This synthesis paper summarizes published proxy climate evidence showing the spatial and temporal pattern of climate change through the Holocene in Arctic Canada and Greenland. Our synthesis includes 47 records from a recently published database of highly resolved Holocene paleoclimate time series from the Arctic (Sundqvist et al., 2014). We analyze the temperature histories represented by the database and compare them with paleoclimate and environmental information from 54 additional published records, mostly from datasets that did not fit the selection criteria for the Arctic Holocene database. Combined, we review evidence from a variety of proxy archives including glaciers (ice cores and glacial geomorphology), lake sediments, peat sequences, and coastal and deep-marine sediments. The temperature-sensitive records indicate more consistent and earlier Holocene warmth in the north and east, and a more diffuse and later Holocene thermal maximum in the south and west. Principal components analysis reveals two dominant Holocene trends, one with early Holocene warmth followed by cooling in the middle Holocene, the other with a broader period of warmth in the middle Holocene followed by cooling in the late Holocene. The temperature decrease from the warmest to the coolest portions of the Holocene is 3.0 ± 1.0 C on average (n ¼ 11 sites). The Greenland Ice Sheet retracted to its minimum extent between 5 and 3 ka, consistent with many sites from around Greenland depicting a switch from warm to cool conditions around that time. The spatial pattern of temperature change through the Holocene was likely driven by the decrease in northern latitude summer insolation through the Holocene, the varied influence of waning ice sheets in the early Holocene, and the variable influx of Atlantic Water into the study region.

Summary1 Studies on the variability of natural fire regimes are needed to understand plant responses in a changing environment. Since vegetation changes might follow or trigger changes in fire frequency, climate models suggest that changes in water balance will accompany current global warming, and the response of fire regimes to Holocene hydro-climate changes and vegetation switches may thus serve as a useful analogue for current change. 2 We present high-resolution charcoal records from laminated cores from three small kettle lakes located in mixed-boreal and coniferous-boreal forest. Comparison with some pollen diagrams from the lakes is used to evaluate the role of the local vegetation in the fire history. Fire frequency was reconstructed by measuring the separation of peaks after detrending the charcoal accumulation rate from any background. 3 Several distinct periods of fire regime were detected with fire intervals. Between c. 7000-3000 cal. year  , fire intervals were double those in the last 2000 years. Fire frequency changed 1000 years earlier in the coniferous-boreal forest than in the mixedboreal forest to the south. The absence of changes in combustibility species in the pollen data that could explain the fire frequency transition suggests that the vegetation does not control the long-term fire regime in the boreal forest. 4 Climate appears to be the main process triggering fire. The increased frequency may be the result of more frequent drought due to the increasing influence of cool dry westerly Pacific air-masses from mid to late Holocene, and thus of conditions conducive to ignition and fire spread. In east Canada, this change matches other long-term climate proxies and suggests that a switch in atmospheric circulation 2-3000 years ago triggered a less stable climate with more dry summers. Future warming is moreover likely to reduce fire frequency.

Summary1 Studies on the variability of natural fire regimes are needed to understand plant responses in a changing environment. Since vegetation changes might follow or trigger changes in fire frequency, climate models suggest that changes in water balance will accompany current global warming, and the response of fire regimes to Holocene hydro-climate changes and vegetation switches may thus serve as a useful analogue for current change. 2 We present high-resolution charcoal records from laminated cores from three small kettle lakes located in mixed-boreal and coniferous-boreal forest. Comparison with some pollen diagrams from the lakes is used to evaluate the role of the local vegetation in the fire history. Fire frequency was reconstructed by measuring the separation of peaks after detrending the charcoal accumulation rate from any background. 3 Several distinct periods of fire regime were detected with fire intervals. Between c. 7000-3000 cal. year  , fire intervals were double those in the last 2000 years. Fire frequency changed 1000 years earlier in the coniferous-boreal forest than in the mixedboreal forest to the south. The absence of changes in combustibility species in the pollen data that could explain the fire frequency transition suggests that the vegetation does not control the long-term fire regime in the boreal forest. 4 Climate appears to be the main process triggering fire. The increased frequency may be the result of more frequent drought due to the increasing influence of cool dry westerly Pacific air-masses from mid to late Holocene, and thus of conditions conducive to ignition and fire spread. In east Canada, this change matches other long-term climate proxies and suggests that a switch in atmospheric circulation 2-3000 years ago triggered a less stable climate with more dry summers. Future warming is moreover likely to reduce fire frequency.

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The charcoal content from laminated lake sediments in Québec, Canada, was estimated from pollen slides and by a sieving method. The resulting charcoal series are compared to estimate the suitability of these two methods to provide a local or regional fire history. The replication of five different charcoal series from the sieving method shows that this method is suitable for fire-history reconstruction. In our laminated sediments, 1cm3 is representative of the charcoal content of the sediment. The large charcoal fragments above 15600 mm2are too scarce, however, to provide a significant charcoal series. Comparison of the sieving charcoal series versus the pollen-slide charcoal-series shows that the two series display a roughly similar pattern. The differences between the two series probably result from the accumulation of small particles that have a regional source area and are transported by air over long distances and from high fragmentation rates due to laboratory treatment. Spectral analysis for the last 2000 years shows that the sieving charcoal series have no significant periodic accumulation rate, whereas the spectral analysis of the pollen-slide charcoal series shows a significant period of about 500 years. Because the charcoal particles from the sieving method are larger than those from the pollen-slide method, which are potentially windborne over long distances, our study suggests that the sieving method series is a proxy of local fire history, whereas the pollen-slide method is more suitable for detecting regional trends in fire history.