For thousands of years, the earth’s temperature has never varied more than a one or two degrees celsius. A rise or fall of 1ºC is approximately equal to one-third of one percent when measured from absolute zero. So the change in the earth’s temperature since the end of the last ice age has not been as much as 1%. Why?
This is because incoming radiation must balance outgoing radiation. Incoming radiation from the sun has remained relatively constant over the historical period, as discussed on my page about the sun. Outgoing radiation is governed by the Planck response : This is that radiation emitted varies by the fourth power of the absolute temperature), which, when applied to the earth’s temperature, shows that outgoing radiation will change by about 1% for every 1/3% change in absolute temperature, i.e. 1º C. So incoming radiation from the sun changes or more is reflected, or if outgoing radiation is blocked, there will be no change.
Because the greenhouse blanket of the earth also has remained almost constant throughout the historical period ground temperatures have kept within a narrow range. A discussion of how carbon cycles maintained constant greenhouse gas levels is beyond the scope of this website. There are many Internet articles about this.
You may wonder, what happens to outgoing radiation when greenhouse gasses heat the lower atmosphere? If solar radiation absorbed by the earth and its atmosphere has not changed, then the heating of the lower atmosphere is balanced by a cooling of the upper stratosphere, above the greenhouse gases. This is currently happening. You can understand this with a simple analogy. If you put more insulation in your home wall, the inside of the house becomes warmer, but the wall beyond the insulation becomes colder, since it receives less heat from the house. The Planck Response will limit the amount that the total earth=atmosphere temperature rises.
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