Exceptional Stratospheric Contribution to Human Fingerprints on Atmospheric Temperature
September 27, 2023
Ben Santer
Wilkes Center Visiting Chair, and Fowler Distinguished Scholar in Residence at Woods Hole Oceanographic Institution and a Visiting Researcher at UCLA’s Joint Institute for Regional Earth System Science & Engineering.
ABSTRACT: In 1967, scientists used a simple climate model to predict that human-causedincreases in atmospheric CO2 should warm Earth’s troposphere and cool thestratosphere. This important signature of anthropogenic climate change has beendocumented in weather balloon and satellite temperature measurements extendingfrom near-surface to the lower stratosphere. Stratospheric cooling has also beenconfirmed in the mid- to upper stratosphere, a layer extending from roughly 25 to 50km above Earth’s surface (S25-50). Until recently, however, S25-50 temperatureshad not been used in pattern-based attribution studies of anthropogenic climatechange. My talk will discuss the first such “fingerprint” study with satellite-derivedpatterns of temperature change that extend from the lower troposphere to the upperstratosphere. Including S25-50 information in the fingerprint increases signal-to-noise ratios by a factor of five, markedly enhancing fingerprint detectability. Keyfeatures of this global-scale human fingerprint include stratospheric cooling andtropospheric warming at all latitudes, with stratospheric cooling amplifying withheight. In contrast, the dominant modes of internal variability in S25-50 havesmaller-scale temperature changes and lack uniform sign. These pronounced spatialdifferences between S25-50 signal and noise patterns are accompanied by a largesignal in S25-50 (cooling of 1-2°C over 1986 to 2022) and S25-50 noise levels thatare over an order of magnitude smaller than the signal. This explains why extending“vertical fingerprinting” to the mid- to upper stratosphere yields incontrovertible evidence of human effects on the thermal structure of Earth’s atmosphere.
Presentation slide deck
Fingerprinting the Climate System
Wednesday, October 4, 2023
Ben Santer
Wilkes Center Visiting Chair, and Fowler Distinguished Scholar in Residence at Woods Hole Oceanographic Institution and a Visiting Researcher at UCLA’s Joint Institute for Regional Earth System Science & Engineering.
Fingerprint research seeks to improve understanding of the nature and causes of climate change. The basic strategy is to search in observed climate records for the patterns of climate change (the “fingerprints”) predicted by a computer model. Fingerprint studies exploit the fact that different factors affecting climate have different characteristic signatures. These unique attributes are clearer in detailed patterns of climate change than in records like the average temperature of Earth’s surface. Fingerprinting is a powerful tool for separating human and natural climate-change signals. Results from this research provided scientific support for the historic 1995 findings of a “discernible human influence” on global climate. Fingerprinting also contributed to work recognized by the 2021 Nobel Prize in Physics. My presentation will look back at efforts to understand the causes of climate change with fingerprint methods. It will also address some of the key scientific challenges ahead, particularly in terms of communicating climate change science and assessing human contributions to the changing likelihood of extreme events.
Presentation slide deck
Not Just Ancient History: Lessons Learned from the 1995 IPCC Report
Thursday, October 5, 2023
Ben Santer
In November 1995, at a plenary meeting in Madrid, the Intergovernmental Panel on Climate Change (IPCC) finalized one of the most famous findings in the history of climate science assessments. The finding consisted of 12 words: "The balance of evidence suggests a discernible human influence on global climate" - the first time the international scientific community claimed to have identified a human-caused signal in observed climate records. Ben Santer, the Convening Lead Author for Chapter 8, tells the story of how and why this finding was reached, and what happened before, during and after the publication of the 1995 IPCC Report.
Ben Santer's Bio
Ben Santer is an atmospheric scientist. He retired from Lawrence Livermore National Laboratory in 2021. He is now a Fowler Distinguished Scholar in Residence at Woods Hole Oceanographic Institution and a Visiting Researcher at UCLA’s Joint Institute for Regional Earth System Science & Engineering. He studies natural and human “fingerprints” in observed climate records. His early research contributed to the historic 1995 conclusion of the Intergovernmental Panel on Climate Change: “the balance of evidence suggests a discernible human influence on global climate”. He served as lead author of a key chapter of that report. Since 1995, Ben has identified human fingerprints in atmospheric temperature and water vapor, ocean heat content, sea surface temperature in hurricane formation regions, and many other climate variables. In his spare time, Ben is an avid rock-climber and mountaineer.