Climate change between the mid and late Holocene in northern high latitudes – Part 1: Survey of temperature and precipitation proxy data

Abstract

Abstract. We undertake a study in two parts, where the overall aim is to quantitatively compare results from climate proxy data with results from several climate model simulations from the Paleoclimate Modelling Intercomparison Project for the mid-Holocene period and the pre-industrial, conditions for the pan-arctic region, north of 60 • N. In this first paper, we survey the available published local temperature and precipitation proxy records. We also discuss and quantifiy some uncertainties in the estimated difference in climate between the two periods as recorded in the available data. The spatial distribution of available published local proxies has a marked geographical bias towards land areas surrounding the North Atlantic sector, especially Fennoscandia. The majority of the reconstructions are terrestrial, and there is a large over-representation towards summer temperature records. The available reconstructions indicate that the northern high latitudes were warmer in both summer, winter and the in annual mean temperature at the mid-Holocene (6000 BP ± 500 yrs) compared to the pre-industrial period (1500 AD ± 500 yrs). For usage in the model-data comparisons (in Part 1), we estimate the calibration uncertainty and also the internal variability in the proxy records, to derive a combined minimum uncertainty in the reconstructed temperature change between the two periods. Often, the calibration uncertainty alone, at a certain site, exceeds the actual reconstructed climate change at the site level. In high-density regions, however, neighbouring records can be merged into a Correspondence to: H. S. Sundqvist (hanna.sundqvist@natgeo.su.se) composite record to increase the signal-to-noise ratio. The challenge of producing reliable inferred climate reconstructions for the Holocene cannot be underestimated, considering the fact that the estimated temperature and precipitation fluctuations during this period are in magnitude similar to, or lower than, the uncertainties the reconstructions. We advocate a more widespread practice of archiving proxy records as most of the potentially available reconstructions are not published in digital form.

Strength of forest-albedo feedback in mid-Holocene climate simulations

“…As it is not possible to measure V w and V s directly in reality, we use the first term of the equation to calculate V w and V s which gives at least an indication on the validity of our results: The mismatch between the model simulations and reconstructions has likely several reasons: (1) the simulations were performed without dynamic ocean and thus neglected important interactions between ocean, sea ice, land, and atmosphere (Otto et al, 2009a;Zhang et al, 2010). (2) The reconstructed temperature values are an unweighted average over the region north of 60 • N (Sundqvist et al, 2010a). (3) The average of the reconstructed temperature depends on the uncertainty in individual reconstructions and the number of sites.…”

Climate change between the mid and late Holocene in northern high latitudes – Part 2: Model-data comparisons

“…In a companion study (Sundqvist et al, 2010) we analyse this data collection in detail, which includes temperature and precipitation reconstructions covering both the mid-Holocene (6000 year BP; 6 ka) and preindustrial (AD 1500; 0 ka) periods. The purpose of that study is to obtain an overview knowledge of the climate change documented in the paleoclimate records, as well as to analyse these changes seen in the reconstructions.…”

“…In Sect. 2, the temperature reconstructions for the northern hemisphere high latitudes from our companion paper (Sundqvist et al, 2010) are summarized. The PMIP simulations used in the current study are described in Sect.…”

Model–data comparison and data assimilation of mid-Holocene Arctic sea ice concentration

“…Vare et al, 2009;Atkinson, 2009). Furthermore, the uncertainties related to the interpretation of proxies or to their dating can also explain some of the discrepancies Sundqvist et al, 2010).…”

“…Braconnot et al, 2007). The MH coincides with the end of a warm period in the Arctic that started about 9 ka (Sundqvist et al, 2010) due to a high orbitally driven summer insolation. Insolation had its maximum at around 11 ka (Berger, 1978) but the warmest conditions have been asynchronous across the Arctic due to the effect of the lingering Laurentide Ice Sheet (Kaufman et al, 2004;Renssen et al, 2009).…”