Fingerprinting the Climate System 

Benjamin David Santer 

climate researcher. Ph.D. 

Lawrence Livermore National Laboratory 

Lecture: May 5 2016 6pm Reception: May 5 2016 5pm 

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Fingerprint research seeks to improve understanding of the nature and causes of climate change. The basic strategy is to search for model-predicted patterns of climate change (“fingerprints”) in observed climate records. Fingerprinting exploits the fact that individual influences on climate have unique signatures. These unique features are clearer in detailed patterns of climate change than in global-mean climate information. Fingerprint methods are a powerful tool for separating human and natural climate-change signals. The results of fingerprint research provide scientific support for findings of a “discernible human influence” on global climate.

Twenty years ago, at the time of publication of the Second Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), most fingerprint studies relied on surface temperature. Critics of this work argued that a human-caused fingerprint should be identifiable in many different aspects of the climate system – not in surface thermometer records alone. Fingerprint researchers responded to this justifiable criticism by moving beyond early “temperature only” studies, interrogating modeled and observed changes in rainfall, water vapor, river runoff, snowpack depth, atmospheric circulation, salinity, and many other climate variables. The message of this body of work is that human-caused fingerprints are ubiquitous in the climate system.

The Yanai lecture affords an opportunity to look back at the scientific and personal lessons learned from over two decades of efforts to fingerprint the climate system – and to tell the story of how the scientific community identified a human-caused warming signal.