  Although anomalous episodical warming of the eastern equatorial Pacific,
dubbed El Ni\~no by Peruvian fishermen, has major (and occasionally
devastating) impacts around the globe, robust forecasting is still limited to
about six months ahead. A significant extension of the pre-warming time would
be instrumental for avoiding some of the worst damages such as harvest failures
in developing countries. Here we introduce a novel avenue towards El
Ni\~no-prediction based on network methods inspecting emerging teleconnections.
Our approach starts from the evidence that a large-scale cooperative mode -
linking the El Ni\~no-basin (equatorial Pacific corridor) and the rest of the
ocean - builds up in the calendar year before the warming event. On this basis,
we can develop an efficient 12 months-forecasting scheme, i.e., achieve some
doubling of the early-warning period. Our method is based on high-quality
observational data as available since 1950 and yields hit rates above 0.5,
while false-alarm rates are below 0.1.
