Reducing Air Pollution Could Increase Methane Emissions From Wetlands Here's What Needs To Be Done

(MENAFN- The Conversation) What if well-meaning policies that reduce one atmospheric pollutant could also increase natural emissions of powerful greenhouse gases?

Our findings, just published in the journal Science Advances , advance an earlier discovery of one such unfortunate interaction. This means that we need to work much harder than we thought to stay within the safe climate limits of the Paris agreement .

The atmospheric pollutant in question is sulphur. Its current and projected decline from clean air policies aimed at reducing acid rain and fine particles, coupled with direct effects of increasing atmospheric CO2 and warming, will lead to larger natural wetland methane emissions than expected.

This is because sulphur has a very specific effect in natural wetlands that reduces methane emissions. On the other hand, CO2 boosts methane production by increasing growth in plants that make the food for methane-producing microbes.

Put simply, sulphur provides the conditions for one set of bacteria to outmuscle another set of microbes that produce methane over limited available food in wetlands. Under the conditions of acid rain sulphur pollution during the past century, this was enough to reduce wetland methane emissions by up to 8%.

If we lift this sulphur“lid” on wetland methane production and increase CO2, we have a double whammy effect that pushes wetland emissions much higher.

We first discovered this effect in the early 2000s with field experiments that simulated acid rain sulphur pollution in the peatlands of North America, Scotland and Scandinavia. Further similar experiments took place on methane-emitting rice.

Now, more than 20 years on, we have better modelling approaches that allow us to use improved estimates of the future of sulphur pollution and CO2 for a range of scenarios. This allows us to link these back to methane emissions.

A water hyacinth meadow in the Pantanal, Brazil. Vincent Gauci , CC BY-NC-ND

The effect is substantial and we estimate that these different factors, in combination, will mean that policy instruments like the global methane pledge, which addresses anthropogenic emissions of methane, may need to work much harder.

More than 150 nations signed up to the global methane pledge at the UN climate summit, Cop26, in Glasgow. The pledge seeks to reduce emissions of anthropogenic methane by 30% on a 2020 baseline by 2030.

If successful, the climate benefit can be substantial (methane is around 30-80 times more potent than CO2 as a greenhouse gas) and fast-acting. This is because methane only lasts in the atmosphere for around 10 years, leading to a rapid 0.2°C climate dividend by 2050.

Read more: Methane is pitched as a climate villain – could changing how we think about it make it a saviour?

However, our findings show that between 8% and 15% of the allowable space for these human-made emissions is disappearing. This is due to the climate, CO2 fertilisation, and sulphur unmasking effects. So, larger cuts are needed to achieve the same Paris climate targets.

This isn't the first time that the loss of an apparent broad climate-cooling action of atmospheric sulphur has been implicated in driving warming at a faster rate than anticipated.

Drainage canal in the Kampar peat swamp forest, Sumatra, Indonesia. Vincent Gauci , CC BY-NC-ND

In 2020, shipping pollution controls were introduced globally to reduce emissions of sulphur dioxide and fine particles that are harmful to human health. This reduction in atmospheric sulphur over the oceans has been implicated in larger warming effects than expected in what has come to be known as“termination shock”.

Part of the warming effect of emitted CO2 is effectively masked by cooling sulphate particles in the atmosphere. If the source of the sulphate is stopped, the remaining sulphur in the atmosphere drops out rapidly, unmasking the warming effect of the CO2 which lasts over 100 years in the atmosphere. For natural wetlands the unmasking effect on methane emissions can take a little longer, more a“termination rebound” than shock – but it soon catches up.

Intentional interventions?

So what can be done? In another paper recently published in Global Change Biology , scientists propose direct intervention in natural wetland methane emissions through adding sulphate to these ecosystems, essentially – and this time deliberately – replacing the sulphate lid on the wetland methane source. This raises questions about what a natural wetland actually is.

Acacia plantation on former peat swamp forest after harvest, Sumatra, Indonesia. Vincent Gauci , CC BY-NC-ND

What are the environmental ethics of deliberately intervening in this manner for ecosystems that are only just recovering from past incidental pollution effects? In emitting methane, they are, ultimately, just performing their natural function and should be protected for the vast carbon stores they contain and the valuable biodiversity that makes these ecosystems their home.

So, we need to go back to the framework set up by the global methane pledge which is prompting much innovation to reduce human emissions from fossil fuel industries, waste and agriculture. We need to work harder on emissions first and foremost while also considering technologies to actively remove methane from the atmosphere.

Atmospheric methane removal technologies are a new and under-investigated approach to managing atmospheric methane and they could be as simple as growing more trees .

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