Atmospheric Carbon Dioxide

 

Earth Atmosphere
Expedition 24 crew member from the International Space (2010). A setting last quarter crescent moon and the thin line of Earth's atmosphere [online]. Available from: <http://spaceflight.nasa.gov/gallery/images/station/crew-24/html/iss024e013421.html>. [Accessed 07th January 2016]. 

Digging back in to academic papers once more, two that have peaked my attention are papers by Retallack (2002) and Pearson and Palmer(2000). 

Retallack’s paper is titled “CarbonDioxide and Climate over the Past 300 Myr”, it was published by The Royal Society in 2002. The paper is referring to the link between CO₂ levels and global warming, and states that there is good supporting evidence for such a link as established by physicochemical experiments as well as geochemical modelling.   Retallack (2002) states in the paper that there is a high temporal correlation between palaeotemperature maxima and atmospheric CO₂ peaks over the past 300 Myr.  Fossilised stomatal indices were used to assess atmospheric CO₂.  “Oxygen isotope (ᵟ18O) composition of marine biogenic carbonate” (Retallack, 2002) revealed the temperatures.  Retallack (2002) goes on to state that despite a large amount of data to support the idea of coupled temperature and CO₂, there is also an argument for an uncoupling but suggests that could be due to CH₄ episodic releases. 

The paper (Retallack, 2002) also states that an elevation in extinction rates often coincide with high CO₂ and palaeotemperatures for both marine and terrestrial life giving example of such incidents in the mid-Permian, late Permian, the early Triassic and earliest Jurassic to name but a few.  Retallack (2002) concludes that there is a strong link between CO₂ and temperature for the past 300 Myr.   

The paper by Pearson and Palmer(2000) looks at things on slightly smaller time scale, I say that with somewhat of a tongue in cheek tone, as although this is the case, it is still a vast time period covering the last 60 Myr.  Published in 2000 in Nature the paper is titled “Atmospheric Carbon Dioxide Concentrations over the past 60 million years”, in order to reconstruct CO₂ concentrations over the past 60 Myr Pearson and Palmer (2000) “use the boron-isotope ratios of ancient planktonic foraminifer shells to estimate the pH of surface-layer sea water”.  They estimate that during the late Palaeocene and earliest Eocene concentrations of 2000 p.p.m. for CO₂ were evident with concentrations decreasing to 500 p.p.m. and remaining below this since the early Miocene.  Pearson and Palmer (2000) conclude that whilst there is evidence for a strong link between CO₂ and temperature that in the cases of, as they call it “super greenhouse conditions” (pCO₂ > 1,000p.p.m.) other feedbacks should also be considered such as “tectonic alteration of the ocean basins” (Pearson and Palmer, 2000). 

 

So we again see that evidence suggests a strong link between CO₂ and temperature.  We also get a brief glimpse of just how varied  CO₂ levels can be.  I include a picture of Earth atmosphere as a small way of illustrating the fragility of it, that thin blue line illustrating all that separates our home from the harshness of Space yet at the same time exhibiting incredible robustness.       

 

References;

Pearson, P. N. and Palmer, M.R (2000). Atmospheric carbon dioxide concentrations over the past 60 million years. Nature. 406, pp.695 - 699.

Retallack, G.J (2002). Carbon dioxide and climate over the past 300 Myr. The Royal Society. 360, pp.659 - 673.