On 7 Jan, 22:56, "Jack May" <
[email protected]> wrote:
> "Stephen Harding" <[email protected]> wrote in message
>
> news:Zhxgj.9242$Xo1.4668@trnddc06...
>
> > Jack May wrote:
> >> "Stephen Harding" <[email protected]> wrote in message
> > I think I read that during the Carboniferous period that
> > the earth was as hot as it has ever been.
>
> > ISTR that one of the reasons was due to large amounts of
> > water vapor in the air (volcanoes? geothermal activity?).
> > Can't remember what the source of it was. Maybe just
> > evaporation from oceans.
>
> > At any rate, the air can be very heavily saturated with
> > water without it raining, or without rain clearing up
> > the humidity. Check out many of the tropical locations
> > of the world where heavy rains don't lessen humidity.
>
> From:
>
> http://www.wxdude.com/humidity.html
>
> Air can only hold 100% relative humidity. For rain the 100% relative
> humidity is at the altitude where the rain is coming from, not the ground
> where the humidity gage is normally. It takes some time for the 100%
> humidity "mist" to form into drops which fall as rain. There are cases
> where there can be super cooled water being more than 100%, but that is
> rare.
>
> So for all practical purposes vapor is not going to do much to increase
> global warming because it will precipitate out as rain when it reaches 100%
> humidity at some place in the atmosphere. Since we get rain now, the air is
> often saturated at some place with the maximum moisture it can hold.
There are three gases emitted by aircraft which contribute to global
warming: H2O, CO2 and NOx The most obvious is the water vapour which
forms condensation trails - clouds of frozen ice crystals. Since the
air in the upper troposphere (the level at which most commerical
planes fly) is naturally very dry, water vapour emitted by aircraft
can make a big difference. Sometimes the contrails cover the whole
sky. Have you ever wondered, why the sky is so much clearer in remoter
locations?
Although these contrails reflect a little sunlight away from earth,
they reflect back to earth much more invisible infra-red (heat)
radiation which would otherwise escape to space - and therefore they
have an overall warming effect. This is hard to measure accurately,
because the contrails eventually spread out and become
indistinguishable from natural cirrus clouds.
Not all of the water vapour forms contrails, but water is itself a
"greenhouse gas" which also traps this outgoing infra-red radiation.
Each water molecule traps much more heat and also survives much longer
at this height than it would do at sea-level.
Jet-fuel - kerosene - is a mixture of substances produced by
distilling crude oil, which can be represented by C13H28. The chemical
equation for burning it is as follows:
2C13H28 + 40O2 =>26CO2 + 28H2O
So you can see, that for every 14 water molecules produced, the
aircraft must also emit 13 of CO2. This is also a greenhouse gas and
will stay in the atmosphere warming the earth for an average of 100
years, some of it for 1000s of years. There's no way that you can get
the energy from such fossil fuel without producing that much CO2. It's
not a by-product that can be "scrubbed" from the exhaust.
