http://iopscience.iop.org/1748-9326/7/3/034020/pdf/1748-9326_7_3_034020.pdf
Environ. Res. Lett. 7 (2012) 034020 A Pasini et al
In a previous paper (Attanasio et al 2012), we considered
bivariate analyses between natural or anthropogenic forcings
and global temperature, and found GHG Granger causality
effects on temperature since the 1940s, while TSI and other
natural forcings do not Granger-cause temperature in the
same period. Here, due to the evidence that natural variability
affects temperature behavior on decadal time scales—see,
for instance, DelSole et al (2011) and Wu et al (2011)—we
extend our information set to one of the indices of the
Pacific Decadal Oscillation (PDO), the Atlantic Multidecadal
Oscillation (AMO) or El Ni˜no Southern Oscillation (ENSO).
As is well known, a trivariate extension gives to the Granger
technique a better reliability with respect to a bivariate
analysis (see, for instance, L¨utkepohl 1982).
In this paper the recent climatic role of the Sun is
investigated in this trivariate framework.
2. Data
Time series of mean annual data since the middle of the 19th
century to 2007 are considered for the following variables:
HadCRUT3 combined global land and marine surface
temperature anomalies (Brohan et al 2006): data available
at
Data available from CRU (since 1850);
TSI (Lean and Rind 2008), with background from Wang
et al (2005): data available at
www.geo-fu.berlin.de (since
1850);
CO2, CH4 and N2O concentrations (Hansen et al 2007):
data available at
Data.GISS: Data and Images (since 1850);
greenhouses gases total (CO2 C CH4 C N2O) radiative
forcing (GHG) has been calculated as in Ramaswamy et al
(2001);
Southern Oscillation Index (SOI), related to ENSO
(Ropelewski and Jones 1987, Allan et al 1991, K¨onnen
et al 1998): data available at
Data available from CRU
soi/soi.dat (since 1866);
Pacific Decadal Oscillation (PDO) (Smith and Reynolds
2004): data available at ftp.ncdc.noaa.gov/pub/data/ersstv2/
pdo.1854.latest.st (since 1854);
Atlantic Multidecadal Oscillation (AMO) (Enfield et al
2001): data available at
Climate Research Data
timeseries/AMO (since 1856).
