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The Earth's energy balance is the equilibrium between incoming solar radiation and outgoing thermal radiation, and is influenced by the Earth's albedo, atmospheric conditions, and greenhouse gases

Summary​

The Earth's energy balance describes the equilibrium between incoming solar radiation and outgoing thermal radiation. Approximately 340 W/m² of solar energy reaches the atmosphere, with 30% reflected back to space through the albedo effect and 70% absorbed by Earth's systems. Greenhouse gases trap outgoing infrared radiation, creating the greenhouse effect. Current estimates show a net energy imbalance of 3 W/m² due to increased greenhouse gases (4 W/m² forcing) partially offset by current aerosol levels (-1 W/m²). This imbalance drives temperature changes quantified through Equilibrium Climate Sensitivity, estimated at 1.2°C – 4.8°C per W/m² forcing. Maintaining this balance is crucial for sustaining Earth's current climate conditions.

The Earth's energy balance refers to the equilibrium between the amount of solar energy the Earth receives from the Sun and the amount of energy the Earth radiates back into space. The energy balance is influenced by a variety of factors, including the amount of solar radiation it receives, the Earth's albedo (or reflectivity), and the Earth's atmospheric conditions. The conditions for sustaining the current life on Earth depend on the energy balance remaining relatively stable.

Incoming solar radiation:

The Sun emits energy in the form of sunlight, primarily as shortwave radiation (visible light, ultraviolet, etc.). About 340 watts per square meter (W/m²) of solar energy reaches the Earth's atmosphere on average 1.

Reflection and absorption:

Due to the albedo effect, around 30% of the incoming solar radiation is reflected back into space by clouds, the Earth's surface (especially ice and snow), and atmospheric particles 2. This reflective property is known as Earth's albedo. The remaining 70% of solar energy is absorbed by the Earth's surface, oceans, and atmosphere, warming the planet. Aerosols in the Earth's atmosphere also contribute to the albedo effect.

Outgoing radiation (infrared radiation):

The Earth emits energy back into space as longwave radiation (infrared radiation) after absorbing solar radiation. Infrared radiation is the heat that you can feel from a hot object when you are near, but not touching it. The greenhouse effect, caused by gases in the atmosphere such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), is the process by which greenhouse gases in the atmosphere trap this infrared radiation that is being radiated from the Earth's surface.

When the Earth's energy balance is disrupted, it can cause the Earth's temperature to change. Currently, greenhouse gases are estimated to be increasing forcing by 4 W/m², while aerosols are reducing forcing by around 1 W/m², resulting in a net imbalance of around 3 W/m² 3. When an imbalance occurs, the Earth's temperature will change until a new equilibrium is reached. The measure for the magnitude of this change is known as Equilibrium Climate Sensitivity (ECS), and is estimated to be 1.2°C ± 0.3°C per W/m² of forcing and 4.8°C ± 1.2°C per W/m² of forcing for a doubling of CO₂ 3.

Sources​

Footnotes​

  1. Wild, M., Folini, D., Schär, C., & et al. (2013). The global energy balance from a surface perspective. Climate Dynamics, 40(11-12), 3107–3134. https://doi.org/10.1007/s00382-012-1569-8 ↩

  2. Goode, P. R., Qiu, J., Yurchyshyn, V., Hickey, J., Chu, M.-C., Kolbe, E., Brown, C. T., & Koonin, S. E. (2001). Earthshine observations of the Earth's reflectance. Geophysical Research Letters, 28(9), 1671–1674. https://doi.org/10.1029/2000GL012580 ↩

  3. Hansen, J. E., Sato, M., Simons, L., Nazarenko, L. S., Sangha, I., Kharecha, P., Zachos, J. C., von Schuckmann, K., Loeb, N. G., Osman, M. B., Jin, Q., Tselioudis, G., Jeong, E., Lacis, A., Ruedy, R., Russell, G., Cao, J., & Li, J. (2023). Global warming in the pipeline. Oxford Open Climate Change, 3(1), Article kgad008. https://doi.org/10.1093/oxfclm/kgad008 ↩ ↩2