  In this study we used HadCRUT4 temperature anomalies for 1950-2013 years in
order to investigate properties of recent warming. Our aim was to separate
changes produced by short-term ENSO variations and to look on temporal and
spatial dynamics of residual temperature anomalies. For this we subtract linear
influence of ENSO index from each HadCRUT4 grid box. We found that residual
global temperature dynamics looks like staircase function: linear trends for
three quasi-stable periods 1950-1987, 1988-1997 and 1998-2013 are near zero and
near all warming occurred during two shifts of 1987/1988 and 1997/1998 years.
  All these allows us to formulate a new hypothesis about recent warming - the
Shifts Hypothesis. It explains the structure of recent warming as follows:
during shifts of 1987/1988 and 1997/1998 the mean value of global temperature
quickly rose, over which natural variability associated with ENSO, PDO and many
other local factors occurs.
  According to IPCC forcing-response paradigm warming process (WP) cleared from
all factors should be continuous warming (may be near linear on the considered
time interval). This idea is inconsistent to the obtained staircase function.
This staircase function may be explained by current IPCC forcing-response
paradigm only if it happened so that the combination of compensating factors is
near the same as anthropogenic greenhouse gases (GHGs) forcing for each
quasi-stable period - 1950-1987, 1988-1997 and 1998-2013. This seems very
unlikely. An alternative and more simple explanation is the existence of some
regulation mechanism (e.g. global thermostat) not presented in IPCC climate
models. This mechanism should maintain global temperature near stable in
1950-1987, 1988-1997 and 1998-2013 periods nevertheless all the time growing
forcing due to anthropogenic GHGs.
