Are wetlands effective against climate change?

Question

In the region where I live, there is a trend that conservation organizations are advocating the conservation and re-valuation of wetlands.

Aside from boosting biodiversity and providing other ecological services, the conservationists argue that wetlands capture a lot of carbon.

I know however that wetlands are notorious for steady state methane emission [1][2], so it sounds dubious whether a single-time carbon-capture or carbon-release can compensate a significant steady-state emission of a potent greenhouse gas.

Are there cost-benefit-analyses out there regarding the effect of wetlands on climate? What is your take?

Answer 1

There's a misinterpretation in the "steady state" part, that's not what the linked paper says. It clearly states the figures are temperature dependent, and it says that in response to global warming wetlands are going to release more Methane and tries to quantify the amount. It concludes that

This finding highlights the importance of limiting global warming below 2°C to avoid substantial climate feedbacks driven by methane emissions from natural wetlands.

'Feedback' is the keyword here. Such a feedback is an accelerated response of a system to global warming. Grossly simplifying, in case of small shallow wetlands CH₄ release is connected to the level of oxic and anoxic conditions, the latter expanding not only in the table of a local 'puddle' but also geographically from lower to higher latitudes with temperature and so releasing more CH₄ in a warmer climate, which warms the climate and so on. But the ability of these ecosystems to bind carbon from the atmosphere drops with rising temperature, and the amount of released carbon rises.

That is by no means an argument against the conservationists who are advocating conservation and re-valuation to help sequester carbon.

This analysis can help inform practitioners and landscape managers [...] foster the worldwide implementation of wetland restoration, creation, and conservation projects for sustainable development and climate change mitigation and adaptation.

So, yes, for now wetlands are effective against climate change as long as anthropogenic global warming is limited.

Answer 2

It seems that there is indeed a strong "climate-case" in favour of wetlands: Below follows a bullet-list of several facts and arguments, which among other things undermine the premises of my question (to a certain degree):

• Currently, 3% of the land surface is covered by peat lands. But it is estimated that up to 1/3 of all terrestrial carbon is stored in those peat lands, giving a big edge in carbon sequestration/m² over any other type of vegetation. Although these peat lands convert some of their intake of CO₂ in the more potent greenhouse gas CH₄, it is clear that the remedy is certainly not to 'drain the swamp' in a short time-window in a way where all the carbon is injected in the atmosphere. Since the latter is exactly the threat posed to many wetlands nowadays, there is clear and in some cases perhaps decisive motivation and urgency for the conservation and protection of existing wetlands.

• Organic methanogenesis appears strongly temperature-dependent: satellite data show the tropical regions as the main global sources. Laboratory experiments roughly confirm that picture, although many questions remain unanswered and methanogenesis seems to depend on a wide range of variables. In any case, in temperate and boreal regions the wetland-contribution in CH₄-emission often pales in comparison to agricultural and industrial sources (in Flanders, agriculture contributes 20-fold the CH₄ contribution from rivers and wetlands). Hence, in densely-populated temperate and boreal regions, the CH₄-emission-argument may be moot since there are more opportune alternative options for climate-change mitigation, with less collateral consequences (wetlands provide biodiversity, hydrological stability etc).

• The argument that wetlands saturate and stop net intake of carbon may be partly false and largely irrelevant: A mature peatland may reach a depth varying from 2 to 20 meters, while a peatland's annual growth is typically of order 1 mm/ year. With some audacity, I propose to infer that a peatland then needs a time of order 10m/(10^-3 m/year)= 10000 years to grow to maturity. During that time, it did absorb carbon to grow. Since 10000 years dwarfs the time-scale in which humanity is to overcome and adapt to climate change, the saturation-argument against reinstating or re-valuation of peatlands is irrelevant. The saturation-argument might be weakened even more if one includes in the calculation the depth of the coal-seam which is often found below a mature peatland.