Tag Archives: Carbon Sink

Global Warming Could Make Peat Bogs Less Of A Carbon Sink

A new study, “An unexpected role for mixotrophs in the response of peatland carbon cycling to climate warming” by Vincent Jassey and others, just came out in Scientific Reports. The study is fairly preliminary, but fascinating, and unfortunately may signal that yet another effect of global warming that would result in more global warming.

What makes this study interesting is that it examines the detailed ecological relationships between several different kinds of organisms in both field and lab settings, in order to get a handle on what they do when conditions warm. Mixotrophs are organisms that mix up their role in the trophic web, shifting between being producers (using sunlight to make carbohydrates) or consumers (eating either producers or consumers). Several different mixotrophs that photosynthesize can be found in aquatic and semi aquatic ecosystems, but in this study only mixotrophic amoebae were considered. But before revealing what these shape shifting strategy shifters are up to, a word about the carbon cycle.

See: What does “Global Warming” mean?

About 770 gigatons of Carbon Dioxide (note: Not Carbon, but the gas CO2) are added to the atmosphere every year from natural sources. About 780 gigatons are taken in by those same systems. This is today; At various times in the past this has been different. Anyway, about 10 gigatons are removed, on average, per year over time. Human activities, including burning fossil fuel and other factors, add about 30 gigatons a year, for an imbalance of +20 gigatons. This has caused the concentration of the greenhouse gas CO2 in the atmosphere to go from somewhere south of 280ppm (parts per million) to just north of 400ppm since the beginning of the Industrial Era. This has caused global warming.

Adding CO2, and thus retaining more heat on the surface of the planet, could increase biological activity in such a way that natural ecosystems absorb more Carbon, thus offsetting the human contribution. Also, CO2 is plant food. So, with more CO2, and a longer growing season, plants could bulk up and take in more CO2 than normally, offsetting the human-caused imbalance. Unfortunately, this does not happen.

Well, plants may well take in a bit more CO2 and convert it to plant tissues, but other things happen as well. For example, expanding the growing season also means melting permafrost in northern climates. There, huge amounts of Carbon sequestered long term is released (as CO2 or methane, which is also a greenhouse gas and eventually converts to CO2). So warming caused by adding CO2 to the atmosphere has an amplifying effect, causing even more warming, and more amplification, and so on. We refer to this as a positive feedback cycle, but it is not positive at all from the perspective of planetary health.

See this for more information about a negative feedback involving plants that turns out to not be a negative feedback.

Of all that CO2 moving in and out of the natural system, about 890 gigatons is interchanging on the land (soils, vegetation, freshwater ecosystems, etc.) while about 670 gigatons interact with the ocean. This means that a good amount more than half of the carbon cycle happens over land. Of that, several percent (estimates vary) happens in relation to peat bogs. Here the numbers can get a bit misleading. The normal amount of Carbon that goes into, or comes out of, the world’s peat bogs over a period of time under normal conditions may be very small compared to the total amount of carbon stored in those bogs, which might be rapidly released as CO2 or methane if certain things happen. For example, peat is a fuel source, and has been widely mined for many years. In other areas, bogs are drained or covered over. Here in the Twin Cities, vast bogs are now Urban Saint Paul (covered over) or farms growing turf or corn (drained) so whatever they were doing in the early 19th century as part of the natural system, they are not doing that any more. The peat that is burned for fuel or used in smelting operations, etc., adds most of its Carbon to the atmosphere all at once, and thereafter contributes nothing to sequestering carbon.

See: How do human CO2 emissions compare to natural CO2 emissions?

For all these reasons, what happens in peat bogs does not stay in peat bogs. Changes to peat bogs that cause changes in their role in the Carbon cycle may be very important under global warming.

Now, think about this for a second. If you have an organism that can either sequester carbon by acting like a plant, or release carbon (as CO2) by acting as an animal (though it is neither), then what that animal is doing matters to the Carbon cycle. Also, if the organism can either grow and reproduce using mainly sunlight, or consume other organisms at a higher rate, that strategy shifting may influence the entire ecosystem. The new research project looks at all of this, and seems to show that on balance, warming up the ecosystem significantly changes the amounts of Carbon released vs. retained in many peat bogs.

From the Abstract:

…little is known about the responses of peatland mixotrophs to climate change and the potential consequences for the peatland C cycle. With a combination of field and microcosm experiments, we show that mixotrophs in the Sphagnum bryosphere play an important role in modulating peatland C cycle responses to experimental warming. We found that five years of consecutive summer warming with peaks of +2 to +8°C led to a 50% reduction in the biomass of the dominant mixotrophs, the mixotrophic testate amoebae (MTA). The biomass of other microbial groups (including decomposers) did not change, suggesting MTA to be particularly sensitive to temperature. In a microcosm experiment under controlled conditions, we then manipulated the abundance of MTA, and showed that the reported 50% reduction of MTA biomass in the field was linked to a significant reduction of net C uptake (–13%) of the entire Sphagnum bryosphere. Our findings suggest that reduced abundance of MTA with climate warming could lead to reduced peatland C fixation.

The way in which MTA biomass reduction reduces peatland Carbon fixation is not entirely clear. I asked Vincent Jassey, the study’s lead author, how the reduction in biomass of the dominant mixotrophs in the Sphagnum bryosphere reduces overall photosynthesis. He told me that what is measured is the overall rate of photosynthesis of the entire ecosystem, and that further research would be needed to assess exactly what is happening. “MTA are living within/between Sphagnum leaves. So, when we measure photosynthesis on Sphagnum, it takes into account the photosynthesis made by MTA as well,” he said. “This is the first time a paper outlines the potential role of MTA in overall Carbon fixation of bryosphere, showing its potential importance for peatlands…we showed that a decrease of MTA abundance/biomass is linked to a decrease of Sphagnum bryosphere photosynthesis. [So far] we made indirect measurements and this needs to be verified in future research.”

The next step, then, is to how MTA benefits the moss. So far, “…these links are largely unknown. This is something I’m working on. We want to quantify more precisely the contribution of MTA photosynthesis to bryosphere photosynthesis in the field in our future research and see if its response to warming will be significant in term of C loss in peatlands.”

I think this research is important for several reasons. One is that this is a step towards understanding a complex ecological system that makes up a significant percentage of terrestrial ecosystems, which may involve inter-species symbiosis or other important interaction. The other is that this system appears to represent yet another case of amplifying feedback in global warming, where more warming ultimately leads to more warming. Decades ago, many scientists hoped or assumed that the anthropogenic greenhouse effect would be at least partly attenuated by negative feedback systems, where more Carbon is sequestered as a result of warming, but we now know that while this does happen, it is more common to find amplifying feedbacks. This, of course, relates to the question of climate sensitivity. Many factors will determine where the global surface temperatures will equilibrate with a doubling of pre-Industrial CO2 levels in the atmosphere, and how organisms or ecological systems respond to warming is part of that.

See: Books on Climate Change: Great ideas for holiday gifts!

I will speculate further and suggest that this is important in relation to the question of carbon sequestering through geo-engineering. It has been suggested that preserving or expanding peat bogs, like growing more trees or similar measures, would help sequester more carbon. But the carbon-sequestering value one places per unit area on various kinds of peat bogs or other wetlands has to be correctly measured and understood. If these values are going to change in a warming world, we need to know this.

Global Warming: Earth, Wind, Fire, and Ice

Focusing on Earth, but also a few tidbits on wind, fire, and ice, some current news and observations about global warming.


As humans release greenhouse gas pollutants (mainly CO2) into the atmosphere, the surface of the Earth, and the top 2000 meters of the ocean, heat up. But some of the CO2 is absorbed into plant tissues and soil, as well as in the ocean or other standing water. Historically, about 30% of the extra CO2 is absorbed into the ocean, and another 30% converted into (mainly) plant tissue. We hope that enough CO2 is absorbed that the effects of greenhouse gas pollution is attenuated, at least a little. Unfortunately, there are two things that can go wrong. First, these “Carbon sinks” — places where the CO2 is either stored or converted into Carbon-based tissue, could stop working. Second, some of these Carbon sinks could reverse course and start releasing, rather than absorbing, Carbon.

The CO2 released in the atmosphere during any given time period starts a process of warming that takes years to finish. We know how much CO2 we have added to the atmosphere (we went from the mid 200’s ppm, parts per million, before this all started to 400ppm). We know how much we are currently releasing and we can estimate how much we will be releasing in coming years. Putting this all together with some very fancy physics and math, we can estimate the amount of surface warming over coming years. This calculation includes the Carbon sinks. If the Carbon sinks stop sinking Carbon, or worse, start releasing previously trapped Carbon, then future warming (next year, next decade, over the next century) will be greater than previously expected.

And there is now evidence that this is happening.

Andy Skuce has written up two pieces, here and here, that explain this. It is also written up here, and the original research is here.

This research suggests that some natural Carbon sinks are slowing down in the amount of Carbon they take in, or perhaps switching to releasing Carbon.

The problem is actually very simple to understand. In order for CO2 to be converted to O2 (free oxygen) and some combination of C and other elements (to make plant tissue), the other elements have to be available in sufficient quantity. For many terrestrial ecosystems, CO2 was a limiting factor (keeping water and sunlight out of the picture or constant). So, adding CO2 means more plant growth. But at some point, the other elements that are required to make plant tissue, such as Nitrogen and Phosphorous (otherwise known as fertilizer) are insufficient in abundance to allow plants to use that CO2. This would reduce or flatten out the amount of extra CO2 that can be trapped in solid form. At this point, the terrestrial biomass starts to release, rather than absorb, CO2.

Why would the terrestrial Carbon sink not simply stop absorbing Carbon, and start to release it? Well, because I as fibbing a little when I said this is simple. The more realistic version of the system has Carbon going in and out of the different parts of the system (atmosphere, ocean water, plant tissue, etc.). With warming temperatures, we expect the release of Carbon from terrestrial systems to increase in rate. So, before nutrient limitation is released, there is Carbon going in and Carbon going out, but on average, mostly going in. With Nutrient limitation on the system, when there isn’t enough Nitrogen or Phosphorus to match up with the CO2, the release continues while the absorption stops. But because of warming, the release not only continues, but increases. So, in coming decades, the net effect is that parts of the terrestrial ecosystem contributes to atmospheric CO2.

At present, climate scientists (mainly in the context of the IPCC) have estimates of future warming that involve estimates of how much CO2 we add to the atmosphere. All the known factors have been taken into account, including the Carbon cycle (which includes Carbon moving between the atmosphere, the ocean, and the plant and soil system at the surface. This research indicates that the numbers have to be changed to account for nutrient saturation.

This graph shows how it works. The black line is the increase in plant growth as originally modeled under a “high-emissions” scenario. This shows a 63% increase in plant growth by the end of the century owing to CO2 fertilization. The red line indicates the amount of extra plant growth that would actually happen due to limitations of Nitrogen. The blue lie indicates the amount of plant growth due to the limitation of Phosphorus. These are 29% and 20%, respectively.


If we include the increase in release of Carbon due to warming conditions (basically, more and faster rotting of dead plant tissue), the existing models produce the black line in the graph below. There is still an increase in plant growth, and the plant-based Carbon sink is still working. If limitations on nitrogen and phosphorus are considered, we get the red and blue lines.


This amounts, approximately, to adding about 14 years of human greenhouse gas pollution (at the current rate) to the time period under consideration (from now to 2100).

So that’s the news when it comes to climate change and the Earth. But what about the wind?


No new research here, just an observation. Where does wind really matter? Where do you really feel the wind? Wind is the expression of the large scale climate system (modified by local conditions) which is in turn the result of the spinning of the Earth and the heating of the planet unevenly by the sun, like it does. A valid rule of thumb is more heat, more wind, but that is a gross oversimplification. At a more complex level, more heat equals more wind doing different things in different places than usual, and also more water vapor in the air, and all this has to do with those times and places where we really feel the wind the most: Storms.

Tenney Naumer (of Climate Change: The Next Generation fame) came across an amazing graphic of the Earth, looking mainly at the Pacific, showing some wind.


The graphic is from here, and I added the “Storm World” just for fun. Except it isn’t really fun. The date of this graphic is, I think, July 5th or 6th.

Your homework assignment is to identify the named tropical storms shown in the graphic.


A few years ago there were some big fires. Australia burned, there were fires in California, Texas, Arizona, various parts of Canada, etc. Climate change and fire experts noted that there is an increase in fires because of global warming, but others argued that there was no significant increase, and we had had periods of abundant fires in the past. In truth, there was evidence of an increase, though maybe not very convincing to some. Also, past inclement conditions are a thing … recent global warming did not invent bad weather or extensive wildfires. But some of those past periods, like the 1930s in the US, are not evidence against current climate change, but rather, evidence of what to expect with climate change. Those periods are only barely as severe as the present state, are usually regional and not global, happened after greenhouse gas pollution was very much a thing and between periods of suppression of warming by aerosols (from volcanoes or industrial pollution). So they matter, but not because they disprove climate change (they don’t) but rather because these past events are windows into the future. But I digress.

The point is, a few years ago, those who are rightfully alarmed about climate change were pointing out the problem of increased wild fires referring mainly to research indicating a dramatic increase in wildfire potential, along with some evidence of actual increased wildfires. And others argued that until there were a lot more flames, there was not a problem.

Well, now we have the flames.

Yesterday (anecdote warning, this is not data) I went outside to check the mail and was assailed by a bank of smoke moving through my neighborhood. It smelled really bad. Assuming there was a house on fire, I dashed back into the house to grab my cell phone, in case I had to dial 911. Returning outside, I walked around and did not see anything obvious burning, but the smoke was coming in from the north. That ruled out a burning oil tank train (the tracks are from the south) and the local munitions dump on fire (that is to the west). But I still couldn’t see where the smoke was coming from. So, I hopped in the car and drove north a couple of blocks, and by the time I got to the nearby Interstate, it became clear that the smoke was simply everywhere, pretty uniformly.

I then guessed at the cause, and returned to my computer where I checked the Wundermap and some other sources. Yup: it was Canada and Alaska, thousands of miles away, pretty much on fire. Here are two graphics to illustrate this.

From the Wundermap:

Screen Shot 2015-07-06 at 5.35.22 PM

And from here:

Screen Shot 2015-07-06 at 10.23.35 PM


Glacial ice is melting, and it is melting faster every year. Earlier in the year we learned that Alaska (on fire, see above) has been losing mountain glacier and ice sheet water at an alarming rate. Now, we are seeing an amazing spike in melting on the surface of Greenland. From here:


The graph is of ice melt extent so far this year. The blue dotted line is the average over recent decades as in dicated. The grey area is 2 standard deviations around that average. The vast majority of observations (nearly 100%) would be in that grey area. The red line is this year. This is what you call unprecedented melting.

Why is this melting happening? Because Greenland is unusually warm, but as expected under global warming. Some of this melted ice will refreeze in the winter. Much of it, however, is going into the sea.