|Credit : Natural Resources Canada, Canadian Forest Service|
But that spooling out of long-buried fossil carbon isn't the only way in which we're pulling at the threads of the planet's complex tapestry. Another thread, that scientists are just starting to understand, is that of the carbon sunk into the wetland wildernesses of peats and bogs. And a study, released last year in Nature Communications, confirms the less-than-firm grip that researchers have on the flow of carbon, for these murkier parts of the planet.
It seems that what was thought to be a carbon sink is able to transform itself into a massive carbon pump - literally in just a flash of smoke.
Carbon is pooled in many places in the complex flow of the carbon cycle. Such 'sinks' are places where carbon is not easily released from, and so is kept from boosting the atmospheric CO2 count. In that sense carbon stores are important buffers against runaway global warming. The biggest such stores are to be found in the oceans, and deeply-buried rocks. But wetlands also play a part in storing carbon, on a smaller scale.
Such peats and bogs are no trifling part of the cycle, though – holding 200-500 billion metric tons of carbon in their thick, black, water-logged soils. The draining of these wetlands, for farming and settlement, poses a real potential risk of unraveling one of the planets most-vulnerable carbon stores. That risk is one that the researchers from Canada wanted to help nail down.
It has been shown previously that draining wetlands can, in many cases, actually increase the amount of carbon being stored in their peaty soils. When these soils are drier, trees grow more profusely – and they lock more carbon up as they grow, as well as enriching the soil. But unfortunately, this new paper shows that when the soils are drier they become more vulnerable to fire. And such wild fires pump massive amounts of CO2 right back into the atmosphere – up to nine times more than the short-term carbon boost from the growing trees.
′Nobody had looked at the impacts of dewatering on fire intensity and associated carbon gains or losses,′ paper co-author Donohue reported. ′Even though the organic matter accumulation doubled over two decades after drainage, severe burning triggered the complete loss of this newly stored carbon, plus a further 450 years' worth of peat accumulation.′
The good news is that maybe – just maybe – we can put a ring-fence around these vital bulwarks in our defense against climate change, before they fall foul of the global land-grab. The bad news is that many wetlands lying in the far north – in a vast ring around Canada and Siberia – are drying out already, as temperatures there soar. And fires there are multiplying. It may well be that some of the threads we have been picking at, are threatening to unravel of their own accord.