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Journal ArticleDOI

Improved spectral comparisons of paleoclimate models and observations via proxy system modeling: Implications for multi-decadal variability

TL;DR: In this paper, a forward proxy modeling approach coupled with an isotope-enabled GCM is proposed to disentangle the various contributions to signals embedded in ice cores, speleothem calcite, coral aragonite, tree-ring width, and tree cellulose, and conclude that the paleoclimate record may exhibit larger low-frequency variability than GCMs currently simulate, indicative of incomplete physics and/or forcings.
About: This article is published in Earth and Planetary Science Letters.The article was published on 2017-10-15 and is currently open access. It has received 39 citations till now. The article focuses on the topics: Climate model.

Summary (2 min read)

2.1. GCM & PSM-Generated Pseudoproxies

  • Each proxy type employs its own unique PSM.
  • The complicated nature of proxy data (e.g. chronological uncertainties and impacts on phasing) precludes point-to-point comparisons of time series, and thus there is a strong case for comparing simulated proxy to the observations in the frequency domain.

3. Case Studies

  • Various approaches including downscaling or bias correction can help to minimize such problems, or paleoclimate data can be aggregated to match GCM grid cell size.
  • For each proxy type, the authors attempt to answer whether the mismatch arises from a lack of low-frequency variability simulated by the GCM SPEEDY-IER, or from a data-model comparison strategy problem.
  • For completeness, the authors report absolute variance for all case studies and the PAGES2k data in SI Section S3.

3.1. Spectral Fingerprinting of Proxy Systems

  • As a first pass, the authors forced each PSM with white noise climate inputs to assess the impact of proxy system processes alone on the shape of the spectra.
  • For ice cores, speleothems, and tree ring widths, the white noise +.
  • For all proxy types, the spectra revert to the shape of the white input climate signal on decadal and longer timescales.
  • Under different PSM formulations these spectra could change significantly, and this non-unicity proves a large source of uncertainty.

3.2.1. Corals

  • Shows that the corals are generally strong SST proxies (or, possibly, that the GCM completely underplays salinity variability).
  • Testing the effects of parametric uncertainty for the corals provides an example of how PSMs can be used to inform data-model comparison.
  • More interestingly, discrepancies exist between the simulated and observed power spectrum on decadal to centennial timescales.
  • Further, if the authors instead evaluate both in terms of absolute variance, the Palmyra record exhibits larger σ at the decadal band as compared to the PSM-simulated data (SI Section S3).
  • While the PSM-generated pseudo-coral captures interannual SST variability similar to observations, the PSM seems not to account for the larger variance in the observations on longer timescales, and this discrepancy remains even when uncertainties in the coral's sensitivity to salinity and δ 18 O S W are taken into account.

3.2.2. Ice Cores

  • On decadal to centennial timescales, differences in the observed vs. simulated spectral slopes are more modest than for interannual, but three of the records tend to increasingly diverge at low frequencies (see Fig. 3 ).
  • 18 O PRECIP vs. the observed ice core values exhibit some agreement on multi-decadal frequencies, but the model does not simulate comparable variance in the observations on longer (>centennial) timescales (see Fig. 3 ).
  • This suggests that neither the GCM, the water isotope physics in the GCM, nor the PSM can account for observed low frequency variability.

3.2.3. Speleothems

  • The speleothem PSM highlights the fact that on interannual to decadal timescales, the authors can essentially obtain a β value in agreement with observations simply as a function of the karst parameters.
  • On longer timescales, the simulated spectra tend to flatten while the observed spectra continue to show increased lowfrequency variance, potentially indicative of climate processes resulting in a spectrum similar to what the authors would expect from a power law system (see Fig. 5 ).

3.2.5. Tree Ring Width

  • Aggressive detrending methods tend to remove low frequency variability (demonstrated by Table 2 ).
  • Table 2 also illustrates the RCS method is most conservative in maintaining low-frequency TRW variability.
  • In general, using the same detrending method for both proxy and pseudoproxy is essential.

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Journal ArticleDOI
TL;DR: The authors showed that the anthropogenic fraction of the total mass loss of a given glacier depends only on the magnitudes and rates of the natural and anthropogenic components of climate change and on the glacier's response time.
Abstract: . Around the world, small ice caps and glaciers have been losing mass and retreating since the start of the industrial era. Estimates are that this has contributed approximately 30 % of the observed sea-level rise over the same period. It is important to understand the relative importance of natural and anthropogenic components of this mass loss. One recent study concluded that the best estimate of the magnitude of the anthropogenic mass loss over the industrial era was only 25 % of the total, implying a predominantly natural cause. Here we show that the anthropogenic fraction of the total mass loss of a given glacier depends only on the magnitudes and rates of the natural and anthropogenic components of climate change and on the glacier's response time. We consider climate change over the past millennium using synthetic scenarios, palaeoclimate reconstructions, numerical climate simulations, and instrumental observations. We use these climate histories to drive a glacier model that can represent a wide range of glacier response times, and we evaluate the magnitude of the anthropogenic mass loss relative to the observed mass loss. The slow cooling over the preceding millennium followed by the rapid anthropogenic warming of the industrial era means that, over the full range of response times for small ice caps and glaciers, the central estimate of the magnitude of the anthropogenic mass loss is essentially 100 % of the observed mass loss. The anthropogenic magnitude may exceed 100 % in the event that, without anthropogenic climate forcing, glaciers would otherwise have been gaining mass. Our results bring assessments of the attribution of glacier mass loss into alignment with assessments of others aspects of climate change, such as global-mean temperature. Furthermore, these results reinforce the scientific and public understanding of centennial-scale glacier retreat as an unambiguous consequence of human activity.

34 citations

Journal ArticleDOI
TL;DR: The authors compared proxy-based reconstructions and climate model simulations of past millennium temperature variability to provide insights into climate sensitivity and feedback mechanism, and found that the latter is more robust than the former.
Abstract: Systematic comparisons of proxy-based reconstructions and climate model simulations of past millennium temperature variability offer insights into climate sensitivity and feedback mechanism...

34 citations

Journal ArticleDOI
TL;DR: It is concluded that climate models appear to contain the essential physics to correctly simulate the spectral continuum of global-mean temperature; however, regional discrepancies remain unresolved.
Abstract: Climate records exhibit scaling behavior with large exponents, resulting in larger fluctuations at longer timescales. It is unclear whether climate models are capable of simulating these fluctuations, which draws into question their ability to simulate such variability in the coming decades and centuries. Using the latest simulations and data syntheses, we find agreement for spectra derived from observations and models on timescales ranging from interannual to multimillennial. Our results confirm the existence of a scaling break between orbital and annual peaks, occurring around millennial periodicities. That both simple and comprehensive ocean–atmosphere models can reproduce these features suggests that long-range persistence is a consequence of the oceanic integration of both gradual and abrupt climate forcings. This result implies that Holocene low-frequency variability is partly a consequence of the climate system’s integrated memory of orbital forcing. We conclude that climate models appear to contain the essential physics to correctly simulate the spectral continuum of global-mean temperature; however, regional discrepancies remain unresolved. A critical element of successfully simulating suborbital climate variability involves, we hypothesize, initial conditions of the deep ocean state that are consistent with observations of the recent past.

29 citations


Cites background from "Improved spectral comparisons of pa..."

  • ...First, climate proxies are known to filter climate inputs (11, 12), so simulated temperatures and proxy measurements are not directly comparable (13, 14)....

    [...]

  • ...However, none of these processes can create scaling on their own (14), suggesting that the observed scaling behavior is a property of the climate and not the proxy archives....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the authors presented the first high-resolution stable isotope ( δ 13 C and δ 18 O) speleothem record from northern Laos spanning the Common Era (∼50 BCE to 1880 CE).

28 citations

Journal ArticleDOI
TL;DR: In this article, the authors assess the potential sources of these discrepancies by comparing 1000-year hemispheric temperature reconstructions based on real-world paleoclimate proxies with climate-model-based pseudoproxies.
Abstract: Model simulations and proxy-based reconstructions are the main tools for quantifying pre-instrumental climate variations. For some metrics such as Northern Hemisphere mean temperatures, there is remarkable agreement between models and reconstructions. For other diagnostics, such as the regional response to volcanic eruptions, or hemispheric temperature differences, substantial disagreements between data and models have been reported. Here, we assess the potential sources of these discrepancies by comparing 1000-year hemispheric temperature reconstructions based on real-world paleoclimate proxies with climate-model-based pseudoproxies. These pseudoproxy experiments (PPE) indicate that noise inherent in proxy records and the unequal spatial distribution of proxy data are the key factors in explaining the data-model differences. For example, lower inter-hemispheric correlations in reconstructions can be fully accounted for by these factors in the PPE. Noise and data sampling also partly explain the reduced amplitude of the response to external forcing in reconstructions compared to models. For other metrics, such as inter-hemispheric differences, some, although reduced, discrepancy remains. Our results suggest that improving proxy data quality and spatial coverage is the key factor to increase the quality of future climate reconstructions, while the total number of proxy records and reconstruction methodology play a smaller role.

27 citations

References
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Journal ArticleDOI
TL;DR: The fifth phase of the Coupled Model Intercomparison Project (CMIP5) will produce a state-of-the- art multimodel dataset designed to advance the authors' knowledge of climate variability and climate change.
Abstract: The fifth phase of the Coupled Model Intercomparison Project (CMIP5) will produce a state-of-the- art multimodel dataset designed to advance our knowledge of climate variability and climate change. Researchers worldwide are analyzing the model output and will produce results likely to underlie the forthcoming Fifth Assessment Report by the Intergovernmental Panel on Climate Change. Unprecedented in scale and attracting interest from all major climate modeling groups, CMIP5 includes “long term” simulations of twentieth-century climate and projections for the twenty-first century and beyond. Conventional atmosphere–ocean global climate models and Earth system models of intermediate complexity are for the first time being joined by more recently developed Earth system models under an experiment design that allows both types of models to be compared to observations on an equal footing. Besides the longterm experiments, CMIP5 calls for an entirely new suite of “near term” simulations focusing on recent decades...

12,384 citations

Journal ArticleDOI
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Journal ArticleDOI
David J. Thomson1
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Abstract: In the choice of an estimator for the spectrum of a stationary time series from a finite sample of the process, the problems of bias control and consistency, or "smoothing," are dominant. In this paper we present a new method based on a "local" eigenexpansion to estimate the spectrum in terms of the solution of an integral equation. Computationally this method is equivalent to using the weishted average of a series of direct-spectrum estimates based on orthogonal data windows (discrete prolate spheroidal sequences) to treat both the bias and smoothing problems. Some of the attractive features of this estimate are: there are no arbitrary windows; it is a small sample theory; it is consistent; it provides an analysis-of-variance test for line components; and it has high resolution. We also show relations of this estimate to maximum-likelihood estimates, show that the estimation capacity of the estimate is high, and show applications to coherence and polyspectrum estimates.

3,921 citations

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3,408 citations

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Frequently Asked Questions (1)
Q1. What contributions have the authors mentioned in the paper "Improved spectral comparisons of paleoclimate models and observations via proxy system modeling: implications for multi-decadal variability" ?

In this paper the authors bridge this gap via a forward modeling approach, coupled to an isotope-enabled GCM. The paper addresses the following questions: ( 1 ) do forward modeled “ pseudoproxies ” exhibit variability comparable to proxy data ? The authors apply their method to representative case studies, and parlay these insights into an analysis of the PAGES2k database ( ? ). The authors conclude that, specific to this set of PSMs and isotope-enabled model, the paleoclimate record may exhibit larger low-frequency variability than GCMs currently simulate, indicative of ∗Corresponding author Email addresses: sylvia 11 dee @ brown. The authors find that current proxy system models ( PSMs ) can help resolve model-data discrepancies on interannual to decadal timescales, but can not account for the mismatch in variance on multi-decadal to centennial timescales.