Posted on 22 June 2024 by John Mason

Skeptical Science is partnering with Gigafact to produce fact briefs — bite-sized fact checks of trending claims. This fact brief was written by John Mason in collaboration with members from the Gigafact team. You can submit claims you think need checking via the tipline.

Was the Medieval Warm Period a global event?

The Medieval Warm Period was regional, not global.

Between 950-1250 AD, temperatures as warm as those in the mid-20th century were isolated to parts of the Northern Hemisphere. Most of the planet was relatively cool.

The regional nature of the warming indicates that internal variability — how and where energy is moved about within the system — was the main cause. In addition, this was one of the quietest periods of the past 2000 years for volcanic eruptions. Fewer eruptions meant fewer sun-reflecting particles in the air.

The Medieval Warm Period’s warming was also short-lived. The Little Ice Age started soon after and continued until the Industrial Revolution, when our fossil fuel burning intensified.

All of Earth’s regions are now warming, and average global surface temperatures are about 1°C higher than during the Medieval Warm Period.

Current global warming will continue as long as humans keep emitting heat-trapping gases into the atmosphere.

Go to full rebuttal on Skeptical Science or to the fact brief on Gigafact

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Sources

Science Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly (Sience)

Nature Consistent multidecadal variability in global temperature reconstructions and simulations over the Common Era

Nature No evidence for globally coherent warm and cold periods over the preindustrial Common Era

Sage Journal The medieval quiet period.

University of Queensland - Medieval warm period

About fact briefs published on Gigafact

Fact briefs are short, credibly sourced summaries that offer “yes/no” answers in response to claims found online. They rely on publicly available, often primary source data and documents. Fact briefs are created by contributors to Gigafact — a nonprofit project looking to expand participation in fact-checking and protect the democratic process. See all of our published fact briefs here.