Can longwave radiation heat the oceans?

[Loudzoo]

Thats my simple question!

 

[Bystander]

Is there some reason it shouldn't?

 

[Loudzoo]

Hi bystander - I read that infra red could not penetrate the ocean but caused evaporation on the surface skin. If that is true then infra red would not be able to heat the ocean like short wave radiation does. Is that true? thanks

 

[Bystander]

The enthalpy of vaporization has to come from somewhere --- you don't suppose IR absorption by water might be the source?

 

[Loudzoo]

Absolutely is the source in this example. But the energy from the incoming IR is not retained by the ocean as heat - its released through evaporation into the atmosphere. So is it correct to think that IR cannot heat (i.e. increase the temperature) of the ocean?

 

[Doug Huffman]

No. IR does heat water but at a very low rate, with not much energy compared to temperature coefficient of water.

 

[Bystander]

Consider also, conduction of heat from the "warm" surface to cooler water layer below the surface. To quote a faculty member from grad school days, "Every calorie looks the same once it's off the bus." Assigning origins and destinations to energies can be misleading.

 

[Loudzoo]

Thanks Doug. The IPCC estimates that a doubling of CO2 in the atmosphere would increase radiative forcing by 3.7W/m2 assuming clear sky conditions. This could only heat water in the top few molecules initially if water is as impermeable to infra red as I understand. Then as Bystander says any heating at the surface which does not evaporate surface skin molecules could be conducted to (or just mixed with) deeper levels. Could you point me in the direction of calculations as to what the magnitude of this heating might be? I completely understand that measuring this through real world observations must be very difficult as the calories are off the bus by then, but someone must have modeled this or tested this in a controlled environment?

 

[Doug Huffman]

The IPCC spins at best and lies at worst. Impeached.

 

[Bystander]

Quick and dirty demonstration? Two liter soda bottle filled with water; measure T in the morning; leave in sun all day; measure T in late afternoon.

 

[Loudzoo]

But sunlight is Short wave radiation ! Bystander - the experiment you suggest would only tell me what I already know that: short wave radiation heats water. I want to understand if infra red can heat water!

 

[Doug Huffman]

https://en.wikipedia.org/wiki/File:Solar_spectrum_en.svg

 

[Loudzoo]

Bystander - I found the following passage on a CAGW skeptic's website (http://climaterealists.com/index.php?id=4245)
"However the effect of downwelling infrared is always to use up all the infrared in increasing the temperature of the ocean surface molecules whilst leaving nothing in reserve to provide the extra energy required (the latent heat of evaporation) when the change of state occurs from water to vapour. That extra energy requirement is taken from the medium (water or air) in which it is most readily available. If the water is warmer then most will come from the water. If the air is warmer then most will come from the air. However over the Earth as a whole the water is nearly always warmer than the air (due to solar input) so inevitably the average global energy flow is from oceans to air via that latent heat of evaporation in the air and the energy needed is taken from the water. This leads to a thin (1mm deep) layer of cooler water over the oceans worldwide and below the evaporative region that is some 0.3C cooler than the ocean bulk below."
The last sentence does seem to be validated with this paper: http://www.nature.com/nature/journal/v358/n6389/abs/358738a0.html
But is the rest fair?

 

[Loudzoo]

Doug - I'm not sure I'm reading your graph correctly but it does seem to show that sunlight at sea level is a mixture of UV, visible and infra red wavelengths. If so - putting a bottle of water in the sunlight and measuring the temp change over a day isn't going to tell me anything about the effectiveness of IR in heating water

 

[Bystander]

The shortwave (visible) is going right on through. That's observation one. A day in the sun will bring the bottle up to 60-70 C. That's observation two. From the Planck radiation law 75% of the energy in sunlight is transmitted at wavelengths longer than the peak intensity wavelength, 500 nm (red).

 

[Loudzoo]

Dear Bystander - I appreciate your patience with me on this and I am grateful. That said, a bottle in the sunlight "experiment" is a blind alley if we're trying to understand the oceans. Low evaporation rates, the conduction of heat through the plastic of the bottle and diffraction of the light through the curved surfaces of the bottle all make such an experiment an extremely poor way to model the ocean temperature / IR relationship. Furthermore your comment on Planck radiation law calculations does not address this question if incoming IR causes evaporation in the ocean skin layer rather than an increase in the temperature of the ocean.

To get back on track do you agree that this graph is representative of the absorption spectrum of liquid water?
http://en.wikipedia.org/wiki/Electr.../File:Absorption_spectrum_of_liquid_water.png

If so - its clear that IR does not penetrate below 1cm and the wavelengths of back radiation from the atmosphere penetrate much less than that (e.g. 1/10^5 metres).

As per the nature article I referenced above (http://www.nature.com/nature/journal/v358/n6389/abs/358738a0.html) the top 1mm of the ocean is typically 0.3C cooler than the bulk mixed layer. Forgive me for being slow - but if most of the total IR radiation and all of the back radiation from the atmosphere penetrates less than the depth of the ocean skin layer that is cooler than the water below - how can IR increase the temperature of the ocean?

These observations suggest to me that almost all of IR radiation incident on the ocean causes evaporation rather than an increase in temperature of the ocean. Where am I going wrong?

 

[Bystander]

IR does not penetrate below 1cm

Where am I going

... not "wrong," into a "semantic ditch," perhaps. If you're going to give me all the solar radiation that penetrates further than 1 mm by the Kebes plot (shorter than 2 μm), you've given me 80 - 90% of the IR. If you define IR as only that radiation that is absorbed in 1 mm or less, and ignore the 0.8 - 2 μm gap between visible and IR acknowledged by a specific argument, you're losing a lot of energy.

 

[Loudzoo]

Thanks Bystander. I think I get where you're coming from. I'll give you whatever IR you want! Thanks to this discussion I think I can now refine my original question a little more clearly:

Can an increase in Atmospheric back radiation (from say increases in atmospheric concentrations of greenhouse gases) lead to increases in ocean temperatures?

For anyone else that is interested in this topic I found this set of articles (and associated comments) really useful.

As with most other discussions in climatology the answer isn't simple . . .

 

[Bystander]

Can an increase in Atmospheric back radiation

What is "back radiation?"

 

[Loudzoo]

its downward longwave radiation. IR radiating from the atmosphere down to the surface of the earth. Not IR direct from the sun.

 

[Bystander]

Heat moves from (hotter/same T/cooler) body/system to (hotter/same T/cooler) body/system?

 

[Loudzoo]

Heat moves from hot to cold obviously.
To summarise (and no doubt over-generalise!) one side of the argument seems to posit that:
solar radiation heats the ocean, but atmospheric radiation only heats the top few molecules. So increased Downward Longwave Radiation (DLR) is unable to transfer any additional heat into the bulk of the ocean, instead the energy goes into evaporating the skin layer into water vapor.

The other side of the argument seems to postulate that:
additional downward longwave radiation must alter the IR flux at the surface of the ocean leading to more IR being trapped in lower ocean layers and maintaining a higher water temperature than would be the case with less downward longwave radiation
so the downward longwave radiation doesn't heat the ocean but it slows the cooling that would happen with less DLR

And quite frankly I'm confused! What do you think?

 

[Loudzoo]

I should also add that I'm very much aware that none of the stuff I've read on this is in the peer reviewed literature. Wozniak et al (2013) "Light abosrbtion in sea water" looks like it might be just what I need - but its paywalled . . . any other suggestions would be gratefully received

 

[Bystander]

Heat moves from hot to cold obviously.

Not being "flip" with you --- just wanted to be sure we're both working from the same initial set of ideas/postulates/principles.

And quite frankly I'm confused!

Welcome to the wonderful world of energy "balances" in non-equilibrium systems. The system we're "analyzing" (hah!) has as heat sources the sun, ~ 10^-4steradians at ~ 5800 K or 1-1.3 kW/m² at Earth surface, and crustal heat leak of 10-30 mW/m², negligible. The heat sink is 4π steradians at ~ 4 K, the CMB. What else do we know? Some fraction of incident solar radiation is reflected, what fraction is subject to some uncertainty; some fraction is transmitted, very small through the atmospheric "halo", but enough to illuminate an otherwise totally eclipsed moon; and, some fraction is absorbed by atmo-, hydro-, and lithospheres, exchanged by conduction, convection, and radiation, and radiated to the CMB.

What are the exchange rates for each mechanism among the spheres? How good are the models? How good are the measurements? How do we know which "bus" which calorie came in on?

 

[Loudzoo]

Thanks Bystander that makes me feel better but I can't help feel disappointed that certain reputable scientists describe the science as settled. It seems then that comments within CAGW community that the recent plateau / pause / hiatus in global mean atmospheric temperatures might be explained by the "missing heat" being "trapped" in the deep oceans is not a scientific conclusion from research but merely a hypothesis. Furthermore it seems proving that rising atmospheric CO2 concentrations can heat the ocean is also very difficult. It remains only a hypothesis.

 

[Bystander]

https://www.physicsforums.com/threads/climate-change-global-warming-policy.757267/
You may or may not have read this; you're playing by the rules far as I can say, but please keep it in mind.

 

[Loudzoo]

I read that (as well as the other policy posts) before I started posting - and I hear you. I have no agenda other than to understand the physics. I don't know who is right and who is wrong and I don't have any pet theories of my own. As a human being I'd love to think CAGW is bunk because otherwise we're in serious danger. As someone who respects the truth and power of science and scientists I'd love to think its true because of the overwhelming scientific consensus. I understand the popular theory well enough but I don't understand the physical process of how additional CO2 in the atmosphere can lead to higher ocean temperatures. Can you help me? Many thanks again for your time and patience.

 

[Bystander]

I understand the popular theory well enough but I don't understand the physical process of how additional CO2 in the atmosphere can lead to higher ocean temperatures. Can you help me?

We can tip-toe through the argument/theory as you and I "understand" it, and as I think it's intended to explain things. So long as questions/doubts are based on established physical principles and we confine ourselves to resolving such questions/doubts within those principles, there shouldn't be any complaints.

 

[Loudzoo]

That would be extremely helpful and if at any point there are suitable publications that I can go and read rather than have you waste time - please direct me accordingly.
If I may be so bold as to start.
CO2 is a "greenhouse gas" because it is an efficient absorber and emitter of various wavelengths of IR radiation. Without greenhouse gases in the atmosphere the Earth's atmosphere would be some 33C cooler on average. Approx 3C of that can be attributed to CO2 at current concentrations. Because the effectiveness of CO2 is logarithmic each doubling of CO2 atmospheric concentration leads to approx 1C increase in global mean atmospheric temperature. IPCC estimates in AR5 of 1.5C to 4.5C per doubling rely on positive feedbacks from water vapour in the atmosphere. The wide range is because we don't understand how positive the net feedback process is. As a generalisation of the popular theory does that sound about right?
An increase in CO2 atmospheric concentrations will increase IR radiation in the atmosphere and as a result will increase downward IR radiation from the atmosphere to the Earth's surface. Where this "extra" CO2 strikes land it will warm the surface, increase convection, conduction and radiation increasing surface atmospheric temperatures.
As we've already touched on - where the "extra" downward IR strikes the ocean the effect is much less clear. Does the "extra" energy mainly increase evaporation rates or does it lead to increased temperatures in the water column?

 

[Bystander]

Looks like a good place to start; give me a day here to get my mind organized in terms of what I know, think I know, and what I've no clue about. Saves prying my feet from my mouth later.

 

[Loudzoo]

perfect - thank you

 

[Loudzoo]

I found the Wozniak 2007 work by the way: http://www.springer.com/cda/content/document/cda_downloaddocument/9780387307534-c2.pdf

I don't know whether its peer reviewed as its from a book rather than a journal. It seems very thorough . . .

 

[Loudzoo]

Bystander - I hope you don't mind but I'm going to keep posting things that might be relevant as I find them.

I found this article at realclimate.org (generally viewed as being on-message with the IPCC). It won't necessarily help us understand the physics but if it correct it does give us some idea of the magnitude of the IR / ocean temperature relationship:
http://www.realclimate.org/index.php/archives/2006/09/why-greenhouse-gases-heat-the-ocean/

 

[Bystander]

Without greenhouse gases in the atmosphere the Earth's atmosphere would be some 33C cooler on average. Approx 3C of that can be attributed to CO2 at current concentrations.

This (the 3 C out of 33 C differential) appears to be the "first/principle/primary" postulate from which the argument is developed, and bothers me no end. The 33 C total greenhouse effect is the difference between a "global mean temperature" which can be called a real measurement, and a hypothetical "gray body" radiation steady state temperature, neither of which are presented with any uncertainties that I've seen (haven't done a global search, but am not used to having to do other peoples' error analyses). Dissections into contributions from various mechanisms, either as actual heat fluxes, or ΔT values, have likewise been less than transparent to me regarding methods and uncertainties.

It's beginning to look like we need to start me (literally) at the top with insolation values (1300, 1000, 1100) for incoming, direct surface incident, and direct plus scattering surface incident radiation, and track down the uncertainties in those measurements, and then look at reflected and absorbed radiation and those uncertainties, et cetera.

I wrote the whole "whatever" off forty years ago, and haven't really bothered to pay much attention since. So it's going to be a bit slow and painful getting me up to speed on "state of the art" regarding actual measurements by, and arguments from the proponents.

 

[Loudzoo]

To be honest - starting from first principles would help me no end as well. I think I first heard the theory in about 1986 (when I was 10) and have been "studying" it on and off ever since - including specialising in Climatology, and Quaternary Environments for my Geography degree at Oxford in the mid-90's. None of that is particularly relevant other than to say that we can take as long as we need - I'm not in any rush. I do think its an important area to understand though for obvious reasons.

 

[Drakkith]

An increase in CO2 atmospheric concentrations will increase IR radiation in the atmosphere and as a result will increase downward IR radiation from the atmosphere to the Earth's surface. Where this "extra" CO2 strikes land it will warm the surface, increase convection, conduction and radiation increasing surface atmospheric temperatures.
As we've already touched on - where the "extra" downward IR strikes the ocean the effect is much less clear. Does the "extra" energy mainly increase evaporation rates or does it lead to increased temperatures in the water column?

As far as I know the increased evaporation rates are due to the increase in temperature, so you can't have one without the other.

 

[Bystander]

"Total Solar Irradiance," ref. 17 and 18 from Wiki http://en.wikipedia.org/wiki/Sunlight , 1360.5 -1363 to 1365.5-1367 W/m²; a 1.5 - 2.5 W/m² variation over long-term solar cycles, and 0.3% difference between total irradiance as measured in two series of measurements covering ~ 70's to present day. Forty to fifty years, ± 0.3 %, is decent calorimetry. Earth's orbit, aphelion and perihelion, other parameters are known to far smaller uncertainty, and TSI as a function of day of the year can be expressed to same uncertainty as that of the measurement series. So we know incoming irradiance to ± 0.3 % year-round. Need to check Wiki's citations, but they look decent (no J. Irreproducible Results type stuff).

Since Δq ~ 4σ_S.-B.T³ΔT the uncertainty in solar irradiance shouldn't affect black body numbers significantly, and we can take this much as well known.

Next step is to identify uncertainties in the 1050 and 1120 W/m², for direct surface insolation and directly transmitted plus scattered surface insolation figures from Newport, ref. 3 in http://en.wikipedia.org/wiki/Sunlight . Haven't got this one handy at the moment. Use of the word "about" in the Wiki article may not mean anything, but, "one step at a time."

 

[Loudzoo]

As far as I know the increased evaporation rates are due to the increase in temperature, so you can't have one without the other.

That's exactly my understanding. The downward longwave radiation works to increase the temperature of the ocean skin which increases evaporation, ceteris paribus. The question we hope to answer is whether this process can ever heat the mixed layer or ocean bulk. If changes to DLR are quickly offset by changes to the evaporation rate (in a linear fashion) then "long term" ocean temperatures are unlikely to be sensitive to changes in DLR.

 

[my2cts]

Short answer: of course it can and it will, all other effects being equal. Any radiation will. Its a no brainer.
Somewhat longer:
A large fraction will be absorbed by the water, some is reflected. Depending on the wavelength this happens in the top 100 microns (6.3 um) , still 1 million or so molecules thick, or in the top few meters (10 um). This process delivers heat to the ocean. This does not mean the ocean temperature rises since so many other mechanisms are involved.

 

[my2cts]

but atmospheric radiation only heats the top few molecules./QUOTE]
The top mmm or meters . That is a lot more than the thickness of a water molecule.

 

[Loudzoo]

Re: my2cts
Thanks for the clarification. Yes - my "top few molecules" comment for representing one side of the argument is I suspect an exaggeration. Its not my understanding but what others have said.

This does not mean the ocean temperature rises since so many other mechanisms are involved.

Its this question that I really want to drill down on and get a handle on.

 

[my2cts]

You need to do really good measurements, easier said than done, or run a really good model.
Maybe the latter is your best option.

 

[PeterDonis]

Without greenhouse gases in the atmosphere the Earth's atmosphere would be some 33C cooler on average.

This factoid is often quoted, but it leaves out a key factor, namely latent heat transport via the hydrologic cycle: water evaporates from the surface (mainly the ocean), rises into the upper atmosphere, and condenses there into clouds and precipitation. The net effect is to transport heat (as latent heat carried by the water vapor) from the surface to the upper atmosphere, where it can more easily escape to space.

The reason this is important can be illustrated by considering the following series of scenarios:

(0) A hypothetical Earth with an atmosphere completely transparent to both incoming and outgoing radiation. The average surface temperature of such an Earth would be approximately 255 K, based on thermal equilibrium with incoming Solar radiation covering the cross-sectional area that the Earth presents to the Sun.

(1) A hypothetical Earth with an atmosphere that had the same greenhouse effect as the actual one, but was still completely transparent to incoming radiation, and which had no other heat transport processes (i.e., no convection, no hydrologic cycle, no weather, etc.). The average surface temperature of such an Earth would be (IIRC--it's been a while since I looked at the details of these calculations) about 333 K, which is 60 C or 140 F--i.e., hotter than the hottest surface temperature ever recorded on the actual Earth (134 F in Death Valley).

(2) The actual Earth, with both the greenhouse effect and the hydrologic cycle. The average surface temperature is about 288 K.

Notice that the 33 C (or 33 K) temperature difference quoted is between (0) and (2), but that difference is not just due to the greenhouse effect; it's due to a balance between the greenhouse effect and the hydrologic cycle. It's also worth noting that the average surface temperature is actually not the best thing to look at to understand what's going on: you need to look at the profile of temperature vs. altitude in the atmosphere.

 

[PeterDonis]

You need to do really good measurements, easier said than done, or run a really good model.

A model is only going to be "really good" if it is repeatedly improved based on comparison between the model outputs and really good measurements. So no matter what, you need really good measurements. One of the key issues with our current (relatively poor) understanding of the Earth's climate is that we don't have really good measurements, and without them, there's no way to spot where our models are going wrong.

 

[PeterDonis]

As a human being I'd love to think CAGW is bunk because otherwise we're in serious danger.

It's worth pointing out here that this does not follow; even if "CAGW is bunk" (which I personally think it is, at least the CO2 alarmism part of it), we could still be in serious danger, because we don't understand very well how the climate works. We could be in for another ice age soon; we don't know whether, or when, this might happen. Various other human activities besides CO2 emissions could be significantly affecting the climate (my personal candidate is land use--we have drastically changed the land surface of the planet); we don't know which ones, or how big their effect is. So the common "skeptic" argument that, since CAGW is bunk, there's nothing to worry about, is not a valid argument.

 

[Bystander]

As far as I know the increased evaporation rates are due to the increase in temperature,

Vapor pressure is a function of temperature. Evaporation rate is a function of heat transport to the phase interface and of material transport from the interface.

many other mechanisms are involved

That's what we're trying to pin down.

good measurements

These are what we're trying to identify.

good measurements.

(ditto)

other human activities besides CO2 emissions could be significantly affecting the climate (my personal candidate is land use--we have drastically changed the land surface of the planet); we don't know which ones, or how big their effect is. So the common "skeptic" argument that, since CAGW is bunk, there's nothing to worry about, is not a valid argument.

"... could be significantly affecting the climate ..." Yes. At the moment, we're trying to pin down what's been measured, and how well, rather than what probably needs to be examined in detail.

"Jemand anderes?"

 

[Loudzoo]

Thanks Peter and Bystander - very valid points in my humble opinion.

 

[Bystander]

Seems to have settled back down to a "dull roar." Apparently no concerns regarding insolation rate at the upper boundary, 1363 W/m² ± 0.3 %, + 3 % at perihelion and - 3 % at aphelion, the uncertainty of orbital parameters being insignificant, with an eleven year solar cycle variation of ± 0.05 - 0.08 %, peaking at 1979, 1990, 2001, and 2012. Stet?

Area of the Earth disc intercepting solar radiation is ~ 1.25 x 10⁸ (km)², with an atmospheric halo area at 100 km altitude of 4 x 10⁶ (km)², ~ 3 % of total intercepted radiation. "Total" over the disc, or "mean" rates per unit area (W/m²)? "Total" is a bit perilous given lack of data on a fine enough scale; "mean" is likewise perilous with its implication of integration of data on a meaningfully fine scale. "Mean" and "total" also include the possibility of remote (satellite or lunar instruments) radiometry. The object at this point is to examine the uncertainties in the 1050 and 1120 W/m² values for directly transmitted surface insolation, and directly transmitted plus scattered surface insolation cited (Newport http://www.newport.com/Introduction-to-Solar-Radiation/411919/1033/content.aspx ) in the Wiki "Sunlight" article. There are no citations in the Newport article and that pretty much leaves us in the "air" regarding partitioning of reflected, transmitted, and absorbed radiation fluxes. Anyone aware of measurements of total reflection, or transmission over a broad band, rather than just visible or other limited bands, by geosynchronous or lunar or other suitably remote instruments?

Energy/power balance may not be necessary at this stage of the argument, but I'll feel a lot more comfortable examining the IR details if there is a total balance with which they must be consistent.

Okay, now everybody jump in, and try to stick to balancing total insolation with total of reflected, transmitted, and absorbed radiation. Please do not use "albedo" without specifying a definition/band width.

 

[Bystander]

So, it's off to the library for J. Gee. Whiz, Geochim. et Cosmochim., Phys. Rev., and what else? Any suggestions? I've found nothing regarding the uncertainties that bother me in two days on the net.

 

[FactChecker]

Are you only interested in the direct warming by IR? It seems like warming the surface must indirectly warm the lower levels either by heat transfer down or by reducing heat transfer up.