最近の気候変動における内因と外因

Abstract

By using a simple energy balance climate model and observed surface air temperature data, we investigate several internal and external causes of the globally or hemispherically averaged recent climatic change. Among the external causes, the increase of atmospheric CO2 concentration brings a warming trend of the surface air temperature, which may be detected in the next thirty years with a statistical confidence limit of more than 78%; the volcanic activity is responsible for the decade-to- decade temperature change and the effect of the anthropogenic aerosols may have contributed to the recent temperature changes. Also, we examine the effects of multiplicative and additive stochastic forcings as internal causes. Although Nicolis (1988) noted the increase of the temperature variance by the multiplicative stochastic forcing, we could not find such a monotonic increase in the variance of the temperature observed in the last hundred years. The additive stochastic forcing may contribute to a year-to-year temperature variation, and its magnitude corresponds to 0.22-0.28% of the input of the solar radiation at the top of the atmosphere.