A recent article in the Guardian explains why scientists now believe that soil’s potential to soak up climate changing carbon dioxide has been overestimated by as much as 40%….
Hopes that large amounts of planet-warming carbon dioxide could be buried in soils appear to be grossly misplaced, with new research finding that the ground will soak up far less carbon over the coming century than previously thought.
Radiocarbon dating of soils, when combined with previous models of carbon uptake, has shown the widely assumed potential for carbon sequestration to combat climate change has been overestimated by as much as 40%.
Scientists from the University of California, Irvine (UCI) found that models used by the UN’s Intergovernmental Panel on Climate Change (IPCC) assume a much faster cycling of carbon through soils than is actually the case. Data taken from 157 soil samples taken from around the world show the average age of soil carbon is more than six times older than previously thought.
Mark Cochrane, our resident climate scientist, recently picked up on this at Chris Martenson’s Peak prosperity blog and wrote the following……?
The article points again to the problems with global models of climate change. Those who generally complain about ‘models’ usually do so to try to imply that they are wrong and that this therefore means that they are overstating climate change. The fact of the matter is that although they are ‘wrong’, the errors, in principle, are just as likely to understate as overstate the situation. In reality, the science tends to be conservative, as scientists are usually constrained to using what is statistically defensible for many of the parameters within their models, so the likelihood of understating known issues (e.g. ice sheet collapses) is greater than substantially overstating them, which is why the vast majority of new findings point out that climate change is progressing faster than we have been estimating.
The famous quote by George Box “All models are wrong, but some are useful” nicely sums up the state of things. Much of what we do in this world is based on our internal modeling, some of which is of high accuracy, “the sun comes up every morning”, and other ideas somewhat less so, “I’m a safe driver so driving is not risky”. Weather models are notoriously inaccurate but we find quite a lot of utility in consulting them anyway. They may not be absolutely ‘right’ but they are usually reasonably close to the ultimate conditions. Climate models have multitudinous components but their ultimate function basically boils down to calculating the balance between sources and sinks of carbon in the atmosphere, then estimating what the ramifications are of the net changes in type and amounts of the so-called greenhouse gases.
Sources are emissions from things like burning fossil fuels, and positive feedbacks like melting permafrost that releases a portion of the carbon stock, that has literally been frozen in place for millennia, to the atmosphere as the climate warms. Sinks are things like ocean uptake of carbon as higher atmospheric carbon dioxide concentrations force the gas into the water, like occurs in your soda bottle or beer can. Negative feedbacks are those that ultimately bring the system back into balance after excessive emissions and include things like plants soaking up carbon and ultimately depositing some of it for long term storage in soils, in addition to transformation of silicate rocks to carbonate rocks as mountains erode and deposit sediments into the sea, soaking up atmospheric carbon in the process.
As I have mentioned before, the existence of a positive or negative feedback is only part of the story, we also need to know the rate at which it proceeds and ultimately how long it might continue. If you put a match to a high concentration of an explosive gas (say hydrogen) the positive feedback of energy release from a few molecules transferring energy to the proximate molecules will proceed very rapidly but not for very long before the process runs its course in the explosion. On the other hand, eroding the Himalayan mountains down to sea level will soak up immense amounts of carbon dioxide from the atmosphere but will take millions of years to accomplish.
All of which is providing context for what the He et al. (2016) paper is saying. Soil carbon is a catch all term for many chemical compounds in soils that have carbon as a component. This makes the ‘organic’ component of soils. If you are modeling the rate at which carbon can get soaked up by soils you need to know the processes involved and calibrate them using parameters that balance the rates at which carbon enters and leaves the soil. What the new research is showing is that the current Earth Systems Models (ESMs – components of Global Climate Models – GCMs) currently underestimate the age of organic materials (carbon) in existing soils which effectively means that they overestimate the rate at which carbon is likely to be sequestered through plant growth/soil formation in the future. The upshot being that the models are currently estimating that soils will soak up potentially twice as much carbon between now and 2100 as seems likely. If the carbon isn’t getting soaked up it means that it could pile up in the atmosphere for longer than presently estimated and act to warm the planet more than currently projected.
As in all scientific matters, these results will be tested by other scientists and either be verified, refuted or refined. So what does it signify if this is correct? The soil component is only one pool among many but the net fluxes are what matters in the climate situation. For example:
With a Net Terrestrial Uptake of 3.0, the findings could indicate that this should be better described as 1.5-2.0. This could conceivably move the net atmospheric increase from 4.0 to 5.0 or so, a 25% increase. Non trivial. That said, what it probably means is that existing errors in other components of the modeling are either partially overstating emissions or global photosynthesis or understating net oceanic uptake. Therefore, instead of a 25% increase in atmospheric carbon there would be a smaller compounding increase between now and 2100, how small is the question. Future studies will be aimed at teasing these interacting components apart.