Climate variation in New Zealand and the Southwest Pacific
Climate variation in the New Zealand and Southwest Pacific region is very much a subset of climate variation within the global climate system. The climate in any place over a particular time period is determined by processes within the Earth-atmosphere system, as well as external components. Those regarded as external to the system include the Sun and its solar output, the Sun-Earth geometry, and the Earth's slowly changing orbit around the Sun. These features determine the mean climate, which may vary owing to natural causes within the climate system. The Earth absorbs radiation from the Sun, mainly at the surface. This energy is then redistributed by the circulation of the atmosphere and ocean and radiated to space at longer wavelengths, as described in Chapter 4. On average, for the entire globe, the incoming solar energy is balanced by outgoing terrestrial radiation. Any factor that alters the quantity of radiation received from the Sun or lost to space, or alters the redistribution of energy within the Earth-atmosphere system, can effect climate. Therefore, change in the energy available to the climate system is essentially a radiative forcing.