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An idea about reducing Global Warming

Aitch

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This is probably a very impractical idea; could anyone here explain why.

As I understand it (could be wrong) global warming is due to excess energy in the atmosphere. Could this not be collected (lots of wind farms and whatever) and then used to power one or more giga/tera/peta/whatever lasers to fire the energy out into space?

Energy from sunlight could also be collected and, instead of hanging around contributing to the problem, fed to the same lasers.

You'd obviously need to cut down man's contribution to greenhouse gases as well. And convert people to a low/efficient energy use life-style. And probably lots of other things too.

There's probably an obvious reason why this wouldn't work. What is it? I suspect it's the collection of the energy that would put the mockers on the idea, or the number of lasers necessary, but don't know enough to say.
 
It's not that that idea is completely impossible, it's just that it's a very roundabout way of doing things.

The basic problem with global warming is that the sun sends light energy to the earth with a spectrum that peaks in the yellow part of the visible spectrum. The atmosphere lets this through fairly easily. The earth, being colder, re-emits this as chiefly infra red radiation, which is blocked in part by water vapour and carbon dioxide, trapping the energy in the atmosphere. What you're describing is taking the sun's rays, capturing them, and then sending them back out to space again in a form that would easily penetrate the atmosphere. It would be far more straightforward to cut out the middle man and put a load of mirrors on the ground rather than solar panels. But that would mean covering a very large fraction of the earth's surface with mirrors for it to make a difference.

But then again, the idea of changing the earth's albedo is the basis for many proposed climate management ideas. A fair few involve making clouds optically thicker through the addition of seed aerosol and thereby reflecting more radiation back to space than they would do otherwise.
 
How would you collect the energy?

If you suggest solar cells, then we need to cover a fairly large fraction of the earth with these. Its not going to happen.

If not, then sunlight is absorbed and heats things up. The laws of thermodynamics prevent getting energy from the atmosphere as long as its temperature is uniform. We can only use variations in temperatures and pressures. In fact, this is related to using wind energy. Again, we just can't produce a large enough amount to make a difference.

One more remark, why fire it to space? We can burn less fuels instead.
 
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PS The wind farms bit would be a bit of an odd one - if you could somehow harvest enough wind energy from the atmosphere comparable to the amount of energy you want rid of, there's no telling what that would do to global weather patterns, so it doesn't really bear thinking about.
 
I was trying to say that we cant get enough energy out of wind farms. Managed to get that wrong somehow. :boggled:
 
Doctor Evil said:
How would you collect the energy?
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That was one of my caveats - apart from wind-turbines and solar cells, what else is there?

Doctor Evil said:
One more remark, why fire it to space?
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To cut down on the total amount of energy in the Earth system.

Spud1k said:
PS The wind farms bit would be a bit of an odd one - if you could somehow harvest enough wind energy from the atmosphere comparable to the amount of energy you want rid of, there's no telling what that would do to global weather patterns, so it doesn't really bear thinking about.
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A bit off topic, but... IIRC the weather system is supposed to be a chaotic one - ie small inputs give large effects. Is anyone looking into the effect the increasing number of wind-farms will have on the weather?
 
Doctor Evil said:
There is not need to do that. We can just burn less fuel. The energy is then stored in a form which does not affect GW.
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Maybe I have misunderstood things, or I'm not explained my thinking very well.

If GW is due to an excess of energy, due to retention of externally sourced (solar) and that 'lost' into the atmosphere due to inefficient use, then don't we need to lower this level by getting rid of at least some of the excess.

Otherwise, even cutting back on what we use and devising ways of using it more efficiently (ie cut down the loss), we will cut down the increase in the excess, but it will still be an excess.

As I said, I could be misunderstanding the situation - it's a long time since I was at school.
 
Aitch said:
A bit off topic, but... IIRC the weather system is supposed to be a chaotic one - ie small inputs give large effects. Is anyone looking into the effect the increasing number of wind-farms will have on the weather?
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Not sure on that but gut feeling tells me that the effect of wind turbines is minuscule compared to other anthropogenic perturbations (e.g. greenhouse gases, aerosols, changes in land use).
 
Aitch said:
Maybe I have misunderstood things, or I'm not explained my thinking very well.

If GW is due to an excess of energy, due to retention of externally sourced (solar) and that 'lost' into the atmosphere due to inefficient use, then don't we need to lower this level by getting rid of at least some of the excess.

Otherwise, even cutting back on what we use and devising ways of using it more efficiently (ie cut down the loss), we will cut down the increase in the excess, but it will still be an excess.

As I said, I could be misunderstanding the situation - it's a long time since I was at school.
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It's not that the idea in general is wrong per se, it's just that (as alluded to by Dr Evil) if you can capture the energy, it would be far better to put it to use rather than beaming it back into space. This would save burning some fossil fuels that would otherwise have been used for whatever application you have. I don't have the figures to hand, but the amount of warming caused by a tonne of CO2 in the atmosphere over the course of its lifetime is much greater than the energy than was released by the combustion of the fuel that generated it.
 
Spud1k said:
....I don't have the figures to hand, but the amount of warming caused by a tonne of CO2 in the atmosphere over the course of its lifetime is much greater than the energy than was released by the combustion of the fuel that generated it.
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I doubt that can be substantiated by using co2 atmospheric residence durations and the molecular absorption.

From a long range perspective the co2 in the air came from a hydrocarbon which came from a plant which got its co2 from the air. Oops, we started with airborne co2 .

The net of that cycle should be zero.
 
One thing that you need to remember is that "energy" comes in many different forms. It can be quite difficult to convert energy to the form that we want, which would include in this case converting it to some form of energy that could be emitted from a man-made station on earth. As has already been mentioned, if we could do that, hydrocarbons would not be what fueled our society.

Increasing albedo may have resulted in the warm period of the Cretaceous (dinosaur times). Just see this article about albedo simulations.
 
mhaze said:
I doubt that can be substantiated by using co2 atmospheric residence durations and the molecular absorption.

From a long range perspective the co2 in the air came from a hydrocarbon which came from a plant which got its co2 from the air. Oops, we started with airborne co2 .

The net of that cycle should be zero.
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OK, I should have been more specific.

The net cycle of CO2 is zero, but remember that if carbon is transferred from the atmosphere/biosphere system to the lithosphere or deep hydrosphere, it is, in effect, taken out of the system as far as anything on the surface is concerned. This happens through sedimentation of biological material or transport of dissolved CO2 to the deep ocean. If we were to stop burning fossil fuels tomorrow, it is predicted that if the concentration of CO2 in the atmosphere would slowly begin to fall again (but this is on the scale of decades IIRC).

My point is that I think you could do a very, very rough calculation based on the radiative forcing of anthropogenically-produced CO2 and its estimated atmospheric lifetime when treated as a perturbation to the pre-industrial earth system. But this would only be a ballpark figure, obviously.
 
Sorry, correction. I should have said 'atmospherically active lifetime' rather than 'atmospheric lifetime' in the last paragraph.
 
Spud1k said:
OK, I should have been more specific.

The net cycle of CO2 is zero, but remember that if carbon is transferred from the atmosphere/biosphere system to the lithosphere or deep hydrosphere, it is, in effect, taken out of the system as far as anything on the surface is concerned. This happens through sedimentation of biological material or transport of dissolved CO2 to the deep ocean. If we were to stop burning fossil fuels tomorrow, it is predicted that if the concentration of CO2 in the atmosphere would slowly begin to fall again (but this is on the scale of decades IIRC).

My point is that I think you could do a very, very rough calculation based on the radiative forcing of anthropogenically-produced CO2 and its estimated atmospheric lifetime when treated as a perturbation to the pre-industrial earth system. But this would only be a ballpark figure, obviously.
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Well, that's the "radiative imbalance" hypothesis which requires as one supporting leg an atmospheric residence time for CO2 of hundreds of years. Schwartz 2007 figures it is about 5 years, Shaviv 2-10.
 
mhaze said:
Well, that's the "radiative imbalance" hypothesis which requires as one supporting leg an atmospheric residence time for CO2 of hundreds of years. Schwartz 2007 figures it is about 5 years, Shaviv 2-10.
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Are you referring to DOI: 10.1029/2007JD008746? In that, Schwarts quotes the CO2 lifetime as 100 years. He gives 5 years as the recovery time of the atmosphere to a temperature perturbation.

Anyway, whatever the lifetime, doesn't change the fact that the rough calculation should be doable.
 
“Heat Capacity, Time Constant, and Sensitivity of Earth’s Climate System,” was authored by Brookhaven National Lab scientist Stephen Schwartz. (LINK)

Table 3 may interest you. (rough calcs)

r

is the time constant of interest, estimated at 5 years.

From the paper-

...there is a growing body of observational evidence to suggest that the time over which changes in climate can take place can be quite short, just a few years. High-resolution studies of temperature change in ice cores as inferred from isotope ratios and other variables demonstrate substantial widespread temperature change in periods as short as five to ten years [Taylor et al., 1997; NRC, 2002; Alley et al., 2003]. The view of a short time constant for climate change gains support also from records of widespread change in surface temperature following major volcanic eruptions.


 
Right, which is what is referred to as the 'Effective climate system time constant', which is not the same quantity as the atmospheric lifetime of CO2. This is taken from the end of section 6 in the pdf you linked to:

In contrast an abrupt decrease in emissions of CO2 would result in only minimal decrease in GMST because of the long lifetime (ca 100 years) associated withexcess atmospheric CO2.
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