Is global warming a fact?

andrewBR

I don't guess that the global warming is a fact!
Tha planet is very strange, but this the result of the millions years of evollution
For me, this is normal, the planet needs change!!!

sylas

The original source of warming for the Earth is the Sun. Nothing else even comes close to making the slightest difference as an energy source. All climate impacts come from changing in some way the flow of energy that comes from the Sun.

The Sun itself is remarkably constant; but the way that energy flows through the Earth is not. Earth radiates all the energy it receives from the Sun. This is called "energy balance". There can be a short term imbalance with energy actually being stored or released from the Earth, but this cannot last. The amount of energy is too large.

What makes a difference for temperature is basically two things.

• Albedo. How much solar energy gets reflected. Reflected energy does not contribute to heating.
• Emissivity. This is a measure of how efficient the Earth is at radiating heat. This is where carbon dioxide makes a difference. It makes it a bit harder for the thermal energy radiated from the Earth to get out into space; and that means you end up with higher temperatures just to keep radiating the same amount of energy.

To accept the physics of greenhouse gases MEANS to recognize a strong effect on temperature from just this effect. The physics involved implies higher temperatures when you have more greenhouse gases.

Cheers -- sylas

eachus

Yep, the physics is easy--if you have growing levels of greenhouse gases (GHG) in the atmosphere. However, the primary GHG is water vapor. If the amount of water vapor was constant, then it would be easy to make working models of the atmosphere that include radiative forcing from CO2. But it is not that simple by any means. Clouds increase albedo, and thus reflect more sunlight, but they also trap heat, preventing radiative cooling from the ground or ocean under the clouds. So do clouds cause warming or cooling? Both, and sometimes at the same time. :-(

Remember that I am in favor of reducing CO2 levels. I just don't think that radiative forcing from CO2 is real.

There is not much research money these days for studying the Gaia hypothesis, that natural feedback paths make Earth's climate self regulating. But given that the solar constant has not been constant when looked at over billion year timescales, something has kept Earth from being an iceball or a Venus-like hothouse.

To be perfectly fair, current research seems to indicate that the Earth did go through an iceball (or slushball) phase several times over half a billion years ago. But it didn't stay locked in that mode. There are scientists trying to fit models that make CO2 responsible for leaving the icehouse mode. I happen to favor mountain building as the solution. And the long north-south mountain chain along the Pacific edge of the Americas as why the recent (in geological terms) Ice Ages didn't become Iceball Ages.

sylas

My primary interest in this is from a long time interest in science education and issues where science gets misunderstood in the public sphere. What we ought to do policy wise is a social issue, which is best informed after we understand the best available relevant science.

The radiative forcing of CO₂ is one of the simplest and most elementary aspects of the whole science of climate. The physics of it has been known since the nineteenth century, and it can be quantified quite accurately with calculations from a couple of decades ago. (The full calculation is pretty arduous and requires a lot of computer time to integrate over the vertical atmosphere profile and over the electromagnetic spectrum.)

The result is 5.35 W/m² of forcing per natural log of CO₂, accurate to 10% or so. The major reference for this is

• Myhre et al., (1998) New estimates of radiative forcing due to well mixed greenhouse gases, Geophysical Research Letters, Vol 25, No. 14, pp 2715-2718.

Note that the forcing is not in terms of temperature, but energy flux. This is what forcing means.

The next obvious question, of course, is what consequences the additional energy flux has for temperature. It will increase temperature of course; but how much? This is the source of the real uncertainties and open questions in climate science; the complex nature of the Earth response.

As temperatures rise, you get increasing specific humidity, and this (as you point out!) is the major greenhouse gas on Earth. This increase in humidity is measured, and it works as a strong positive feedback, basically amplifying the response to ANY forcing.

The other major effect is changes to weather patterns, and cloud in particular. This (as you point out) is very complicated. Most research indicates that the net effect of changing cloud in a situation of increasing temperatures is another positive feedback; although its magnitude is one of the greatest sources of uncertainty and even its sign is subject to question; under certain conditions it will be a negative (moderating) feedback.

You don't need a Gaia hypothesis for that, or self-regulation. Even with mostly positive (amplifying) feedbacks you tend to get reasonable long term stability. There's been a lot of very significant climate change over that period. For example: consider the cycle of ice ages over the last 2.8 million years (Quaternary period). Those are very large climate shifts, and they are driven by very small changes in Earth's orbit, we think. That requires some strong positive amplifying feedbacks to give such large swings in climate.

The only reason the swings don't go to a slushball or to a Venus like hothouse is that the feedbacks are still subcritical, so the response to a bounded forcing is itself bounded. Trying to marry that with the idea of "self-regulation" is rather odd.

Be that as it may, there's plenty of scope for looking at longer term feedback processes.

That is a very strange idea. You don't need any particular "reason" why recent Ice Ages don't go to slush balls. The only way to get the extreme slush ball is a runaway positive feedback. You don't need anything special to prevent this; and in particular you could probably have the Americas flat as a pancake without causing slushballs from the small forcings involved in the ice ages.

Ironically, the major effects of Earth's current arrangement of continents is to reduce the stability of climate, and contribute to the case where we've been having these large swings in climate in and out of Ice Ages with what are comparatively small orbital forcings. That is, these are not moderating influences; but actively help bring about large climate swings.

See, for example, Shifting Continents and Climates, a background article at Oceanus (23 Feb 2004) at the Woods Hole Oceanographic Institute.

Cheers -- sylas

ViewsofMars

Hi :)

I used to live on an island, and it was there I fell in love with the whales, dolphins and porpoises. I don’t want them to suffer. I’m especially fond of dolphins because they are super intelligent and playful creatures. I found this article which made me sad.

The Impact of a Changing Climate on Whales, Dolphins and Porpoises by Wendy Elliott, WWF Global Species Programme, and edited by Mark Simmonds, Whale and Dolphin Conservation Society (WDCS).

http://www.wdcs.org/submissions_bin/..._hot_water.pdf

On a happier note, a friend of mine gave me a present. It was a huge gourd that had small (three inch) strokes of blue and white little whales on it and was painted by a killer whale. I have a photograph of the whale painting the gourd! It's awesome. Everytime I look at it I think of the beauty that is alive and breathing, which brings me joy. There was a "Certificate of Authenticity" that came along with the gourd. It reads, "Shouka, Killer Whale (Orcinus orca) is one of Six Flags Discovery Kingdom's most enthusiastic painters. Painting is one of the many fun activities Shouka enjoys with her trainers between shows. She painted her first gourd in honor of the 2nd annual Mare Faire. She loves a lot of attention from her trainers, dolphin companions, and other human friends. She can often be heard outside Shouka Stadium when she is vocalizing with excitement during a variety of activities such as painting, mimicking her trainers and eating ice."

eachus

Maybe I didn't spell it out well enough. So I'll let H. L. Mencken try: "For every complex problem, there is a solution that is simple, neat, and wrong." In this case the assumption that blows up is that the CO2 is evenly distributed throughout the atmosphere. We now know that assumption is wrong in two dimensions. CO2 is heavier than air, so anthropocentric CO2 tends to stay in the lower atmosphere, where it does not contribute to radiative forcing or global warming. (CO2 from volcanoes is injected into the upper atmosphere, and tends to stay there. But that is a different issue.)

The other simplifying assumption that fails is that anthropocentric CO2 is distributed evenly in latitude. NASA has some nice animations which show just how wrong this is--there are two belts of anthropocentric CO2 in the mid-latitudes in both hemispheres, while the CO2 concentration in higher latitudes and at the equator is much lower.

Put it all together, and anthropocentric CO2 doesn't do much forcing, if any. But remember what I said, that I am very much in favor of reducing CO2 emissions because the current levels are already killing people--but elderly people and people with asthma, not by global warming.

A good test of how well someone understands the issues is their attitude towards nuclear power. Nuclear power is the only remotely reasonable replacement for base load coal plants today. You are allowed to be opposed to liquid metal fast breeder reactors (LMFBRs) but that is a detail. I don't know of anyone who still wants to build LMFBRs to close the nuclear fuel cycle. Today, gas cooled and molten salt breeders are a much safer, and actually less expensive alternative.

sylas

You spelt it out just fine. It is not that I fail to understand you; it is that we disagree. Put more bluntly; you are incorrect, and spelling it out in more detail only underlines the problems.

Variation in CO₂ levels is not enough to make a significant difference to the forcing in different parts of the Earth. The extra weight is irrelevant; the various gases are well mixed in the troposphere and do not separate out by weight until you get above the tropopause. The global warming impact of greenhouse gases is due to their existence below the tropopause, because their crucial role is to leave the bulk of atmospheric thermal emissions from the tropospause, which is much colder than the surface.

A recent thread has been started on improved details in CO₂ measurements from the NASA AIRS project. See the thread AIRS and Atmospheric Carbon Dioxide. The measurements shown are for mid-troposphere, and the variation is only a few percent -- as expected for well mixed gases in the turbulent troposphere. The variation is far less that the steady increase occurring at all latitudes and all altitudes as atmospheric CO₂ levels continue to rise.

It is a requirement of this forum that controversial claims be backed up by suitable scientific references. In this case, your assertions about a separation of CO₂ by weight, and of a lack of any contribution to forcing for anthropogenic CO₂ is in conflict with very elementary atmospheric physics.

By "much" you mean about 2%? Did you even read that research?

CO₂ levels are pretty much irrelevant for direct impact on health, at least at the levels seen in the normal atmosphere. The effect of atmospheric CO₂ on asthma is negligible. Again, you should support claims like this.

I have quoted the references for forcing of 5.35 W/m² per natural log CO₂. This is a well established forcing, not in any credible doubt. Your claims about variation in CO₂ levels don't appear to appreciate how small these variations actually are. Anthropgenic CO₂ mixes all through the atmosphere, and by basic thermodynamics it necessarily gives a substantial radiative forcing. The forcing due to CO₂ increases since pre-industrial times is about 1.7 W/m², corresponding to a rise from 280ppm to 385ppm, and the source of this increase is anthropogenic, as established by the Suess effect and also by simple bookkeeping with the magnitude of fluxes involved.

The impacts or social issues or policy issues are not on topic in this thread. The question is simply about getting the science of climate right. Is global warming a fact? Yes it is; and so also is the significance of CO₂ as a major contributing factor to increasing temperatures.

What remains uncertain is the magnitude of climate response to various forcings (sensitivity), the associated patterns of climate change as the globe heats up, and also the contribution of various other forcings, both non-greenhouse forcings, and greenhouse forcings from other gases.

Cheers -- sylas

Xnn

eachus;

Global warming due human emission of CO2 is a fact. However, the rate of change is so slow (0.02C/year) that it is difficult to measure and easy to dismiss. Even over 10 years, 0.2C is a small change.

On a typical day, temperatures vary by 10C between day and night.
While from one day to the next, 3 or 4 C is not unusual.

So, even though the science of global warming from CO2 is well understood and documented, we will continue to find people that are quick to reject it without taking the time to understand it.

Some of the opposition is due to a lack of knowledge, but others are driven by fear and political motives.

Bill Illis

Anyone ever put Myhre's forcing estimates into the Stefan-Boltzmann equations.

If the total forcing increase from GHGs is 1.7 W/m2, the Stefan-Boltzmann equations predict very little temperature change from an increase this small.

Surface TempK Today = (390 W/m2/5.67E-08)^.25 = 287.98K = 15.0C

Surface TempK Pre-Ind = (388.3 W/m2/5.67E-08)^.25 = 287.66K = 14.7C

So either Myhre's estimates are not really the traditional watts/metre^2 measure we use normally or the Stefan-Boltzmann equations aren't even being used.

ViewsofMars

The American Association for the Advancement of Science has the “Science Insider” with articles pertaining to this discussion. I think it’s worthy of a review. Thanks.

http://blogs.sciencemag.org/cgi-bin/...IncludeBlogs=9

sylas

Yes, they have. What the Stefan-Bolzmann equations give you is called "non-feedback response". But note that the forcing calculation by Myhre is not based on Stefan-Bolztman. It is based on radiative transfers up and down a transparent atmosphere. The calculation you are doing is a kind of check to see how the known forcing of CO₂ matches up with the observed changes in temperature.

The difference with the real climate on Earth is that as temperature increases, so also do other aspects that bear upon energy balance. Ice melts (increasing albedo), humidity increases (more greenhouse, but less lapse rate) cloud changes (altering both greenhouse and albedo in complex ways); plus also changes in vegetation and land cover.

All this becomes feedback, either positive or negative, which bears upon "climate sensitivity" to either amplify or damp the base non-feedback response.

I mentioned this in my earlier post, as an aspect of climate that is NOT well known. The base non-feedback response is pretty well constrained, but it does not suffice to let you infer the temperature impact.

There are several omissions in your application of Stefan-Boltzmann, even ignoring the effects of all the feedback processes. Most importantly, you are mixing up a surface temperature change with a forcing that is defined with respect to the top of the atmosphere.

Here is a better way of doing it. The Earth is not a black body emitter. You must consider both albedo and emissivity.

The Earth has an albedo of about 0.3, which means that about 30% of the solar input is reflected, and does not give any heating. Also, the radiation into space from the Earth corresponds to an effective temperature of about 255K. This is because of the greenhouse effect, which gives Earth an effective emissivity. Surface temperature is about 288K, because of the additional blanketing effect of the atmosphere.

You get into the right ball park by using a grey-body approximation relating surface temperature to the absorbed solar energy. For a grey-body, the Stephan-Boltzmann relation is

[tex]Q = \sigma \epsilon T^4[/tex]

Q is the thermal emission flux from the top of the atmosphere, and ε is an effective emissivity. T is the surface temperature.

The solar constant is about 343 W/m² over the surface of the planet. 30% of this is reflected, leaving 240 W/m² energy absorbed. This is what Earth emits as thermal radiation; it is the value for Q. T is the surface temperature, about 288K.

The value for ε is about 0.6; but in fact we can cancel it as follows.

[tex]\frac{dQ}{dT} = 4 \sigma \epsilon T^3 = 4Q/T[/tex]

The rate of change of energy emitted with temperature is about 4 * 240 / 288 = 3.3 W/m²/K. This is a non-feedback response. For every 3.3 W/m² of forcing (change in Q) we should get about a degree of temperature change -- ignoring feedbacks.

The 1.7 W/m² forcing corresponds to a bit over half a degree.

You obtain a slightly smaller value because you are using Stephan-Boltzmann at the surface, with Q=390 as the emission of radiation from the surface. But that's the wrong comparison for a forcing, which by definition is the change in energy balance at the top of the atmosphere. The method with a non-unit emissivity will give you a closer value for the proper application of Stefan-Boltzman to a forcing. There are in the literature more detailed calculations considering the emissivity of the atmosphere and the fact that the Earth is not a uniform sphere. The value obtained is around 3.2 W/m²/K; close to the simple approximation I used above.

There are a number of important provisos with this number.

• It ignores all feedbacks. This is one of the major open questions in climate research. Most of the available evidence indicates a net positive feedback, to give a substantial amplification of the base response. A small minority of researchers propose a zero or negative feedback, but over all they have not been made a good scientific case for this, and nearly all estimates suggest that the base response is increased by a factor of around 2 to 4 times.
• This is an equilibrium response. Since it takes a long time for the ocean to heat up in response to a new forcing, you don't get all this temperature increase realized at once. Research indicates at present a steady flux of energy flowing into the ocean. This represents a forcing that is not yet realized as a surface temperature increase.
• It ignores all other forcings; there's more than CO₂ involved.

As it turns out, these additional considerations mostly cancel out. The effect of time delay with heating of the ocean works in the short term rather like a negative feedback, and so the observed amplification short term is smaller than than full equilibrium response. The other additional forcings are both positive and negative, and of comparable magnitudes each way.

The net effect is that the base response is not that far off what we should experience; generally estimated to be a small amplification over base response.

So.... a naive application of Stefan-Boltzman to CO₂ levels alone gives about half a degree of heating. And the actual temperature rise we have observed is in a similar ballpark... around 0.7 degrees.

For more discussion in other threads:

• Feedback is now being discussed in thread The AGW climate feedback discussion.
• Base response is discussed, with references, in msg #69 of thread "Physics of Global Warming", and msg #47 of "Ocean heat storage". The values given for base response from the literature are about 3.2 W/m²/K.

Cheers -- sylas

Xnn

Bill; That's a good point.

Although I apply the Stefan-Boltzmann differantly, I still get a similar answer; 0.5C.

Basic Stefan-Boltzmann equation:

Temp (K) = [2*TSI*emissitivity*(1-albedo)/(4*5.67*x10^-8)]^(0.25)

TSI: Total Solar Irradiance - Watts/m^2
emissitivity; nominally 0.81 - unitless
albedo; nominally 0.3 - unitless

The 1.7 watt/m^2 forcing is applied to what could be considered to be the net incoming radiation term:

TSI*(1-albedo)/4

net result 0.5C of warming since pre-industrial times due to human influence and including solar changes.

The IPCC gives a global mean radiative forcing value since pre-industrial times of 1.6 watts/m2 with a range of 0.6 to 2.4. This includes all greenhouse gases, land use, black carbon, aerosols, contrails and solar irradiance.

What's missing are the feedbacks from water vapor and snow/ice melting albedo changes. So, feedbacks have made the observed warming greater than that from the underlying inital changes.

Bill Illis

I guess I have a number of issues with the standard explanations for the physics of global warming (and thanks to sylas and Xnn for indulging me here):

First, the Stefan-Boltzmann equations are the fundamental equations governing radiation physics and temperature. I really think that global warming theory needs to be consistent in some form with these proven and successful equations.

Second, the Stefan-Boltzmann equations are logarithmic. The surface of the Earth needs to add 5.5 W/m2 to go up by 1.0K but the Sun needs to add 50,000 W/m2 to increase its temperature by 1.0K. We can't use averages covering many different radiation levels in these calculations. It must be done on each individual extra watt, one at a time - the differential rather than the average.

Third, there are four different levels of the atmosphere which are emitting at 240 W/m2. Traditionally, the tropopause is defined as the level where the Earth is in equilibrium with the Solar forcing - the first level where that occurs is about 4 kms up - lower than the top of Mount Everest and lower than the definition of the tropopause.



Fourth, all the effective action of the greenhouse effect operates below this 4 km level. We use the term "Emissivity or even the Lapse Rate" but isn't this really just the time delay it takes for an Infra-Red photon from the surface to random walk/bounce around the atmosphere and the surface before it reaches the 4 km level and eventually escapes back into space. The average time a photon from the Sun spends in the Earth system is only 18 hours (some make it to the deep ocean and spends a thousand years in the Earth system while the majority of the energy represented by photons from the Sun escapes to space overnight after bouncing around a million individual atmosphere molecules. For every 240 W/m2 coming in from the Sun, an extra 150 w/m2 is time-delayed/accumulated near the surface to provide the Greenhouse Effect and keep the surface 33K warmer than the equilibrium temperature at 4 kms high.

Fifth, since these issues are so complicated and prone to error, why do we not look at the empirical evidence of the paleoclimate to provide an independent verification of the theory. Since the issues are so theoritical, we should go back to ground and see what has really happened in the climate per doubling of CO2. The actual/estimated temperature and CO2 history of the climate does not verify the 3.0C per doubling estimate. The paleoclimate is only consistent with 1.0C to 1.5C per doubling.

Maybe I am way off base here, but these issues are not addressed in the standard explanation. It only takes a 25% error in the estimates from the standard explanation to make a huge difference in the global warming per doubling estimate.

ViewsofMars

I'm fond of the ocean as one can tell by a previous posting. As a responsible citizen of planet Earth, and a concerned one at that, it's important for me to learn about my environment and the options available. Foremost, I like to share with others so they are informed as well. :)

sylas

No problem; questions are good!

I think I just showed that it is, didn't I?

Let me make one quick suggestion; as an advertisement. I think you are going to love this.

Ray Pierrehumbert of the University of Chicago is about to bring out a new undergraduate level textbook on climate science, and the book is really excellent for someone who wants just the science and who loves maths -- which seems like it might be you. It gets very technical, but you can dip into bits of it at a time. The whole draft is up on the website as a link to an 18 Mbyte pdf. The book is basically finished, and it is going to publishers soon, and this draft will be removed, apparently. Get yourself a copy now, while you still can! I have found this a really useful resource for learning about the underlying background and physics of energy flows in the atmosphere.

The web page for the book is The Climate Book, and the link to the pdf is in "Current draft" and he's still soliciting comment on this draft. When the book comes out, it will be

• Pierrehumbert, Ray. "Principles of Planetary Climate" (Cambridge University Press, 2010)

This goes through basic underlying physics to let you infer (or at least understand how to infer) from first principles such things as lapse rate, tropopause height, surface temperature, and so on, for essentially any planet. It is designed to be used as a teaching text, in which students solve such problems at all levels of detail, up to major computing projects. The book also comes with lots of supporting computer code. In brief, this does climate without weather. It goes very deep into simple energy flow models without using the fluid dynamics that would be needed for all the details of circulation and currents in the atmosphere and oceans.

Chapter 2 is thermodynamics in a nutshell, and chapter 3 is elementary models of radiation balance -- and specifically this is where Stefan-Boltzman law is introduced.

The atmosphere is transparent, to varying degrees. If you look at a thin slice of atmosphere at a specific level, it radiates almost nothing. When you look downwards, you are receiving radiation from all the levels below. The atmosphere is not a grey body. That is a useful teaching simplification to get started on some of the principles, but in general you can't actually use Stefan-Boltzman laws. You need frequency dependent equations, or the Planck radiation laws. Here's typical spectrum of emission from the top of the atmosphere.

I've added some labels to point to various features. As you can see, the spectrum is not a simple blackbody spectrum. In some bands, the atmosphere is pretty much transparent. In these bands, the spectrum follows closely the curve for a temperature of about 288K; this is thermal radiation coming up from the surface.

In other bands, the atmosphere is almost opaque. The "saturated region" is an example, and here the curve closely follows a spectrum for close to 220K, which is the temperature of the tropopause and lower stratosphere. Basically, the only radiation in this band that can escape to space is emitted from high in the atmosphere, where it is cold. This is mainly a CO₂ absorption band.

The complex behaviour on the left hand side of the diagram is caused mainly by the greenhouse effects of water vapour, which is not well mixed throughout the atmosphere, and hence does not have a simple relationship to a particular temperature. The effective emission altitudes in this band are somewhere in the troposphere.

Now in your diagram, the vertical axis is distance. Physically, it is easier to use pressure as a vertical co-ordinate, as this actually tells you the mass of the atmosphere at any level. Check out Earth Atmosphere Model, an education site at NASA. This represents the atmosphere in three bands: the troposphere with temperature falling with altitude, the lower stratosphere with near constant temperature, and the upper stratosphere with temperatures rising with altitude. In this model, the pressure tells you that about 2.5% of the atmosphere by mass is above the lower stratosphere... the region of your graph with constant temperature. Everything above that has minimal effect on Earth's energy balance. It's just too thin.

At any given altitude, you will have radiant energy flowing up, and down. As well as this, in the troposphere you have energy flowing upwards by convection, including latent heat. This is what maintains the lapse rate in the troposphere. At each level, you absorb a small amount of the radiation, and also emit a small amount based on temperature, according to the frequency dependent Plank radiation laws.

This all gets very technical in full detail, but by the time you finish chapter 4 of the text, you have pretty much what you need to explain and derive temperature profiles in an atmosphere of a given composition and with a given solar input.

The level of the tropopause varies with latitude. Emissivity and lapse rate has nothing at all to do with time delays. Lapse rate is mostly determined by the thermodynamics of adiabatic movement of air. Emissivity is simply a measure of how effective a material is at interacting with radiation. It is frequency dependent, and in an atmosphere you have emissivity per unit mass, which ends up letting you define an "optical depth", or a measure of transparency.

We do look at paleoclimate. But the available data is not sufficient to give you great accuracy; I have never seen anyone proposing such a tightly constrained sensitivity estimate from paleoclimate data. Neither have I seen such a low estimate. Do you have a reference?

The most important period for helping constrain climate sensitivity is the Last Glacial Maximum.

• Thomas Schneider von Deimling et al (2006) Climate sensitivity estimated from ensemble simulations of glacial climate in Climate Dynamics 27(2-3) pp 149-163.

From the abstract:

Our inferred uncertainty range for climate sensitivity, constrained by paleo-data, is 1.2-4.3^oC and thus almost identical to the IPCC estimate. When additionally accounting for potential structural uncertainties inferred from other models the upper limit increases by about 1^oC.

You are not at all off base in noting that sensitivity estimates are very uncertain. They tend to be in the range 2 to 4.5 degrees per 2xCO2. However, as I have noted, this sensitivity depends on the various complex feedback processes at work, and cannot be inferred from a simple non-feedback Stefan-Boltzman treatment.

Cheers -- sylas

Xnn

No, emissivity and the lapse rate are two entirely different properties from each other and from the time it takes a photon to bounce around.

When a photon enters earth atmosphere 1 of 2 things happen.
First, it might just be reflected and will immediately exit the earth atmosphere.
In this case, the time is measured in nanoseconds since light travels so fast.
Second, it might be absorbed. If it gets absorbed, then it will be re-radiated according to the stefan boltzmann law. By this law, the re-radiated energy will be somewhere in the infrared part of the spectrum which is readily absorbed by all the greenhouse gases and clouds in the atmosphere. I've never seen any authoritative estimate of how long it takes these infrared photons to make it into outer space, but I know that some of them never do. Instead, the energy is transported by thermals or water vapor. That it, mechanical process are important within the troposphere.

Anyhow, emissivity of the atmosphere is basically the ratio between the outgoing infrared radiation at the top of the atmosphere compared to the flux on the surface. It is a unitless number as it is just a ratio. CO2 levels have a direct influence on emissivity.

Lapse rate is how quickly the atmosphere cools off with elevation. There is probably some complicated relationship between emissivity and lapse rate, but I've never seen one.


Sylas provided a good response, but I'll like to add the the middle plicone is also being studied. The conclusions are that there is more warming found during that time than can be explained with the standard 2-4.5C/CO2 doubling. This is due to changes in vegetation and melting of Greenland and Antarctica; feedbacks which have not been taken into account by most climate models.


http://www.giss.nasa.gov/research/fe...ene/page2.html

ViewsofMars

I'm impressed by all contributors! :) Everyone is eager to add to the pot of information. I do like that.