Climate scientists have warned of wild weather in the year ahead as the start of the global "El Niño" climate phenomenon exacerbates the impacts of global warming. As well as droughts, floods and other extreme events, the next few years are also likely to be the hottest on record, scientists say.

In the UK, a Met office spokesman said yesterday that the El Niño event was likely to cause a hot, dry summer, following a warm June, but said could have other unpredictable effects on weather in Britain and north west Europe. "Much depends on how much the El Nino deepens in the next few months."

El Niño - "the child" in Spanish - was named by fishermen in Peru and Ecuador because the phenomenon arrives at Christmas there. It is part of a natural meteorological cycle that happens roughly every 3-7 years and affects weather worldwide for a year or more. It is caused by changes in ocean temperatures, with the first sign being abnormal warming in the Pacific .

Sea surface temperatures across an area of the Pacific ocean almost the size of Europe have now been increasing for six months and will inevitably trigger worldwide weather turbulence for the next year, said a spokesman for the US National Oceanic and Atmospheric Administration (Noaa). "An El Niño has started. It has a significant influence on global weather, ocean conditions and marine fisheries. Its impacts have included damaging storms, severe flooding and drought in Indonesia", he said.

El Niño is also strongly linked to droughts in Africa, Australia and Asia, and wetter-than-normal weather in much of the US and South America. There are growing concerns that its intensity and frequency may be affected by climate change.

At this stage, both US and Australian climate scientists say this may be a medium-strength El Niño, but they have warned the temperatures in the eastern Pacfic are still rising and it could develop further.

"Temperatures in the Pacific are around 1°C above average, and sub-surface temperatures up to 4°C warmer than normal. " said a spokesman for Australia's Bureau of Meteorology.

The last major El Niño in 1998 killed over 2,000 people and caused billions of dollars worth of damage to crops, infrastructure and mines in Australia and Asia. It led directly to forest fires in South East Asia, to a collapse of fish stocks in South America and a drought threatening 700,000 people in Papua New Guinea.

Strong El Niños frequently have long-lasting social and economic effects on countries. The 1991-92 event led to the major droughts in Africa and food shortages that left 30 million people at risk of malnutrition and set back development for a decade.

Development groups yesterday said the arrival of a new El Niñowas worrying because it will add to the effects of climate change and the worldwide economic recession, which has led to hundreds of millions extra hungry people.

Oxfam said it had alerted its teams around the world. "This could be the hottest year in known history. Poverty and climate change is enough of a challenge: an El Niño will only make things harder," said Steve Jennings, Oxfam's disaster risk reduction manager. "We are really concerned it will result in intense droughts in Southern Africa and floods in Eastern Africa."

2009 has already been marked by an unusual weather patterns in SE Asia, and stubborn droughts and major floods in Australia, the US, China and Latin America.

India has been experiencing much weaker annual monsoon rains this year and searing temperatures. Rains have been up to two weeks late with temperatures reaching the high 40C in some areas. Water levels in the Ganges, Indus, Narmada, Sabarmati, Godavari and other rivers of the Kutch were this week at dangerously low levels.

Droughts in Australia, Argentina and Northern China, some of the worst ever recorded, have reduced food supplies and led to major water problems.

A recent academic study of El Niño patterns even suggests the French Revolution was caused in part by an unusually strong El-Niño effect between 1789-93, which resulted in poor crop yields Europe.

But the Noaa spokesman said not all not all effects of El Niño are negative. "On the positive side, El Niño can help to suppress Atlantic hurricane activity. In the US, it typically brings beneficial winter precipitation to the arid Southwest, less wintry weather across the North, and a reduced risk of Florida wildfires."

Major recent El Niños:

1972-73 Peru: The world's largest fishery collapsed

1991-1992: Southern Africa experienced one of its worst droughts, affecting close to 100 million people.

1994-5: The US was hit with two of the most severe floods and storms ever recorded.

1997-8: Africa experienced a major drought, Ecuador and Peru suffered over 10 times more rainfall than usual. Malaysia, Indonesia and Brazil were hit by droughts leading to huge numbers of forest fires.

2002-3: The rise in sea surafce temperature was lower than other years but Australia suffered some of its worst ever droughts.

- Hannah White