by Dr ir. F. van den Beemt, March 15, 2022 in ScienceTalks
The 2021 UN Climate Change Conference, COP 26, resulted in several countries making statements that they would aim to reduce their emissions of greenhouse gases, particularly CO2, based on the fear that these gases are warming the Earth dangerously by what they call the greenhouse effect. But fear is a bad counselor. Understanding the matter reduces anxiety. The purpose of this article is to inform a broad audience about the greenhouse gas CO2 without going into scientific detail, for the latter see [1].
The Earth Thermostat: ensuring a livable temperature on Earth.
The sun heats the Earth with mostly visible light. Our water planet, the Earth, cools down by invisible heat radiation to space. The Earth’s surface, the oceans, and the atmosphere store heat to varying degrees. Wind- and water flows distribute heat all over the Earth. The evaporation process of water transmits energy from the surface into the air. Warm air rises until it cools and forms clouds. Clouds reflect incoming sunlight back to space that otherwise would have warmed the Earth’s surface. Clouds emit heat radiation to space and also some back to the Earth’s surface. These and many more heat transport processes act together as a planet-wide thermostat to create the livable temperature on Earth that we enjoy today.
The terrestrial thermostat knows no rest.
If the Earth’s surface warms up for any reason, this thermostat acts until a new equilibrium is reached. This equilibrium is never static, however, it fluctuates because the wind, convection, precipitation, and all the other dynamic natural processes continually adjust. The atmosphere shows dynamic, cyclic and chaotic characteristics.
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Figure 1 ( copied from Figure 10 in [2]): Effects of changing concentrations of CO2 on the filtered spectral flux at the mesopause altitude of 86 km. The smooth blue line is the spectral flux, from a surface at the temperature of 288.7 K for a transparent atmosphere with no greenhouse gases. The green line is with the CO2 removed but with all the other greenhouse gases at their standard concentrations. The black line is with all greenhouse gases at their standard concentrations. The red line is for twice the standard concentration of CO2 but with all the other greenhouse gases at their standard concentrations. Doubling the standard concentration of CO2 (from 400 to 800 ppm) would only cause a forcing increase (the area between the black and red lines) of 3.0 W m−2.
Above clouds, the water vapor concentration decreases where CO2 concentration stays nearly constant. Within the upper troposphere and the stratosphere, the CO2-specific part of the emission by clouds and water vapor will be again absorbed but now mainly by CO2. Within the thin stratosphere, CO2 emits to space as our satellites detect.
Heat emission to space at top of the atmosphere
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