Weather Banter - View Single Post - Stephen Hawking and Carl Sagan on the Greenhouse Effect

Monkey Clumps

On Aug 13, 2:34*pm, Xan Du wrote:
On 8/13/2010 2:06 PM, Monkey Clumps wrote:

On Aug 13, 1:55 pm, Xan *wrote:
On 8/13/2010 12:42 PM, Monkey Clumps wrote:
On Aug 13, 12:31 pm, Xan * *wrote:
On 8/13/2010 11:08 AM, Monkey Clumps wrote:
On Aug 13, 7:46 am, * * *wrote:
On Aug 13, 11:20 am, * * *wrote:
On 13 Aug, 04:31,
wrote:
On Aug 11, 8:26 pm, Roger * * *wrote:
On Aug 11, 8:17 pm, Roger * * *wrote:
Please see:

http://www.youtube.com/watch?v=mu1PicT0TMU

Below are lecture notes from a college course:

The greenhouse effect of Venus

--- Venus' perpendicular solar flux is ~2600 W/m2

* *From geometry, we can calculate the average solar flux over the
surface of Venus. It is approximately 661 W/m2.
Venus is very reflective of sunshine. In fact, it has a reflectivity
(or albedo) of 0.8, so the planet absorbs approximately 661 X 0.2 =
132 W/m2.
By assuming that the incoming radiation equals the outgoing radiation
(energy balance), we can convert this into an effective radiating
temperature by invoking the Stefan-Boltzmann law (total energy = _
T4). We find that T=220K.
But Venus’ surface has a temperature of 730K!!!
The explanation for this huge discrepancy is the planet’s greenhouse
effect.

The greenhouse effect of Earth

--- Earth's perpendicular solar flux is ~1350 W/m2

* *From geometry, we can calculate the average solar flux over the
surface of Earth. It is approximately 343 W/m2.
The earth has a much lower albedo than Venus (0.3), so the planet
absorbs approximately 343 X 0.7 = 240 W/m2.
By assuming that the incoming radiation equals the outgoing radiation,
we can convert this into an effective radiating temperature by
invoking the Stefan-Boltzmann law (total energy = _ T4). We find that
T=255K.
Earth’s surface has a temperature of 288K
While much smaller than Venus’ greenhouse effect, earth’s is crucial
for the planet’s habitability. Without the greenhouse effect, the
temperature today in Los Angeles would be about 0 degrees Fahrenheit.

* * *Venus' surface atmospheric pressure is about 90 times that of
earth. *Venus's *surface gravity is about 10% less than that of earth
so Venus's atmosphere, just about all CO2,, is about 100 times as
dense as earth's.

CO2 makes up not quite 0.04% of earth's atmosphere, so Venus has about
100/0.0004 = 250,000 times as much CO2 as earth.

Oh wow, we better stop the economy now just in case! Lol.

From

http://en.wikipedia.org/wiki/Idealized_greenhouse_model

and

http://www.geo.utexas.edu/courses/38...ures/chap2.pdf

that 250,000 times as much CO2 on Venus results in a magnification of
warming from

132 *Watts /m^ 2 to *about 16,127 watts/M^2 or an effective 16,127/132
= 122 atmospheres.

122 venus atmospheres *1earth atmosphere/250,000 venus atmospheres =
0.000488 atmospheres warming, or about *0.18 watts.

Comparing the global warming caused by Venus' atmosphere to global
warming caused by Earth's CO2 doesn't cut the mustard. *Obviously
many bands are saturated, making increases in CO2 much less effective
than a linear ratio would imply.

Incidentally the general consensus is that , a doubling of CO2 would
increase the flux by about 3.7 watts.

* *From Trenbeth's figures

http://www.cgd.ucar.edu/cas/Trenbert...FK_bams09..pdf

the flux at earth's surface is about 492 watts, giving us a
temperature of about 288 K.

Plugging in that 3.7 watt increase, and remembering that temperature
is roughly proportional * *to the 4th root of the wattage flux,

(493.7/490)^0.25 = * 1.00188

for a temperature increase of 288*0.00188 = 0.54 K

- A. McIntire- Hide quoted text -

- Show quoted text -- Hide quoted text -

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Unfortunately, McIntyre is a stupid with an enormous agenda and is not
correct. Neither has he tried to publish this nonsense, as he knows it
wouldn't get past the laughter in the editor's office. Go see NASA and
let them tell you about radiative transfer theory. Google is waiting.
If not, you the previous poster and all the deniers can stay as
ignorant of the facts as you were before.

Seems the only thing Dawlish adds to these discussions are insults and
name calling. Everyone who disagrees is "stupid". *McIntire posted
numbers showing the theoretical increase purely from the greenhouse
effect being about half a degree.

Vostok ice cores and other long term temperature reconstructions show
that the mean temperature anomaly between glacial and interglacial
periods is 12C. *0.54C / 12 C * 100 =~ 4.5%.

And your point is?

A single scalar value without context is meaningless, so I gave it some.

Hardly something to spend trillions
of dollars over. The catastrophic effect of AGW predicted by warmists
depends of course on various positive feedbacks being fed into their
models. *The impacts of the positive feedbacks are highly
speculative. *In addition, the impact of potential negative feedbacks
such as increased cloud cover are unknown. *The basic greenhouse
properties of CO2 are not in dispute. *The overall sensitivity of the
climate system is.

It would seem that uncertainties should be studied, not ignored. *Your
arguments here are curious.

Where did I suggest that they shouldn't be studied? *Studying
uncertainties is fine.

I misunderstood your argument, I apologize.

Spending trillions of dollars trying to
reconfigure the worlds energy infrastructure based on those same
uncertainties is not.

AGW is not the only reason to begin weaning ourselves from fossil fuel..
* *The supply/demand curve is a good one. *Getting the hell away from the
Middle East is another. *The overall pollutive nature of fossil fuels is
a third.

Note that I have no love of the environmental lobby for their decades
long opposition to nuclear power. *Carbon emissions in the US would not
be such a large issue if we had been continually adding nuclear
generation capacity. *France is the poster child of success in this
area, with nearly 80% of their electricity generation coming from
nuclear fission -- the highest in the world. *Natural gas and coal
constitute nearly 75% of US electricity generation, 20% is nuclear.

Whether you like it or not, energy prices are going to go up. *The
argument here is whether to be reactive or proactive in dealing with it.