OCEAN HEAT CONTENT CALCULATION IMPROVEMENTS FOR EARTH’S ENERGY IMBALANCE QUANTIFICATION

Abstract

Earth’s Energy Imbalance, the difference between incoming and outgoing radiation at the top of the atmosphere, is stored in the atmosphere, land surface, cryosphere, and ocean, but is stored overwhelmingly (~90%) in the ocean on interannual and longer time scales. This imbalance, which is reflected in ocean heat uptake, is a primary indicator of the magnitude of change in energy the Earth’s system as well as an essential variable for understanding short-term variations and their effects on long-term regional and global climate change. The primary methods for calculating ocean heat content all depend on situ measurements of ocean subsurface temperature. The ocean subsurface temperature observing system as it is currently configured, with a substantial but not exclusive contribution from autonomous Argo profiling floats, is shown here to allow estimation of annual global ocean heat uptake with an uncertainty well below that possible with earlier ocean observing systems. It is also shown that maintenance and improvement of a global best quality ocean temperature profile database will lower uncertainty, both historically and for the current observing system and compensate to some extent for areas of sparse data in both direct calculation from observation and in data assimilation models. It is also shown that improvements to the methods used for mapping the inhomogeneous and anisotropic observations onto a regular grid spanning the global ocean will reduce uncertainty historically, currently, and into the future. On shorter monthly timescales regional changes in the Earth’s Energy Imbalance requires tracking the storage within the atmosphere, land, and cryosphere, and the heat transport within the ocean especially to depths where the energy is stored on longer time scales, in addition to ocean heat uptake. Monthly heat uptake estimates discussed here can be utilized with additional terms from atmosphere/land and ocean/sea ice reanalyses to provide Earth's Energy Imbalance estimates on these shorter time-scales in the future.