Observed and modelled ΔTs agree within their uncertainties (Fig. Surface temperature calculations are conducted automatically to minimize the differences between the modelled and observed δ.
For one realization, about 360 runs from 50,000 years B. to present were necessary with different values for each parameter.
However, another important climate driver, volcanic forcing has generally been underestimated prior to the past 2,500 years partly owing to the lack of proper proxy temperature records. P.), a gradual return to a volcanically unperturbed state can be found in modeled 60–90°N average temperatures and in the reconstructed Greenland temperatures.
records lack strong centennial to millennial-scale variability (e.g., the Medieval Climate Anomaly and Little Ice Age; Fig. We find that 27% of the Holocene Greenland temperatures are higher than the present multi-decadal average (1988–2015, hereafter “the recent decades”; Figs 1 and 2a, Fig. The reconstructed temperature reached the present level around 9,500 years B. This is likely because borehole temperature reconstructions are unable to capture sharp transitions such as the one from the cold Younger Dryas to the warm Holocene due to the smoothing effect by diffusion of heat in the ice-sheet (Methods). We consider autocorrelation of the time series to evaluate the significance of correlations by estimating the effective degree of freedom that depends on the effective decorrelation time95% confidence levels are considered as significant. A correction to this article is available online at https://doi.org/10.1038/s41598-018-21307-y.
P., which is earlier than that of the borehole based reconstruction (around 8,000 years B. Consistent with an earlier conclusion Greenland Summit temperature and its proxies over the Holocene. Reported uncertainty ranges are 2σ standard deviation unless otherwise stated. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Different bandpass filters were applied for (e,f,g,h) and (i) with 400–4000 year bands and 200–2000 year bands after linear detrending, respectively (Methods). Five additional experiments were conducted with sets of forcings that excluded one out of the GHG, orbital, volcanic, solar, and ice-sheet forcings at a time (Fig. An experiment with fixed present-day ice-sheet configuration indicates that the temperature rise from the beginning of the Holocene to 7,000 years B. was the result of the retreating Laurentide ice-sheet played a minor role on the middle to late Holocene cooling (Fig. Particularly, through changes in ocean heat content, the Younger Dryas could have had an impact on temperature trends in the early Holocene (12,000–10,000 yrs B. In addition, through weakening of the Atlantic Meridional Circulation and associated reduction in poleward oceanic heat transport, deglacial meltwater fluxes could have influenced the Northern hemispheric climate until 7,000 years B, P., and particularly during the 8.2 ka B. In our model experiments, volcanic impacts on climate show clear multi-decadal to millennial variabilities (Fig.
Red dotted lines in (e–i) show bandpass-filtered Greenland temperatures, which are compared to (e) modeled NH average temperatures (Methods), and VII, (f) Na. In these simulations, meltwater inputs from retreating Northern Hemispheric ice-sheets were not taken into account. Two numerical experiments exhibit significantly different temperature trends from the middle Holocene to the present (Fig. Recent studies indicate that large volcanic eruptions separated by several decades could induce decadal to centennial cooling in the northern hemisphere (e.g., Little Ice Age) by sea-ice/ocean feedbacks long after volcanic aerosols are removed from the atmosphere. Values are relative to averages of the past 1,000 years.