Climate implications of Holocene Sea level changes

A few years ago Andrew Kemp and coauthors published a sea level reconstruction for the last two millennia from two salt marshes in North Carolina. Reconstructed sea-level was relatively stable until the start of the 20th Century, when it started to rise rapidly, consistent with the instrumental record. Kemp et al compare their reconstruction with sea-levels estimated from a 1500-year long global temperature reconstruction using a semi-empirical model and find that the two reconstructions are consistent. This agreement suggests that the recent warm period is anomalous in the last two millennia.

Climate sceptics didn’t much like the paper, perhaps because it showed that recent sea-level rise is anomalous and perhaps because it confirmed that the 1500-year long temperature reconstruction from Mann et al (2008) is substantially correct. But Kemp et al is a single study, perhaps local factors somehow made this site insensitive to sea-level changes, or chronological uncertainties created artefacts in the reconstruction.

A new paper by Lambeck et al reconstructs sea level over the last 35000 years from sea-level indicators from across the tropics. The sites used are remote from the complicating influences of ice sheets which simplified corrections required for land uplift or subsidence.

Solution for the ice-volume Equivalent Sea Level (esl) function and change in ice volume. (A) Individual esl estimates (blue) and the objective estimate of the denoised time series (red line). Inset gives an expanded scale for the last 9,000 y. (B) The same esl estimate and its 95% probability limiting values. Also shown are the major climate events in the interval [the Last Glacial Maximum (LGM), Heinrich events H1 to H3, the Bølling-Allerød warm period (B-A), and the Younger Dryas cold period (Y-D)] as well as the timing of MWP-1A, 1B, and the 8.2 ka BP cooling event. (C) The 95% probability estimates of the esl estimates. (D) Estimates of sea-level rate of change.

Solution for the ice-volume Equivalent Sea Level (esl) function and change in ice volume. (A) Individual esl estimates (blue) and the objective estimate of the denoised time
series (red line). Inset gives an expanded scale for the last 9,000 y. (B) The same esl estimate and its 95% probability limiting values. Also shown are the
major climate events in the interval [the Last Glacial Maximum (LGM), Heinrich events H1 to H3, the Bølling-Allerød warm period (B-A), and the Younger
Dryas cold period (Y-D)] as well as the timing of MWP-1A, 1B, and the 8.2 ka BP cooling event. (C) The 95% probability estimates of the esl estimates. (D)
Estimates of sea-level rate of change.

I want to focus on the mid to late Holocene part of the sea-level curve, about which Lambeck et al write:

A progressive decrease in rate of rise from 6.7 ka to recent time. This interval comprises nearly 60% of the database. The total global rise for the past 6.7 ka was ∼4 m (∼1.2 × 106 km3 of grounded ice), of which ∼3 m occurred in the interval 6.7–4.2 ka BP with a further rise of ≤1 m up to the time of onset of recent sea-level rise ∼100–150 y ago (91, 92). In this interval of 4.2 ka to ∼0.15 ka, there is no evidence for oscillations in global-mean sea level of amplitudes exceeding 15–20 cm on time scales of ∼200 y (about equal to the accuracy of radiocarbon ages for this period, taking into consideration reservoir uncertainties; also, bins of 200 y contain an average of ∼15 observations/bin). This absence of oscillations in sea level for this period is consistent with the most complete record of microatoll data from Kiritimati (23). The record for the past 1,000 y is sparse compared with that from 1 to 6.7 ka BP, but there is no evidence in this data set to indicate that regional climate fluctuations, such as the Medieval warm period followed by the Little Ice Age, are associated with significant global sea-level oscillations.

This new sea level reconstruction is in substantial agreement with the reconstruction of Kemp et al, and hence confirm that the temperature reconstruction of Mann et al (2008) is substantially correct. It is not possible to have  large multi-century scale changes in mean global temperature as this would cause sea level changes that are inconsistent with the reconstructions.

Rahmstorf’s (2007) semi-empirical model suggests that sea-level should rise after a global temperature increase at the rate of 3.4 mm/yr/°C. This rate will eventually decrease to zero as sea level reached equilibrium with the new global temperature, but can be assumed to be linear for a few centuries. A 0.3°C temperature anomaly over 200 years would cause a sea level change larger than reconstructed. Hence, any temperature anomalies must either be of short duration or of small magnitude.

The progressive rise in sea levels throughout the Holocene gives us some evidence towards resolving the Marcott et al vs Liu et al Holocene climate conundrum. The rise is consistent with Liu et al model-based estimates of increasing Holocene temperatures because of increasing greenhouse forcing (at least in terms of trend, I haven’t checked the magnitude). The progressive rise in sea levels is more difficult, but not impossible, to reconcile with Marcott et al. Sea level could rise despite global cooling if a) contributions from continued ice melt (probably in Antarctica) or b) slow adjustment of the deep ocean to Holocene temperatures after the cold glaciation can overwhelms the effect of cooling surface water and the (relatively small) glacier and ice sheet regrowth in the late Holocene. I don’t know the Antarctic melt history well enough to comment on the first possibility, and am doubtful about the second as much of the ocean overturns relatively quickly so should reach equilibrium within a few thousand years.


Predictably, this paper has caught the attention of WUWT. Just as predictably, they have little sensible to write about it.

First, Eric Worrall writes

The abstract notes that on longer timescales, SLR[sea level rise] up to at least 40mm / year has been observed – so in this context “a few” mm per year does not seem particularly alarming, and is well within the range of natural variation.

This is foolish. Only when the great ice sheet of the last glaciation were melting at their fastest rate did the sea level rise approach 40mm/yr. The last few thousand years without major ice melt is a much more appropriate background for comparison. When the sea level rose at 40mm/yr, there were no towns, cities, agricultural land, nuclear power stations or railway lines that needed protecting. There are now.

Worrall’s second claim is not stupid

The fluctuation claim – the claim that sea level change in the last 150 years is faster than any change over the last 6000 years – is very much dependent on accurate dating of each of the proxy series. As we saw with the Hockey Stick controversies, any uncertainty about dating proxies tends to impose a strong hidden averaging effect on the data series, smoothing away peaks and troughs.

Chronological uncertainty will tend to artificially smooth the reconstruction. This is probably a minor problem. First the 200 yr bins used in the Lambeck et al calculation are large relative to the typical chronological error on a date in the late Holocene. Second, the data would still show the sea-level anomalies and these would propagate into the uncertainty. Woodroffe et al (2012) finds no evidence of substantial sea-level fluctuations in the last 5000 years.

Not to be out done, Anthony Watts adds

So, if we had sea levels of 16-31 feet higher than the present 100,000 years ago, well before the dawn of the industrial revolution, what caused that? Inquiring minds want to know.

Inquiring minds found out long ago: insolation. From the IPCC AR5 5.3.4

LIG WMGHG concentrations were similar to the pre-industrial Holocene values, orbital conditions were
very different with larger latitudinal and seasonal insolation variations. Large eccentricity and the phasing of precession and obliquity (Figure 5.3a–c) during the LIG resulted in July 65°N insolation peaking at ~126 ka and staying above the Holocene maximum values from ~129 to 123 ka. The high obliquity (Figure 5.3b) contributed to small, but positive annual insolation anomalies at high latitudes in both hemispheres and negative anomalies at low latitudes

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About richard telford

Ecologist with interests in quantitative methods and palaeoenvironments
This entry was posted in climate, Fake climate sceptics, Peer reviewed literature, Silliness, WUWT and tagged , , , . Bookmark the permalink.

10 Responses to Climate implications of Holocene Sea level changes

  1. Catalin C says:

    I am quite dismissive towards Liu et al (2014) since not many people realize (fortunately neither do many AGW-deniers) that it is not only challenging Marcott at al (2013) but also to some extent the tens of reconstructions of the last 1000 years including PAGES2K or Mann at al (2008). IMHO the real problem shown by Liu et al (2014) is regarding the current modeling of the amount of heat transfer to deep (and possibly abyssal) ocean, something where we already know models are poor from the temperature evolution in the last 15 years or so. I also believe the models (at least as used by Liu) might be (possibly severely) underestimating the forcing that comes from ice.

    • I would certainly like to see more information about Liu’s model output to check that the dynamic vegetation and deep ocean are doing sensible things.

      Liu et al model-grid might actually be more sensitive to ice forcing as Marcott et al have no observations from the Laurentide Ice Sheets – the models do.

      Marcott et al is certainly vulnerable to seasonal biases. Have you checked how robust the PAGES 2k reconstructions are to seasonality?

  2. Pat Cassen says:

    Regardless of the models, is not the sea level data robust? That potential conflict with Marcott (and many regional reconstructions) seems to me to be the main issue.
    Incidentally, Richard, I have learned much from your posts – thanks.

    • It is not my speciality, but I have no reason to doubt the Lambeck’s work. I think the trends are likely to be robust, and am fairly confident about the lack of substantial variability at the >200yr time scale.
      The slightly surprising lack of data for the last millennia makes the reconstruction from this part of the record less robust (but it is very well constrained at this end of the time period).
      I think that it is easier to reconcile the sea-level reconstruction with Liu than Marcott, but either is possible depending on Antarctic ice loss, which I think is the largest unknown in the late Holocene (at least to me).

  3. Paul S says:

    On Liu et al. models, the accompanying paper (Timm and Timmermann 2007) for the Loveclim (actually ECBilt-Clio) model run indicates it didn’t include volcanic forcings. This could be important for the trajectory of the past two thousand years.

    Thinking about it, if you exclude volcanic forcings you would surely expect slightly increased warming trends compared to a situation including volcanic forcing, particularly given that the long-term warming component of volcanic events (CO2 release) is included in the prescribed model CO2 concentration.

    Do these type of model runs somehow include a constant volcanic term to take this into account?

    • The obvious problem for including volcanic forcing in a Holocene length model run is that the reconstruction of volcanic forcing by Crowley and Unterman (2013) only goes back 1200 years (I don’t know whether it would be possible to extend this record or if it depends on short high-resolution ice cores). A second problem is that it makes no sense to include volcanic forcing in a model with accelerated forcing (The FAMOUS model).

      Does it matter that volcanic forcing is excluded?

      If you want to compare the last 1000 years with the instrumental/palaeo record, then it is critical to include volcanic forcing. If you are interested in the Holocene trends then I suspect not. Unless there is a trend in volcanic activity, you wouldn’t expect much volcanic-induced trend in the model or real climate, just some high frequency variability. The mean temperature will be slightly to warm in the absence of volcanic forcing. If this lack of volcanic cooling caused a spurious warming trend, then it would be apparent in control runs.

  4. John Mashey says:

    “The rise is consistent with Liu et al model-based estimates of increasing Holocene temperatures because of increasing greenhouse forcing ”

    I haven’t dug into this enough to have a firm opinion, but help me on this:
    Given the graph you show in the conundrum post, and give the sharp rise, followed by slow fall in either Marcott or the model, site-stack, biased, I’d think that: at the peak temperature, the system would not be at equilibriumL
    a) SLR would lag the temperature rise,
    b) So that SLR would continue, but a decelerating rate though the Holocene, until in fact it got cold enough for reglaciation to start, which hasn’t happened.
    c) I think that’s consistent with Ruddiman, et al(2011), which postulated a slow temperature decline slowed by human CO2/CH4, with later jiggles, before the Industrial Revolution, including LIA from (CO2 drop, volcanoes, Maunder).

    Anyway, can you say more about plausible lag times between temperature changes and Sea Level changes

    • The time taken for sea level to reach equilibrium after an abrupt temperature rise is not well constrained. There are three main components with different time scales.

      • The upper few hundred metres of ocean will warm fairly rapidly, probably a few centuries.
      • The deep ocean will take much longer to reach equilibrium. Ocean turnover takes several millennia, the sea level response will take even longer due to mixing. However, although the deep ocean is thick, the expansion due to temperature increases is not proportionally large because water expands less when under pressure.
      • The cryosphere will also take millennia to respond. The last of the Laurentide ice sheet survived well into the Holocene.

      A handle on the duration of the first two components could be obtained from Earth Models of Intermediate Complexity (eg LoveCLIM) that have a free ocean surface (ie sea level can change).

      The dynamical response will be more complex. If the climate warmed then cooled, I suspect that the rapid change in the surface water (and well ventilated parts of the deep ocean) will overwhelm the slow response of the deep ocean, but would want to see model results to support this.

      There are some Holocene records of the deep ocean which might be useful for determining the response time. The records I know best from the northern North Atlantic show rapid responses, but this well ventilated part of the ocean is probably atypical. Data from the central Pacific may well show a difference pattern.

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