Oceanic carbon sinks

So nature deals with increasing carbon dioxide emissions by sucking up more of it. Plants take more and grow faster. The increased partial pressure of CO₂ causes more of it to be absorbed by the oceans. On land more plants is a good thing, but in the oceans more CO₂ leads to increased acidity which can be devastating for the flora and fauna.

Recently there were two interesting papers, one in Nature and the other in Nature Geoscience, that looked at Earth's carbon sinks. I've written about the studies in The Economist's Babbage blog. I took the chance to speak to some of the leading researchers in the field: Ashley Ballantyne at the University of Colorado, Corinne Le Quéré at the University of East Anglia (and not involved in the climate scandal), Jean-Baptiste Sallée of the British Antarctic Survey and Jorge Sarmiento at Princeton University. The conversations helped me learn a number of things. I'm sharing those here:

1. The ocean in the southern hemisphere take up most of the CO₂ because of their large unbroken waters. But this absorbed gas is not evenly spread out. Some pockets have a lot more of it than others.
2. This ocean also absorbs a lot of the heat that is getting trapped because of excess greenhouse gases. By one estimate almost 70% of it. As oceans warm up, their capacity to hold CO₂ reduces. These carbon sinks could become carbon sources at some point.
3. The lack of an ozone layer leads to localised cooling in the Antarctic. Global warming causes most of the heating in the tropics. This temperature difference causes stronger winds which could whip up deeper ocean layers bringing up CO₂-rich waters which won't be able to absorb as much of it as they do now.
4. Land carbon sinks could become carbon sources, too. Increased temperature leads to growth of microbes in the soil. These will then consume more of organic matter and convert it into CO₂, which they do already but the plant consumption of CO₂ is able to keep that in check.

Climate change is a very complex phenomenon. I knew that but these conversations made me realise just how much we don't know (PS: this is not to doubt that humans are causing global warming). Only after a few questions, all researchers started answering the question by first saying 'We don't know, but one theory is...'. Oceanic carbon sinks, in particular, are a big area of debate, mostly because of the lack of hard data. Things are changing, but are they changing fasting enough?

A list of main references for The Economist piece:

1. Ballantyne et al., Nature, 2012, 488, 70
2. Salée et al., Nature Geoscience, 2012, ASAP
3. Climate change: What lies beneath - The Economist
4. Argo project, UK Met Office
5. Climate Variability and Predictability (CLIVAR)

Ballantyne AP, Alden CB, Miller JB, Tans PP, & White JW (2012). Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years. Nature, 488 (7409), 70-2 PMID: 22859203

Sallée J-B, Matear RJ, Rintoul SR, & Lenton A (2012). Localized subduction of anthropogenic carbon dioxide in the Southern Hemisphere oceans. Nature Geoscience DOI: 10.1038/ngeo1523