Title: Fingerprinting with the Vertical Structure of Atmospheric Temperature Changes and the Volcanic Contribution to the “Hiatus” in Recent Warming

My talk will cover two recently published studies on the nature and causes of recent climate change. The first study shows that observational satellite data and the model-predicted response to human influence have a common latitude/altitude pattern of atmospheric temperature change. The key features of this pattern are global-scale tropospheric warming and stratospheric cooling over the 34-year period of satellite temperature records (1979 to 2012). Current climate models are highly unlikely to produce this distinctive signal pattern by internal variability alone, or in response to naturally forced changes in solar output and volcanic aerosol loadings. A “human influence” signal can be detected in all cases, even if tests are performed against natural variability estimates with much larger fluctuations in solar and volcanic influences than those observed since 1979. These results highlight the very unusual nature of observed changes in atmospheric temperature.

Despite continuing increases in atmospheric levels of greenhouse gases, global-mean temperatures at the surface and in the troposphere have showed relatively little warming since 1998. This so-called ‘slow-down’ or ‘hiatus’ has received considerable scientific, political, and popular attention. The second part of my talk (which was motivated by pioneering research performed by Susan Solomon and colleagues) examines the contribution of early 21st century volcanic activity to the ‘hiatus’ in global warming. Signatures of some of these eruptions are identifiable in satellite observations of stratospheric aerosol optical depth, tropospheric temperature, and short-wave fluxes at the top of the atmosphere. Neglect of early 21st century eruptions in climate model simulations partly explains why current climate models overestimate the tropospheric warming observed since 1998.