Modeled and Observed Stratospheric Temperature Changes: Implications for Fingerprint Studies

Abstract

Changes in the vertical structure of atmospheric temperature are an important “fingerprint” of human effects on global climate. These changes are mainly driven by human-caused increases in atmospheric levels of and other well-mixed greenhouse gases. Key features of this fingerprint are warming of the troposphere, the lowest layer of the atmosphere, and cooling of the stratosphere, the layer above the troposphere. Cooling in the lower stratosphere (from roughly 15–20 km above Earth's surface) also arises from human-caused depletion of stratospheric ozone. While lower stratospheric cooling diminished in the 21st century, largely due to the emerging “healing” of stratospheric ozone levels after the Montreal Protocol, strong cooling of the mid- to upper stratosphere continued unabated. Satellite observations of this distinctive fingerprint are in accord with current state-of-the-art climate model estimates of human-caused temperature changes. The claim to the contrary made in the recent US Department of Energy review of climate science is factually incorrect.

Plain Language Summary

Human-caused changes in carbon dioxide and stratospheric ozone have altered the temperature structure of Earth's atmosphere, warming the lower atmosphere—the troposphere—and cooling the layer above the troposphere (the stratosphere). This canonical “fingerprint” of human effects on climate has been predicted for over 50 years by simple and more sophisticated climate models, and is identifiable with high confidence in satellite temperature data. A recent claim to the contrary in a report by the US Department of Energy is incorrect.

Key Points

• Human fingerprints, marked by tropospheric warming and stratospheric cooling, are evident in Earth's changing atmospheric thermal structure
• A claim to the contrary in a recent report of the US Department of Energy is incorrect
• Climate models are capable of capturing the observed reduced cooling of the lower stratosphere in the early 21st century