Rethinking Climate Change Metrics

How Global Temperature Anomalies Mislead the Climate Conversation

The discussion surrounding global temperature anomalies and their role in climate science has sparked considerable controversy. Critics of the use of global temperature anomalies, which I am one of, as a primary metric for representing climate change argue that this approach can be reductionist and misleading, presenting relatively mild warming in a way that appears more alarming than it actually is. This article will investigate the reasons behind these claims, examining the scientific, statistical, and communication aspects of global temperature anomalies.

Global temperature anomalies are calculated by comparing the current global temperature with a baseline average, typically the average temperature over 30 years. By focusing on the difference between the current temperature and the baseline, anomalies can highlight trends and changes in the climate.

Source: https://berkeleyearth.org/global-temperature-report-for-2023/

The use of global temperature anomalies is primarily driven by the need to provide a coherent and comparable way to track temperature changes across the entire planet. Absolute temperature measurements can vary widely from one location to another (see the figure below of temperature variation on a single day in China this month and then see my article about the absurdity of global average temperature)…

…and from one season to another, making it challenging to discern global trends from raw temperature data alone. Temperature anomalies are used to effectively normalize this data, allowing scientists to compare temperature changes in different regions and at different times to a common baseline (we will come back to the baseline problem). It is claimed that this approach helps to identify patterns of warming or cooling that may be indicative of broader climate trends, regardless of the inherent variability in absolute temperatures. However, this approach has its limitations.

One of my main criticisms is that the presentation of temperature anomalies can exaggerate the perceived significance of warming. Since the anomalies are often reported in degrees Celsius or Fahrenheit relative to a baseline, even small changes can appear dramatic. For example, a global temperature anomaly of 1°C over a century and a half is relatively minor but is presented as evidence of significant climate change. This creates a distorted perception of the severity of warming, especially when these figures are not contextualized within the natural variability of the Earth's climate system.

Source: https://www.researchgate.net/figure/Dynamics-of-global-surface-temperature-during-the-Cenozoic-Era-reconstructed-from-18-O_fig6_309651389

Furthermore, the choice of baseline period can significantly affect the interpretation of temperature anomalies. Baselines are typically selected from a historical period of 30 years, as recommended by the World Meteorological Organization. However, the selection of a particularly cold or warm period as the baseline can make current temperatures appear more anomalous than they might be if a different baseline were chosen. This selection process can introduce bias or lead to accusations of manipulating data to emphasize a climate emergency narrative.

One controversial choice for a baseline is the use of a period within the Little Ice Age (LIA),