The El Niño weather phenomenon is 'supersizing before our eyes' as it threatens to wreak havoc on the UK in autumn and early winter, experts have warned.Scientists from the World Meteorological Organization (WMO) said the climate pattern – where Pacific sea surface temperatures become significantly warmer than average – is now 'firmly established' and is set to have huge impacts on rainfall and temperatures globally, triggering floods, drought and extreme heat.Forecasts indicate an 'exceptionally huge likelihood of nearly 100 per cent' that El Niño will cause problems until February – the first time such an unequivocal update has been issued.In the UK, El Niño is likely to make autumn and early winter colder, wetter and stormier, according to the Met Office. UN Secretary-General Antonio Guterres said: 'El Niño is being supersized before our eyes. The science leaves no room for doubt: the planet is in uncharted waters – and those waters are heating up.'Sea surface temperatures are rising, temperatures keep climbing and the world is in the danger zone of extreme weather.'The race now is between rising risks and our commitment to take climate action and protect people. We must win that race.' Scientists warned El Niño is 'firmly established' and 'being supersized before our eyes' as temperatures continue to rise Experts said the phenomenon will have huge impacts on rainfall (pictured) and temperatures across the globeThe El Niño Southern Oscillation is a naturally occurring climate cycle that shifts between hot El Niño years and cool La Niña years once every two to seven years.As we enter an El Niño phase, the powerful trade winds that normally blow hot water across the Pacific towards Australia weaken, or even reverse.That prevents cool waters welling up from the deep ocean below and causes hot water to collect near the surface off the west coast of South America.Eventually, that warm water starts to spread out, raising the average global temperature and causing major disruptions to weather patterns around the globe.The WMO said sea surface temperatures in the region at the heart of El Niño are already well above average and are continuing to rise.The developing El Niño has gathered pace dramatically in recent months, with Pacific Ocean temperatures now more than 2C above average in some regions.Scientists say the warmth lurking beneath the surface is even more remarkable, with some underwater areas reaching a staggering 8C above normal.For September to November this year, the WMO's forecasts indicate there will be above-normal temperatures across almost all land areas around the world. Forecasts indicate an 'exceptionally huge likelihood of nearly 100 per cent' that El Niño will wreak havoc until February