I’ve had this paper open for weeks now. Slogging through bits. Finally got to where I think I know what matters in it.
It suggests that there is an ocean regulation of CO2 levels and clearly has bought into the notion that CO2 controls temperatures, as it asserts that there is a tipping point, but to the cold side, when CO2 “sequestration” into the deep ocean increases. My initial thought was that the idea of a ‘tipping point, but to colder’ would be best for an article. I still think there is a bit of PR Value in that, as they assert that the formation of Northern Hemisphere Ice Sheets is due to the change of CO2 sequestration. But as I’m convinced that convection dominates, not CO2, to then tout a tipping point to cold based on CO2 conflicts with my sense of propriety.
But I still kept pondering… I think the key bit is simply that they find changes in the Antarctic Circumpolar Current with temperature, and that change of current changes the rate of overturning of the deep ocean waters. This is a control point on the CO2 outgassing of the ocean. It says, in essence, CO2 levels in the air change based on ocean currents. If they have in the past, we ought to expect it today, too. If when it is colder we have more sequestration, then during warm times ought their not be more outgassing?
Basically, it shows the mechanism by which temperature modulates CO2 via the ocean.
From down in the “conclusions” section:
Chapter 2 demonstrated that with the global cooling trend of the Late Neogene came dramatic changes in the circulation of the abyssal Southern Ocean that may have amplified global cooling and helped to establish Northern Hemisphere ice sheets. The Antarctic Divergence, the southern boundary of the Antarctic Circumpolar Current (ACC), provides the main pathway through which waters deeper than 2500 m are exposed to the atmosphere. Thus, once the Antarctic cryosphere reached a stage in the late Pliocene whereby sea ice expansion and water mass stratification began to inhibit Southern Ocean ventilation, CO2 sequestration within the abyssal Southern Ocean was able to drive continued global climatic cooling through a positive feedback cycle.
Not only can the Drake Passage modulate water flow, and cold injection, into the Pacific (by sending excess flow up the coast of South America) but atmospheric CO2 as well.
That leaves even less for that CO2 as causal argument and puts even more on the scale on the side of natural oscillations of ocean currents. Basically, while I think they have the ‘CO2 as causal’ for warming wrong; they do show that CO2 modulates with warming and cooling via ocean turnover changes.
They do find some limits to when. They claim that it only happens under a more extreme range of climate when Antarctic Ice Sheets have grown large. But if that is so, then why do we want more Antarctic ice these days? ..
Until the Antarctic cryosphere reached this advanced stage in late Pliocene, however, the build-up of ice on Antarctica did not have an effect on the vertical or interbasinal δ13C or δ18O gradients in the Southern Ocean. Despite the growth of the West Antarctic Ice Sheet in the late Miocene, the water column in both the Atlantic and Pacific sectors of the Southern Ocean remained well-mixed, well-ventilated, and of uniform temperature until the expansion of sea ice in the late Pliocene
Basically they have demonstrated a potential tipping point, but only to the downside and to cold, based on TOO LITTLE CO2 and more Antarctic Ice. Exactly the two things the Warmistas want. Which leaves me wondering all the more why they want them…
Update – yes, just 24 minutes after posting
I ran into this chart on a page discussing various catastrophes of the past, environmentally speaking.
It largely casts the story in the light of CO2 as climate causal, and attempts to assert that when there were human die-offs, that let the forests grow and sequester CO2, leading to cold.
Their major point being that long term deforestation is letting CO2 levels rise (a point I’ve made before, though the other way around, that letting trees grow would drop levels rapidly).
But what caught my eye the most about the graph is just how much CO2 levels Have Changed Historically. Where were the SUVs and jet airplanes in 1700 during that dramatic rise? How about in 600 AD? It simply says that there are fairly large swings of CO2 based on things unrelated to fossil fuels.