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« Antarctic fox | Main | Repeal the Climate Change Act »
Sunday
May222011

Antarctic fox

I think I've mentioned that there was a certain amount of fraternisation across party lines at the reception after the Cambridge Conference. Josh and I had a nice chat to Dr Emily Shuckburgh, who works at the British Antarctic Survey as well as being a scientific adviser to the Department of Energy and Climate Change.

Since that time we've exchanged a few emails and, with my recent blog posts touching on the issue of ocean heat mixing, Dr Shuckburgh thought her own research might be of interest:

Here's Dr Shuckburgh's introduction:

"Sometimes you have to go to the ends of the earth in the pursuit of scientific progress. The oceans cover 70% of our planet and yet there is still much we don’t know about the flow of water around and through them.

To predict future climate we need to find out how global ocean flows may be changing over time. Some ocean waters are very salty and some are very cold. The big unknown is how much these different waters mix together because this has a massive effect on ocean flows.
For a while now scientists have suspected that there are a few key mixing hot-spots in the world’s oceans and that one of them may be in Drake Passage. But how can we check? Well, satellites can give us information about the sea surface, but to look below the surface we are largely dependent on scientists going to sea and taking measurements themselves.
So recently I helped lead a team of UK and US colleagues to the remote and inhospitable Southern Ocean on a mission to investigate…

The more technical version is on the project website, where there is also a link to a semi-technical description.

And here's Dr Shuckburgh herself.

 

 

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Reader Comments (59)

Dear Dr Wolf,

This is from Frank et al 2010 (verbatim):

Values of γ for the early period (1050–1549) indicate a lower mean (4.3 p.p.m.v. per °C) and narrower distribution (s.d. = 3.5 p.p.m.v. per °C) than estimates for 1550–1800 (mean = 16.1; s.d. = 12.5 p.p.m.v. per °C), with distributions overlapping between 0.8 to 31.7 p.p.m.v. per °C (Fig. 3).

[...]

The distributional differences suggest that estimates are temporally biased, γ is not time invariant, and/or the mean climatic states during these two intervals are not comparable. The higher values for γ during the late period result from the strong LIA CO2 dip around 1600, whereas the low values during the early period are associated with less variable CO2 fluctuations. Although occurring around the coldest period of the past millennium (Fig. 2a), the LIA CO2 decline is unique in the context of the past two millennia, both in magnitude and in its rate of change19.

If γ is not time invariant and is dramatically higher in value in colder periods compared to warmer ones, as stated above, it is clearly a mechanism by which our living earth will bring down CO2 values once cooling is initiated in the system (for some or the other reason).

May 23, 2011 at 9:31 PM | Unregistered CommenterShub

Eric,
Thanks for your comment. Remember, the readers of blogs like this differ considerably in background and motivation but not all of us, far from, believe that 120 odd ppm cannot possibly affect climate.
Anyway, 5 degrees change from an ice age to an interglacial is dramatic. Changes in forcing must have been amplified somehow. So far we agree. But I don't see how this can be proof that CO2 played a major role in amplification. That assumes a very big sensitivity to CO2. Not a crazy assumption, but not proven either. And there are other reasons to believe that sensitivity may not be that high.

May 23, 2011 at 10:11 PM | Unregistered Commenterj

I will make a last contribution on this thread because I can see that I am being much more directly questioned on a new one!

Shub, I now know what you are looking at in Frank. However your inference from their data is definitely not that of Frank et al. What they say is that, using their analysis, the sensitivity of carbon release or uptake to temperature is probably higher in the period 1550-1800 than in the period 1050-1549. The first thing to say is that there is a huge uncertainty on both estimates, because the temperature variability in these periods is small (range of order 0.4 degrees), and the CO2 variability is also small (range about 6 ppmv around the little ice age, and only about 2 ppmv during 1050-1549, less than the current trend over a single year). They also point out that they are effectively making the assumption that the CO2 over this period was entirely controlled by temperature. But even if we take their result at face value, it does not say that the sensitivity is higher during a cooling, because the period 1550-1800 includes both a small drop of CO2 around 1600 and a small rise just before 1800, ie both a cooling and a warming.

I think they have done an interesting piece of work, and put at least some limit on the possible carbon cycle feedback, but your interpretation is definitely not justified by their work. One thing we can say is that during the much stronger change out of the last glacial, CO2 rose by about 90 ppmv while global average temperature rose by perhaps 5 degrees, and Antarctic temperature by 10 degrees, showing a sensitivity over that change of about 18 ppmv/(degree of global temperature), or 9 ppmv/(degree of Antarctic temperature) . If most of the relevant processes are in the Southern Ocean then the latter figure might be more important. However to extend that to any future warming begs the question of whether the changes that caused the glacial-interglacial CO2 change (which as Emily has explained are most likely to do with overturning and stratification of the ocean) extend to even warmer temperatures or not. It’s issues like this that explain why we need to understand the processes (hence the DIMES cruise), in parallel with doing something like Frank et al did, which is trying to get the most information possible from inevitably uncertain data.

That was the specific, but the two comments from pax and j both raise the question of whether the palaeo record PROVES that CO2 played a role in the climate swings from glacial to interglacial. The answer is no, they don’t prove it because that is not how science works. What the ice core record is good for is as a dataset to try to falsify hypotheses. The underlying physics leads us to expect that increasing CO2 and decreasing ice cover will lead to atmospheric warming. The ice core record gives us the data to try to disprove this: if we saw a period where there was a sustained and significant change in CO2 and no change in global temperature (assuming other forcings were more or less constant), then this would suggest our underlying model (by which I mean our conceptual understanding of the physics, not a numerical model) was wrong. But we don’t find that: the ice core record of climate is well-explained by orbital changes, CO2, and ice sheet changes, along with the expected feedbacks in water vapour, sea ice etc. However, you are both right, it is never proven, always a working hypothesis waiting for something even more plausible to come along.

The only way to PROVE that CO2 causes climate warming would be to do a deliberate experiment: release lots of it into the atmosphere in a short time and then wait a century or so to see what had happened to climate…….

May 24, 2011 at 9:00 AM | Unregistered CommenterEric Wolff

Eric - thanks for your two responses. As you are demand, one last quick question: If we are to believe early instruments, CO2 concentrations have increased from c.280ppm in the early 1800s to around 390ppm in the present. That's an increase of more than 40%, yet the best long term temperature datasets - http://oi49.tinypic.com/rc93fa.jpg - show barely any warming. So just how much CO2 do you think we need to release before we have a perceptible effect on global average temperatures?

After looking into the whole issue for the last few years, my conclusion is that anthropogenic CO2 emissions have a tiny (if any) effect on global temperatures, and in any case warming is better than cooling. For example, where I live in Scotland was under a mile of ice 12000 years ago, and even in this inter-glacial the growing season is barely 4 months long. (Fresh snow above 2000 feet this morning and it is currently only 7C down here in the strath. I really shouldn't need to say this to someone who must know the ice core data like the back of your hand, but enjoy the Holocene while it lasts! http://jonova.s3.amazonaws.com/graphs/lappi/gisp-last-10000-new.png ;)

May 24, 2011 at 11:46 AM | Unregistered Commenterlapogus

Dear Dr Wolf,
I have carefully read your reply and my thanks to you for it. I do agree that there can be disagreement on how to interpret the results of Frank et al, but on that note, I would like to add that I do not agree with some of your remarks.

[1] True, my inference from Frank et al is not something they make explicitly in their paper. However the data that support the inference are very much in the paper. The bimodal distribution of values of carbon sensitivity to temperature is distinct and available for everyone to see.

[2] I can understand why my overall inference sounds like a bit of a stretch to you, but I am safely within the realm of conjecture (Frank et al is just one paper). Far more certain inferences are drawn in climate science with far less sketchy data, for example, simply because they support some or the other grand unified theory of climate.

[3] Admitting the limits of just having the results of one paper, Frank et al's results definitely admit the conclusion that there is likely a high sensitivity of CO2 to temperature for the first few C fall of temperature (given that that was all that was observed in the LIA). Other factors may come into play with further drops and the sensitivity may certainly not remain as high then.

I am intrigued by the possibility of deliberate earth experimentation that you refer to. What if we release a known quantity of a very powerful greenhouse gas which then is well mixed, and we obtain temperature results after 10 years (instead of hundred, lets just say) and compare with model outputs?

Once again, thanks for your engagement

May 24, 2011 at 1:22 PM | Unregistered CommenterShub

Very fast responses to the direct questions here:

Lapogus, the best reconstructions of global average temperature show a warming of about 0.8 degrees over the last century. That is clearly perceptible, but whether that is all due to the CO2 increase is uncertain; and of course we have not yet realised all the temperature change expected from the existing CO2 level of about 390 ppmv: it takes some decades for the full effects of a given concentration to be realised due to the thermal inertia of the ocean. But I have no problem with the idea that warming will give pluses as well as minuses: that is on the way towards policy rather than science.

Shub: Re your para 3: Frank et al definitely say nothing about the response to a few degrees fall in temperature, because there is nothing more than a few tenths of a degree change in the period they looked at.

May 24, 2011 at 6:08 PM | Unregistered CommenterEric Wolff

Thanks for your reply Eric. I agree that "prof" is not really part of science, only mounting evidence or dis-prof. You have observations which agree with the hypothesis that the CO2 release caused by an initial forcing due to orbital changes or whatever causes the temperature to rise more than what you'd otherwise expect (based on computer models I presume). I don't actually see anything wrong with this sort of reasoning so long as it is clearly communicated what it is - you have to go by what you have. It is however a fundamentally different sort of scientific argument than more "traditional" science where you "prove" the hypothesis more directly with an experiment or observation in nature. The CLOUD experiment is a good example of the latter, a mechanism is proposed and an experiment is performed.

Just a small analogy:

A car is stolen and we are "certain" that only persons A, B and C could have done it.

Evidence 1: A and B have been seen at a bar when the crime was committed, hence it must be C (because we can't think of who else then could have stolen the car).

Evidence 2: C was filmed by a surveillance camera breaking into and stealing the car.

I think most would agree that 1 is very weak evidence since it rests on our inability to imagine who else could have done it besides A B or C, new knowledge may change the entire premise. Evidence 2 is much less sensitive to unknown facts.

So even though you can't prove anything in science there is a very big difference between "inverse" evidence like my analogy 1 and e.g. observing gravitational lensing. Yet, when the message hits the general public Catastrophic AGW (= positive feedback) is "proven" by "science" just like gravity.

May 24, 2011 at 8:43 PM | Unregistered Commenterpax

Dr Eric
Regarding your reply about para [3]

By the same token then, we can learn nothing at all from Frank et al 2010, because the average global temperature change is well within a degree and a half.

May 26, 2011 at 1:27 AM | Unregistered CommenterShub

Looked like a rather calm day as far as days on the water go. Based on how it looked off the back of the yacht I'm guessing that the water down there is normally much rougher! It's only a few weeks into the winter and I'm already missing being out on the water!

Nov 27, 2011 at 7:28 PM | Unregistered CommenterBranden deBuhr

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