The changing flow of energy through the Earth’s Climate System
Radiant energy from the sun is unevenly absorbed in the Earth system because of the sun-Earth geometry, and the annual and diurnal cycles. The energy is transformed into internal energy (temperature-related sensible heat), latent energy (associated with phase changes of water), potential energy (associated with height and gravity), and kinetic energy (associated with motion). The energy may be stored in atmospheric, ocean, cryosphere and land heat reservoirs and moved around mainly by the atmosphere and ocean, which give rise to our weather and climate. Ultimately it is radiated back to space as infrared radiation, and for a stable climate the global mean outgoing and incoming radiation must balance. However, there is an energy imbalance caused by increasing greenhouse gases in the atmosphere, and most of the imbalance, over 90%, goes into the ocean. Accordingly, ocean heat content (OHC) provides a primary indicator of climate change, along with sea level rise.
Regional energy and water imbalances drive heat transports in the atmosphere and ocean currents, and through evaporation, precipitation, and runoff. Natural variability, especially El Niño, plays a small role globally, but can be significant locally. By adopting a holistic approach that includes top-of-atmosphere (TOA) radiation, vertically-integrated atmospheric transports, surface energy fluxes, and ocean heat transports, closure of the energy and water cycles on regional scales can be achieved. A new formulation of the energetics of the atmosphere and the climate system is used to refine estimates of the surface energy fluxes as a residual of TOA and atmospheric energetics. When the surface flux is combined with OHC estimates, ocean heat transports can be computed and validated with in situ observations. Understanding the disposition of the energy imbalance is essential for determining how climate change is manifested.