Rates of ancient climate change may be underestimated?

An interesting paper in Nature Communications (David B. Kemp, Kilian Eichenseer and Wolfgang Kiessling, doi:10.1038/ncomms9890), and yet oddly unreported, or at least not in the corner of the blogosphere that I watch (did I miss you? Sorry, tell me). True, its not easy to interpret, but even so I’m surprised. I was hoping that someone was going to tell me what to think, but until they do here’s what I’ve thunk for myself. Let’s start with their abstract:

Recently observed rates of environmental change are typically much higher than those inferred for the geological past. At the same time, the magnitudes of ancient changes were often substantially greater than those established in recent history. The most pertinent disparity, however, between recent and geological rates is the timespan over which the rates are measured, which typically differ by several orders of magnitude. Here we show that rates of marked temperature changes inferred from proxy data in Earth history scale with measurement timespan as an approximate power law across nearly six orders of magnitude (10^2 to >10^7 years). This scaling reveals how climate signals measured in the geological record alias transient variability, even during the most pronounced climatic perturbations of the Phanerozoic. Our findings indicate that the true attainable pace of climate change on timescales of greatest societal relevance is underestimated in geological archives.

Hmm, well, that’s all obvious yes? No, indeed not. Their conclusion (my bold) is clear enough, but not quite why it follows from their analysis. The conclusion, if correct, is relevant: if you ask any number of people, including me, exactly why 2 oC is dangerous when we’ve seen changes bigger than that in the past, I’d give you various answers but quite high up would be rate-of-change which – as the paper says – is believed to be significantly faster than the geological record (For example, the niche evolution of vertebrates, inferred from ancestor–descendant comparisons over millions of years, has been contrasted with projected rates of climate change in this century to conclude that the rate of warming exceeds the adaptive potential of animals by orders of magnitude. Our work indicates instead that geological episodes of climatic or evolutionary change likely fail to capture the true pace of changes on timescales of most relevance for understanding the impact of similar changes today.) The paper (as far as I can see) doesn’t actually say that isn’t true any more; but it does say the speed of past change has been underestimated. There’s some PR which helpfully reassures you the team emphasise that their research doesn’t negate present-day concerns over climate change, but rather highlights a gap in our understanding of ancient climate change. Or some different PR.

The challenge (because this is in bastard Nature, and therefore compressed as though paper were going out of fashion) is to follow their chain of logic. Happily, there’s a helpful picture:

kemp1

The scaling relationship predicts that for every 10-fold increase in measurement timespan, there is an approximately 8-fold decrease in the recorded rate of temperature change. The logical explanation for this scaling is that climate change does not proceed in a linear, monotonic manner, but is instead characterized by transient stasis and reversals, even during episodes of extreme warming. Similar explanations have been put forward for observed timespan-dependent scaling in other Earth system processes, notably sedimentation rates and evolution. Geological temperature changes defined at typically centennial to multimillennial timespans cannot capture the full
variance of the climate system operative at shorter timescales; aliasing variability that is readily apparent from higher resolution and more recent records.

So, I can kinda understand that: temperature change isn’t linear, as we observe, its fairly wiggly. Any time you dice up a long-term trend you’ll find shorter term trends, and the relationship indicates that the maximum of those short term trends will be larger than the long term trend. Put that way it almost sounds obvious. They then make some attempt at a crude correction for that in their figure 3:

kemp3

I’m not sure how valid that is, but let’s lay aside that concern for the moment and notice that present-day rates are ~0.02 oC/year, which is still about 10 times faster than the Bolling-Allerod, which is the fastest even-vaguely-recent event in their records.

Caution: more than usually, I’m uncertain exactly how to interpret this thing; if people point out my errors in the comments, I’ll correct it. Anyone called Dr A who happens to be in the Waterman on Tuesday is also welcome to knock some sense into me over a pint.

12 thoughts on “Rates of ancient climate change may be underestimated?”

  1. >”The paper (as far as I can see) doesn’t actually say that isn’t true any more”. ‘That’ being current “rate-of-change is believed to be significantly faster than the geological record”

    Well of the 7 recent points on the graphs, 6 are clearly below the trend lines drawn with the other marginally below. Which implies, even if not said in the paper, the following:

    From some PR:
    “Professor Wolfgang Kiessling, from FAU, adds that rates of warming through ancient episodes of large-scale climate change were probably much quicker than previously thought, perhaps similar to, or exceeding, the pace of warming today.

    The team emphasise that their research doesn’t negate present-day concerns over climate change”

    Even if we accept/assume the current rate is a little below the worst rates actually occurring in the past and the concern is about whether current rate “exceeds the adaptive potential of animals” then you might want to take account not only of the rate of climate change but also on any other restrictions such as on the ability of animals to move to more suitable locations as the conditions change. Human land use changes restricting animal movements may well severely aggravate issues caused by CC and rate of CC.

    Secondly, if these periods of most rapid CC during longer slower periods caused evolution in animals, we might expect this to occur again then the implications of this are very uncertain but we might not like the effects.

    So this research certainly doesn’t completely negate present-day concerns over climate change. Perhaps it has a partial countering effect on overdone claims like rate of CC “exceeds the adaptive potential of animals by orders of magnitude” Now you have to bring in other things in order to make the case.

    So perhaps this makes the dialog about CC more complex? Maybe that helps reduce numbers of extreme environmentalists?

    I do not believe this is new or complex or difficult to follow but it is nice to see the size of the effect estimated.

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  2. The climate response during the PT and PE events arguably provides some constraint on how fast things can move in the near future. Establishing that the constraint is weaker doesn’t strike me as good news in any sense. And it’s not as if the PETM and especially the PT event would be walks in the park if they happened today.

    Don’t worry, crandles, hardly any environmentalists pay attention to this stuff.

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  3. I haven’t read the paper (naughty!) but one thing that must be guarded against is data selection bias in terms of timescale. I’m thinking specifically of Pleistocene glaciation/deglaciation events, where the timescale *sampling* is much denser than the endpoints. Thus we know that, e.g., the recent deglaciation proceeded at about 3.5° in 3500 years, but **we also know that similar rates occurred on smaller timescales too** because we have that subsampled data. Do such subsamples show up on the graphs? I guess I’ll have to read the paper …

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  4. This is news? No, this is taught in freshman geology class known as Rocks for Jocks. The most popular example is the spotty humanoid fossil record which the creationist nutters use to deny evolution. In this case, the spotty record is used by scientists to paint a scary picture of the present.

    As any child can understand, when your sampling interval is 500-years, it is impossible to know what the decadal and centennial rates of change were. It’s also impossible to know if your random sample is hitting the highs and/or the lows. Also, what are the effects of weathering, compaction and diagenesis on the paleo record versus the calibration period.

    Of course, this is why stitching instrument to proxy records make the perfect advertising disguised as science to sell catastrophic global warming without having to actually say catastrophe by using alternate catch-phrases like “unprecedented. ” This has given plausible deniability to the CAGW meme to the promoters of exaggeration which is the anchor talking point in the international press reporting from Paris.

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  5. By contrast, Howard, it is apparent from ice cores that the magnitude of recent rate of change of CO2 is not reflected in what we see in the past many 100’s of ,000s of years.

    As far as I know, there is an enormous body of work covering what we know about past climate change, so we are spoilt for material if we choose to seek information with which to inform ourselves.

    Maybe you could provide us with a list which published science papers addressing past temperature changes are unsound due to espousing a non-scientific “CAGW meme…promoters of exaggeration”?

    Because it seems to me your chief complaint is that this enormous body of work contains very little support for your choice of pre-conceived belief.

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  6. Craig: What didn’t you understand about plausible deniability? Unprecedented claims of unusual rates of change are based on a comparison of data set resolutions of days versus century’s, millennia, etc, Like tacking on a instrument blade to a flattened proxy stick or hump in the case of Marcott.

    I can’t help it if you don’t understand how the past becomes more fuzzy and smeared and lumped. The earth is a great equalizer and filter through time.

    This sloppy thinking and ignorance of basic geology just adds fuel to the denier fire.

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  7. Howard – you are regurgitating talking points that you read on a denial site. I say this because you haven’t a *clue* as to proxy resolution. Tree rings are *annual* data – not smeared over centuries. Ice cores going back thousands of years can also have resolutions of annual or near annual resolution. For instance:

    The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, were investigated at high temporal resolution from the North Greenland Ice Core Project ice core. The deuterium excess, a proxy of Greenland precipitation moisture source, switched mode within 1 to 3 years over these transitions and initiated a more gradual change (over 50 years) of the Greenland air temperature, as recorded by stable water isotopes. The onsets of both abrupt Greenland warmings were slightly preceded by decreasing Greenland dust deposition, reflecting the wetting of Asian deserts. A northern shift of the Intertropical Convergence Zone could be the trigger of these abrupt shifts of Northern Hemisphere atmospheric circulation, resulting in changes of 2 to 4 kelvin in Greenland moisture source temperature from one year to the next.”

    High-Resolution Greenland Ice Core Data Show Abrupt Climate Change Happens in Few Years

    [In an effort to retain symmetry here, I’ve deleted your last sentence -W]

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  8. Not regurgitating anything, just using my imagination based on miles and miles of coring.

    Tree-rings are not good proxies full stop. Ice cores are not global.

    There is no global high frequency proxy records that can be used to compare with the instrument record. Therefore, rates of change cannot be compared.

    [In an effort to retain civility here, I’ve deleted your last sentence -W]

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  9. Howard:

    [J]ust using my imagination based on miles and miles of coring.

    Not using training or analysis or formulas created by experts, just your imagination? And you wonder why we aren’t takingyou seriously?

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