  How strong are quantitative contributions of the key natural modes of climate
variability and the anthropogenic factor characterized by the changes of the
radiative forcing of greenhouse gases in the atmosphere to the trends of the
surface air temperature at different latitudes of the Northern and Southern
Hemispheres on various time intervals? Such contributions to trends are
estimated here from observation data with the simplest empirical models.
Trivariate autoregressive models are fitted to the data since the 19th century
and used to assess the impact of the anthropogenic forcing together with
different natural climate modes including Atlantic Multidecadal Oscillation,
El-Nino / Southern Oscillation, Interdecadal Pacific Oscillation, Pacific
Decadal Oscillation, and Antarctic Oscillation. For relatively short intervals
of the length of two or three decades, we note considerable contributions of
the climate variability modes which are comparable to the contributions of the
greenhouse gases and even exceed the latter. For longer intervals of about half
a century and greater, the contributions of greenhouse gases dominate at all
latitudes as follows from the present analysis of data for polar, middle and
tropical regions.
