Earth's Energy Balance & Atmosphere
Earth's Energy Balance
The temperature of the planet depends on the balance between how much shortwave radiation emitted by the sun is absorbed by the earth (about 73%), how much is reflected back into space (about 27%), and how much longwave infrared radiation earth emits into space. As this infrared radiation emitted from earth’s surface passes through the atmosphere on its way to space, some is absorbed, heating the planet. This heating process is called the greenhouse effect. The greenhouse effect has been crucial to maintaining earth’s energy balance and temperature throughout its history, making the planet habitable. Recently, scientists have concluded that earth’s energy system is out of balance, as increasing concentrations of greenhouse gases are causing additional energy to be absorbed. As of 2007, IPCC scientists are over 90% certain human-induced (anthropogenic) greenhouse gas emissions have caused the global increase in average temperature since the mid-20th century. Recent studies have shown that it is very difficult to explain the warming of the past 50 years without the role of athropogenic greenhouse gas concentrations.
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PhysicalGeography.net's shortwave and longwave radiation diagrams
Dr. Lean and Dr. Ammann discuss Solar Radiation, Cosmic Rays, Greenhouse Gases and the respective roles of human-induced climate forcing (greenhouse gas concentrations) and natural forcing (solar forcing and volcanic activity) in global warming at the American Meteorological Society's Environmental Science Seminar Series
The Earth’s atmosphere is comprised of gases: nitrogen, oxygen, argon, carbon dioxide and tiny amounts of other gases and water vapor.
The Greenhouse Effect
Certain gases in the atmosphere trap energy from the sun that would normally escape into space. Water vapor, carbon dioxide, nitrous oxide, methane and chlorofluorocarbons are the main greenhouse gases. This trapping of energy by atmospheric gases is called the greenhouse effect, which helps to regulate the temperature of the planet. Without it, the planet would be extremely cold hence the greenhouse effect is critical to life on earth. However, increases in greenhouse gases have changed the natural balance.
Effects of Increases in the Concentration of CO2 in the Atmosphere
The combustion of coal, oil and gas by humans has increased the level of carbon dioxide in the atmosphere. It is estimated that the pre-industrial atmosphere was 280 parts per million (ppm) carbon dioxide. The concentration of carbon dioxide in the atmosphere is currently estimated to be at 380 ppm and is quickly increasing. Recently, scientists analyzed tiny bubbles of air trapped in ice cores in Antarctica that show a record of gases in the atmosphere. Scientists concluded that current carbon dioxide and methane concentrations in the atmosphere are the highest in the past 800,000 years. The ice cores show that the period when earth was warm corresponded to higher levels of greenhouse gases. (Read more)
In its AR4 Synthesis Report, the Intergovernmental Panel on Climate Change (IPCC) states: “most of the global average warming over the past 50 years is very likely due to anthropogenic greenhouse gas increases… Anthropogenic warming over the past three decades has likely had a discernible influence at the global scale on observed changes in many physical and biological systems.”
Clouds affect Arctic climate because they trap heat and their tops reflect sunlight back into space during certain seasons. There has been more cloud cover in the Arctic in recent years. Learn more about how clouds affect climate at NOAA's website
Learn more about Arctic Temperature UNEP/GRID-Arendal's Trends in Arctic temperature, 1880-2006 NOAA's Arctic Surface Air temperatures web page Learn more about how precipitation factors into Arctic climate and the hydrological cycle here
The Intergovernmental Panel on Climate Change (IPCC)
The IPCC is a scientific intergovernmental body set up by the World Meteorological Organization (WMO) and by the United Nations Environment Program (UNEP). The IPCC was established to provide the decision-makers and others interested in climate change with an objective source of information about climate change. Learn more at IPCC's website or read the IPCC Fourth Assessment Report
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