this is what we are studying in my a level geography. La Nina is the process where nature tries to return back to the normal walker circulation - but sometimes La Nina can make things TOO normal. For example in the walker circulation there is usually high pressure over south America. during a big La Nina event the result would be extremely high pressure over SA, resulting in droughts etc.
Scientists believed that 2006 would be a record hurricane year after the 2005 season. but 2006 was a relatively docile year for hurricanes. This could be because of an El Nino event starting that year. El Nino could be helping stop global warming.
