If the world's weather was not being disturbed enough by El Nino just wait until its sister, La Nina, comes along. Our science editor Dr David Whitehouse reports

Over the past year or so the El Nino effect has affected weather patterns all over the world.

The El Nino or 'little child' is the unusual warming of the sea surface in the western Pacific.

This warm water current then moves eastwards towards South America disrupting the normal pattern of precipitation and air currents. The results can be felt worldwide.

During the last month, however, scientists have noticed the stirring of what has been called El Nino's little sister, La Nina.

La Nina is the opposite of El Nino. Satellite observations have revealed unusually cool ocean temperatures in the eastern equatorial Pacific. The last such event was observed in 1995.

Drought in Brazil has been caused by El Nino

In the tropics global climate variations caused by La Nina tend to be the opposite of El Nino. At higher latitudes things are more complicated but in general winters are warmer and summers are cooler.

The United States National Atmospheric and Ocean Administration (Noaa) says that la Nina conditions are developing in the Pacific and will affect our weather systems later this year and throughout next year.

Worldwide climate changes caused by El Nino and La Nina are not new. However, thanks to monitoring satellites our ability to see them begin, is.