  Most of the existing prediction methods gave a false alarm regarding the El
Ni\~no event in 2014. A crucial aspect is currently limiting the success of
such predictions, i.e. the stability of the slowly varying Pacific climate.
This property determines whether sea surface temperature perturbations will be
amplified by coupled ocean-atmosphere feedbacks or not. The so-called Bjerknes
stability index has been developed for this purpose, but its evaluation is
severely constrained by data availability. Here we present a new promising
background stability index based on complex network theory. This index
efficiently monitors the changes in spatial correlations in the Pacific climate
and can be evaluated by using only sea surface temperature data.
