| 03 Sep 2025
Natural wetland methane emissions simulated by ICON-XPP
Abstract. Methane emissions from natural wetlands account for about 1/3 of global methane emissions, and thus have a significant climatic impact due to methane’s high global warming potential. Among the sources of methane, those from natural wetlands have the highest uncertainty, and it is thus of key importance to understand and reduce the uncertainties in the estimates of the wetland emissions to be able to close the global methane budget. Using a coupled land and atmosphere setup, a new implementation of interactive wetlands and wetland methane emissions into the ICON-XPP Earth System Model was used to test the sensitivity of the wetland methane emissions to a number of hydrological and biogeochemical model assumptions of which some are mimicing anthropogenic influences on the Earth System. Averaged over the historical period (1855–2014) the simulated emissions are 166.2 (156.3–181.2) Tg(CH4) yr-1. For the 2000–2012 period the equivalent numbers 182.3 (154.3–205.1) Tg(CH4) yr-1 are in good agreement with estimates from other studies. Wetland methane emissions rise by about 12 % during the historical period, mainly since 1980, an increase which is due to an enhanced carbon cycle caused by the CO2 fertilization associated with rising atmospheric CO2 concentrations. The modeled emissions are very sensitive to changes and assumptions in the model hydrology, some dependencies only revealed through the interaction with the atmosphere (changes in the moisture recycling patterns). Therefore offline land models are only of limited value to test the influence of changes in model hydrology, which is also influenced by changes in terrestrial vegetation.
I have several minor, editorial comments:
You say “interactive” as a key feature of your model, but I am almost sure that you mean “iterative”
An interactive model requires some back and forth response of the user, whereas iterative model uses a calculation that repeats estimating the solution until convergence to an accurate solution.
You did not describe any interface for collecting interactive user response. I therefore assume that you mean “iterative”.
On second reading, I think that by “interactive” you mean that the atmosphere is driving and getting feedback from the surface emission model. That will make it a “coupled atmosphere-land surface model”. You do use the term “coupled model” in the discussion. I still don’t think “interactive” is the best term to use here.
Abstract
As your main goal is stated “to test the sensitivity of the wetland methane emissions”, and especially because your model is not globally validated to the methane emissions, please provide more information on what you found in that regard to sensitivity to different anthropogenic effects, and less details about what the exact numbers for methane emission were as determined by the model.
General editing
In L68 and everywhere else in the manuscript, correct “wetland extend” to “wetland extent”. “Extend” is a verb. The noun is “extent”.
You need a comma before every “e.g.”, and before most “which”, after “therefore”, and around “however”.
Methods
L66 – what do you mean by “5”? (“...presented in Marthews et al. (2015) and 5.”)
Subsection 2.2 – were these parameters constant EVERYWHERE? That is highly unrealistic
L97 “via diffusion, ebullition and plant aerenchyma”. Where did you come up with the diffusion parameters, and especially the aerenchyma transport parameters?
Discussion
L268-278 this sentence is way too long. I got lost. Please break it to shorter statements.