The Medieval Warm Period: A Global Phenomenon?

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Irrational Fear Substack

Skepticism and Science - Deciphering the True Scale of Historical Climate Fluctuation
Dr. Matthew Wielicki
Mar 9, 2024

The debate over the characteristics and impact of the Medieval Warm Period (MWP), roughly dated from 950 to 1250 AD, lies at the heart of discussions on historical climate variability and its implications for understanding current climate change.

Following the publication of the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report in 2001, the MWP was essentially erased from the paleoclimatological record in favor of the ‘hockey stick’ graph. This disappearance remains a point of contention that has been particularly prominent in public and scientific debate.

The ‘hockey stick’ graph, first published by Michael Mann, Raymond Bradley, and Malcolm Hughes in 1999, depicted temperature anomalies over the past millennium. It showed relatively minor temperature fluctuations for most of the last millennium (the "shaft" of the hockey stick) and a sharp rise in temperatures in the 20th century (the "blade" of the hockey stick). This presentation suggested that the modern warming period has been unprecedented over the last millennium. This finding has been at the core of calls for robust measures aimed at addressing climate change.

 

However, skeptics claim that the MWP was both global in extent and warmer than current temperatures in many regions. Evidence for this comes from several angles, suggesting that the established narrative underestimates the period's warmth and geographic reach. Here, I explore these skeptical viewpoints, considering the evidence and arguments they put forth.

Firstly, a significant point of contention is the geographical distribution of climate proxies, such as tree rings, ice cores, sediment cores, and historical records. Initial research heavily focused on Europe and the North Atlantic, painting a picture of a distinctly warm period in these areas during the MWP. Critics argue that this early focus resulted in a skewed perception of the MWP as a primarily regional phenomenon. However, as research has expanded to include more diverse geographical areas, evidence suggests a more globally synchronized warm period has emerged.

Studies have confirmed the presence of the MWP in various regions of China, with the evidence indicating a heterogeneity in its expression across different areas. For instance, in Northeast China, temperature proxy data from lake sediments, peats, and stalagmites over the last 2000 years show varied patterns of the MWP's occurrence. Specifically, a pronounced warmth from the 9th to 13th centuries was indicated by a stalagmite layer thickness record from Shihua Cave, Beijing. The Tibet region's temperature reconstructions, based on ice cores, tree rings, and lake sediments, also suggest warm periods aligning with the MWP, though with differences in visibility and extent across the proxies. Note that modern warming in China began in the 17th century, similar to the reconstruction of Loehle & McCullah 2008 shown above and long before anthropogenic emissions of GHGs.

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In conclusion, skeptics of the mainstream view of the MWP argue from various angles, suggesting that biases in proxy data, underrepresentation of certain regions, and a failure to fully account for natural climate variability could mean that the characteristics of the MWP are underestimated or misunderstood. These arguments highlight the complexity of reconstructing past climates and the need for a nuanced understanding of the evidence before claims that modern warming is unprecedented.

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Imagine  My Shock!

 

Bjorn Lomborg

@BjornLomborg

 

Misinformation experts are perhaps not quite unbiased "Experts leaned strongly toward the left of the political spectrum" Data from Harvard Misinformation Review, survey of 150 misinformation experts https://misinforeview.hks.harvard.edu/wp-content/uploads/2023/07/altay_survey_expert_views_misinfo_20230727.pdf

(here with left to the left and right to the right)

 

 

4:38 PM · Feb 16, 2024

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