Quote:
Originally Posted by Peter Ward
An important factor in calculating a heavy jet’s optimum operating altitide is the ISA deviation. Some 30 years ago this was typically a random variation around the “standard” ISA temperature...I know this to be true...as often I was the young recruit that had to do the calculation to see if we could climb or not. (I’ve probably made hundreds of not thousands of such calculations)
Nowdays a flight management computer works out the optimum level, however the ISA deviation is almost always hotter than ISA. I’ve observed the trend for some years now’and can only conclude the upper atmosphere is several degrees hotter than it used to be. Hence I dont think its unreasonable hypothesis that our earth’s atmosphere is retaining more moisture, hence more cloud.
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This follows the same thing that usually happened over much longer geological time scales (ice ages). What Peter describes is the green house effect, CO2 and water vapour trap heat within the atmosphere instead of allowing the heat to be emitted into space.
The Earth systems are self regulating though, as the Earth heats up more cloud cover forms which slows down heat escape making the Earth even hotter. It is this mechanism that caused Venus' runaway greenhouse effect; Venus had a mass volcanic event causing mass CO2 out gassing.
What staves off a runaway greenhouse on the Earth is that cloud cover reflects sunlight. So, although the Earth is trapping in heat it isn't receiving as much so eventually we end up in an ice age. Due to a lack of heat reaching the Earth through the cloud cover the Earth cools off which eventually means less cloud cover and we're back where we started.