Losses of soil carbon under global warming might equal U.S. emissions | Hacker News Reader

Losses of soil carbon under global warming might equal U.S. emissions

news.yale.edu

80 pointsreirob20 comments

People have been trying to examine this from several directions, including remote sensing to quantify how much CO2 is being generated as these stocks warm (http://above.nasa.gov/about.html?#about). The overview article in Nature that this press release refers to is:

http://www.nature.com/nature/journal/v540/n7631/full/540047a...

and the technical article by Crowther et al. is:

http://www.nature.com/nature/journal/v540/n7631/full/nature2...

Thanks for the links

Obviously the landscape is going to be drastically affected, would the melting permafrost not allow for more tree growth which might squash some of the increase in C02 release (albeit a tiny fraction)?

Correct me if I'm wrong, but I think it's a common misconception that trees store a really large amount of carbon, usually it is dwarved by the carbon associated with the soil where the trees grows. Over generations, in particular in a rainforest, enormous amounts of carbon are put into the soil, and burning down the forest doesn't just release the carbon from the trees, but many times that number from the soil. Regrow the trees, and you only recapture a fraction of what is released. I imagine you're going to get a similar effect from permafrost melting.

Yes - also, old growth forests/rainforests are mostly one-and-done carbon sinks. They grow, absorb a bunch of carbon, and then their growth rate drastically drops.

Do you know this, or are you just giving your intuition?

I tried a quick Google search to see if this is true, and they don't seem to agree. (However, they are mostly talking about individual trees, not whole forests.) A couple links:

1. "Traditionally, two conflicting viewpoints about tree growth have coexisted. One view was that after an initial increase in growth rate, trees would grow more slowly as they age. Another theory posits that growth rates should increase with increasing tree size. The study results support the latter, showing that in most cases growth rates increase as trees age. This was found to be true for 87 percent of the species reviewed. For the group of largest trees in the study, scientists observed this phenomenon in 97 percent of the species. This translates into a growth rate nearly three times faster for trees with a trunk diameter of 100 centimeters (39 inches) than for trees with a 50-centimeter (20-inch) diameter within a species."

http://environment.yale.edu/yer/article/carbon-capture-tree-...

2. "A 2,000-year-old giant sequoia is just cranking out wood, said Steve Sillett, a professor at Humboldt State University in California who has conducted recent research on the big trees. Other long-lived trees like coast redwoods and Australia's Eucalyptus regnans also show an increase in wood production during old age, according to an article Sillett published in the journal Forest Ecology and Management."

http://news.nationalgeographic.com/news/2012/12/121205-sequo...

3. "This supposition is supported by the fact that we, like others (15), see no consistent evidence for changes in growth rates for individual trees during their lifetimes"

http://www.pnas.org/content/102/51/18502.full.pdf

Clearly - as you note - the individual-tree analysis in (3) [I did not read the others] is not relevant to the point raised by the comment you are addressing. (In turn, that comment/speculation itself is not really relevant to the point above it.)

The above papers seem to be an attempt to answer the question, "Can't we just re-capture the carbon released from deforestation/logging by re-planting small trees in these areas," and the answer seems to be "not on a 1:1 basis".

You almost feel that an old growth forest by definition does not increase its stock of carbon held in trees. Trees can't become denser and taller forever (although sequoias seem to give that a good go).

This is correct, even for Arctic regions.

According to [1], net production of carbon in Alaskan Arctic regions is about 0.14 kg / meter-squared, per year. But soil content is about 14 kg / meter-squared. Crudely, that means 100 years of net carbon production would be sequestered in soil carbon.

[1] http://www.biogeosciences.net/11/4271/2014/

Thanks for the link, very interesting.

Permafrost is actually a huge carbon sink as frozen plant matter does not decay trapping a lot of carbon. Now on 10,000+ year time scales it may be a net gain, but people are really only concerned eight very short term (<200 year) effects.

PS: Bogs have a similar effect which is why you can dry and then burn them.

I wonder if the losses of soil carbon are not solely caused by global warming. Poor land management via grazing methods, biodiversity loss and desertification, deforestation, and ocean life die offs could all release co2 into the atmosphere independent of fossil fuels. Can we measure these?

So... self-sustaining feedback loop? :(

Let us be a bit more honest here. Current numbers are near four hundred ppm and not even most exaggerated places them past eight hundred. Commercial greenhouses can hit 1k and even that isn't hazardous exposure levels. Man made levels are dropping but in the end, we are actually very close the lowest levels in our planet's history and may be too low.

Plants prefer higher numbers and being below 500 is actually been shown to be bad for them while double that is beneficial to greenery.

So there are issues with the climate we will face but CO2 levels are probably the least of them

Problems directly arising from CO2 concentration are not a big concern. But higher CO2 concentrations cause further problems, such as ocean acidification and climate change. That's what people are worried about right now, not outright suffocating due to excessive CO2.

This is a strange non-sequitur. The concern is about the warming effect of the atmospheric CO2, not about whether it's safe to breathe. The particular concern of this article is about the potential for positive feedback in warming.

I'm not sure that this is the whole picture, though. There were really high levels of CO2 millions of years ago but the life at that time was adapted to it. Rising CO2 and temperatures will cause ecological damage to life currently unsuitable for it (e.g. corral reefs) and also economic damage from things including rising sea levels.

I just wanted to point out the downvote button isn't a "disagree" button. One can make the case that arguing over climate science is flamebait, so if you want to downvote on those grounds then go ahead. But people shouldn't be punished for making specious arguments.

Unless someone is deliberately trolling, it's better to engage with them than to negate them by downvoting. Such engagement is what makes hackernews more highbrow and interesting than, say, reddit.

Huh? IMO, the parent's comment is a perfect example of something deserving of downvotes: "Why are you arguing something that has absolutely nothing to do with the article, or really even global warming in general, and displays a complete lack of understanding about what the discussion is even about."

In other words, I can't imagine that engaging with someone whose argument is basically "CO2 isn't a problem because plants love CO2" is going to lead to any sort of insightful discussion.

I don't think it will lead to particularly insightful discussion either. But my point is that on the assumption the OP is acting in good faith, it's better to try to persuade them than to silence them. You don't convert people by taking away their voice.

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