Earth's Energy Budget

The accounting of incoming solar and outgoing terrestrial energy flows that determines the planet's mean temperature and its imbalance.

Definition

Earth's energy budget is the balance between the radiant energy the planet receives from the Sun and the energy it returns to space, together with the internal flows of heat that redistribute it.

Scope

Covers the partitioning of incoming solar radiation among reflection, atmospheric absorption and surface absorption; the surface energy balance including sensible and latent heat fluxes; outgoing longwave radiation; planetary albedo; and the small top-of-atmosphere imbalance associated with ongoing warming and ocean heat uptake.

Core questions

• How is incoming solar energy partitioned among reflection, absorption and surface heating?
• What are the magnitudes of the major energy flows in and out of the climate system?
• What does a persistent top-of-atmosphere imbalance imply for the climate system?

Key theories

Global energy balance accounting

A quantitative framework that tracks shortwave and longwave fluxes plus turbulent and latent heat exchanges to close the planetary energy budget and diagnose any net imbalance.

Mechanisms

Of about 340 watts per square metre of incoming solar radiation averaged over the globe, roughly 100 is reflected by clouds, aerosols and the surface, and the remainder is absorbed. The surface returns energy as longwave emission, sensible heat and latent heat carried by evaporation; the atmosphere radiates to space at its effective emission temperature. A small residual imbalance, currently slightly positive, is stored mostly in the oceans.

Clinical relevance

The energy budget is the observational foundation for detecting climate change, validating climate models, and quantifying ocean heat uptake from a measured top-of-atmosphere imbalance.

History

Early budget estimates by Dines and Houghton were refined through the satellite era; the Earth Radiation Budget Experiment and later the CERES instruments provided global flux measurements, and synthesis studies by Trenberth and colleagues and by Stephens and colleagues established the modern budget.

Key figures

• Kevin Trenberth
• Graeme Stephens

Seminal works

• trenberth2009
• stephens2012

Frequently asked questions

What is Earth's planetary albedo?

Planetary albedo is the fraction of incoming solar radiation reflected back to space, about 0.3, set mainly by clouds, aerosols, snow, ice and bright surfaces.