The authors use as a measure of ENSO an index of sea surface temperature in the eastern Pacific Ocean (a commonly used measure). They find:
that ENSO systematically affects country level temperature and rainfall in the tropics... A rise in the ENSO index by +1°C increases local temperatures in the tropics by +0.27°C and lowers rainfall by -4.6 cm on average (combined over two years). For temperate countries, temperatures actually fall due largely to changes in atmospheric and ocean circulations, but only by half as much, and there is a small but insignificant positive effect on rainfall.More importantly though, they find:
A +1°C increase in the ENSO index lowers cereal yields -2%, total cereal production -3.5%, and agricultural income -1.8% on average across the tropics. These effects are highly statistically significant and suggest that rises in prices do not fully compensate countries for declines in agricultural output... crop yields increase in temperate countries when the tropical Pacific warms, albeit with a smaller magnitude that is less significant.Given that some (but not all) research suggests that future climate change will be linked to stronger ENSO events (for a great review see here), these results suggest that poor countries (which are disproportionately located in the tropics) could face decreased agricultural output, decreased food security, and decreased economic growth in the future. Perhaps it also helps to explain in part the poor past growth trajectories of these countries as well.