<p class="lead" id="first">Global weather fluctuations called El Niño events are likely to become more frequent by 2040, a new study shows.</p><p>El Niño -- the unusual warming of surface waters in the eastern tropical Pacific Ocean -affects climate, ecosystems and societies worldwide.</p><p>The study examined four possible scenarios for future carbon emissions, and found increased risk of El Niño events in all four.</p><p>This means El Niño events and associated climate extremes are now more likely "regardless of any significant mitigation actions" to reduce emissions, the researchers warn.</p><p>Lead author Dr Jun Ying, from the Second Institute of Oceanography, Ministry of Natural Resources in China and the University of Exeter, said: "We know from previous studies that, when measuring El Niño changes in terms of rainfall shifts in the eastern equatorial Pacific, models predict an increase in the frequency of events.</p><p>"This study shows that those changes could happen after the next two decades."</p><p>The study, published in <em>Nature Climate Change</em>, examines the "time of emergence" of changes in the tropical Pacific using state-of-the-art climate models.</p><p>The time of emergence is defined as when the signal of climate change emerges from the usual background noise of natural climate variability.</p><p>When looking at changes in El Niño rainfall patterns, the best estimate of the time of emergence of changes converges on 2040 in all of the four emissions scenarios considered.</p><p>Co-author Professor Mat Collins, from the University of Exeter and part of the Global Systems Institute, added: "What surprised us is that changes emerge regardless of the scenario we look at.</p><p>"Because rainfall in the tropics is associated with the warmest sea surface temperatures (SSTs), it is the relative changes in SST that are more important than the absolute change.</p><p>"This leads us to the rather stark conclusion that these changes are essentially unavoidable."</p><p>The study was carried out by Dr Ying as part of a year-long Chinese Scholarship Council sponsored visit to the University of Exeter.</p><p>The paper is entitled: "Emergence of Climate Change in the Tropical Pacific."</p>