title: Forced and unforced ocean temperature changes in Atlantic and Pacific tropical cyclogenesis regions.
abstract: Previous research has identified links between changes in sea surface temperature (SST) and hurricane intensity. We use climate models to study the possible causes of SST changes in Atlantic and Pacific tropical cyclogenesis regions. The observed SST increases in these regions range from 0.32 degrees C to 0.67 degrees C over the 20th century. The 22 climate models examined here suggest that century-timescale SST changes of this magnitude cannot be explained solely by unforced variability of the climate system. We employ model simulations of natural internal variability to make probabilistic estimates of the contribution of external forcing to observed SST changes. For the period 1906-2005, we find an 84% chance that external forcing explains at least 67% of observed SST increases in the two tropical cyclogenesis regions. Model "20th-century" simulations, with external forcing by combined anthropogenic and natural factors, are generally capable of replicating observed SST increases. In experiments in which forcing factors are varied individually rather than jointly, human-caused changes in greenhouse gases are the main driver of the 20th-century SST increases in both tropical cyclogenesis regions.
authors.affiliation: Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Santer
authors.forename: T M L
authors.initials: TM
authors.lastname: Wigley
authors.forename: P J
authors.initials: PJ
authors.lastname: Gleckler
authors.forename: C
authors.initials: C
authors.lastname: Bonfils
authors.forename: M F
authors.initials: MF
authors.lastname: Wehner
authors.forename: K
authors.initials: K
authors.lastname: Achutarao
authors.forename: T P
authors.initials: TP
authors.lastname: Barnett
authors.forename: J S
authors.initials: JS
authors.lastname: Boyle
authors.forename: W
authors.initials: W
authors.lastname: Brüggemann
authors.forename: M
authors.initials: M
authors.lastname: Fiorino
authors.forename: N
authors.initials: N
authors.lastname: Gillett
authors.forename: J E
authors.initials: JE
authors.lastname: Hansen
authors.forename: P D
authors.initials: PD
authors.lastname: Jones
authors.forename: S A
authors.initials: SA
authors.lastname: Klein
authors.forename: G A
authors.initials: GA
authors.lastname: Meehl
authors.forename: S C B
authors.initials: SC
authors.lastname: Raper
authors.forename: R W
authors.initials: RW
authors.lastname: Reynolds
authors.forename: K E
authors.initials: KE
authors.lastname: Taylor
authors.forename: W M
authors.initials: WM
authors.lastname: Washington
mesh_terms: D001267:Atlantic Ocean; D003198:Computer Simulation; D004190:Disasters; D017752:Greenhouse Effect; D006801:Humans; D008962:Models, Theoretical; D010140:Pacific Ocean; D012623:Seawater; D013696:Temperature; D013997:Time Factors; D014329:Tropical Climate