Weather and climate Weather and climate have a profound
influence on life on Earth. They are part of the daily
experience of human beings and are essential for health, food
production and well-being. Many consider the prospect of human-
induced climate change as a matter of concern. The IPCC Second
Assessment Report (IPCC, 1996) (hereafter SAR) presented
scientific evidence that human activities may already be
influencing the climate. If one wishes to understand, detect and
eventually predict the human influence on climate, one needs to
understand the system that determines the climate of the Earth
and of the processes that lead to climate change. In common
parlance the notions "weather" and "climate" are loosely
defined1. The "weather", as we experience it, is the fluctuating
state of the atmosphere around us, characterised by the
temperature, wind, precipitation, clouds and other weather
elements. This weather is the result of rapidly developing and
decaying weather systems such as mid-latitude low and high