Scientists at Livermore National Laboratory in California can now measure human effects on climate into the mid-to upper stratosphere with five times more assurance than previously. Differences between tropospheric (lower layer of the atmosphere) and lower stratospheric temperature trends have long been recognized as a “fingerprint” of human effects on climate.
Early pattern-based studies seeking to discern a human fingerprint in weather balloon and satellite atmospheric temperature data previously neglected the mid- to upper stratosphere, where the temperature signal of CO2 increase is expected to be considerably larger than in the troposphere or the lower stratosphere.
The early research yielded warming of the troposphere and cooling of the stratosphere, with cooling predicted to amplify with greater height above the tropopause. The vertical profile of temperature predicted was subsequently confirmed by more complex models and observations.
The new work expands on these earlier fingerprint studies that relied solely on Microwave Sounding Unit (MSU) data for estimating latitude-height profiles of atmospheric temperature change. In the new study, the team compared the atmospheric temperature trends seen in improved satellite data sets to those obtained in newer model simulations of the historical period. The simulations provided estimates of the expected “signal” due to human influence on the climate.
The team also used an ensemble of pre-industrial control runs with no year-to-year changes in human or natural external factors. The control runs provide multi-model estimates of the differences resulting from natural internal variations in climate.
The scientists concluded that the satellite-observed changes in atmospheric temperature were consistent with the human-caused changes.