  Complex networks have been used intensively to investigate the flow and
dynamics of many natural systems including the climate system. Here, we develop
a percolation based measure, the order parameter, to study and quantify climate
networks. We find that abrupt transitions of the order parameter usually occur
$\sim$1 year before El Ni\~{n}o ~ events, suggesting that they can be used as
early warning precursors of El Ni\~{n}o. Using this method we analyze several
reanalysis datasets and show the potential for good forecasting of El Ni\~{n}o.
The percolation based order parameter exhibits discontinuous features,
indicating possible relation to the first order phase transition mechanism.
