[allovernow]

One other interesting point to add to the list. If you look at plots of historic CO2 estimates derived from the Vostok ice core [1], you'll notice that we are presently at the very peak (in time) of a climate cycle that aligns almost perfectly with four other cycles from the last ≈400k years. Now two points here:

1. It is extremely unlikely that anthropogenic emissions would align so conveniently with the tip of a natural climate cycle. There must be some other factor underlying the correlation, and/or the influence of human emissions is overstated.

2. The argument is that there is an alarming discrepancy between current measured CO2 and historic data derived from cores. However, core data is an estimate based on a number of assumptions regarding capture and diffusion of gasses during and post ice formation, and I have not come across any literature which questions whether ice core derived CO2 values may underestimate historic CO2 levels. Indeed, there are hints from plant data that this may be the case, but publishing such a conclusion would probably be career suicide in the current politicized academic climate.

The first point alone indicates that some natural degree of warming is to be expected at this point in natural climate variations, something which is never mentioned by proponents of climate change. The second point, if true, would mean that the effects of human activity on global climate are over stated and the current evolution of the system is normal, beyond our control, and/or has happened in the past almost exactly as it is happening now.

1. http://www.antarcticglaciers.org/glaciers-and-climate/ice-co...

[svara]

You're probably confused by the fact that (1) they are plotting ice core based CO2 concentrations as years before 1950 and (2) the time resolution of the ancient ice core data is quite low, while all the anthropogenic action happened in the last 150 y or so (and about 50% of the CO2 addition happened in the last 50).

Look at [0] for a more authoritative source and specifically compare the 800 and 400 ky data to the 2000-year (Law Dome, Antarctica) data. This will show you that we are indeed at the top of a very slow CO2 cycle, but that we added about 100 ppm on top of that in the past ~100 y! This is more than the amplitude of the underlying cycles.

[0] https://cdiac.ess-dive.lbl.gov/trends/co2/ice_core_co2.html

[allovernow]

What I'm saying is that all of our historic CO2 data comes from cores, which are a proxy for paleo-CO2 levels. The theory is that bubbles of atmospheric gas are trapped in ice as it forms over thousands of years. What I'm saying is that there's the possibility that this trapping is imperfect, and ratios of atmospheric gassed may change after being sequestered, such that past ppm values are underestimated, and the currently measured values are not unusual in history, and are rather consistent with the peak that historic core data shows us to be at.

In fact, here [1] is a well sourced article which highlights at least one indication that this is the case - historic CO2 estimates derived from plant stomata are much higher and closer to contemporary measured levels than ice core data. Then there is the idea of time averaging smoothing out peaks, and we can only speculate/model the loss of resolution.

It's very easy for a well intentioned group of researchers to reason themselves into a corner, particularly when things like institutional momentum, political biases, and understandable doomsday concerns influence the kinds of questions scientists ask and the paths they are willing to take to find answers. Because this research has broad effects on economic, social, and corporate policy, it is dangerous to close off one side of questioning behind an apparent consensus, not to mention it's simply bad science.

>the time resolution of the ancient ice core data is quite low, while all the anthropogenic action happened in the last 150 y or so

All the more reason to be open to questioning.

1. https://wattsupwiththat.com/2010/12/26/co2-ice-cores-vs-plan...

[svara]

The blog post you cited seemed pretty dodgy to me, so I went ahead and looked closely at the work they base many of their conclusions on, a PhD thesis from 2004 by Kouwenberg [0]. Specifically the data in Fig. 5.4 (p. 57) is what they base much of their argument on.

Kouwenberg herself however doesn't believe the crazy 300-700 AD CO2 excursion to around 400 ppm and spends a lot of time looking at alternative explanations, finally concluding on p. 65:

"""

The extremely low number of stomata per mm needle length in the Tsuga heterophylla record at Jay Bath between 300 and 700 AD does not appear to result from extremely high atmospheric CO2 levels at the time, but coincides with the establishment of the species during a period of major disturbance at the site. The open, exposed setting after this disturbance probably provided highly stressed growth conditions for pioneering, early-successional T. heterophylla trees.

"""

Of that, there is of course no mention in the blog post you cited.

Importantly, of course, none of this is really that relevant to the discussion of anthropogenic global warming, since we know that we are putting CO2 into the atmosphere, and that CO2 in the atmosphere traps heat.

I'm really starting to see a pattern here, where facts that contain some grain of truth are used out of context to sow doubt, and everything just evaporates as soon as you look more closely (and then the next tangentially relevant fact is brought up)... It's probably quite effective - I mean, who is going to read that blog post you linked and then do what I just did and actually dig into the sources? I did that because I took the "advice" I got in this comment section to heart and wanted to give my "opponents" the benefit of the doubt.

[0] PDF available at https://dspace.library.uu.nl/bitstream/handle/1874/243/full....

[kaybe]

> What I'm saying is that there's the possibility that this trapping is imperfect, and ratios of atmospheric gassed may change after being sequestered..

Do you seriously think that we don't consider these things? Seriously?

[linuxftw]

There's also evidence that CO2 lags temperature increase historically, meaning CO2 was not the causative agent for temperature increase, rising CO2 might be an artifact of increase temperatures.

[svara]

At that point you're questioning pretty basic physics. What part of the influence of CO2 concentration on the infrared transmittance of the atmosphere are you questioning [0]? Extraordinary claims require extraordinary evidence.

[0] https://en.wikipedia.org/wiki/Greenhouse_effect#Mechanism

[allovernow]

The "basic physics" contradicts the data. Your error is approaching this enormously complex question with the assumption that climate science is unquestionably correct. This lag is a glaring discrepancy that begs resolution. No, it doesn't mean climate science is totally wrong, but this attitude of unquestionability is absolutely pervasive in both society at large and academia, and gives deniers a justifiable reason for suspicion.

And I'm not some snot nosed programmer looking in from outside. I'm a former geoscientist and I saw this pressure firsthand, even at a relatively conservative University.

[svara]

It is of course totally possible and consistent with mainstream climate science for CO2 levels to trail temperature under some conditions, for example when the temperature is driven by Milankovich cycles. [0]

I was attacking the implied invalid conclusion that rising CO2 levels would therefore not drive temperature.

But, to address the point in more detail, look at the data in [1]. CO2 typically does not lag temperature. If you cherry-pick points in time at the beginning of a Milankovich-induced temperature increase it may, and this is adequately explained by outgassing of CO2 from the oceans, driven by the sun. [2]

> [...] this attitude of unquestionability is absolutely pervasive in both society at large and academia, and gives deniers a justifiable reason for suspicion.

I try to find citations for what I write here, and address specific points, both to teach myself the science and to keep the discussion honest. If everybody here did this there would certainly be no "attitude of unquestionability".

I agree that it can probably seem that way on cursory look. I personally find it hard to always keep cool when faced with a barrage of pseudo-scientific points that don't hold up to scrutiny. More importantly, I find the implicit arrogance really hard to stomach, i.e. thinking that a huge field of scientists is too stupid to understand some "obvious fault" that someone posted on their blog. Maybe that makes me unfair to some participants who are just trying to understand the issue better and / or have an honest discussion. I'm sorry if that was the case.

[0] Lorius et al. 1990, https://pubs.giss.nasa.gov/abs/lo03000u.html

[1] Petit et al., 1999, Fig. 3, available from https://escholarship.org/uc/item/7rx4413n

[2] https://skepticalscience.com/co2-lags-temperature-intermedia...

[linuxftw]

It's not me questioning physics. CO2 levels lagged historic temperature increases. It's up to the CO2-causes-warming people to explain it.

[imtringued]

I don't get it. Climate change critics try to find one flaw in some straw man argument and then denounce the whole field as a lie. CO2 isn't the only thing that causes warming and no, scientists are not stupid enough to not account for these things. I mean this statement is trivial to disprove because methane and tons of other things also act as greenhouse gases or amplify heating. It doesn't change the threat caused by higher temperatures. 4°C are 4°C and we can bet on going way beyond that tiny puny number if no ones gives a damn.

[linuxftw]

It's one flaw of many. First, nobody really trusts the temperature data. Second, the earth was much hotter before. Third, there was an ice age, now there isn't, planet was already warming. Fourth, water vapor is recognized as the most powerful greenhouse gas. Fifth, we don't believe solar energy is being adequately accounted for.

We have a what we consider a lot of holes, big import holes, in the theory. These issues are immediately dismissed. The fact that people can say with a straight face that water vapor increases global warming, yet is not the primary cause, even though it's the strongest greenhouse gas, is beyond believe. It defies comprehension, I will never, ever take the CO2 theory serious, and I'll be here encouraging others to think for themselves as well.