V. Ramaswamy, National Oceanic and Atmospheric Administration (NOAA)

Abstract

The numerical modeling of the Earth system comprising the components of atmosphere, ocean, biosphere and cryosphere, is based on mathematical formulations which arise from fundamental principles in physics, chemistry, and dynamics. The principles eschew the governance of the conservation laws of energy, momentum, and mass. The components have significant differences in their characteristic timescales such that the interactions across the components lead to a host of important phenomena ranging from the weather to seasonal to annual to decadal and longer timescales. A particularly important element is the natural variations of the coupled system superposed on which are key factors forcing changes in the variables. An example is the anthropogenic climate change e.g., increases in greenhouse gases. The combination of variability and the trend imposed by forced climate change has given rise to the concept of non-stationarity of the Earth system, with anomalously aperiodic excursions in variables across timescales signifying the occurrence of extremes that can be of serious societal concern (e.g., droughts, heat waves, hurricanes). An additional challenge in mathematical representations in the model and quantification of climate state is the uncertainties in the processes that stem from gaps in basic knowledge e.g., convection, clouds, and aerosol pollution. How these uncertainties affect the confidence in the computational simulations is becoming an important aspect of understanding the Earth’s climate sensitivity and future climates.