[mmunroe]

In 1978 I was working in a large group helping to develop more efficient solar cells. Every week someone gave a talk at lunch. One day a visiting researcher, Albert Rose, gave a talk in which he gave an interesting global perspective on energy use and global warming. These are from the notes which he distributed.

Limits to Growth Related to Energy Use

“A Global View of Solar Energy in Rational Units” by Albert Rose of Boston University ,1978.

One solar unit is equal to the solar power striking the earth averaged throughout the day and throughout the year. If it is applied to the earth as a whole, it is equal to the average solar power striking the whole earth’s surface. If it is applied to a part of the earth (e.g. the United States) it is equal to the average solar power falling on that part of the earth. It is true that one solar unit is larger for Arizona than for Vermont. The variation, however, is within a multiplier of two. The same is true for almost all the significant areas of the earth.

Table I. (from the appendix)
Energy Consumption in Solar Units*
Percentage of a Solar Unit

One Solar Unit is equal to 200 Watts per square meter for 12 hours a day 365 days per year (average)
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Units* - Percentage - Remarks
1.0 100% Average earth temperature would be that of boiling water.

10 -1 10% Tropical Climate (8 degree C rise in temperature)

10 -2 1% Future Absolute Upper Limit of Energy Consumption based on a level that would result in a maximum 1 degree C global temperature rise.

10 -3 0.1% Existing average US level

10 -4 0.01% Existing average world level

10 -5 0.001% Food (crops)
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Ok, now this is the meaning of the six levels of energy usage that are explained in the table above.

The first entry, opposite the solar power of one unit, is “Boiling Water.” It means that if the generation of power by the world were equal to the sunshine incident on the earth.

That is to say, if we were to double the heat load on the earth, so that we were twice what we receive from the sun, the mean temperature of the earth would rise close to that of boiling water (actually, about 80 degrees centigrade).

Whether it is 80 C or 100 C is not very important. What should be clear is that this rate of energy consumption is not possible on a world wide basis. This means that an “earth friendly” energy usage is somewhat between normal sunshine and something about 1 percent more.

The present mean temperature of the earth, about 293 K or 20 C, is the temperature the earth needs to radiate the one unit of solar power already normally incident upon it from the sun plus the energy that we are adding from various other sources such as coal, gas and nuclear. You don't have to count hydro, photovoltaic or wind energy of course because that is already included as solar.

Right now, although our average US energy generation equals 1/1000th or 0.1% in our cities it is really much greater. And in fact the temperature of the cities is higher. The cities would be even more than a few degrees warmer but they are air cooled and the heat load is distributed to the neighboring regions.

There are a couple of other interesting aspects of this sort of perspective. One is that with sufficient insulation houses receive enough incident solar energy to be warm. We heat them to make up for all the heat that is lost by radiation, conduction and convection.

The other thing is that there is more than enough energy for household illumination striking just a small portion of the roof every day.

The message is that when we consider exotic future sources of energy we must realize that even if we find an unlimited source of additional energy, we must consider the efficiency of its use and recognize that the heat load associated with additional energy usage must be kept to a level no greater than 10 times that of the present (1978) US consumption.

It may be that these numbers are not exactly as represented. These are very general statements. However the principle is important. Unless we figure out how to make a big heat radiator to deal with the extra energy, it might be a good idea, if we ever find that "miracle power source" that we use it somewhere off the earth to do our manufacturing and to run all our big computers.

By the way, in the computer field, we are trying to figure out how to dissapate 300 watts per blade in an AdvancedTCA blade server chassis. There are 16 blades in a 23 inch equipment rack for cards 14 inches high and 11 inches deep. All that heat is going to go somewhere eventually. These computers are big energy hogs.

[onequestionwonder]

I thought of this a long time ago. Though since this guy also considered the problem in a lot more depth close to three decades ago, that isn't saying much.

It's covered somewhat obliquely (to me at least) in what you've posted above, so I'll rephrase it as I thought of the argument and hopefully word it well.

Let's say we had solar cells that were cheap, efficient, and could solve the problems anticipated arising in the next few years.

Assume just for argument's sake 50% efficiency for our solar cells.

50% of incident solar radiation is converted to electricity, some fraction is absorbed by the cell and directly turned to heat, and some is reflected directly back into space (though not as much as before).

Just about all of the electricity generated is going to wind up as heat excepting that which is converted into stored potential energy (chemical, gravitational potential energy, etc), with the bulk becoming heat from motors, lights, electronic chips operating...

The net result is that a portion of energy that would have directly reflected into space is now used on earth, with virtually all of it becoming heat.

Obviously this changes the earth's albedo (been a while since I studied this, hope that's right) and the heat balance leading to a higher average temperature for earth. We've all heard of what relatively small average temperature increases (1 or 2 degrees C mean) do, so...

Without doing any numbers (because I don't think I'm capable of it), I'd think that it would take several thousands of years for this forcing (not considering any GHG effects) to have measurable effects on the climate.

But it seems that in the 'long run' you'd still be faced with this.

You might even extend the argument. Successful fission (or even fusion) that were sustainable for tens of thousands of years would inject heat into the environment that was previously stored in radioactive elements (and released over a really long time by decay, and much less efficiently since earth isn't going to last as long as some of those decay chains), rapidly compared to the normal course of events.

In this case since 'normal' reflectivity is maintained for earth, it takes even longer, but you are still changing earth's climate. And if you hope for intense energy using civilization to last as long as say ten thousand years, eventually this problem is going to be faced.

Or maybe not. This is obviously a pretty complicated problem to analyze. (An example: normal vegetation and where all the energy eventually flows to) Plus we are constantly emitting high wavelength radiation into space constantly as it is. Maybe could climate models would reveal a low amount of heat injection (compared to incident solar) changes the balance and average temperature very little.

An interesting problem. It needs to be analyzed, but it's going to be a long time before this is important as opposed to GHG global warming.

[mmunroe]

You can get a good idea of how rapid this change would be if you look at other ways of increasing the amount of energy that is "injected" into our climate system.

Consider the effect of a large asphalt parking lot as compared to an open grass covered field. The temperature rise is rapid. In this case instead of being reflected, the energy is absorbed and radiated as longer wave radiation which is then absorbed by the atmosphere.

When we think of lowering the amount of energy being injected into the system (night) the cooling process is noticeable in minutes. The temperature rise from increasing the energy being added would be just as quick.

However, you are right, it is a long slow process because it involves the industrialization of large areas.

I suppose that the geopolitical changes resulting from the inevitable changes in the oil economy will probably transform our society radically well before global industrialization will transform our climate.

Of course, there are also other more sudden and dramatic instruments of climate change ahead, such as the build up of fresh water in the north Atlantic basin. These potential changes result from the global warming that is already occurring as a result of our present day energy economy.

So for a multitude of more urgent reasons, new sources of energy could insulate portions of society from the dire consequences of both oil depletion and climate change.