Natural factors: Internal variability

You need to have Flash Player 10 or above installed to view this video

You can download the most recent version of Flash Player here for free

    Professor Iain Stewart explains how some changes in climate have no external trigger. These changes are instead caused by interactions within the climate system itself, often involving positive feedbacks. One example of such ‘internal variability’ is the El Niño–La Niña cycle, which can cause temporary warming and cooling. But these changes are short-term, only lasting a few years. No known natural climate cycles cause the type of long-term global warming trend observed since 1970.