Paleoclimate Data–Model Comparison and the Role of Climate Forcings over the Past 1500 Years*

Phipps, Steven J.; McGregor, Helen; Gergis, Joëlle; Gallant, Ailie J. E.; Neukom, Raphael; Stevenson, Samantha; Ackerley, Duncan; Brown, Josephine R.; Fischer, Matt J.; Ommen, T. D. van

doi:10.1175/jcli-d-12-00108.1

Cited by 130 publications

(120 citation statements)

References 85 publications

(124 reference statements)

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“…4): SST simulated by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Mk3L model 26 , run with the cumulative addition of orbital (O), greenhouse gas (G), solar (S) and volcanic (V) forcings; and by the LOVECLIM model 27 , run with individual forcings as for CSIRO Mk3L, plus land-use forcing (L) and with all forcings (All). These simulations were matched to the 57 Ocean2k reconstructions (Methods).…”

Section: External Forcing Of the Global Sst Coolingmentioning

confidence: 99%

“…These simulations were matched to the 57 Ocean2k reconstructions (Methods). The CSIRO Mk3L simulations 26 suggest that OGS forcings combined give rise to only a weak and non-significant cooling trend, and are insufficient to explain the long-term Ocean2k global SST cooling trend ( Fig. 4a; Supplementary Table S14).…”

Section: External Forcing Of the Global Sst Coolingmentioning

confidence: 99%

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Robust global ocean cooling trend for the pre-industrial Common Era

et al. 2015

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International audienceKnowledge of natural climate variability is essential to better constrain the uncertainties in projections of twenty-first-century climate change 1–5. The past 2,000 years (2 kyr) have emerged as a critical interval in this endeavour, with sufficient length to characterize natural decadal-to-centennial scale change, known external climate forcings 6 and with distinctive patterns of spatiotemporal temperature variations 7. However, reconstructions for the full 2 kyr interval are not available for the global ocean, a primary heat reservoir 8 and an important regulator of global climate on longer timescales 9–11. Here we present a global ocean sea surface temperature (SST) synthesis (Ocean2k SST synthesis) spanning the Common Era, which shows a cooling trend that is similar, within uncertainty, to that simulated by realistically forced climate models for the past millennium. We use the simulations to identify the climate forcing(s) consistent with reconstructed SST variations during the past millennium. The oceans mediate the response of global climate to natural and anthropogenic forcings. Yet for the past 2,000 years — a key interval for understanding the present and future climate response to these forcings — global sea surface temperature changes and the underlying driving mechanisms are poorly constrained. Here we present a global synthesis of sea surface temperatures for the Common Era (ce) derived from 57 individual marine reconstructions that meet strict quality control criteria. We observe a cooling trend from 1 to 1800 ce that is robust against explicit tests for potential biases in the reconstructions. Between 801 and 1800 ce, the surface cooling trend is qualitatively consistent with an independent synthesis of terrestrial temperature reconstructions, and with a sea surface temperature composite derived from an ensemble of climate model simulations using best estimates of past external radiative forcings. Climate simulations using single and cumulative forcings suggest that the ocean surface cooling trend from 801 to 1800 ce is not primarily a response to orbital forcing but arises from a high frequency of explosive volcanism. Our results show that repeated clusters of volcanic eruptions can induce a net negative radiative forcing that results in a centennial and global scale cooling trend via a decline in mixed-layer oceanic heat content

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Section: External Forcing Of the Global Sst Coolingmentioning

confidence: 99%

Section: External Forcing Of the Global Sst Coolingmentioning

confidence: 99%

Robust global ocean cooling trend for the pre-industrial Common Era

et al. 2015

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“…Sequentially included forcings has been implemented, for example, by Phipps et al (2013), but is not satisfied by the Jungclaus et al (2010) set of simulations. However, we want to use this data set to compare simulations driven by low-or high-amplitude solar forcings, and we demonstrate in Appendix B that this can be done by a significance test allowing a particular forcing to have influence on the real climate.…”

Section: A Moberg Et Al: Statistical Framework For Evaluation Of CLmentioning

confidence: 99%

“…Such a long-term temperature trend is expected to result from the slowly changing orbital climate forcing, which is large in extratropical regions within the growing season (see e.g. Phipps et al, 2013). This problem should be most prominent in records where RCS standardization was not used.…”

Section: Climmentioning

confidence: 99%

Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 3: Practical considerations, relaxed assumptions, and using tree-ring data to address the amplitude of solar forcing

et al. 2015

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Abstract.A statistical framework for evaluation of climate model simulations by comparison with climate observations from instrumental and proxy data (part 1 in this series) is improved by the relaxation of two assumptions. This allows autocorrelation in the statistical model for simulated internal climate variability and enables direct comparison of two alternative forced simulations to test whether one fits the observations significantly better than the other. The extended framework is applied to a set of simulations driven with forcings for the pre-industrial period 1000-1849 CE and 15 tree-ring-based temperature proxy series. Simulations run with only one external forcing (land use, volcanic, smallamplitude solar, or large-amplitude solar) do not significantly capture the variability in the tree-ring data -although the simulation with volcanic forcing does so for some experiment settings. When all forcings are combined (using either the small-or large-amplitude solar forcing), including also orbital, greenhouse-gas and non-volcanic aerosol forcing, and additionally used to produce small simulation ensembles starting from slightly different initial ocean conditions, the resulting simulations are highly capable of capturing some observed variability. Nevertheless, for some choices in the experiment design, they are not significantly closer to the observations than when unforced simulations are used, due to highly variable results between regions. It is also not possible to tell whether the small-amplitude or large-amplitude solar forcing causes the multiple-forcing simulations to be closer to the reconstructed temperature variability. Proxy data from more regions and of more types, or representing larger regions and complementary seasons, are apparently needed for more conclusive results from model-data comparisons in the last millennium.

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“…(e.g., Schmidt et al, 2013;Phipps et al, 2013;Fernández-Donado et al, 2013;Coats et al, 2013). With regard to the latter, the abundance of paleoclimate data during this period provides numerous estimates of past climatic conditions against which GCMs can be tested (Jansen et al, 2007;Randall et al, 2007;González-Rouco et al, 2009).…”

Section: H Beltrami Et Al: Glacial Cycle Impactmentioning

confidence: 99%

Numerical studies on the Impact of the Last Glacial Cycle on recent borehole temperature profiles: implications for terrestrial energy balance

et al. 2014

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Abstract. Reconstructions of past climatic changes from borehole temperature profiles are important independent estimates of temperature histories over the last millennium. There remain, however, multiple uncertainties in the interpretation of these data as climatic indicators and as estimates of the changes in the heat content of the continental subsurface due to long-term climatic change. One of these uncertainties is associated with the often ignored impact of the last glacial cycle (LGC) on the subsurface energy content, and on the estimate of the background quasi steadystate signal associated with the diffusion of accretionary energy from the Earth's interior. Here, we provide the first estimate of the impact of the development of the Laurentide ice sheet on the estimates of energy and temperature reconstructions from measurements of terrestrial borehole temperatures in North America. We use basal temperature values from the data-calibrated Memorial University of Newfoundland glacial systems model (MUN-GSM) to quantify the extent of the perturbation to estimated steady-state temperature profiles, and to derive spatial maps of the expected impacts on measured profiles over North America. Furthermore, we present quantitative estimates of the potential effects of temperature changes during the last glacial cycle on the borehole reconstructions over the last millennium for North America. The range of these possible impacts is estimated using synthetic basal temperatures for a period covering 120 ka to the present day that include the basal temperature history uncertainties from an ensemble of results from the calibrated numerical model. For all the locations, we find that within the depth ranges that are typical for available boreholes (≈ 600 m), the induced perturbations to the steady-state temperature profile are on the order of 10 mW m −2 , decreasing with greater depths. Results indicate that site-specific heat content estimates over North America can differ by as much as 50 %, if the energy contribution of the last glacial cycle in those areas of North America that experienced glaciation is not taken into account when estimating recent subsurface energy changes from borehole temperature data.

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Paleoclimate Data–Model Comparison and the Role of Climate Forcings over the Past 1500 Years*

Cited by 130 publications

References 85 publications

Robust global ocean cooling trend for the pre-industrial Common Era

Robust global ocean cooling trend for the pre-industrial Common Era

Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 3: Practical considerations, relaxed assumptions, and using tree-ring data to address the amplitude of solar forcing

Numerical studies on the Impact of the Last Glacial Cycle on recent borehole temperature profiles: implications for terrestrial energy balance

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