“Unexpected: Cooler Little Ice Age Had More Fires – And Medieval Warmth Outpaced Today in New Brunswick”

The paper “High-resolution Forest and fire dynamics from Fish Lake, New Brunswick, Canada, during the last millennium” (published in The Holocene, 2026, Vol. 36(1), pp. 15–27; DOI: 10.1177/09596836251378004) by Ryan J. Collins, Jeannine-Marie St-Jacques, Kelly A. Kyle, Les C. Cwynar, and Charles V. Cogbill provides a detailed palaeoecological reconstruction from a 124 cm sediment core collected in February 2023 from Fish Lake (46° 8′ 38.32″N, 66° 53′ 12.64″ W, 206 m elevation, near Fredericton, NB).

The core spans approximately AD 890 to 2023, with pollen analysis at 1 cm intervals (10-year resolution across 125 samples), microcharcoal for fire history, and pollen-based climate reconstructions. The age-depth model uses rplum (Bayesian framework) with four AMS ¹⁴C dates on terrestrial macrofossils and 15 ²¹⁰Pb dates, ensuring a robust chronology (e.g., no reversals, high model agreement index).

Core Chronology and Methods

• Dating: Bayesian rplum model in R, incorporating 4 AMS ¹⁴C dates on terrestrial macrofossils (conifer needles/wood at depths yielding calibrated ranges like AD 1032–1177 to AD 1722–1814) and 15 ²¹⁰Pb dates (CRS model for upper 32 cm). The core spans AD ~890–2023 with high confidence (no age reversals, good MCMC agreement).
• Pollen: 125 samples at 1 cm intervals (10-year resolution), minimum 400 terrestrial grains counted, processed with standard methods (HCl, KOH, acetolysis). Zonation via CONISS + broken stick test; PCA for ordination.
• Charcoal: Macrocharcoal (>150 μm) at 0.5 cm intervals (249 samples), analyzed via WinSeedle for area, peaks detected with CharAnalysis (SNI ≥3, 99th percentile threshold).
• Climate Inference: WA-PLS on pollen percentages calibrated to a Maritimes subset (301 sites, 43°–50°N, 61°–74°W) from the North American Modern Pollen Database (v1.8). Best performance: spring (MAM) temperature (2 components, R² = 0.57, RMSE = 1.50°C, average bias = -0.02°C, max bias = 3.07°C via leave-one-out cross-validation). Modern analogs assessed via squared chord distance (close ≤15.87 for 75% of samples; modern ≤24.37 for another 22%; poor/no analogs mostly post-~1800–1900).

Vegetation Dynamics (Pollen Zones) Six zones highlight shifts in the Acadian Forest (mixed hardwood-softwood, red spruce Picea rubens signature):

• Zone I (AD ~895–1045, early MCA): Deciduous-dominated (high Betula, Tsuga canadensis, Fagus grandifolia); mature closed forest.
• Zone II (AD ~1045–1265, mid-MCA): Rise in Pinus diploxylon; declines in Betula, Tsuga, Fagus; some disturbance indicators (Salix, Myrica).
• Zone III (AD ~1265–1530, MCA-LIA transition): Conifer resurgence (Picea mariana/rubens/glauca, Abies balsamea); further deciduous drops; Ostrya peak.
• Zone IV (AD ~1530–1720, mid-LIA): Conifer dominance accelerates; Ambrosia (ragweed) first appears ~AD 1680 (early Acadian French agriculture signal).
• Zone V (AD ~1720–1840, early colonial): Continued conifer rise (P. glauca notable); herbs/Poaceae/Ambrosia increase; Pinus strobus recovery then decline.
• Zone VI (AD ~1840–present): Peak disturbance (highest Poaceae, Ambrosia, herbs); conifers high but influx declining; P. strobus max percentage; “borealization” trend (deciduous decline, conifer/herb rise) climate-initiated in LIA but human-accelerated post-settlement.

What the Article Claims

Richard’s post states:

• Pollen-reconstructed spring (MAM) temperatures affirm the Medieval Climate Anomaly (MCA, AD 900–1400) was 1°C warmer (3.2°C) than both the Little Ice Age (LIA, AD 1400–1850) at 2.2°C and the modern period (1850 to present).
• It cites the study’s MCA average of 3.2°C and LIA average of 2.2°C.
• It extends this to claim the MCA was warmer than today, adding references to other regional sites showing “no net warming since the 1800s and 1-3°C cooling from the MCA to the LIA.”
• It highlights higher LIA fire frequency as counter to expectations (more fires in cooler period due to fuel changes).

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New Study: Canada’s New Brunswick Was 1°C Warmer Than Today During The Medieval Warm Period

From No Trick Zone

By Kenneth Richard

Pollen-reconstructed New Brunswick (Canada) spring temperatures affirm the Medieval Warm Period or Medieval Climate Anomaly (MCA, 900-1400 CE) was 1°C warmer (3.2°C vs. 2.2°C) than both the Little Ice Age (LIA, 1400-1850 CE) and modern period (1850 to present).

Other sites in this region also show no net warming since the 1800s and 1-3°C cooling from the MCA to the LIA.

This new research also identifies a higher frequency of natural forest fires during the LIA cooling period than the warmer MCA.

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