title: Human and natural influences on the changing thermal structure of the atmosphere.
abstract: Since the late 1970s, satellite-based instruments have monitored global changes in atmospheric temperature. These measurements reveal multidecadal tropospheric warming and stratospheric cooling, punctuated by short-term volcanic signals of reverse sign. Similar long- and short-term temperature signals occur in model simulations driven by human-caused changes in atmospheric composition and natural variations in volcanic aerosols. Most previous comparisons of modeled and observed atmospheric temperature changes have used results from individual models and individual observational records. In contrast, we rely on a large multimodel archive and multiple observational datasets. We show that a human-caused latitude/altitude pattern of atmospheric temperature change can be identified with high statistical confidence in satellite data. Results are robust to current uncertainties in models and observations. Virtually all previous research in this area has attempted to discriminate an anthropogenic signal from internal variability. Here, we present evidence that a human-caused signal can also be identified relative to the larger "total" natural variability arising from sources internal to the climate system, solar irradiance changes, and volcanic forcing. Consistent signal identification occurs because both internal and total natural variability (as simulated by state-of-the-art models) cannot produce sustained global-scale tropospheric warming and stratospheric cooling. Our results provide clear evidence for a discernible human influence on the thermal structure of the atmosphere.
authors.affiliation: Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, Livermore, CA 94550.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Santer
authors.forename: Jeffrey F
authors.initials: JF
authors.lastname: Painter
authors.forename: Céline
authors.initials: C
authors.lastname: Bonfils
authors.forename: Carl A
authors.initials: CA
authors.lastname: Mears
authors.forename: Susan
authors.initials: S
authors.lastname: Solomon
authors.forename: Tom M L
authors.initials: TM
authors.lastname: Wigley
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Gleckler
authors.forename: Gavin A
authors.initials: GA
authors.lastname: Schmidt
authors.forename: Charles
authors.initials: C
authors.lastname: Doutriaux
authors.forename: Nathan P
authors.initials: NP
authors.lastname: Gillett
authors.forename: Karl E
authors.initials: KE
authors.lastname: Taylor
authors.forename: Peter W
authors.initials: PW
authors.lastname: Thorne
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Wentz
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D002980:Climate; D003198:Computer Simulation; D017753:Ecosystem; D057232:Global Warming; D006801:Humans; D008962:Models, Theoretical; D013472:Sunlight; D013696:Temperature; D018707:Volcanic Eruptions
keywords: climate change detection; climate modeling
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