Greenhouse effect, 2010-2017
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The greenhouse effect is produced when the Earth's surface and atmosphere absorbs solar energy and reradiates the energy back into space. A portion of the absorbed energy is emitted by land and oceans, absorbed by the Earth's atmosphere, and reradiated back to the Earth. The greenhouse effect is one of several climate forcings, which are the major drivers of Earth's climate, alongside solar activity, volcanic eruptions, and aerosols.[1][2]
Background
Sunlight brings energy to the Earth in the form of ultraviolet radiation. Around one-third of the solar energy that reaches the Earth's atmosphere is then reflected back into space, while two-thirds of the energy is absorbed by the Earth's surface and atmosphere. On average, the Earth balances the absorbed solar energy by radiating the same amount of energy back into space. A significant amount of the energy emitted by the Earth's surface, including its land and oceans, is absorbed by clouds and the Earth's atmosphere and reradiated back to Earth, warming the planet's surface. This is commonly known as the greenhouse effect and is similar to how a greenhouse's glass walls reduce airflow and increase the temperature inside. The Earth's average surface temperature would be below -18°C (Celsius) without the natural greenhouse effect and would make Earth inhospitable for carbon-based life.[1][2][3]
The main contributors to the greenhouse effect are known as greenhouse gases, which include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Greenhouse gases can absorb and reradiate heat because they are composed of three or more atoms, which are held together loosely and vibrate after they absorb heat. These atoms release heat that is then re-absorbed by other greenhouse gas molecules. A portion of this heat remains in the atmosphere or returns to warm the Earth's surface.[1][2]
The two most important gases are water vapor and carbon dioxide (CO2), while methane, nitrous oxide, ozone, and other gases also contribute to the greenhouse effect, though they are less abundant. The atmosphere's two most abundant gases—nitrogen and oxygen—produce little to no greenhouse effect. Atmospheric greenhouse gas concentrations are affected by natural and human-caused emissions of gases and absorption of gases by oceans, surface ice, plants, forests, biological organisms, and more.[4][5]
The image below shows how the greenhouse effect is produced.
Illustration of the greenhouse effect
Impact on climate and global temperature
The greenhouse effect caused by greenhouse gases is known as a climate forcing; climate forcings are the major influencers of Earth's climate. Along with greenhouse gas concentrations, climate forcings include changes in the sun's energy output, volcanic eruptions, and the presence of aerosols (small airborne particles from human-made and natural sources). Climate scientists study the impact of greenhouse gases on global temperature compared to other factors and thus their contribution to global warming (defined as a rise in global average temperature) over time, as greenhouse gas concentrations and global temperatures have fluctuated over periods of hundreds, thousands, and millions of years.[6][7]
In addition, scientists observe other factors that may influence the greenhouse effect and other climate forcings. These factors are feedbacks, which are processes that can either accelerate or reduce the warming effects of climate forcings like the greenhouse effect. A positive feedback can increase warming, while a negative feedback can reduce warming. The following positive and negative feedbacks can affect the impacts of the greenhouse effect on warming.[8][9]
- Clouds: Clouds reflect back into space approximately one-third of all sunlight that hits the Earth's atmosphere. Increased cloudiness caused by more water in the atmosphere can limit the amount of sunlight from hitting the Earth's surface, resulting in less absorbed heat and less warming.
- Precipitation: A warmer atmosphere that holds more water can increase precipitation, though not in all regions. Changes in precipitation patterns can result in more water available for plants, which remove carbon dioxide (a greenhouse gas, also known as CO2) from the atmosphere. Increased plant growth could result in more CO2 absorption from the atmosphere and thus less warming.
- Forested areas: As negative feedbacks, forests, trees, and other plants remove CO2 from the atmosphere and thus can reduce warming that may be the result of increased CO2 in the atmosphere. However, forests and plants may also be cut down so that land is cleared for agriculture or other uses, which results in less CO2 absorption.
- Ice: Compared to ocean surfaces, which are dark and absorb heat more quickly, ice is white and thus quickly and more easily reflects sunlight. More ice and glaciers result in greater heat reflection and thus less warming. However, greater sea ice and glacier melting reduces this reflection and allows the ocean to absorb more heat and accelerate warming. This process is known as the ice albedo feedback.
See also
Footnotes
- ↑ 1.0 1.1 1.2 United Nations Intergovernmental Panel on Climate Change, "What is the Greenhouse Effect?" accessed June 30, 2017
- ↑ 2.0 2.1 2.2 American Chemical Society, "What is the Greenhouse Effect?" accessed June 20, 2017
- ↑ UCAR Center for Science Education, "The Greenhouse Effect," accessed June 30, 2017
- ↑ Science News for Students, "Explainer: Global warming and the greenhouse effect," May 27, 2010
- ↑ U.S. Energy Information Administration, "What are greenhouse gases and how do they affect the climate?" accessed July 11, 2017
- ↑ AccuWeather, "What are Climate Forcings?" accessed July 22, 2017
- ↑ Climate of Concern, "Basics of Climate Science - Feedbacks," accessed July 11, 2017
- ↑ OSS Foundation, "Climate Feedback/Sensitivity," accessed July 20, 2017
- ↑ National Aeronautics and Space Administration, "The Study of Earth as an Integrated System," accessed July 22, 2017