 2011). This risk is particularly important in the world's high latitudes because they contain nearly half of the world's wetlands (Lehner and Döll, 2004) and because the high latitudes have been and are forecast to continue experiencing more rapid warming than elsewhere (Serreze et al, 2000;IPCC, 2013).…”