The Science of Climate Change

kbd512 · 2019-01-24 19:05:19

Louis,

The numbers I'm working off of is the technology actually exists in the commercial world. In other words, things that someone with money can actually purchase. Apart from what I post, I also get the sense that you don't actually read the documents that you post. The figure you cited is an aspirational goal of the program and not representative of actual steel consumption per MW of output using present technology. DoE's goal is to provide 20% of production by 2030. The figure I provided was for 33%. You keep comparing apples and oranges, to what end I don't know.

The document you referenced mentioned using 103,000kg of stainless steel in "next generation" wind turbines per MW of output. That means a minimum of 206t of steel per 2MW wind turbine using designs that don't actually exist in the commercial world. Roughly speaking, DoE's aspirational goal is to reduce steel consumption per MW of nameplate capacity by just under 30%. The document was also drafted 7 years ago. Energy consumption of 7 years ago was not what it is today. More people and more technology means more energy consumption.

7 years on, 2MW wind turbines that actually achieve a capacity factors in the mid 30's to mid 40's have very tall masts and contain quite a bit of steel as a consequence. All of the newer wind turbines are built with tall masts. That isn't just coincidental. There's an engineering purpose behind doing that and it's related to physics.

SpaceNut · 2019-01-29 20:54:38

https://www.nbcnews.com/mach/video/ener … 3286723625

https://www.nbcnews.com/mach/science/wh … ncna963996

SpaceNut · 2019-01-31 18:26:40

Warming Seas May Increase Frequency of Extreme Storms

We know that colder waters sink more co2 within them and when they warm the co2 is being released...

They found that extreme storms - those producing at least 0.12 inches (3 millimeters) of rain per hour over a 16-mile (25-kilometer) area - formed when the sea surface temperature was higher than about 82 degrees Fahrenheit (28 degrees Celsius). They also found that, based on the data, 21 percent more storms form for every 1.8 degrees Fahrenheit (1 degree Celsius) that ocean surface temperatures rise.

https://www.nasa.gov/mission_pages/aqua/index.html

sea-surface-temp-2015-el-nino-pacific-ocean-different-1997-1998-hg.jpg

louis · 2019-01-31 19:48:55

We "know" lots of things about weather and climate. We just don't know how they all interact to produce the specific conditions we experience.

We also know that as societies industrialise their ability to withstand storms increases exponentially...to the extent that even the worst storms result in very little loss of life.

I presume no one is suggesting we de-industrialise the world so that again - as was the case in the mid 20th century - storms could kill tens or hundreds of thousands of people.

Let's move from alarmism to rational debate.

SpaceNut wrote:

Warming Seas May Increase Frequency of Extreme Storms
We know that colder waters sink more co2 within them and when they warm the co2 is being released...
They found that extreme storms - those producing at least 0.12 inches (3 millimeters) of rain per hour over a 16-mile (25-kilometer) area - formed when the sea surface temperature was higher than about 82 degrees Fahrenheit (28 degrees Celsius). They also found that, based on the data, 21 percent more storms form for every 1.8 degrees Fahrenheit (1 degree Celsius) that ocean surface temperatures rise.
https://www.nasa.gov/mission_pages/aqua/index.html
http://www.spxdaily.com/images-hg/sea-s … 998-hg.jpg

GW Johnson · 2019-01-31 22:22:05

The science is clear on this. You don't need the fancy models and proxy temperature records to understand what is happening and why, but those data and modeling items do help quantify things. Sure the various models disagree, but the sense of those widely-differing answers is the same: quit polluting the atmosphere with greenhouse gases.

Simple enough. Not easy to do in a big way, but you need to start somewhere.

Distasteful to those not yet done making money from fossil fuels, who are usually rich enough and powerful enough to buy the politicians to keep the status quo going. Ever-increasing numbers of people will soon enough start dying from this, but the rich and powerful cannot let that interfere with profit now. Oh, no! Cannot do that! Not at all.

So what's the value of a human life? Depends on what business you are talking about. Last I heard, for an airline company, it's $5000. For most municipalities, the price of a set of stop signs at a problem intersection (a few $thousand) is usually a death toll exceeding half a dozen (for a price per life in the $1000-2000 range). Etc.

And way too cheap.

GW

Last edited by GW Johnson (2019-01-31 22:24:53)

SpaceNut · 2019-02-01 19:04:21

The ecological regulations have been rolled back such that profits can be enlargened at the cost of our lives being shortened by the increase in pollution of all types.

kbd512 · 2019-02-03 16:47:08

SpaceNut,

Without a cheap and abundant energy source required to create the food, clean water, medicine, shelter, etc that life as you know it depends upon, at affordable prices, your life will unavoidably be shorter as a consequence of all the deleterious effects that energy starvation produces. My proof for that statement is the average lifespan of people living in countries that do not have access to those products at prices that their citizens can afford. If you know of a country that does not have widespread access to food, clean water, and shelter at affordable prices, as a function of unaffordable energy costs, wherein the people living there lead longer and more productive lives, then please share it with the rest of us. I'd love to know how we can use the least affordable and reliable energy sources to lead longer and more productive lives.

SpaceNut · 2019-02-03 18:11:02

The nations List of the oldest people by country

Thes are 100 years plus and back at the birth time were not all that advanced or with much energy....

https://www.cbsnews.com/pictures/who-li … xpectancy/

kbd512 · 2019-02-03 19:11:36

SpaceNut,

Uh, boss. All those countries in your links rapidly industrialized and used fossil fuel energy to do it. Medicine didn't not rapidly advance in the 20th century because our doctors were walking or riding donkeys to see their patients in ever-increasing numbers.

Life expectancy in the USA, 1900-98 men and women

Magical thinking aside, what's the plan?

louis · 2019-02-03 19:13:16

But the science is also clear that the Earth gets greener as temperature increases so we can grow more food. Do you want us to grow less food as the population ramps up to 10 billion?

I think climate alarmism is overdone. We can more to green energy pretty seamlessly and then we won't be adding carbon. In fact energy will be so cheap we can afford to extract carbon if necessary.

GW Johnson wrote:

The science is clear on this. You don't need the fancy models and proxy temperature records to understand what is happening and why, but those data and modeling items do help quantify things. Sure the various models disagree, but the sense of those widely-differing answers is the same: quit polluting the atmosphere with greenhouse gases.
Simple enough. Not easy to do in a big way, but you need to start somewhere.
Distasteful to those not yet done making money from fossil fuels, who are usually rich enough and powerful enough to buy the politicians to keep the status quo going. Ever-increasing numbers of people will soon enough start dying from this, but the rich and powerful cannot let that interfere with profit now. Oh, no! Cannot do that! Not at all.
So what's the value of a human life? Depends on what business you are talking about. Last I heard, for an airline company, it's $5000. For most municipalities, the price of a set of stop signs at a problem intersection (a few $thousand) is usually a death toll exceeding half a dozen (for a price per life in the $1000-2000 range). Etc.
And way too cheap.
GW

SpaceNut · 2019-02-03 19:39:11

Yes Kbd512 medical care and medicines in general even in the poorer energy nations was the path for longevity.

Louis higher temperature where there is little water causes crops to fail and that is the drawback of the climate change. Only areas that retain enough water benefit from the higher temperatures.

elderflower · 2019-02-04 08:36:06

Really temperatures aren't the major issue in global warming. We and other creatures can adapt our behaviours or move. Crops planted in a given area may need to be changed, migration paths may get longer or shorter, we may build cities in the northern parts of Canada, Alaska, Russia and Scandinavia. The biggest and most immediate issue will be ice loss from Greenland and Antarctica. The resulting rise in sea level will devastate low lying areas such as the one outside my window. Considering the amount of investment and the number of cities and dwellings that stand within 3 metres of High Water Springs, we all need to worry about this.

kbd512 · 2019-02-04 09:07:13

Louis,

In order to merely accept the premise of AGW as portrayed by the IPCC and media, you have to believe in some impossible things.

1. A trace gas (CO2) in an open thermodynamic system (Earth) creates climatic forcing effects significantly greater than that of a radiatively restricted black body cavity that absorbs and traps nearly all incident input solar radiation and also doesn't permit convection to carry the heat away.

2. The thermodynamic behavior of a half-irradiated sphere that doesn't restrict convection, as a prototypical greenhouse does, and isn't a blackbody similar in behavior to a radiatively restricted blackbody cavity, somehow produces a greater warming effect than a radiatively restricted blackbody cavity with little to no convective cooling.

3. The greenhouse theory, that's based upon blackbody equations to begin with, somehow applies to Earth, which is not a blackbody and doesn't behave as a blackbody does in response to input thermal energy.

4. The entire theory about why greenhouses are warmer than the surrounding environment, namely opacity to re-emisson of long wave radiation, that was subsequently disproved many decades ago through actual experimentation, is in fact how Earth's thermodynamic system behaves. There's no convective heat transfer in a greenhouse and that's why the heat is trapped and increases warming. Put a hole in the top of the greenhouse and the temperature plummets. The people who believe in the greenhouse theory are theorizing that the CO2 in the Earth's atmosphere somehow precludes convective cooling (hot air rising and cold air from the next layer of atmosphere sinking and cooling) and blocks radiative cooling (merely slowing the rate of cooling, which is all that CO2 is actually capable of doing within a narrow band of Earth's atmosphere, is insufficient) and somehow coming up with more thermal energy from the re-radiation process than existed as input thermal energy to begin with.

5. Some of these people also assert that their computer models are an accurate representation of Earth's future climate even though the models' temperature predictions diverge from measured temperature increases. We can't accurately predict the weather more than a week out, but somehow we have computer models that can accurately predict global average temperatures decades into the future? If past performance is any indicator, that claim is dubious at best.

6. These people also assert that CO2 is a pollutant. That's a very interesting assertion, given that all plant life on Earth would cease to exist without adequate levels of CO2 in the atmosphere. During the last glaciation cycle, the CO2 concentration in the atmosphere dropped to levels very close to the levels at which plant life would be subject to mass extinction. The idea that climate is incredibly sensitive to CO2 concentration is also rather perplexing given the fact that the historical period which saw the greatest increase in biodiversity was also associated with atmospheric CO2 concentrations that are several multiples of what we have today. Nobody I'm aware of has attempted to explain why CO2 increases lag temperature increases in the geologic record, either. I was always taught that cause can never follow effect, else causality is broken. I guess correlation has now been substituted for causation.

Well, there it is. Six impossible things before breakfast. Someone let Alice know when it's time to slay the Jabberwocky.

kbd512 · 2019-02-04 09:26:04

Elderflower,

Why can't we figure out why humans are so stupid that they build enormous cities within mere feet of oceans and other low-lying areas subject to flooding? I always thought that we were going to spend enormous amounts of money that we don't have on "green energy" and that was going to fix the problem. If spending money we don't have on energy technology that works poorly is a potential solution, then why not spend even more money to move entire cities to places not subject to flooding? After all, it'll be great for jobs, right? We should start building cities in northern Canada? Like the ones that were under 3km of ice during the last major glaciation?

Perhaps we need to learn to adapt ourselves to Earth's ever-changing environment, rather than adapting Earth's climate to humanity's desire to behave like that proverbial stick in the mud. If the major coastal cities are not under water two decades from now, then we'll have expended a lot of effort and money to produce a lot of nothing of any great utility. Maybe the fact that Earth's surface is about 70% water should've been a clue about where we should have elected to build major cities. It's hilarious that everyone seriously considering going to Mars is bringing suitable habitation with them, but here on Earth we just expect the Earth to cooperate with our desires regarding where we can live. Maybe one day someone will get the bright idea that living conditions are always subject to change and plan accordingly.

SpaceNut · 2019-02-04 19:02:20

People like to own ocean front property to be able to smell the breeze, to be able to take a dip on a sandy breach... its sort of hard to do that from say Kansas.....but ya how would you be compensated for the ownership... or is swamp land ok

kbd512 · 2019-02-04 20:30:39

SpaceNut,

If you live near a large body of water, then you deal with the problems associated with living near the water. We've known for at least a few thousand years that such areas were subject to flooding and wind damage from severe storms. Hurricanes hit beaches with regularity, even before this AGW idea existed. People have persisted with re-building there after their homes and buildings were demolished by hurricanes and floods time and time again. Maybe, just maybe, nature is trying to tell us something.

elderflower · 2019-02-05 04:43:59

It's short term economics that makes us build near water. It is driven by transport costs. Short term I will probably get away with it, long term I will be dead.

louis · 2019-02-05 18:02:43

Quite - look at Netherlands. About a quarter of the land is below sea level! But this tiny, quite northerly, country has 17% of the world's food exports!

kbd512 wrote:

SpaceNut,
If you live near a large body of water, then you deal with the problems associated with living near the water. We've known for at least a few thousand years that such areas were subject to flooding and wind damage from severe storms. Hurricanes hit beaches with regularity, even before this AGW idea existed. People have persisted with re-building there after their homes and buildings were demolished by hurricanes and floods time and time again. Maybe, just maybe, nature is trying to tell us something.

SpaceNut · 2019-02-06 18:29:09

2018 was world's fourth hottest year on record, scientists confirm

World 1.5F hotter than average set between 1951 and 1980
Current five-year stretch the warmest since records began
The world in 2018 was 1.5F (0.83C) warmer than the average set between 1951 and 1980, said Nasa and the National Oceanic and Atmospheric Administration (Noaa). This means 2018’s average global temperatures were the fourth warmest since 1880, placing it behind 2016, 2017 and 2015.

Is there possibly another cause to the effect that we are seeing such as Unexpected magnetic north pole changes mean new world magnetic model map but its my understanding that the south pole is not moving so the earth tilt is changing....

That would make us warmer in summer and not as cold in winter....

Void · 2019-02-06 21:25:57

Josh advised me to not play in this neighborhood, but I will stop by briefly, with some possibly happy news.
https://oilprice.com/Energy/Energy-Gene … ecade.html
Quote:

Bank Of America: Oil Demand Growth To Hit Zero Within A Decade

Of course that means a slowing of the increase of use, and then a decline in use of oil. Presumably coal as well, even more so.
Natural gas is not as much of an issue.

I like to look at www.oilprice.com when I am bored. It seems like a strange place because they are unhappy when the price of oil goes down.

There are things to learn. Such as a reason our gasoline prices are low now is that shale oil is so light that it is harder to get diesel and jet fuel from it, so they have to process more of it, and that means that more gasoline gets produced than they prefer.

As for climate change, there are two positives to look at. North America will respond better than the rest of the world in general, as our farmlands run north and south in range as well as east to west. So, on a warm up/dry out, then you have to shift crops (Unless you have a dust bowl situation). There is actually significant farmable land also in regions of Canada and Alaska.

And another sort of happy thought, is if some mid range powered nations have a nuclear war and cause a nuclear winter, the temperatures being already biased up, helps us get through it.

I don't absolutely believe in the greenhouse effect unless it is for Mars? Well, I think it may be overblown, but is a problem.

I'm Done.

SpaceNut · 2019-02-07 19:55:28

This is why the Earth wobbles as it spins, according to NASA

It would seem that ice melt is behind the movement of the poles.

Rising temperatures during the 20th century have caused ice to melt in Greenland. Researchers say 7,500 gigatons of ice – equal to the weight of more than 20 million Empire State Buildings – melted into the ocean over that time.
The ice melt, combined with Greenland's location on Earth, plays a role in how the Earth wobbles. "There is a geometrical effect that if you have a mass that is 45 degrees from the North Pole – which Greenland is – or from the South Pole, it will have a bigger impact on shifting Earth's spin axis than a mass that is right near the Pole,"

570bfa5d2e00006400950f8d.jpeg?cache=dxslfasbor&ops=scalefit_720_noupscale

190206-global-heat-map-nasa-2018-gif-2x1-final-cs-1106a_48bb5c4f9e63e8da1ea59e24e15d73a7.fit-760w.gif

elderflower · 2019-02-08 06:33:49

But Greenland is approximately in isostatic equilibrium. Probably still recovering from the melting of about 11000 years ago, but more or less in equilibrium. So when the ice melts the weight comes off the crust and the crust rises. Mantle material flows inward from regions outside the boundary of the present ice cap so these sink a bit. The redistribution of mantle counters the effect of removing the ice and dumping it in the ocean. Just calculating ice loss doesn't tell you how the inertia of the planet will be affected.

JoshNH4H · 2019-02-08 21:45:41

kbd512 wrote:

Louis,
In order to merely accept the premise of AGW as portrayed by the IPCC and media, you have to believe in some impossible things.
1. A trace gas (CO2) in an open thermodynamic system (Earth) creates climatic forcing effects significantly greater than that of a radiatively restricted black body cavity that absorbs and traps nearly all incident input solar radiation and also doesn't permit convection to carry the heat away.
2. The thermodynamic behavior of a half-irradiated sphere that doesn't restrict convection, as a prototypical greenhouse does, and isn't a blackbody similar in behavior to a radiatively restricted blackbody cavity, somehow produces a greater warming effect than a radiatively restricted blackbody cavity with little to no convective cooling.
3. The greenhouse theory, that's based upon blackbody equations to begin with, somehow applies to Earth, which is not a blackbody and doesn't behave as a blackbody does in response to input thermal energy.
4. The entire theory about why greenhouses are warmer than the surrounding environment, namely opacity to re-emission of long wave radiation, that was subsequently disproved many decades ago through actual experimentation, is in fact how Earth's thermodynamic system behaves. There's no convective heat transfer in a greenhouse and that's why the heat is trapped and increases warming. Put a hole in the top of the greenhouse and the temperature plummets. The people who believe in the greenhouse theory are theorizing that the CO2 in the Earth's atmosphere somehow precludes convective cooling (hot air rising and cold air from the next layer of atmosphere sinking and cooling) and blocks radiative cooling (merely slowing the rate of cooling, which is all that CO2 is actually capable of doing within a narrow band of Earth's atmosphere, is insufficient) and somehow coming up with more thermal energy from the re-radiation process than existed as input thermal energy to begin with.
5. Some of these people also assert that their computer models are an accurate representation of Earth's future climate even though the models' temperature predictions diverge from measured temperature increases. We can't accurately predict the weather more than a week out, but somehow we have computer models that can accurately predict global average temperatures decades into the future? If past performance is any indicator, that claim is dubious at best.
6. These people also assert that CO2 is a pollutant. That's a very interesting assertion, given that all plant life on Earth would cease to exist without adequate levels of CO2 in the atmosphere. During the last glaciation cycle, the CO2 concentration in the atmosphere dropped to levels very close to the levels at which plant life would be subject to mass extinction. The idea that climate is incredibly sensitive to CO2 concentration is also rather perplexing given the fact that the historical period which saw the greatest increase in biodiversity was also associated with atmospheric CO2 concentrations that are several multiples of what we have today. Nobody I'm aware of has attempted to explain why CO2 increases lag temperature increases in the geologic record, either. I was always taught that cause can never follow effect, else causality is broken. I guess correlation has now been substituted for causation.
Well, there it is. Six impossible things before breakfast. Someone let Alice know when it's time to slay the Jabberwocky.

There's some real doozies in here, coming from someone who ought to know better.

One simple but incorrect way to model a planet is as a sphere of uniform temperature absorbing and re-emitting light as a modified blackbody. I calculated in this post that if this were the case Earth would have a temperature of about 255 K. The actual mean temperature is 288 K even with substantial nonuniformity (which lowers the mean temperature due to the T^4 law of radiation).

The three canonical modes of heat transfer are conduction, convection, and radiation. Looking at things on a climactic level, temperature differences are too small, conductances too low, and distances too large for conduction to have a major effect (the ground's heat capacity would seem to even things out a bit but this doesn't seem to have much of a practical effect). That leaves convection and radiation. If I were going to build a model, I would look at four types of convection and three types of radiation. Those four convections are ocean convection (through ocean currents), atmospheric convection (through jetstreams and other weather events as well as between different layers of the atmosphere), surface-to-atmosphere convection (i.e. heat transfer from ground or ocean to atmosphere), and convection heat transfer through phase change of water (evaporation/condensation, freezing/melting, etc.). The three radiations are energy received from the Sun, energy emitted by the ground/water, and energy absorption/reflection/transmission/reemission by the atmosphere.

It happens to be the case that the Earth is surrounded by the hard vacuum of interplanetary space, and also the case that conduction and convection require a medium through which to act. It is therefore the case that Earth's heat equilibrium is fundamentally governed by radiation:

As you see above, the bare, uniform-temperature sphere approximation (UTSA) is off by about -11% as compared to the actual observed mean temperature of Earth. By way of comparison, it's off by about +14% for the Moon (The Moon's estimated temperature according to the UTSA is higher than Earth's due to its low albedo; on Earth, the warming effect of an atmosphere is partially cancelled out by the cooling effect of nonuniform temperature), off by about -2% for Mars (my calculated UTSA temp is 206 K and Wikipedia lists the planetary mean as 210 K; this means that the reduction in temperature from nonuniformity and the increase from the atmosphere are roughly equal in magnitude), and -59% for Venus (the planet's temperature is nearly uniform and its thick atmosphere retains heat very effectively; UTSA for Venus is 301 K as calculated in the post linked to above).

You will notice that the thicker a planet’s atmosphere, the higher its mean temperature when compared to UTSA. This is not a coincidence (the relationship is causal), although I don’t believe you could create a simple, valid equation relating the two as you’d need to get deep into the specifics of each planet’s relevant properties.

I won’t speak to the heat transfer properties of glass-walled greenhouses nor the convection vs. radiation question in that case, but the real answer will naturally be a combination of “neither”, “both”, and “it depends”. Perhaps the “greenhouse effect” is misnamed, perhaps not. In either case, it is real. Edit: If it is indeed the case that scientists used to think warming in greenhouses resulted from radiative inhibition but have since found that convective inhibition is a more important factor, then updated their views based on new information they present a good example to all of us

In general, your post suggests a lack of familiarity with the basic concepts of thermal radiation and heat transfer by radiation. This powerpoint provides a good overview that you might do well to read. Let me give you (and anyone else who’s interested in heat transfer, a topic I personally love) some highlights.

Idealizations are often helpful and necessary in physics. We use them often on this forum as well. When calculating the delta-V for a hohmann transfer, we typically assume that the two planets occupy circular, coplanar orbits. When doing kinematics at low speeds, we typically disregard both special and general relativity, instead assuming that objects obey newtonian mechanics in euclidean space. The equivalent idealization for thermal radiation is the blackbody, which both absorbs and emits perfectly across the entirety of the electromagnetic spectrum, from an energy of 0 eV to a wavelength of 0 nm. A blackbody emits radiation according to the Stefan-Boltzmann law: P=σT^4, where P is power per unit area, σ is the Stefan-Boltzmann Constant, and T is the absolute temperature.
The closest real-world approximation to a blackbody is a small hole in a large, well-insulated cavity. Real materials can both transmit and reflect radiation, and are also not perfect emitters, nor do they emit omnidirectionally. Having said that, it is in general possible to establish values of transmittance, reflectance, absorbance, and emittance that are fairly stable over reasonably wide spectra. For real materials we modify the Stefan Boltzman Law by introducing a constant for Emittance (ϵ) which can take values between 0 and 1: P=ϵσT^4. Measured values for the emittance of most common natural materials (water, ice, dirt, sand, trees, etc.) near room temperature is in the range of 0.90-0.95 and gases can be modelled as having an asymptotic emissivity of 1. Earth as a whole has a transmittance of 0, a reflectance (also known as an albedo) of 0.3, and an absorbance of 0.7.
Gases tend to have more complicated absorbance, transmittance, and emittance behaviors which need to be taken into account when modelling their behavior (just as an example: Rather than treating gases as discrete surfaces you can treat them as having infinitesimal coefficients for absorbance, transmittance, and emittance per infinitesimal distance and then [in principle] could calculate properties like the temperature profile and heat flux. More importantly is that gases do tend to have relatively narrow bands of stronger absorbance. It happens to be the case that CO2 absorbs strongly across much of the most intense part of Earth's thermal radiation spectrum. This is also the case for water vapor, and though there is some overlap there are also plenty of regions of non-overlap; and due to the relatively low concentration of CO2 in Earth's atmosphere its bands aren't completely filled. This means that a marginal increase in the amount of CO2 results in a marginal increase in the atmosphere's absorbance on the relevant wavelengths. (Here's a more easily comprehensible measurement for the amount of CO2 in the atmosphere: If you concentrated it to 100% at 1 atmosphere and normal Earth temperatures, prior to the industrial revolution atmospheric CO2 would create a layer 1.3m (4'3") over the Earth. Today, that layer would be 2m (6'6") high.

In short: It should come as no surprise to you or to anyone that our planet represents a very complicated thermal system where the interplay of many different physical processes interact to form an equilibrium. It should also come as no surprise that of these effects one is the strongest. That effect is blackbody radiation.

GW Johnson · 2019-02-09 10:12:28

Hi Josh:

I didn’t know you were an expert in heat transfer. Excellent explanation about greenhouse effect in planetary atmospheres. Yep, it’s quite complicated. But it ain’t fundamentally wrong, despite the disagreements among the various complex models.

Yet that oversimplified model that assumes one average planetary surface temperature has two very good things to recommend it, despite getting the “wrong” answer: (1) the concept is simple enough for anyone to understand, even those not schooled in the subject, and (2) the model responds directly (and primarily) to the IR transmissibility in the atmosphere “window pane” about the solid surface. That’s a real, measurable property that no one can credibly deny.

My take is that simple is better for explicating physics to any audience, while complex is better for getting an answer that is a closer approximation to reality. It is usually wiser to include that distinction, so that the “wrong answer” the simple model gets cannot be the excuse to “discredit” the various more-complex models. I see a lot of that in the propaganda out there.

How are you at hypersonic air friction heating? What I know in detail is based on the ideal-gas equation of state and Mach number-type compressible fluid mechanics. That stuff breaks down at about Mach 8 when the recovery temperatures reach about 5000 F.

GW

JoshNH4H · 2019-02-09 14:21:23

Hey GW,

Thank you for your kind words.

I think it would be going too far to say that I am an expert on heat transfer. However, it was something of a focus of mine in undergrad, including a couple of classes that got into thermal modelling, and something which I have occasionally had the chance to apply professionally.

As far as air friction heating goes, it would be irresponsible for me to go so far as to offer an opinion. I have had the chance to work with supersonic gases on occasion in the form of a light gas gun (up to roughly 1.5 times the gases' speeds of sound) but in general I've had empirical correlations available to describe their behavior.

Talking about science is really hard. Science journalists usually use metaphors, rather than numbers. I understand why they do it (neither they nor their readers can really understand the physics behind most things) but if you would be able to understand it their explanations are usually pretty frustrating.

For anyone who may be interested:

I want to get into a longer description of my simplified temperature model for those who are interested, both in the interests of transparency and because I think it's sort of cool. You can skip past the math and explanations if you'd like: I have a link to a google sheets calculator that will do the math for you at the end of this post.

While I don't have the time or resources that it would take to construct a generalized, precise climate model of the planet (or any other planet), I can construct the much simpler model I described above. I have been calling this model the UTSA Model: Uniform Temperature Sphere Approximation. The basic assumptions that go into this model are as follows:

A planet is a perfect sphere (Accurate to within 5% usually)
A planet will either absorb or reflect away all of the sun's radiation that falls on it (basically accurate)
A planet does not have any atmosphere that interferes either with the absorption (e.g. the Ozone layer or the reflective clouds of Venus) or emission (the greenhouse effect) of radiation (Not accurate; atmospheric effects are pretty much completely disregarded in this model)
A planet has a uniform surface temperature (highly inaccurate)
A planet radiates as a perfect blackbody, as modified by its emittance value (basically accurate once atmospheric effects are disregarded as I talked about in the previous post)
A planet is in thermal equilibrium at all times, with energy received from the Sun being equal to energy lost to space (accurate to within 1%)

You can write the equation for the energy balance as follows:

P_in=P_out

(Power in is equal to power out; units are Watts)

P_in is the energy from the Sun falling on the planet multiplied by that portion of the energy which is absorbed. The equation for this is:

P_in=(1-α)*I*A

Where:
α is the reflectance, also known as the albedo (unitless)
I is the irradiance, also known as the Solar Constant. At 1 AU its value is 1366 W/m^2
A is the cross-sectional area of the planet in m^2; For a spherical planet this is A=π*r^2

Substituting for area:

P_in=(1-α)*I*π*r^2

Now, P_out is governed by blackbody radiation:

P_out=ϵ*σ*A*T^4

(From my previous post)

ϵ is emittance, a unitless constant between 0 and 1
σ is the Stefan-Boltzmann constant, 5.670e-8 W-m^-2-K^-4
A is the emitting area, in this case the entire planetary surface; area of a sphere is A=4*π*r^2
T is the absolute temperature in Kelvin

Substituting for area:

P_out=4*ϵ*σ*π*r^2*T^4

Setting the final equations for P_in and P_out equal to each other:

(1-α)*I*π*r^2=4*ϵ*σ*π*r^2*T^4

Simplifying:

(1-α)*I=4*ϵ*σ*T^4

Solving for T:

T=( (1-α)I/(4ϵσ) )^(1/4)

I is proportional to the inverse of the square of a planet's distance from the Sun. In other words:

I=C/d^2

Where C is the Solar Constant at Earth (1366 W/m^2) and d is a planet's distance from the Sun in AU.
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UTSA Calculator Here

Instructions for use:

The calculator allows you to vary three parameters: Albedo (reflectance), Emittance, and Orbital Radius:

Albedo: Values can generally be looked up on Wikipedia; Earth is 0.3, Mars is 0.2, the Moon is 0.07. For a rocky planet or asteroid with no cloud cover and no values available I recommend a value of 0.25

Emittance: Real values for real planets are probably roughly 0.95 but I recommend using a value of 1 because I don't believe it's possible to measure the emittance of a planet in any meaningful sense.

Orbital Radius: Can be looked up on Wikipedia or wherever; Orbital Radius in AU. Earth and Moon are 1, Venus is 0.72, Mars is 1.52, etc.

This is a very simple calculator. I have started it off with an orbital radius of 1.52, an albedo of 0.2, and an emittance of 1 to give the user an idea of how to use it. Please reenter these values before you exit the calculator because they do not reset automatically.
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The only reason I included emittance as a value which can be modified is so you can calculate the "effective emittance" of each planet or body. This is a non-physical value. It's a number that can be used as a shorthand for atmospheric effects and nonuniform temperature and whatever else. It is a fudge factor and an average, not a physical description of emittance behavior. You can find it by entering the correct values for albedo and orbital radius, and then changing the albedo until the USTA temperature matches the observed temperature. For the Earth and the Moon, the "effective emittance" is 0.61 and 1.7 respectively.

PS: Apologies to the Texans among us who hear UTSA and think "University of Texas, San Antonio"

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