Guest essay by Bob Irvine
Is it true that energy from either an outside source or an increase in insulation will warm a system according to or in proportion to its residence time in that system?
If true, this might explain why changes in GHG concentrations appear to have less affect on global temperatures than similar changes in solar forcing.
1. It is not contested that a black box that absorbs solar energy more efficiently will be warmer inside than a white box with a reflective surface. Is the reason for this that the solar energy has a much shorter residence time in the reflective white box than it does in the black box?
2. If we imagine a change in solar activity that adds 1 W/M2 of energy to the earth system. Some of this energy is deposited directly into the atmosphere and land surface where it is returned relatively quickly to space. A large portion of this energy is, however, deposited directly and by radiation into the oceans. This energy can remain circulating in the oceans for many years sometimes up to 1000s of years. It has an extremely long residence time.
3. Now, can we imagine a similar change in GHG concentration that adds similarly 1 W/M2 to the earth system. These extra GHGs largely and initially affect the atmosphere as they add to the earth’s radiative emission height to space. The water vapour feedback mechanism also works largely in this way. This higher average emission height warms the earth system initially high in the tropical troposphere and by convection the whole atmosphere is warmed. This energy is returned to space relatively quickly.
This warmer atmosphere then insulates the oceans and the oceans become warmer as a result. The energy that is trapped this way in the ocean has an extremely long residence time in the earth system. GHGs do not warm the oceans significantly by radiation.
4. The mechanisms by which a change in GHG concentration and a change in solar activity affect the earth’s surface temperature and heat content are very different with the residence time of the GHG energy likely to be significantly shorter than the residence time of the extra solar energy. If this is true, then the efficacy of a GHG forcing would be significantly lower than the efficacy of a similar solar forcing.
5. Nearly all sensitivity studies base their feedbacks on the assumption that GHG and solar efficacy are approximately equal. The IPCC states this in their reports. The feedbacks used are then feedbacks to an initial warming while feedbacks related to the intrinsic nature of the forcing and its mechanism are not normally considered. In particular, changes in residence times for energy from the different forcings do not appear to be considered.
6. If we give solar activity changes 4 times the efficacy of GHG changes then the Energy Balance Model below can be produced. It is not a bad match with the actual measured temperature and indicates that sensitivity studies should not assume that these efficacies are similar.
7. The model below uses Aerosols, Solar and GHG forcing only and has a reasonable internal variability included based on the PDO and AMO indexes. The change in equilibrium temperature for 1 W/M2 of solar change was 1.4C while a similar change in GHG forcing was assumed to produce about 0.35C of warming at equilibrium or about 1.3C for CO2 doubling. Aerosol forcing is at the lower end of the IPCC range. The differences from 1980 to 2000 may be due to volcanic activity not being included.
8. The higher solar sensitivity fits well with millennial temperature and solar forcing estimates. The variation in millennial temperatures can only be explained by higher solar sensitivity.
9. This Energy Balance Model certainly is a curve fitting exercise, but it does produce the cooling period from 1940 to 1970 and the current temperature hiatus and should be taken into consideration for these reasons.
“This implies that GHG energy is returned to the atmosphere and space very quickly as latent heat of evaporation while solar energy is effectively absorbed to a depth of many meters with consequent delays in equilibrium at the Top of the Atmosphere (TOA).”
It’s apparently too obvious.
“I know that most men, including those at ease with problems of the greatest complexity, can seldom accept even the simplest and most obvious truth if it be such as would oblige them to admit the falsity of conclusions which they have delighted in explaining to colleagues, which they have proudly taught to others, and which they have woven, thread by thread, into the fabric of their lives.”
― Leo Tolstoy
Tolstoy! You magnificent b______! I read your book!
The answer to 1 is no. Materials we see as black and white have similar infrared spectra, unless we’re talking about some exotic materials, perhaps known to JPL or NASA but not to me. They are almost equally efficient radiators. But if the energy source is sunlight (mostly visible and UV light) then one is an efficient absorber while the other is not. Each will achieve equilibrium when it reaches a temperature at which the absorbed radiation is equal to the emitted radiation. For the black object (efficient absorber), the equilibrium temperature is higher than for the white object. Residence time has nothing to do with that.
Scott
In the bean example, rate of input is the other variable that will determine how many beans will accumulate in the bowl.
If we keep the average residence time at 10 seconds, but instead put 2 beans/second into the bowl, then in the 10 second time frame that no beans left, 20 will have entered.
A black box absorbs photons at a faster rate than a white box.
Yes I got a good laugh from your response … Perhaps I can direct you to a kiddie physics forum
https://physics.stackexchange.com/questions/394382/what-are-thermal-photons
I enjoyed that.
Anybody who asks the question “What is the residence time of energy?” does not know what energy is. Energy has the units Kilogram*meters squared/seconds squared. There is no residence time.
The atmosphere radiates energy to space. CO2 at the TOA retards this, which means more energy is still in the atmosphere with more CO2. If anyone could calculate the magnitude of this effect we could all quit worrying about CO2. No one ever has.
Michael Moon
Radiation absorbed by a 5′ deep swimming pool gets converted to internal energy. A portion of that energy gets conducted downwards. That takes time, during which more radiation is absorbed. The longer that energy spends in “downwards or sideways conduction” (for lack of a better term), the greater its residence time.
If the pool were instead 10′ deep for example, average residence time would be greater because it would take longer for heat to be conducted to that greater depth. The greater residence time (given similar rate of input) leads to more internal energy at equilibrium.
I’m sorry, What? Where is this radiation coming from? The water is radiating too, as is the pool, and First and Second Laws apply as always. Are you trying to help me understand something about which you yourself are completely clueless?
Michael
Sorry, I was imagining an outdoor pool, so it receives radiation from the sun and atmosphere.
****
Of course the pool is radiating too. That counts as output.
Energy within the pool, radiating or being conducted downwards or sideways, (anywhere but out of the system) does NOT count as output. That’s the point.
*******
“The atmosphere radiates energy to space. CO2 at the TOA retards this, which means more energy is still in the atmosphere with more CO2.”
In a steady state, a planet would radiate energy to space at the same rate…..with or without CO2 (given a similar albedo).
On the other hand, the energy’s residence time is greater with CO2 than without, which corresponds to the higher temperature.
I understand now what you are saying but you do not need equilibrium for residence time it is simply defined as two points in time
https://en.wikipedia.org/wiki/Residence_time
It’s used for flows and all sorts of things in which there is no way they are in equilibrium
Whether or not it’s useful or not is a whole other question and depends on how you want to define it. There certainly not an off the shelf science definition for it’s use in this situation but it would be possible to make one and you would then get the get a residence time distribution (which is why you do this stuff).
What it does is create a really simple model
I do believe that model match what Climate Science calls a CO2 forcing, does it not?
It is a simplistic model, I am not disputing but I can’t see it is any better or worse than what climate science already does and much rolls on what definitions are given.
LdB
Thanks for that. I’ve never actually read about “residence time” before. As mentioned, I thought of it as “length if stay”.
Originally, I Imagined a line of people running from one end of a football field to the other. If they left one at a time, at a constant rate, then the slower their velocity the more runners would accumulate on the field. That’s because their “length of stay” had increased.
Conversely, if they traveled at the speed of light, each runner would traverse the length of the field in a fraction of a second. So if one runner left each second, most of the time the field would be completely empty. Very short length of stay.
Like you said, it’s a simple way of understanding some of the concepts in climate science. Probably not useful other than that.
Bob wrote: “If we imagine a change in solar activity that adds 1 W/M2 of energy to the earth system. Some of this energy is deposited directly into the atmosphere and land surface where it is returned relatively quickly to space. A large portion of this energy is, however, deposited directly and by radiation into the oceans. This energy can remain circulating in the oceans for many years sometimes up to 1000s of years. It has an extremely long residence time.”
Some technical corrections might be useful. W (watts) isn’t a measure of energy, it is a measure of power (energy per unit time). Heat capacity is the factor that allows use to convert a change in energy (not power) to a change in temperature. W/m2 is (J/s)/m2. Heat capacity is (J/m3)/K. Dividing the former by the latter gives us (K/s)/m, a warming rate which depends on the depth (m) of the material using warmed. In the case of the Earth, that is the depth of the ocean being warmed – which depends on the how long a period you are concerned with. The large changes in SWR associated with the seasons produce average temperature change at 50 m. In other words, you can think of the ocean as a slab of water that undergoes uniformer warming and cooling down to 50 m – the “mixed layer”, the ocean and atmosphere warm up about the same amount seasonally because the ocean is mixed by waves and the atmosphere by winds. All SWR (and DLR) are absorbed by the mixed layer of the ocean, so it doesn’t take a 1000 years to either return to the surface. There is a slow overturning that links the mixed layer and the deeper ocean that requires 1000 years, but the mixed layer equilibrates with the surface and atmosphere first. So forcing by GHGs and forcing by the sun will have exactly the same effect per W/m2.
So (W/m2 divided by heat capacity) times the depth of the mixed layer gives us a warming rate K/s – which appears to increase forever. However, the Earth radiates more to space as it warms. We talk about both radiative forcing and radiative imbalance (across the TOA) in terms of W/m2. Forcing is something that PERMANENTLY perturbs the flux across the TOA (rising GHGs or increased solar output), but the radiative imbalance drops as the planet warms in response to a forcing. A sudden 1 W/m2 forcing initially causes a 1 W/m2 radiative imbalance that gradually decreases with time as equilibrium is approached. Technically, we integrate this decreasing warming rate (from t = 0 to t = infinity) to get equilibrium warming.
Bob wrote: “This implies that GHG energy is returned to the atmosphere and space very quickly as latent heat of evaporation while solar energy is effectively absorbed to a depth of many meters with consequent delays in equilibrium at the Top of the Atmosphere (TOA).” It’s apparently too obvious.
Essentially all SWR is absorbed in the top 10 m of the ocean, where it is mixed by waves and convection. At night (when no SWR is arriving), LWR and evaporation continue to remove heat from the surface. As it cools, surface water becomes more dense and sinks. Water warmed by SWR rises in its place every night This, in addition to mixing by waves, is why water warmed by both SWR and DLR (or GHGs) should produce roughly the same result. If some significant fraction of 160 W/m2 of SWR arriving at the surface of the ocean were buried deep in the ocean, how long would it be before the surface of the ocean froze? (The loss of even 1 W/m2 is enough to cool a 50 m mixed layer of ocean at an initial rate of 0.2 K/year.)
Quoting Tolstoy: “I know that most men, including those at ease with problems of the greatest complexity, can seldom accept even the simplest and most obvious truth if it be such as would oblige them to admit the falsity of conclusions which they have delighted in explaining to colleagues, which they have proudly taught to others, and which they have woven, thread by thread, into the fabric of their lives.”
We can’t conduct an experiment that proves that the forcing from SWR and GHG’s/DLR produces the same amount of warming. There are no observations that contradict the idea that forcing from GHGs causes warming. Theory tells us only how much warming would occur AT EQUILIBRIUM in the ABSENCE OF FEEDBACKS. That is about 1.15 K per 3.7 W or or 0.31 K/(W/m2).
Based on observations (energy balance models), we have observed 0.36 K/(W/m2) of transient (not equilibrium) warming. If we correct for the amount of heat still flowing into the ocean we can calculate we will observe warming of about 0.5 K/(W/m2) at equilibrium. Feedbacks are a perfectly fine explanation for the observed difference between 0.31 and 0.5 K/(W/m2). CERES shows us unambiguously that the planet emits 2.2 W/m2 more LWR per degK of seasonal warming or 0.45 K/(W/m2), not the 0.31 K/(W/m2) that would be expected if feedbacks did’t exist. Since the seasonal change in mean global temperature (not temperature anomaly) is 3.5 K and the change in LWR emission is about 8 W/m2 instead of about the 11 W/m2 we expect without feedbacks, we can be sure positive feedbacks exist.
So there is no contradiction between GHG theory and observation. There is a debate whether observations (EBMs) or AOGCMs product the best estimate of climate sensitivity.
Even if there were a contradiction, you also need to remember that there is a massive reservoir of cold water at the bottom of the ocean that is slowing overturning. If that rate of overturning speeds up, it will get colder. If it slows down, it will get warmer. And the fluid flow in such ocean currents is chaotic and changes without any apparent cause. Temperature change without any change in energy flux across the TOA! For this reason, this is called “unforced variability”. In the Pacific, cold water upwells off the coast of South America, warms as it crosses the Pacific and is buried in the Western Pacific Warm Pool. When this process slows or reverses, the Eastern Pacific is much warmer than usual and we experience an El Nino. Unforced variability. Temperatures around the Atlantic Ocean seems to collectively vary (the AMO), possibly due to chaotic fluctuations the Gulf Stream (or MOC). Also unforced variability. It isn’t clear whether we have identified enough reduction in solar output and volcanic aerosol to explain the LIA, so it also could represent a chaotic fluctuation in our climate.
Chaos and unforced variability make our planet an lousy place to for conduct useful experiments about the relationship between forcing and temperature. We learn about the relationship between GHGs and forcing in the laboratory. When forcing produces a radiative imbalance across the TOA, conservation of energy demands a gradual change in temperature. Uncertainty about feedbacks (temperature dependent changes that also change the flux across the TOA) and the rate at which surface temperature changes penetrate the deep ocean AND chaos all make it impossible to prove that theories about GHGs are wrong by observing the earth.