Arctic ice cap will disappear in 20 years, say scientists

[cbacba]

P = epsilon * sigma * T^4

epsilon = emissivity
sigma = stefan's constant
T = absolute temperature
P = power radiated / unit area (W/m^2)

do simple example - double P
and double double epsilon
what value do you have to change T by for the result to balance?
HINT = T doesn't have to change at all in the example.

What's being absorbed additionally by the ocean? That additional 3.7W/m^2 for a doubling means only that the surface emissions to space are down by 3.7W/m^2. For there to be extra energy in the earth/atmospheric system for the ocean to absorb, there must be a temperature increase somewhere. The 3.7W/m^2 additional absorption means that epsilon increased due to reciprocity. When you apply stefan's law with the new larger epsilon value, P increases meaning that more energy is being radiated outward by the atmospheric section that absorbed the 3.7W/m^2 in the first place. The question becomes whether T (of the atmosphere) needs to increase or decrease to fine tune the new balance.

If the 3.7W/m^2 were an increase due to insolation where emissivity didn't change, then stefan's law dictates that T must increase so that P outputs an additional 3.7W/m^2 to regain balance. It's a rather small change though since it's to the 4th power. But this is not relevent to ghgs as ghgs change emissivity.

it's not about bouncing around. Emission/absorption occur simultaneously. Absorption doesn't mean blocking totally. And this is still with radiative only - ignoring convective and conductive acitivities.

Gases tend to emit in lines. However, at the fluid densities of the troposphere, the factors of molecules bouncing around enter in. I think you might be basically right on what you're trying to say in the last paragraph. In dense atmosphere, some of the absorbed energy is reradiated as is and some is internalized in molecular vibrations and some is kinetic, bouncing the molecule around into others - creating heat. Any wavelength can have that effect. Your microwave heats your tea water by exciting some rotational mode of liquid h2o. If you put that microwave in a walkin freezer and tried to melt an icecube - nothing would happen to the icecube's temperature.

Planck's law is a more detailed accounting of what's going on than stefan's law. It breaks it up by wavelength. It's also the beginning of the transition of classical physics to quantum physics and has the introduction of the photon. It forms a curve that falls off at short wavelengths quickly and has a long tail out towards the longer wavelengths. It's basic shape is the same no matter what the temperature - anything above absolute 0 radiates. The peak location and height (and total energy) do depend upon the temperature. Wien's displacement shows the peak wavelength depends linearly upon the temperature while stefan's law shows the total radiated energy depends upon T^4.

Except in the upper atmosphere which is full of ions and is essentially a vacuum where molecules don't collide frequently things become line absorptions and emissions and laser type phenomenon can occur (stimulated emission - 1 photon triggers a second as it passes by), one sees much more of the classical physics, planck's law, stefan's law etc. Hence, absorbed lines are spread into bands and emissions depend upon temperature in the classical stefan, planck realm. Just because an object has to be 1000C to glow visibly doesn't mean it's not putting out near infrared at lower temperatures. This is classical - not quantum stuff - think averages of quadtrillion billions of molecules giving a classical value not individual molecules doing some thing or another weird quantum factors.

I'm not sure what your question on emissivity is or which statement you mean. Emissivity is not just a single number as it varies with wavelength. It does have an average value that most who deal with it use as an 'engineering' assumption. However, it is a function of wavelength. Again, at lower atmospheric levels, you have bands not lines involved due to the smearing out of the quantum effects into the classical realm. That is the lines have line width and groups of many lines form the bands. Perhaps you are asking if these are what increases in emission rates if they increase in absorption rates?

[Bored Wombat]

Originally Posted by Richard

Why is a warmer world a worse world?

Because of it's lessser ability to support the life that is not extinct today.
It terms of the effect on humans the downside is increased malaria, dengue fever, increased CVD, and malnutrition, increased water stress decreased arable land, displacement of people in many areas, increased floods and droughts, increased storm incidence and intensity, and the cost to the economy of changing land use that is no longer suitable for its current use.
Current human mortality attributable to climate change is about 150,000 people per year. (see: Impact of regional climate change on human health, Patz et. al. Nature 2005)

The Earth has been warmer than it currently is many times in the past and there's never been a suggestion that this causes a catastrophe.

Only a very long time ago. Only a very few living fossils alive today have survived a world that is detectably warmer than it is currently.

Note also the speed of this warming is unprecedented except where it has been a catastrophe. Plant migration takes time. Of course these days there are physical land use barriers to plant migration as well, which is why estimates of the extinction rates of the world's species are up around 25% of all species (See: Extinction risk from climate change, Thomas et. al. Nature, 2004), with worst case scenarios over 50%. (Note that current emissions are worse than the worst case scenario.)

In fact warmth is essential to most life, perhaps a warmer world will actually be a generally better one?

Life adapts to it's environment over millions of years. If that environment is changed over hundreds of years, extinctions result.

But the the weather itself becomes more dangerous in a warmer world, and we haven't even touched the effects of a higher CO2 atmosphere alone, which means lower plant transpiration threatening the worlds rainforests, particularly the Amazon whose West is entirely dependent on transpiration for rainfall, the acidification of the oceans which threatens oceanic calcifying organisms - a very important CO2 sink, as well as the obvious disaster to the oceanic food web if they go extinct, and a reduction in the nutritional value of plants.

[Bored Wombat]

Originally Posted by Gerbil Rebellion

Will reply to your other post after tomorrow.

You don't say, is that what its called, well if GW was affecting the poles in winter as well as in the summer with a constant warming then the amount of sea ice would fall each winter as well and wouldn't return to near similair levels, or is that too much to see when looking at a graph with pretty colours.

The reason that all years have finished above the average amount of ice is that years finish in the northern winter.

[Gerbil Rebellion]

LMAO

[Bored Wombat]

Originally Posted by cbacba

wombat,

I don't have time again to respond in detail to everything in the post.

Why don't you wait until you have enough time before responding at all then?

Total insolation isn't really measurable.

Then you've got no basis to claim that the sun is causing warming.
The consequences of the greenhouse effect on radiative forcing is well understood and calculable from first principles.

This is what has been predicted to cause a warming. A warming has been measured, confirming predictions.

Warming from changes in solar irradiance would cause more warming during the daytime than night, more during the summer than winter, and would warm the stratosphere as well as the troposphere. All these are the opposite to what is observed.

[Bored Wombat]

Originally Posted by cbacba

P = epsilon * sigma * T^4

epsilon = emissivity
sigma = stefan's constant
T = absolute temperature
P = power radiated / unit area (W/m^2)

do simple example - double P
and double double epsilon
what value do you have to change T by for the result to balance?
HINT = T doesn't have to change at all in the example.

Increasing the concentration of CO2 from 0.028% to 0.038% does not double epsilon for the atmosphere. In fact it makes nearly no difference at all in epsilon for the atmosphere.

[Bored Wombat]

Originally Posted by forfi

Sorry ,I meant that the Mercator projection distorts the reality of the landmasses.The sheer size of the former USSR is grossly misrepresented.

That's not a Mercator projection.

A Mercator projection maps the globe to a rectangle.

[forfi]

Like I said ,I have a dislike for smartases

[cbacba]

Originally Posted by Bored Wombat

Increasing the concentration of CO2 from 0.028% to 0.038% does not double epsilon for the atmosphere. In fact it makes nearly no difference at all in epsilon for the atmosphere.

Evidently, you haven't yet grasped that epsilon is not a one value number often used as an engineering simplification but rather a very complicated function of wavelength.

[Bored Wombat]

Originally Posted by cbacba

Evidently, you haven't yet grasped that epsilon is not a one value number often used as an engineering simplification but rather a very complicated function of wavelength.

Only if you are interested in power per unit area as a function of wavelength. Since we are talking about global warming, the relevant value is the total power over all wavelengths in W/m2.

And since temperature and the Stefan-Boltzmann constant are both scalars, the relevant epsilon would be the total epsilon over all wavelengths ... that is to say, the one value number often used as an engineering simplification.

Otherwise your own equation P= ε.σ.T^4 doesn't work. A scalar cannot equal a "very complicated function of wavelength" times two scalars, can it?