Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling
18 June 2020

Three Anniversaries Important for Climate Science

Celebrating the 40th anniversary of three key events in climate change science.

Signal-to-noise ratios (S/N) used for identifying a model-predicted anthropogenic fingerprint in 40 years of satellite measurements of annual-mean tropospheric temperature

In this Comment, LLNL scientists and colleagues focus on understanding how the scientific advances arising from the three 40th anniversary events aided efforts to identify human influences on the thermal structure of the atmosphere. The three efforts include the release of the National Academy Charney report, the publication of a key signal detection paper by Hasselmann, and the start of atmospheric temperature measurements with satellite-based Microwave Sounding Units (MSUs).


In summary, the key findings are the following: 1) The Charney report recognized that fossil fuel burning would yield an appreciable global warming signal; 2) The Hasselmann’s paper provided a rational approach for detecting this signal; 3) MSU data provided the pattern information required for successful application of Hasselmann’s method.


The zeitgeist of 1979 was favorable for anthropogenic signal detection. From the Charney report, which relied on basic theory and early climate model simulations, there was a clear recognition that fossil fuel burning would yield an appreciable global warming signal. Klaus Hasselmann’s paper outlined a rational approach for detecting this signal. Satellite-borne microwave sounders began to monitor atmospheric temperature, providing global patterns of multi-decadal climate change and natural internal variability — information required for the successful application of Hasselmann’s signal detection method. Because of this confluence in scientific understanding, we can now answer the following question: when did a human-caused tropospheric warming signal first emerge from the background noise of natural climate variability? We addressed this question by applying a fingerprint method related to Hasselmann’s approach. An anthropogenic fingerprint of tropospheric warming is identifiable with high statistical confidence in all currently available satellite datasets.

Benjamin Santer
Lawrence Livermore National Laboratory (LLNL)
Santer, B, C Bonfils, Q Fu, J Fyfe, G Hegerl, C Mears, J Painter, et al.  2019.  "Celebrating the Anniversary of Three Key Events in Climate Change Science."  Nature Climate Change 9(3): 180-182.