Climate change roundup: Underestimated ocean heat content and emissions from the peatlands!

A couple articles caught my attention over the past week that give some new modeling information about global warming.  So…I thought I’d do a quick rundown of the major findings of each!

Why hold me at that gate of your secret?

Figure courtesy of whoi.edu

Figure courtesy of whoi.edu

The first could be a big deal – Durack et al report in Nature Climate Change that we have been underestimating the amount of heat stored in near-surface ocean waters.  This is important because, when we talk about global warming, we’re usually talking about sea surface temperatures (SST).  But the ocean holds 90% of the heat content associated with global warming!  The infrared radiation coming back to the surface from the atmosphere is mostly absorbed in the ocean.  Over time, this heat can then travel to the surface to increase the surface temperature, which we measure.

So the ocean is the big player, but, unfortunately, it’s also the big secret!  We don’t know yet how to model ocean dynamics accurately enough in our global climate modeling, so any more information is very welcome.

So how do we exactly measure heat content in the ocean?  Two ways: 1) sending probes to a certain depth and measuring the temperature, and 2) taking global measurements of ocean size changes (amazingly!) by looking at changes in altitude, since the ocean expands and rises with more heat.

Durack et al found that previous data of ocean heat content was based on only a few samples from the Southern Hemisphere.  This could bias total heat content predictions to be too low.  So the authors modeled Southern Hemisphere heat content using a combination of updated direct measurements, indirect altitude changes, and a new partitioning of the Southern Hemisphere data to take into account its sparsity.  This new model indicates that earlier estimates of upper ocean heat content may be a few percent too low.

What does this mean?  It could mean there is much more heat stored in the planet, so temperatures in the future will rise more than anticipated.  However, as Greg Laden discusses on his blog, this could mainly be a first step towards better understanding the ocean’s role in global warming and how heat distributes in those vast waters.  He’s got a great, concise overview I recommend reading.

 

It’s all a matter of oxygen…

Figure courtesy of lehigh.edu

Figure courtesy of lehigh.edu

The other paper develops a new way of modeling methane (CH4) and carbon dioxide (CO2) emissions from peatlands in the northern latitudes.  Peatlands are exactly what they see – regions of land full of peat!  Peat is a mix of partially decayed vegetation and organic matter, and thus is full of potential greenhouse gas emissions, mainly CH4 and CO2.  It’s of great importance to understand how quickly these regions emit GHGs, especially CH4, how emissions changes with temperature and melting ice, and what other variables affect this behavior.

Apparently, previous models have separated peatland regions based on the water table, which can be thought of as the level below which all material is saturated with groundwater.  The region above is aerobic, the region below anaerobic.  This is a major simplification, however, as anaerobicity is determined by oxygen content, which is not perfectly correlated with water table level.  To improve upon this, the authors directly modeled oxygen content instead of using the water table level as a proxy.

The results indicate that this more physically realistic modeling predicts more CH4 emissions and less CO2 emissions than the water table simulations.  This is important because CH4 is 24 times more potent as a GHG, so we must keep a close eye on how much of this molecule is released in the peatlands.

 

Ok, so that’s it!  More heat than we realized is milling about in the ocean and possibly more CH4 emissions could be arising from the peatlands!  Not the best news, but the upside is that we’re continuing to understand these complex systems that are crucial to understanding and preparing for climate change.

References

1)

Fan, Z., Neff, J., Waldrop, M., Ballantyne, A., & Turetsky, M. (2014). Transport of oxygen in soil pore-water systems: implications for modeling emissions of carbon dioxide and methane from peatlands Biogeochemistry DOI: 10.1007/s10533-014-0012-0

2)

ResearchBlogging.org

Durack, P., Gleckler, P., Landerer, F., & Taylor, K. (2014). Quantifying underestimates of long-term upper-ocean warming Nature Climate Change DOI: 10.1038/nclimate2389

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