The "El Nino" climate phenomenon which has helped push global temperatures to record levels and caused extreme weather, floods and droughts, is one of the most powerful ever, experts said.
The climate pattern, which has been in effect since last year, has now peaked but will remain strong and continue to influence world weather conditions in the coming months, the World Meteorological Organisation (WMO) said.
El Nino is the result of interaction between the ocean and atmosphere in an area of the Pacific that occurs irregularly between every two and seven years, affecting the climate and increasing global temperatures.
Its peak tends to occur at the end of the calendar year - giving it its Spanish name for the Christ Child - and the 2015-16 El Nino saw eastern and central tropical Pacific temperatures more than 2C above average late last year.
While the figures provide evidence that the current El Nino is one of the strongest on record, similar to events in 1997-98 and 1982-83, it is too early to tell if it is the strongest ever recorded, the WMO said.
Last year was the hottest year on record globally, with temperatures pushed 0.76C above average by man-made climate change and the strong El Nino, and scientists warn 2016 is likely to follow suit.
WMO secretary general Petteri Taalas said: "We have just witnessed one of the most powerful ever El Nino events which caused extreme weather in countries on all continents and helped fuel record global heat in 2015.
"In meteorological terms, this El Nino is now in decline. But we cannot lower our guard as it is still quite strong and in humanitarian and economic terms, its impacts will continue for many months to come.
"Parts of South America and East Africa are still recovering from torrential rains and flooding.
"The economic and human toll from drought - which by its nature is a slowly developing disaster - is becoming increasingly apparent in southern and the Horn of Africa, central America and a number of other regions," he said.
The 2015-16 El Nino ha been linked to below average rainfall in southern Africa, including Malawi, Mozambique, Zimbabwe and South Africa, while last year's Indian monsoon was well below average.
Droughts in South East Asia helped fuel wildfires in Indonesia, causing pollution that had significant repercussions for health in the region, while El Nino also contributed to a hotter, drier year in Australia.
The phenomenon has also been linked to severe flooding in Paraguay and scientists are predicting above average rainfall in the next few months for parts of Mexico, Peru, Ecuador, Paraguay, Brazil, Uruguay and Argentina.
But parts of central America and Caribbean countries have been affected by severe drought, while El Nino is also affecting temperature and rainfall patterns in North America.
And record ocean temperatures, in part caused by El Nino, have contributed to a major coral bleaching event, a process which damages and destroys coral reefs and affects the species and people that rely on them.