Complexities in Evaluating the Pace of Climate Change — How Will Drying Peatlands Affect the Carbon Cycle?

© 2011 Peter Free

 

03 November 2011

 

 

The answer is that we can’t yet tell — and that’s the point about complexity’s ability to surprise us

 

Bear with me on this one.  It’s a paradoxically good illustration of why making specific and quantifiable predictions about climate change is difficult.

 

 

Drying northern peatlands and climate surprises

 

A recent, more or less fortuitous “natural” study about burning peatlands juxtaposed two probably important facts:

 

First, revegetation, due to the drying of northern peatlands, can actually increase carbon sequestration from the atmosphere by two-fold — which theoretically would assist in reducing the pace of global warming.

 

On the other hand, the same de-watering of peatlands can lead to fires, which increase carbon release into the atmosphere by nine-fold — which would very much aggravate climate warming.

 

 

Citation

 

M.R. Turetsky, W.F. Donahue, and B.W. Benscoter, Experimental drying intensifies burning and carbon losses in a northern peatland, Nature Communications, doi: 10.1038/ncomms1523 (01 November 2011)

 

How this study was done

 

The study examined what happened, when drained wetlands near Slave Lake (Alberta, Canada) caught fire in 2001.  Researchers were able to compare carbon sequestration and release effects between burned and unburned portions.

 

 

Background about peatlands — and why they matter to climate

 

I use Wikipedia here because its article on peat is well written and documented.

 

Wikipedia estimates that about 60 percent of the world’s wetlands take the form of peatlands, where much of the vegetation is only partially decayed and held in that state by acidic and anaerobic conditions.

 

These places are also called “bogs, moors, muskegs, pocosins, mires, and peat swamp forests.”

 

Such lands cover about 2 percent of the world’s terrestrial area:

 

The world's peatlands are thought to contain 180 to 455 billion metric tons of sequestered carbon, and they release into the atmosphere 20 to 45 million metric tons of methane annually.

 

The peatlands' contribution to long-term fluctuations in these atmospheric gases has been a matter of considerable debate.

 

© 2011 Peat, Wikipedia (visited 03 November 2011) (paragraph split)

 

 

“So what happens when peatlands dry up, either from climatic warming or from human activity?”

 

If peatlands dry out, the watery acidic conditions that held the decaying matter in suspended state are going to disappear.  That means vegetative decomposition resumes, with its attendant release of carbon dioxide — generated from carbon in the plant materials — back into the atmosphere.

 

Because CO2 contributes to global warming, drying peatlands theoretically contribute to increased temperatures.

 

And, as the cycle of warming continues, more of the peatlands will presumably dry up, even without human beings intentionally de-watering them.

 

Positive feedback, commonly called a “vicious circle,” ensues.  More climate warming leads to more wetland drying, which leads to increased carbon dioxide release, which leads to still more warming and escalated drying — and so on.

 

 

Of course, it never is quite that simple — de-watering peatlands is not always bad for global warming

 

Research has shown that carbon dioxide sequestration from the atmosphere can actually increase two-fold, when de-watered peatlands permit forests and other vegetation to invade.

 

In contrast to dead peat, new plants actively take up CO2.  That’s one reason why people who want to control global warming would like to see us reforest de-forested regions.

 

 

On the other hand, burning peatlands probably aggravate climate warming

 

This is where the mathematically fun part comes in.

 

According to the study, if the dried peat burns, it releases nine times the amount of carbon dioxide back into the atmosphere (than it did before it burned).

 

So, in sum, we have two climate-affecting alternatives for dried peatlands:

 

In the first, drying encourages the in-growth of new plants that take up 2 times the CO2 that the peat sequestered previously.

 

In the second, the dried peat catches fire and releases 9 times the CO2 that it had before.

 

In regard to climate warming, we have a “battle” between the ratios.

 

At least theoretically, too frequent or too geographically extensive peat fires would overwhelm the benefit of new plants’ contributions to mitigating climate change:

 

[D]rainage also increased carbon losses during wildfire ninefold to 16.8±0.2 kg C m−2, equivalent to a loss of more than 450 years of peat accumulation.

 

Interactions between peatland drainage and fire are likely to cause long-term carbon emissions to far exceed rates of carbon uptake, diminishing the northern peatland carbon sink.

 

© 2011 M.R. Turetsky, W.F. Donahue, and B.W. Benscoter, Experimental drying intensifies burning and carbon losses in a northern peatland, Nature Communications, doi: 10.1038/ncomms1523 (01 November 2011) (from the abstract, paragraph split)

 

 

“Gimme an example of peatland fires’ probable magnitude of effect, Pete”

 

Fred Pearce, writing in the NewScientist, gives us a good example of the impressive magnitude of peat fires’ effect on climate:

 

The peat bogs of Borneo and the neighbouring territories of Sumatra and Irian Jaya are up to 20 metres deep and cover more than 200,000 square kilometres.

 

They contain 50 billion tonnes or more of carbon - far more than the forests above.

 

As farmers clear the forests by burning, the bogs catch fire and release carbon for months afterwards.

 

In 2002, Rieley and his colleagues estimated that during 1997 and 1998 smouldering peat beneath the Borneo forests released between 0.8 and 2.6 billion tonnes of carbon into the atmosphere.

 

That is equivalent to 13 to 40 per cent of all emissions from burning fossil fuels, and contributed to the CO2 peak in 1998.

 

© 2004 Fred Pearce, Massive peat burn is speeding climate change, NewScientist (06 November 2004)

 

 

Citation — to Fred Pearce’s scientific source

 

Susan E. Page, Florian Siegert, John O. Rieley, Hans-Dieter V. Boehm, Adi Jaya, and Suwido Limin, The amount of carbon released from peat and forest fires in Indonesia during 1997, Nature 420(6911): 61-65 (07 November 2002) (paragraph split)

 

 

Citation — to outstanding lay coverage of the same Indonesian fires

 

Cat Lazaroff, Indonesian Wildfires Accelerated Global Warming, Environmental News Service (08 November 2002)

 

 

The moral? — nothing about predicting the specific effects and magnitude of climate change is simple

 

And, paradoxically, that is why “averaged” trends are meaningful.