An imperative to monitor Earth's energy imbalance

Abstract

The current Earth's Energy Imbalance (EEI) is mostly the result of human activities and is driving global warming. The absolute value of EEI represents the most fundamental metric defining the status of global climate change and will be more useful than using global surface temperature. EEI can best be estimated from Ocean Heat Content changes, complemented by radiation measurements from space. Sustained observations from the Argo array of autonomous profiling floats and further development of the ocean observing system to sample the deep ocean, marginal seas, and the sea ice regions are crucial to refining future estimates of EEI. Combining multiple measurements in an optimal way holds considerable promise for estimating EEI and thus assessing the status of global climate change, improving climate syntheses and models, and testing the effectiveness of mitigation actions. Progress has been and can be achieved with a concerted international effort. Earth's energy imbalanceWeather and climate on planet Earth arise primarily from differential radiative heating and resulting movement of energy by the dynamic components of the climate system: the atmosphere and the oceans. Both of these fluids can move heat and moisture through advective processes by atmospheric winds and ocean currents, as well as through eddies, large-scale atmospheric jet streams and convection. Other major components of the climate system include sea ice, the land and its features (including albedo, vegetation, other biomass, and ecosystems), snow cover, land ice (including the ice sheets of Antarctica and Greenland, and mountain glaciers), rivers, lakes, and surface and ground water. About 30% of the incoming solar radiation is reflected and scattered from clouds and the Earth's surface back to space. The remaining absorbed solar radiation (ASR) in the climate system is transformed into various forms (internal heat, potential energy, latent energy, kinetic energy, and chemical forms), moved, stored and sequestered primarily in the ocean, but also in the atmosphere, land and ice components of the climate system. Ultimately it is radiated back to space as outgoing longwave radiation (OLR) [1][2][3] . In an equilibrium climate there is a global balance 2 between the ASR and OLR, which determines the Earth's radiation budget 1-2 . Perturbations of this budget from internal or external climate variations create EEI 4 , manifested as a radiative flux imbalance at the top of the atmosphere (TOA).The EEI is shaped by a number of climate forcings, some of which occur naturally and others that are anthropogenic in origin. A sense of the relative importance of these factors for a given timescale is obtained through estimates of their "Effective Radiative Forcing" (ERF, Fig. 1). The phenomena giving rise to changes in ERF vary regionally and over time. Internal climate variability occurs from day-to-day and month-to-month associated with weather systems and phenomena like the MaddenJulian Oscillation (MJO) that cause short-term changes in cloudiness 5 . On ...

Observed and simulated full-depth ocean heat-content changes for 1970–2005

“…Since the beginning of the industrial revolution, increased emissions of long-lived greenhouse gases such as carbon dioxide have resulted in an accumulation of thermal energy in the climate system von Schuckmann et al, 2016) via the associated net energy imbalance at Earth's top-of-atmosphere (TOA). It is estimated that more than 90 % of the excess heat is stored in the ocean and is manifested by ocean warming (Loeb et al, 2012;Balmaseda et al, 2013;Rhein et al, 2013;, i.e., an increase in global ocean heat content (OHC; Levitus et al, 2012;Abraham et al, 2013).…”

Reconciling Estimates of Ocean Heating and Earth’s Radiation Budget

“…For an equilibrium climate, the absorbed solar radiation (the total incoming short wave radiation minus that which is reflected back into space by Earth's albedo) is balanced by the planetary emitted long wave (LW) radiation, over some suitable long-term average. Anthropogenic global warming arises from elevated greenhouse gas concentrations that lead to a persistent imbalance in Earth's radiation budget (ERB) and an accumulation of thermal energy in the Earth system, which is the root cause of the various facets of observed climate change [1]. This picture is complicated by substantial short-term variations in the net radiation at top-of-atmosphere, owing to internal weather and climate variability within the Earth system [2][3][4][5].…”

“…On multi-decadal timescales, it is estimated that >90% of the planetary heating associated with Earth's energy imbalance (EEI) goes directly into warming of the global oceans, with much smaller amounts going into heating of the land, atmosphere and ice cover [1,6]. Climate models suggest that the global ocean becomes the dominant term in Earth's energy budget on timescales longer than about 1 year [4].…”

Observational Advances in Estimates of Oceanic Heating

“…Overall, the OHC curves prior to the mid 2000s have large error-bars, and the year-to-year variations typically show limited agreement with the net TOA fluxes estimated from satellite products [38,64]. It is therefore for about a decade (since the Argo fleet neared completion) that the observing system has been adequate for the global analysis of upper OHC changes, although a persistent spread between the various 0-2000 m OHC estimates still hampers a robust closure of the current Earth energy budget [71].…”