IPCC’s New “Hockey Stick” Temperature Graph

by haakonsk at wattsupwiththat.com

The United Nations’ Intergovernmental Panel on Climate Change (IPCC) published their latest assessment report (AR6) in 2021. In 2023, the Clintel Foundation published a report which criticizes AR6.

Clintel is short for Climate Intelligence, and the Clintel Foundation doesn’t think there’s a climate emergency. Overall, Clintel’s main criticism is that the IPCC hasn’t reviewed the scientific literature in an objective way, as is their stated mission.1)

This article focuses on the topic of chapter 2 of the Clintel report: The Resurrection of the Hockey Stick.

What is a “hockey stick” temperature graph?

The image below shows a “hockey stick” temperature graph for the past 1000 years. This particular version is from the Summary for Policymakers of the IPCC’s third assessment report from 2001, and it applies only to the Northern Hemisphere.

The graph is called a hockey stick graph because the shape somewhat resembles an ice hockey stick with a long, flat “shaft” and a big “blade” shooting up at the end. If there had been more variability in the temperature before the “blade” – meaning that the “shaft” wasn’t flat – then it wouldn’t be a hockey stick graph.

Short summary

A “hockey stick” temperature graph has made a comeback in the latest IPCC report from 2021 (AR6), after being absent in the fourth and fifth reports.

Unlike the previous two reports which included multiple temperature estimates, AR6 relies on just one temperature estimate for the past 1000-2000 years, sparking criticism.

Moreover, this single estimate has itself been criticized. The perhaps most important issue relates to a method that incorrectly generates hockey stick temperature graphs from non-hockey stick data.

In general, the quality and amount of data that can tell us something about past temperatures quickly decline when we go further back in time. Based on the currently available data, it might therefore be impossible to know whether the global temperature of the past 1000-2000 years has a hockey stick shape or not.