The sun is continuously sending out solar radiation in all directions. Sunlight that reaches Earth’s surface and atmosphere is either absorbed or reflected. Absorbed energy gets re-radiated the in the form of infrared, also known as longwave radiation. Infrared radiation is invisible to our eyes, but we feel it as heat.
In the atmosphere, greenhouse gases and clouds absorb and re-radiate heat, affecting the temperature of our planet.
On this page:
- What is the re-radiation of heat?
- Earth system models about the re-radiation of heat
- How human activities influence the re-radiation of heat
- Explore the Earth System
- Links to Learn More
For the classroom:
Global Change Infographic
The re-radiation of heat contributes to the energy budget; the amount of energy available on Earth that drives system processes and phenomena. The re-radiation of heat is an essential part of How the Earth System Works. Click the image on the left to open the Understanding Global Change Infographic. Locate the re-radiation of heat icon and identify other Earth system processes and phenomena that cause changes to, or are affected by, the re-radiation of heat.
What is the re-radiation of heat?
Solar radiation is shortwave, high-energy radiation, including visible light. When solar radiation is absorbed, it transfers its energy to Earth’s surface or atmosphere causing the temperature of the land, air, or water to increase. Because Earth is much cooler than the Sun, it re-radiates energy as longwave, lower-energy wavelengths than it absorbs. This absorbed energy is re-radiated as infrared radiation, which we feel as heat.
The amount of heat re-radiating from any area of Earth’s surface is influenced by many factors, including how much solar radiation is absorbed at that location (please visit the absorption and refection of sunlight page to learn more). Some of the heat re-radiated by Earth’s surface and atmosphere is lost back to space.
However, most of it gets reabsorbed and re-radiated in the atmosphere many times by greenhouse gases and clouds, a process known as the greenhouse effect.
Earth system models about the re-radiation of heat
This Earth system model is one way to represent the essential processes and interactions related to the re-radiation of heat. Hover over the icons for brief explanations; click on the icons to learn more about each topic. Download the Earth system models on this page.
The re-radiation of heat is affected by the concentration of greenhouse gases. Additionally, the coverage and distribution of clouds, both vertically and horizontally, can have opposite influences on Earth’s climate. Thin, high clouds, such as cirrus clouds, are colder than the surface of the Earth and absorb outgoing heat, resulting in less heat returning back to space and contributing to the greenhouse effect. In contrast, thick, low clouds, such as stratus clouds, are highly reflective and closer in temperature to the surface of the Earth, and do not contribute as much to the greenhouse effect as high clouds. To learn more about clouds, visit the absorption & reflection of sunlight page.
Heat is also re-radiated from the oceans shaping regional climate and ecosystems. To learn more about how heat is transported in the ocean, visit the ocean circulation page.
How human activities influence the re-radiation of heat
The Earth system model below includes some of the human activities that directly affect the re-radiation of heat in the atmosphere through the emission of greenhouse gases. Greenhouse gases increase the amount of heat in the atmosphere by absorbing and re-radiating heat. As the amount of heat in the atmosphere increases, so, too, does Earth’s average air temperatures, a phenomenon known as global warming. Not shown in this model is how humans alter Earth’s surface and atmosphere to change the amount of solar radiation that is absorbed instead of reflected back into space (to learn more, please visit the absorption/ reflection of sunlight page). Hover over or click on the icons to learn more about these human causes of change and how they influence the Earth system.
Explore the Earth System
Each of the bolded terms on this page (e.g. burning of fossil fuels, photosynthesis, etc.) and the icons in the Earth system models link to other pages where you can learn more about the processes and phenomena connected to the re-radiation of heat. Visit these other pages to continue your exploration of the Earth system. Alternatively, explore the Understanding Global Change Infographic and find new topics that are of interest and/or locally relevant to you.
To learn more about teaching the re-radiation of heat, visit the Teaching Resources page.
Links to Learn More
- NASA: Earth’s radiation budget
- The National Weather Service’s up-to-date satellite images from NOAA’s geostationary (GOES) satellites, which detect the amount of infrared emitted from clouds and Earth’s surfaces
- NASA map of Earth’s global emissivity
- NASA Earth Observatory: Clouds and Global Warming
- NASA Earth Observatory: Clouds and Radiation