Euan Mearns, who runs a blog called Energy Matters, had a post in 2014 about The Vostok ice core: Temperature CO2 and CH4. This post has apparently had 8000 reads, is probably one of the most read texts on the subject, and yet, according to this post,
the Climate Science community continues to ignore the fairly profound implications of what the data actually shows.
The key issue appears to be a lag between temperature changes and CO2/CH4 changes that led Eaun to conclude that
variations in CO2 and CH4 are both caused by global temperature change and freeze thaw cycles at high latitudes. These natural geochemical cycles makes it inevitable that CO2 and CH4 will correlate with temperature. It is therefore totally invalid to use this relationship as evidence for CO2 forcing of climate, especially since during the onset of glaciations, there is no correlation at all.
CO2 in the past played a negligible role. It simply responded to bio-geochemical process caused by changing temperature and ice cover.
I left a couple of comments, but only one has appeared, so I thought I would quickly write this post. The reason why the climate science community has probably ignored the profound implications in Euan’s posts is – I think – because they’re not really very profound. Firstly, this is data from a single site (Vostok). Even though greenhouse gases may be well-mixed, the temperature is not. You need to be a little careful when using this single site to infer something about global temperatures, and the relationship between temperature changes and CO2/CH4 changes. Maybe more importantly, though, what the data indicates is not really all that surprising.
It is certainly not the case that CO2 is the main driver of the glacial cycles. The trigger for the glacial cycles is probably orbital variations, in particular large changes in solar insolation at high northern latitudes. However, the net change in solar insolation (globally) is small, so it cannot – by itself – produce much in the way of warming/cooling. What is thought to happen is that these changes trigger either ice sheet retreat, or ice sheet advance (depending on whether we’re moving into a glacial, or out of a glacial). This changes the planetary albedo which produces either warming (ice sheet retreat) or cooling (ice sheet advance).
This warming/cooling then results in the release/uptake of CO2 from the oceans, and also influences vegetation (which itself produces an albedo change and releases, or takes up, CO2). The change in atmospheric CO2 (and CH4) then produces more warming/cooling, causes further retreat/advance of the ice sheets, and further changes in vegetation. These different processes (albedo changes and changes in atmospheric CO2/CH4) then together produce the temperature changes that move us into, or out of, a glacial period.
A key point is that CO2 does indeed respond to temperature changes (through ocean outgassing/uptake and changes in vegetation) and – in the context of the glacial cycles – is more properly a feedback, than a forcing. This, however, does not mean that it is not a greenhouse gas and that changes in its concentration in the atmosphere will not influence global temperatures (it clearly does). We really cannot explain the glacial cycle without including the influence of changes in greenhouse gas concentrations in the atmosphere.
This paper by James Hansen and Makiko Sato provides a nice explanation of the process and indicates that changes in atmospheric greenhouse gas concentrations (mainly CO2 and CH4) is responsible for about half of the glacial cycle temperature changes and that this is consistent with an equilibrium climate sensitivity of about 3oC ± 1oC. There are also a couple of nice Skeptical Science posts that discuss the whole CO2 lags temperature issue.
Of course, I’m not an expert on this, so may not have explained this as well as I could have. Also, maybe I have missed something and maybe what Euan Mearns has presented is indeed profound and should not be ignored by the climate science community. However, if I have learned something in my years as a research scientist; when you think you’ve discovered something profound and everyone else ignores it, maybe it really isn’t as profound as you initially thought.
Through the beauty of Twitter, people have provided some relevant references. Gavin Foster suggests that the newer West Antarctic Ice Sheet Divide Ice Core resolves some of the age issues. He also highlights this paper, the abstract of which says:
We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. …..We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.
and this paper (which is discussed – I think – in the Skeptical Science posts I highlighted), the abstract of which says:
Differences between the respective temperature changes of the Northern Hemisphere and Southern Hemisphere parallel variations in the strength of the Atlantic meridional overturning circulation recorded in marine sediments. These observations, together with transient global climate model simulations, support the conclusion that an antiphased hemispheric temperature response to ocean circulation changes superimposed on globally in-phase warming driven by increasing CO2 concentrations is an explanation for much of the temperature change at the end of the most recent ice age.
Steve Forden also highlighted a paper that says:
The robust lead of Antarctic temperature over CO2 concentration during several recent glacial–interglacial transitions inferred from the Antarctic ice cores apparently contradicts the concept of CO2-driven climate change and still remains unexplained……….our results provide an explanation for the observed Antarctic temperature lead over CO2 concentration. It is shown that the interhemispheric oceanic heat transport provides a crucial link between the two hemispheres. We demonstrate that temporal variations of the oceanic heat transport strongly contribute to the observed phase relationship between polar temperature records in both hemispheres……Based on our results, we argue that the analysis of leads and lags alone, without a comprehensive understanding and an adequate model of all relevant climate processes, cannot provide direct information about causal relationships in the climate system.
we show that the increase in CO2 likely lagged the increase in regional Antarctic temperature by less than 400 yr and that even a short lead of CO2 over temperature cannot be excluded. This result, consistent for both CO2 records, implies a faster coupling between temperature and CO2 than previous estimates, which had permitted up to millennial-scale lags.