Observing and Modeling Earth’s Energy Flows

This article reviews, from the authors’ perspective, progress in observing and modeling energy flows in Earth’s climate system. Emphasis is placed on the state of understanding of Earth’s energy flows and their susceptibility to perturbations, with particular emphasis on the roles of clouds and aerosols. More accurate measurements of the total solar irradiance and the rate of change of ocean enthalpy help constrain individual components of the energy budget at the top of the atmosphere to within ±2 W m^?2. The measurements demonstrate that Earth reflects substantially less solar radiation and emits more terrestrial radiation than was believed even a decade ago. Active remote sensing is helping to constrain the surface energy budget, but new estimates of downwelling surface irradiance that benefit from such methods are proving difficult to reconcile with existing precipitation climatologies. Overall, the energy budget at the surface is much more uncertain than at the top of the atmosphere. A decade of high-precision measurements of the energy budget at the top of the atmosphere is providing new opportunities to track Earth’s energy flows on timescales ranging from days to years, and at very high spatial resolution. The measurements show that the principal limitation in the estimate of secular trends now lies in the natural variability of the Earth system itself. The forcing-feedback-response framework, which has developed to understand how changes in Earth’s energy flows affect surface temperature, is reviewed in light of recent work that shows fast responses (adjustments) of the system are central to the definition of the effective forcing that results from a change in atmospheric composition. In many cases, the adjustment, rather than the characterization of the compositional perturbation (associated, for instance, with changing greenhouse gas concentrations, or aerosol burdens), limits accurate determination of the radiative forcing. Changes in clouds contribute importantly to this adjustment and thus contribute both to uncertainty in estimates of radiative forcing and to uncertainty in the response. Models are indispensable to calculation of the adjustment of the system to a compositional change but are known to be flawed in their representation of clouds. Advances in tracking Earth’s energy flows and compositional changes on daily through decadal timescales are shown to provide both a critical and constructive framework for advancing model development and evaluation.     

Climate and Earth’s Energy Flows

Under equilibrium conditions, climate can be viewed in simple terms as the average energy pathways that incoming solar radiation takes before exiting the system in order to maintain overall energy balance. Similarly, future climate change will ultimately be determined by how the Earth’s energy balance and average energy pathways change in response to external radiative forcings, such as anthropogenic greenhouse gases, and internal redistributions. Here, we give an overview of climate research in the context of Earth’s energy flows and make the case for improved observations of total energy as a more physically robust metric of climate change than the commonly used surface temperature record.     

The Role of Water Vapour in Earth’s Energy Flows

Water vapour modulates energy flows in Earth's climate system through transfer of latent heat by evaporation and condensation and by modifying the flows of radiative energy both in the longwave and shortwave portions of the electromagnetic spectrum. This article summarizes the role of water vapour in Earth's energy flows with particular emphasis on (1) the powerful thermodynamic constraint of the Clausius Clapeyron equation, (2) dynamical controls on humidity above the boundary layer (or free-troposphere), (3) uncertainty in continuum absorption in the relatively transparent "window" regions of the radiative spectrum and (4) implications for changes in the atmospheric hydrological cycle.     

Changes in Earth’s Energy Flows and Clouds in 228-Year Simulation with a High-Resolution AGCM

We have examined long-term changes in Earth’s energy flows at top of the atmosphere (TOA) and at Earth’s surface (land and ocean) by using 228-year simulation of a high-resolution global atmosphere model, MRI-AGCM3.2. It is found that the net downward short wave (SW) radiation (absorbed solar radiation, ASR) at TOA significantly increases during twenty-first century in agreement with a previous study. However, in the present study, the reason for the change is an increase in clear sky SW absorption by increased water vapor in the atmosphere, while it is a decrease in cloud amount in the previous study. It is also found that the long wave (LW) cloud radiative forcing for atmosphere is positive and increasing during twenty-first century in agreement with a previous study. The reason for the change in the present study is an increase in absorption by water vapor of the downward LW radiation emitted from clouds, while it is reductions of cloud amount in the middle troposphere in the previous study.     

Tracking Earth’s Energy: From El Ni?o to Global Warming

The state of knowledge and outstanding issues with respect to the global mean energy budget of planet Earth are described, along with the ability to track changes over time. Best estimates of the main energy components involved in radiative transfer and energy flows through the climate system do not satisfy physical constraints for conservation of energy without adjustments. The main issues relate to the downwelling longwave (LW) radiation and the hydrological cycle, and thus the surface evaporative cooling. It is argued that the discrepancy is 18% of the surface latent energy flux, but only 4% of the downwelling LW flux and, for various reasons, it is most likely that the latter is astray in some calculations, including many models, although there is also scope for precipitation estimates to be revised. Beginning in 2000, the top-of-atmosphere radiation measurements provide stable estimates of the net global radiative imbalance changes over a decade, but after 2004 there is “missing energy” as the observing system of the changes in ocean heat content, melting of land ice, and so on is unable to account for where it has gone. Based upon a number of climate model experiments for the twenty-first century where there are stases in global surface temperature and upper ocean heat content in spite of an identifiable global energy imbalance, we infer that the main sink of the missing energy is likely the deep ocean below 275?m depth.     

Impact of space energetic particles on the Earth’s atmosphere (a review)

The state of the Earth??s upper atmosphere is formed with the participation of impacts by energetic particles, such as galactic cosmic rays, protons of solar proton events, and precipitation of relativistic electrons. Changes in the neutral composition and the thermal and dynamical regime of the upper atmosphere during periods of disturbances caused by the influence of energetic particles are considered.     

Comments on “Core Eigenmodes and Their Impact on the Earth’s Rotation”

Surveys in Geophysics -