Guest post by Ron House
As readers will know, I have been thinking about the hullabaloo about CO2 and global warming and I quickly concluded that CO2 is no threat, won’t do any significant warming (which would be good anyway), and is in fact 100% good for the planet. But someone said to me, if CO2 is no danger, that doesn’t mean that humans are not causing a danger in some other way. Of course I agreed with this, because there are lots of things humans are doing wrongly and thereby causing terrible damage to our world (and the CO2 storm in a teacup is distracting us all from fixing those real problems).
My friend then went on, however, to propose that the danger was still global warming and that the mechanism was, instead of CO2 greenhouse warming, the mere fact that human technology gives off heat. All the power used by all the machines and transport and so on eventually ends up as waste heat. Maybe that is in itself enough to cause us serious warming trouble? So I did some calculations.
According to the laws of thermodynamics, the process of doing useful work must necessarily lose some of the energy from the fuel in the form of waste heat; and that heat, well, heats. In other words, because of the huge extra amount of useful work we do, we create excess heat that would not have been here otherwise, and that heat has to either be dissipated somehow, or else raise the temperature.
The factors that have caused the ice ages, as we saw, are primarily small changes in insolation (heating) by the Sun. The changes can happen because the Sun’s energy output changes or because of cyclic changes in the Earth’s orbit and inclination, etc., changing the amount of heat that actually arrives on the surface. Changes in the Earth’s orbit are believed to be the triggers for the onset of ice ages, and the changes in heating caused by those changes are thought to be quite small compared to the total power output of the Sun. This might lead us to suspect that human-caused changes in the amount of heat at the surface might indeed have a significant effect on the climate.
To answer this question, we need to compare the amount of variation due to the Sun with the amount of heat emitted by industrial civilisation. if the latter is ‘in the same ballpark’ as the former, then human civilisation might be holding off the onset of a new ice age.
Although there is much dispute about the exact mechanism that causes the onset of ice ages, much of it doesn’t concern us right now because one basic fact is clear: somehow or other, the responsibility lies with changes in the amount of heat received from the Sun.
One theory is that the cause is Northern Hemisphere summer cooling. At our current stage in geological history, the North Pole is surrounded by land masses, which are snowed under every winter. If the summers became just a bit colder, then some of that winter snow would remain on the ground throughout summer, and would then turn to ice. The ice will reflect sunlight much better than green plants or dirt or even liquid water, so the cooling will accelerate and the next summer will be even colder and leave even more ice lying around. And so the planet falls into an ice age. Retained heat in the oceans slows down the changes and ‘smooths over’ short-term effects, but once the process starts, the killing ice eventually reclaims its deathly kingdom.
Dr David Archibald suggests that a key measure of this process is the amount of insolation at 65° north latitude. The power of the Sun at 65°N is about 476 Watts per square metre. That means that at midday in mid-summer at, say, Reykjavik (at 64°N, almost the only significant city anywhere close to 65°N), the Sun has about the power of five old-style incandescent light bulbs. When summer sun at this latitude is sufficient to melt the winter snowfall, all is well. Other factors in this calculation are the length of summer (because, for example, a longer, but slightly cooler summer might melt more ice than a shorter warmer one) and how high in the sky the Sun is in mid summer. And the higher it is in summer, the deeper and colder the long winter ‘night’ will be. The factors are complex and researchers disagree as to how exactly they should be combined in order to make good predictions, but some combination of these factors decides whether we bask in life-giving warmth or flee the deadly cold. We cannot hope to make predictions from the kind of short overview we are doing here, but we can get an idea of the magnitudes involved.
How much radiant energy the Sun has in the past or will in the future shine upon the Earth at this latitude can be reliably calculated from basic physical and astronomical properties of the way the Earth orbits the Sun and how that orbit changes with time. This is not an uncertain thing like the forecasts of climate models; it is not exactly easy to calculate, but it depends only upon the extremely well verified equations of Newtonian physics (or, if you prefer a few thousands of a percent more accuracy, relativity). If we didn’t know how to do these calculations, we could never have landed men on the Moon or flown discovery missions past Saturn and on to Uranus and Neptune. Yes, we do know how to make these calculations and we know it very reliably.
When the calculations are done, we find that at the depth of the last ice age, around 22,000 years ago, the Sun’s power (again at 65°N) was around 463Wm-2. On the other hand, at the height of our own interglacial, the Holocene, which occurred about 11,000 years ago (yes, we have been on the downward slope ever since—though you would never guess it from the hairy scary stories about warming in the media) the summer insolation at 65°N was about 527Wm-2. In other words, we have:
| What | When | Sun’s Power |
|---|---|---|
| Previous Ice Age | 22,000 years ago | 463Wm-2 |
| Holocene Peak | 11,000 years ago | 527Wm-2 |
| The Perfect Time | Now | 476Wm-2 |
From these figures, we may make the following inferences:
- The difference between peak warmth and deepest cold was around 55Wm-2;
- The current value, being only 13Wm-2 above the value at the depth of the ice age, is almost all the way back to ‘cold conditions’; it may be that only stored ocean heat is keeping us out of an ice age (for now).
Moving on, how do these power figures compare with human energy output (mainly by burning fossil fuels)?
Human energy usage in 2006 was 491 exajoules. This translates to an average power usage of 15.56 terawatts each second (divide by the number of seconds in a year). To compare this with the Sun’s power as discussed above, we need to average this over the entire planet. The Earth’s surface area is 510 million sq. km., which gives 30,500 W per sq. km, or 0.03Wm-2. One final adjustment is needed to allow us to do the comparison: the Sun’s insolation given above was as received at noon, whereas this figure is an average over the whole planet. Since the planet’s area is four times the areas of a circle of the same radius, we must multiply by four, giving about 0.12Wm-2 as our final figure for comparison.
The human energy output of about 0.12Wm-2 is clearly overpowered by even the smallest of the numbers we have looked at so far. The 13Wm-2 difference between ice age conditions and today is at least a hundred times larger than human energy output. We might delay a killer ice age slightly, but our heating of the planet is nowhere near large enough to save us.
Are we heating the Earth too much – with heat?
As readers will know, I have been thinking about the hullabaloo about CO2 and global warming and I quickly concluded that CO2 is no threat, won’t do any significant warming (which would be good anyway), and is in fact 100% good for the planet. But someone said to me, if CO2 is no danger, that doesn’t mean that humans are not causing a danger in some other way. Of course I agreed with this, because there are lots of things humans are doing wrongly and thereby causing terrible damage to our world (and the CO2 storm in a teacup is distracting us all from fixing those real problems).
My friend then went on, however, to propose that the danger was still global warming and that the mechanism was, instead of CO2 greenhouse warming, the mere fact that human technology gives off heat. All the power used by all the machines and transport and so on eventually ends up as waste heat. Maybe that is in itself enough to cause us serious warming trouble? So I did some calculations.
According to the laws of thermodynamics, the process of doing useful work must necessarily lose some of the energy from the fuel in the form of waste heat; and that heat, well, heats. In other words, because of the huge extra amount of useful work we do, we create excess heat that would not have been here otherwise, and that heat has to either be dissipated somehow, or else raise the temperature.
The factors that have caused the ice ages, as we saw, are primarily small changes in insolation (heating) by the Sun. The changes can happen because the Sun’s energy output changes or because of cyclic changes in the Earth’s orbit and inclination, etc., changing the amount of heat that actually arrives on the surface. Changes in the Earth’s orbit are believed to be the triggers for the onset of ice ages, and the changes in heating caused by those changes are thought to be quite small compared to the total power output of the Sun. This might lead us to suspect that human-caused changes in the amount of heat at the surface might indeed have a significant effect on the climate.
To answer this question, we need to compare the amount of variation due to the Sun with the amount of heat emitted by industrial civilisation. if the latter is ‘in the same ballpark’ as the former, then human civilisation might be holding off the onset of a new ice age.
Although there is much dispute about the exact mechanism that causes the onset of ice ages, much of it doesn’t concern us right now because one basic fact is clear: somehow or other, the responsibility lies with changes in the amount of heat received from the Sun.
One theory is that the cause is Northern Hemisphere summer cooling. At our current stage in geological history, the North Pole is surrounded by land masses, which are snowed under every winter. If the summers became just a bit colder, then some of that winter snow would remain on the ground throughout summer, and would then turn to ice. The ice will reflect sunlight much better than green plants or dirt or even liquid water, so the cooling will accelerate and the next summer will be even colder and leave even more ice lying around. And so the planet falls into an ice age. Retained heat in the oceans slows down the changes and ‘smooths over’ short-term effects, but once the process starts, the killing ice eventually reclaims its deathly kingdom.
Dr David Archibald suggests that a key measure of this process is the amount of insolation at 65° north latitude. The power of the Sun at 65°N is about 476 Watts per square metre. That means that at midday in mid-summer at, say, Reykjavik (at 64°N, almost the only significant city anywhere close to 65°N), the Sun has about the power of five old-style incandescent light bulbs. When summer sun at this latitude is sufficient to melt the winter snowfall, all is well. Other factors in this calculation are the length of summer (because, for example, a longer, but slightly cooler summer might melt more ice than a shorter warmer one) and how high in the sky the Sun is in mid summer. And the higher it is in summer, the deeper and colder the long winter ‘night’ will be. The factors are complex and researchers disagree as to how exactly they should be combined in order to make good predictions, but some combination of these factors decides whether we bask in life-giving warmth or flee the deadly cold. We cannot hope to make predictions from the kind of short overview we are doing here, but we can get an idea of the magnitudes involved.
How much radiant energy the Sun has in the past or will in the future shine upon the Earth at this latitude can be reliably calculated from basic physical and astronomical properties of the way the Earth orbits the Sun and how that orbit changes with time. This is not an uncertain thing like the forecasts of climate models; it is not exactly easy to calculate, but it depends only upon the extremely well verified equations of Newtonian physics (or, if you prefer a few thousands of a percent more accuracy, relativity). If we didn’t know how to do these calculations, we could never have landed men on the Moon or flown discovery missions past Saturn and on to Uranus and Neptune. Yes, we do know how to make these calculations and we know it very reliably.
When the calculations are done, we find that at the depth of the last ice age, around 22,000 years ago, the Sun’s power (again at 65°N) was around 463Wm-2. On the other hand, at the height of our own interglacial, the Holocene, which occurred about 11,000 years ago (yes, we have been on the downward slope ever since—though you would never guess it from the hairy scary stories about warming in the media) the summer insolation at 65°N was about 527Wm-2. In other words, we have:
| What | When | Sun’s Power |
|---|---|---|
| Previous Ice Age | 22,000 years ago | 463Wm-2 |
| Holocene Peak | 11,000 years ago | 527Wm-2 |
| The Perfect Time | Now | 476Wm-2 |
From these figures, we may make the following inferences:
-
- The difference between peak warmth and deepest cold was around 55Wm-2;
- The current value, being only 13Wm-2 above the value at the depth of the ice age, is almost all the way back to ‘cold conditions’; it may be that only stored ocean heat is keeping us out of an ice age (for now).
Moving on, how do these power figures compare with human energy output (mainly by burning fossil fuels)?
Human energy usage in 2006 was 491 exajoules. This translates to an average power usage of 15.56 terawatts each second (divide by the number of seconds in a year). To compare this with the Sun’s power as discussed above, we need to average this over the entire planet. The Earth’s surface area is 510 million sq. km., which gives 30,500 W per sq. km, or 0.03Wm-2. One final adjustment is needed to allow us to do the comparison: the Sun’s insolation given above was as received at noon, whereas this figure is an average over the whole planet. Since the planet’s area is four times the areas of a circle of the same radius, we must multiply by four, giving about 0.12Wm-2 as our final figure for comparison.
The human energy output of about 0.12Wm-2 is clearly overpowered by even the smallest of the numbers we have looked at so far. The 13Wm-2 difference between ice age conditions and today is at least a hundred times larger than human energy output. We might delay a killer ice age slightly, but our heating of the planet is nowhere near large enough to save us.
Are we heating the Earth too much – with heat?
Ron House June 3, 2010As readers will know, I have been thinking about the hullabaloo about CO2 and global warming and I quickly concluded that CO2 is no threat, won’t do any significant warming (which would be good anyway), and is in fact 100% good for the planet. But someone said to me, if CO2 is no danger, that doesn’t mean that humans are not causing a danger in some other way. Of course I agreed with this, because there are lots of things humans are doing wrongly and thereby causing terrible damage to our world (and the CO2 storm in a teacup is distracting us all from fixing those real problems).
My friend then went on, however, to propose that the danger was still global warming and that the mechanism was, instead of CO2 greenhouse warming, the mere fact that human technology gives off heat. All the power used by all the machines and transport and so on eventually ends up as waste heat. Maybe that is in itself enough to cause us serious warming trouble? So I did some calculations.
According to the laws of thermodynamics, the process of doing useful work must necessarily lose some of the energy from the fuel in the form of waste heat; and that heat, well, heats. In other words, because of the huge extra amount of useful work we do, we create excess heat that would not have been here otherwise, and that heat has to either be dissipated somehow, or else raise the temperature.
The factors that have caused the ice ages, as we saw, are primarily small changes in insolation (heating) by the Sun. The changes can happen because the Sun’s energy output changes or because of cyclic changes in the Earth’s orbit and inclination, etc., changing the amount of heat that actually arrives on the surface. Changes in the Earth’s orbit are believed to be the triggers for the onset of ice ages, and the changes in heating caused by those changes are thought to be quite small compared to the total power output of the Sun. This might lead us to suspect that human-caused changes in the amount of heat at the surface might indeed have a significant effect on the climate.
To answer this question, we need to compare the amount of variation due to the Sun with the amount of heat emitted by industrial civilisation. if the latter is ‘in the same ballpark’ as the former, then human civilisation might be holding off the onset of a new ice age.
Although there is much dispute about the exact mechanism that causes the onset of ice ages, much of it doesn’t concern us right now because one basic fact is clear: somehow or other, the responsibility lies with changes in the amount of heat received from the Sun.
One theory is that the cause is Northern Hemisphere summer cooling. At our current stage in geological history, the North Pole is surrounded by land masses, which are snowed under every winter. If the summers became just a bit colder, then some of that winter snow would remain on the ground throughout summer, and would then turn to ice. The ice will reflect sunlight much better than green plants or dirt or even liquid water, so the cooling will accelerate and the next summer will be even colder and leave even more ice lying around. And so the planet falls into an ice age. Retained heat in the oceans slows down the changes and ‘smooths over’ short-term effects, but once the process starts, the killing ice eventually reclaims its deathly kingdom.
Dr David Archibald suggests that a key measure of this process is the amount of insolation at 65° north latitude. The power of the Sun at 65°N is about 476 Watts per square metre. That means that at midday in mid-summer at, say, Reykjavik (at 64°N, almost the only significant city anywhere close to 65°N), the Sun has about the power of five old-style incandescent light bulbs. When summer sun at this latitude is sufficient to melt the winter snowfall, all is well. Other factors in this calculation are the length of summer (because, for example, a longer, but slightly cooler summer might melt more ice than a shorter warmer one) and how high in the sky the Sun is in mid summer. And the higher it is in summer, the deeper and colder the long winter ‘night’ will be. The factors are complex and researchers disagree as to how exactly they should be combined in order to make good predictions, but some combination of these factors decides whether we bask in life-giving warmth or flee the deadly cold. We cannot hope to make predictions from the kind of short overview we are doing here, but we can get an idea of the magnitudes involved.
How much radiant energy the Sun has in the past or will in the future shine upon the Earth at this latitude can be reliably calculated from basic physical and astronomical properties of the way the Earth orbits the Sun and how that orbit changes with time. This is not an uncertain thing like the forecasts of climate models; it is not exactly easy to calculate, but it depends only upon the extremely well verified equations of Newtonian physics (or, if you prefer a few thousands of a percent more accuracy, relativity). If we didn’t know how to do these calculations, we could never have landed men on the Moon or flown discovery missions past Saturn and on to Uranus and Neptune. Yes, we do know how to make these calculations and we know it very reliably.
When the calculations are done, we find that at the depth of the last ice age, around 22,000 years ago, the Sun’s power (again at 65°N) was around 463Wm-2. On the other hand, at the height of our own interglacial, the Holocene, which occurred about 11,000 years ago (yes, we have been on the downward slope ever since—though you would never guess it from the hairy scary stories about warming in the media) the summer insolation at 65°N was about 527Wm-2. In other words, we have:
| What | When | Sun’s Power |
|---|---|---|
| Previous Ice Age | 22,000 years ago | 463Wm-2 |
| Holocene Peak | 11,000 years ago | 527Wm-2 |
| The Perfect Time | Now | 476Wm-2 |
From these figures, we may make the following inferences:
-
- The difference between peak warmth and deepest cold was around 55Wm-2;
- The current value, being only 13Wm-2 above the value at the depth of the ice age, is almost all the way back to ‘cold conditions’; it may be that only stored ocean heat is keeping us out of an ice age (for now).
Moving on, how do these power figures compare with human energy output (mainly by burning fossil fuels)?
Human energy usage in 2006 was 491 exajoules. This translates to an average power usage of 15.56 terawatts each second (divide by the number of seconds in a year). To compare this with the Sun’s power as discussed above, we need to average this over the entire planet. The Earth’s surface area is 510 million sq. km., which gives 30,500 W per sq. km, or 0.03Wm-2. One final adjustment is needed to allow us to do the comparison: the Sun’s insolation given above was as received at noon, whereas this figure is an average over the whole planet. Since the planet’s area is four times the areas of a circle of the same radius, we must multiply by four, giving about 0.12Wm-2 as our final figure for comparison.
The human energy output of about 0.12Wm-2 is clearly overpowered by even the smallest of the numbers we have looked at so far. The 13Wm-2 difference between ice age conditions and today is at least a hundred times larger than human energy output. We might delay a killer ice age slightly, but our heating of the planet is nowhere near large enough to save us.
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Jeez, as a heating consultant, I’ve been saying this for years though! I thought it was just me – you release heat energy into the atmosphere and it has to go somewhere…into the atmosphere! I have never known the actual figure we give off, and whether or not it’s doing anything, but I’ve wondered if it was coincidence that it’s Northern Hemispheric.
Leftists and pols must hate this. It is a tyranny of numbers!
We’re busy doing almost all of our human activities on the 14.5% of the earth’s surface that is useful to us, but still there are those convinced we’re “ruining” the planet. Go figure.
There are a couple of flaws in that argument, although the conclusion is probably correct.
1. The start of the argument talks about feedback caused by the ice on the poles. Feedback is the big unknown.
2. It appears to assume that the heat generated is dissipated. If most human heat is generated at ground level is it not possible that more will be retained? A true greenhouse effect where convection is stopped in a power factory or home retaining the heat at the surface.
3. My understanding was that most of the heat island effect was due to land use changes – roads and buildings rather than direct fuel burning . suppression of wind and reduction of reflected heat. I thought the argument for mankind stopping the last ice age was based on land use changes for farming.
Can you provide the numbers used in the calculations (distance from the sun at solstice, equinox, tilt of the earth etc?)
Lets have another bit of perspective.
The 2004 Sumatra-Andaman earthquake produced the equivalent of : 370 years of energy use in the United States at 2005 levels of 1.08×1020 J. (yes I know – attributed to Wikipedia)
Every day there are hundreds of earthquakes over the earths surface. Total daily anthropogenic energy output is dwarfed by just a few of those natural events.
Excellent analysis Ron. Nothing like numbers to put things into perspective. Is the biggest difference the obliquity of the ecliptic allowing more heat north of 65°N during this interglacial period?
I always thought that there should be at least some impact on global temperatures by the simple fact of our technology creating heat that was not present previously. While I understand it is likely a small impact, I thought that the actual ‘observed’ temperature change was also small, and the large number of factors could include something as simple as hundreds of millions of automobiles generating heat. Steve M. thought it was an extremely minute impact, but there was a paper by Bo Nordell and Bruno Gervet a year or so ago that tried to calculate what the thermal impact of our technology might be. This is complicated stuff, and I am still of the belief that there could easily be a measurable impact of our generating heat with our technology, just like there could easily be a measurable impact due to the change in land use.
So, set against a ~3.7Wm-2 for a doubling of CO2 concentration from pre-industrial times, hmmm … that’s non-trivial.
Perhaps there are a number of positive feedback factors related to the increased reflectivity of ice-covered land and the higher altitude at the top of the glacial surface to make the Earth sensitive to relatively small reductions of solar energy.
There would also be increased absorption of CO2 back into the ocean as it cooled. I have been told that there is evidence of plant CO2 starvation during the glacial periods.
We are but a blip on our planets journey towards it’s ultimate engulfment by our giant Red sun on our universe’s ultimate drive towards maximum entropy.
An interesting perspective and not surprising. But, what if we slow the rotation of our planet with all the windmills we are building – hmmmmmmm?
http://www.gecdsb.on.ca/d&g/astro/music/Galaxy_Song.html
What about the heat energy radiated by humans?
What about the heat energy provided by the respiration of humans?
Sweat? There are lots of BTUs to be had there.
I suspect that a more relevant calculation would be how much heating of the first 1 km of atmosphere is due to human activity. See urban heat island effect.
Remember all heat transfer is not radiation.
Dang! And I was about to go out and fire up my Weber to save humanity.
This calculation isn’t good news for the planet and certainly not good news for the climate change folks. (those arguing warming anyway.) I begin to wonder why there hasn’t been this kind of study put forth before. With the implications of this calculation it would seem that we need to perfect better carbon fuel usage and also alternate fuel/energy sources. (I think nuclear is the only viable option.) Hopefully our scientific community will step up and end the madness and begin to prepare us for the cold to come. The current picture isn’t very pretty.’
Concerning the oil spill in the gulf. I wonder what would happen if all the unemployed fishermen were to be paid $80.00/barell for any oil they could recover from the surface of the gulf. I think there would be many innovative methods discovered to reduce the area of the spill and the thickness of the layer.
Bill Derryberry
John Mason,
Is this what you were thinking of?
“John Mason says:
June 3, 2010 at 5:37 am
We are but a blip on our planets journey towards it’s ultimate engulfment by our giant Red sun on our universe’s ultimate drive towards maximum entropy.”
Yes, what you say may be correct but it most likely will not occur today!
UHI really is caused by humans so it should be called AUHI (anthropogenic), and if we look closer, it is caused by human digestion, and in turn, increased LWR from human ingestion is caused by garbage food (aka.”fast food”); then, by all means, one of the greatest polluters is non other than the “prophet” himself, best known as “El Gordo”, “the fat one”.
Have you perceived, when riding a public transportation vehicle, that some people, emit more IRR?, those are the GWRs.: They are the ones to be blamed!
Now, being more serious, our atmosphere, the AIR around us, ya know, can´t hold too much warm, its volumetric heat capacity, per cubic cemtimeter is 0.00192 joules, while water is 4.186, i.e., 3227 times.
Then, only if the “prophet” goes to the beach and he takes a bath, we´ll be in trouble, otherwise we don´t.
Just imagine what will happend if tomorrow the sun does not comes out from the east…so, don´t let them fool you: It is and it always has been THE SUN!
Be praised our sole life giving star!
By all means, let’s stop the next ice age.
If it’s all about melting ice and snow in the Northern Hemisphere, soot should help.
BTW Our advice for you, living in that self-denominated “developed world”, you better begin worrying about your economy, about reality: Only those who produce goods for selling know, they will eat tomorrow, so….
In the meantime those boys over at the UN reckon that meat will do for us all . . .
http://www.telegraph.co.uk/earth/earthnews/7797594/Eat-less-meat-to-save-the-planet-UN.html
It really is worse than we thought when these guys can still indulge in collective silliness.
Steve in SC…
The energy radiated by humans and all living creatures comes almost exclusively from the sun (captured and converted to chemical energy through photosynthesis), so to do as you suggest would be double-counting. The contribution of chemotrophs (which extract energy from chemicals and minerals, rather than the sun) is almost certainly inconsequential.
In fact, although it doesn’t matter in this perspective, the energy we are getting from fossil fuels is also, in fact, chemically sequestered energy from the sun (converted the hydrocarbons by photosynthesis hundreds of millions of years ago). So every time you drive your car, you are using ancient solar power.
The main point stands, however, that actual heat generation by the burning of fossil fuels is inconsequential as compared to most other factors (albedo changes, solar insolation changes, and GHG effects, to name a few).
Regarding UHI, the globe’s population is of course highly concentrated in cities. So all the heat output is concentrated in a very small area near ground level. At that level it certainly does beging to make a difference.
“According to the laws of thermodynamics, the process of doing useful work …”
Anthony, you forget the green-red alliance don’t want to work. They want to sit around selling personal carbon credits to working people while they express themselves artistically in green paradise. That’s the day job anyway. At night it is forming alliances with Islamists over the internet so they can bring down “capitalism” and those evil Jews.
One only has to fly from Sydney to Singapore and cross the vast uninhabited wilderness of North Western Australia to realise that there is still plenty of wild lands and oceans about in which humans have had no impact at all. While a city might throw off a lot of heat, cities are but a flea on the dogs back of wilderness that most of the globe encompasses.
Re Larry 5.27am. Heat can’t be retained in a house or factory once equilibrium is reached when all the heat generated in the house is lost to the surroundings. If you turn up the central heating and burn more gas, the surface temperature of the house rises until the heat being lost once again equals that generated.