Greenhouse impact: “How a chilly ambiance can heat the Earth’s floor”
Dr. Roy Spencer writes on Fb:
Wayne Rowley has requested me to elucidate how a chilly ambiance can heat the Earth’s floor (which is what occurs in international warming principle), a query I’ve been requested many instances within the final 20+ years.
To begin with, the temperature of something relies upon upon the charges of vitality GAIN and vitality LOSS. When these 2 are equal, temperature stays the identical; if they’re unequal, the temperature modifications.
Everybody is aware of that rising the speed of vitality acquire will increase temperature: e.g. flip up the warmth beneath a pot of water on the range, or flip up the thermostat in your own home in winter.
However you may as well enhance temperature by decreasing the speed of vitality LOSS: put a lid on the pot of water whereas holding the flame beneath it fixed, including insulation to the partitions of a heated home whereas holding the speed of furnace heating the identical.
Now, observe that in these examples, the lid is *cooler* than the heated water, and the partitions (in winter) are cooler than the heated dwelling inside, but they’ll make the hotter object even hotter nonetheless. Your garments in winter (or summer time) hold you hotter than in the event you had no garments on, although the garments are cooler than your physique temperature. The examples are actually countless.
So, for the ambiance, the online circulate of infrared radiation from the floor to the “chilly” depths of outer area is tremendously diminished by the ambiance (the so-called “greenhouse impact”), holding the floor hotter than if the ambiance was not there, absorbing and emitting its personal infrared radiation. (An attention-grabbing facet impact is that whereas the greenhouse impact retains the floor and decrease layers of the ambiance hotter, the higher ambiance is definitely made colder. The identical occurs in the event you add increasingly insulation to the partitions of a heated home.)
How does this apply to international warming? Including CO2 to the ambiance from fossil gas burning barely enhances the ambiance’s means to maintain the floor hotter by decreasing the speed of vitality loss by the floor. The query is, by how a lot? The *direct* impact of a doubling of atmospheric CO2 is small, solely about 1 deg. C. However oblique modifications within the ambiance ensuing from that direct warming (“feedbacks”) can both amplify it or cut back it. I consider these feedbacks will restrict the warming to significantly much less that what we’re being advised by local weather modelers.
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