A new El Niño has begun. The sporadic Pacific Ocean warming, which can disrupt weather patterns across the world, is intensifying, say meteorologists.

So, over the next few months, there may be increased drought in Africa, India and Australia, heavier rainfall in South America and increased extremes in Britain, of warm and cold. It may make 2010 one of the hottest years on record.

The cyclical phenomenon, which happens every two to seven years, is a major determinant of global weather systems. The 1997-98 El Niño combined with global warming to push 1998 into being the world's hottest year, and caused major droughts and catastrophic forest fires in South-east Asia which sent a pall of smoke right across the region.

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At present, forecasters do not expect this El Niño to equal that of 1998, but it may be the second-strongest, and concerned groups, from international insurance companies to commodity traders, to aid agencies such as Oxfam, have begun to follow its progress anxiously. Its potential for economic and social impact is considerable.

Professor Chris Folland, of the Met Office Hadley Centre for Climate Prediction and Research, said: "We are likely to see more global warming than we have seen in the past few years, which have been rather cool. In fact, we are already seeing it."

El Niño is a periodic warming of the normally cold waters of the eastern tropical Pacific, the ocean region westwards out from South America along the line of the equator. Since the Pacific is a heat reservoir which drives wind patterns around the world, the change in its temperature alters global weather. An El Niño is defined by ocean surface temperatures rising by more than 0.5C above the average.

This El Niño is well beyond that, says the Climate Prediction Center of the US National Weather Service. "Sea surface temperatures remain +0.5 to +1.5 above average across much of the equatorial Pacific Ocean," the centre reported last week. "Observations and dynamical model forecasts indicate El Niño conditions will continue to intensify and are expected to last through the northern hemisphere winter of 2009-10."

The last El Niño was in 2006-07 and, at its peak, sea surface temperatures averaged about 0.9 degrees above normal. But this is a stage which has already been reached by this one.

The last El Niño, comparatively weak though it was, is thought to have been partly responsible for the extraordinarily warm weather in Britain between the summer of 2006 and the spring of 2007: July 2006 was Britain's hottest month, autumn 2006 (September, October and November) was the warmest autumn, winter 2006-07 (December, January and February) was the second warmest in Britain, and April 2007 was our warmest April.

People have forgotten this because there then began our recent cooler and wetter period, with Britain's two "washout summers" of 2007 and 2008, and they may, in turn, have been associated with the counter-phenomenon of La Niña, a cooling of the eastern tropical Pacific waters, which followed. The start of the present El Niño was one reason the Met Office predicted a "barbecue summer" for 2009.