Wouldn't fusion reactors also cause global warming?

  • #1
somega
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A fusion reactors releases a lots of energy.
Most of this energy will end up as thermal energy after it has been used by the consumers.
Wouldn't this heat up the earth?

People use the energy to run cookers, drive cars, light up houses, etc.
This energy (99%?) will end up as thermal energy where it can no longer be used.

If fusion reactors can produce energy at a lower price as today, people will use more energy.
Global warming would be stronger than today...
 

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  • #2
stevendaryl
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The amount of energy that the world receives from the sun is around 10,000 times as much energy as all humans consume in all forms. So the warming effect of power production is pretty insignificant. The world is mostly heated by the sun.
 
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  • #3
berkeman
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Welcome to the PF. :smile:
A fusion reactors releases a lots of energy.
Most of this energy will end up as thermal energy after it has been used by the consumers.
Wouldn't this heat up the earth?

People use the energy to run cookers, drive cars, light up houses, etc.
This energy (99%?) will end up as thermal energy where it can no longer be used.

If fusion reactors can produce energy at a lower price as today, people will use more energy.
Global warming would be stronger than today...
That is a very good question, especially so since you marked your thread at the "B" basic level.

I'm certainly no expert on global warming (and for a number of reasons, we only allow GW threads on the PF that are based on peer-reviewed science), but your question touches on an important distinction. It's a good point that converting inert materials into heat (like burning wood like our ancestors have done for a long time), or converting natural energy cycles like water evaporation / rain / hydroelectric power into home heating contribute to warming the Earth a bit more compared to if we were not here doing that. But as pointed out by @stevendaryl that amount of added heat is very small compared to the "insolation" energy from the Sun.

The larger issue is if our activity here on Earth can change how the insolation changes the overall climate of the Earth, and that is the subject of much peer-reviewed research. The changes to Earth's atmosphere from extensive burning of fossil fuels for energy production and the changes in the reflectivity of the Earth due to deforestation (and the associated loss in carbon-storing plants) appear to have contributed more to the global warming issues that we are studying now.

Does that distinction make sense?
 
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  • #4
CWatters
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I recall this issue was addressed in a paper published a few years ago. I'll try and find it.

Edit: I'm struggling to find it. I recall it looked at the amount of energy humans could generate and the effect this might have on climate change even if it was all from carbon emission free sources.
 
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  • #5
somega
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The point with the energy the sun is sending to us makes sense and convinced me.
Nuclear fusion seems to be the energy source of the future...
Thank you very much...
 
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  • #6
Keith_McClary
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In pre-industrial times the Earth's temperature was determined by a balance between energy from sunlight and energy radiating into space (mostly infrared). If you released a bunch of heat it would warm the planet, but on a timescale of months it would return to the equilibrium temperature.
If you add CO2 to the atmosphere, it blocks the infrared radiation from escaping (but not the incoming sunlight), so the equilibrium temperature rises. CO2 is removed from the atmosphere by natural processes, but on a timescale of thousands of years.
 
  • #7
essenmein
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The waste heat issue, in reality any energy we use ultimately heats our environment, currently the "waste heat" is ~0.028W/m2, vs ~2.9W/m2 for human green house gases. (Flanner, M. G. (2009) Integrating anthropogenic heat flux with global climate models, Geophys. Res. Lett., 36, L02801, http://www.agu.org/pubs/crossref/2009/2008GL036465.shtml. )

So waste heat is contributing about 1%, its not inconceivable that with an abundant cheap energy source that does not produce CO2 that we would/could increase our energy use by 100x (factor in some population growth, developing nations increasing energy use to match western countries etc), so at some point direct heating will become an issue.
 
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  • #8
tech99
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So waste heat is contributing about 1%, its not inconceivable that with an abundant cheap energy source that does not produce CO2 that we would/could increase our energy use by 100x (factor in some population growth, developing nations increasing energy use to match western countries etc), so at some point direct heating will become an issue.
I think that all decisions about human activity, whether involving climate, energy, information technology, economies, politics, health, entertainment, etc must be seen as trying to change a very large and complex system. It is like the principle of Le Chatellier - it opposes change. The climate system seems to be stable at the present, although having to shift to maintain that condition; we know it is a control system using negative feedback, but part of it involves the software possessed by mankind in the brain. If the system functions as it always has, it will oppose change and remain stable. But we do not understand the human part of it, and why and how it works. It is a possible supposition that the brain is doing the bidding of our genes, and we do not know if they are going to seek survival at any cost to the planet.
In the case of fusion power, it is possible that cheap energy would give unexpected results, by boosting economies such that climate change is not abated, whether by increased population, land take, emission of methane, or increased air travel etc.
 
  • #9
artis
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In simpler words I think what you folks are saying here is that currently the heat directly produced as a byproduct of our activity is so small that it alone couldn't affect climate change but because we receive most of our heat from the sun , building up more CO2 in the atmosphere blocks the removal of that heat which increases average temps.
So currently CO2 is the problem and not direct heat released from objects that we heat up.

If we assume that in the future our direct heat as byproduct capacity might increase with new cheap energy sources we might also think that if those energy sources would be carbon neutral this increase in heat would be much counteracted by the decrease in atmospheric CO2 which would make Earth lose more heat back to space and even things out?
 
  • #10
essenmein
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Just to clarify, water vapor is the main green house gas, CO2 triggers a small change in atmospheric temp, which then causes an increase (or decrease) in water vapor (air temp dramatically affects its ability to hold water), which then drives the bulk of the over all temperature change. So we don't have to change CO2 by much to cause a large swing in temps.

So basically if the warming source is not CO2, but say direct heating, the overall climatic effect due to change in vapor pressure of water is still going to cause an increase in green house gas.
 
  • #11
Keith_McClary
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what you folks are saying here is
The crucial point I was trying to make is that if we had only fusion and we turned it off, the Earth would be back to radiative equilibrium in months. But even if we turn off all FF burning, all the cumulative CO2 will still be with us for thousands of years.
 
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  • #12
Buzz Bloom
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But even if we turn off all FF burning, all the cumulative CO2 will still be with us for thousands of years.
Hi Keith:

I have no problem believing what the quote says is correct, except it omits that over time some of the all gets removed. An interesting related question is: If we turn off all FF burning, how long would it take for the current CO2 level to return to a more modest level than it currently has reached, for example, say a level corresponding to the year 1990 when the average global temperature above the 1950 level was about one-half of the current temperature above the 1950 level?

See https://www.climate.gov/news-features/understanding-climate/climate-change-global-temperature .

Regards,
Buzz
 
  • #13
Keith_McClary
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how long would it take for the current CO2 level to
This gets a bit complicated because of how CO2 dissolves in the oceans.

...and Then There's Physics says:
You can also play around with this Geologial Carbon Cycle model. The 7.5 x 10^{12} is about 0.1 GtC per year and is meant to represent volcanic outgassing. If you set the transition CO2 spike to about 300 GtC, that will start atmospheric CO2 at about 400ppm. You can then vary the simulation CO2 degassing rate. Setting it to about 375 would be about half our current annual emissions (about 5GtC per year). Atmospheric CO2 continues rising. To get it to stabilise on century timescales (i.e., to not rise for centuries) you need to reduce emissions to below 10% of current emissions.
 
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  • #14
Buzz Bloom
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This gets a bit complicated because of how CO2 dissolves in the oceans. . . . "To get it to stabilise on century timescales (i.e., to not rise for centuries) you need to reduce emissions to below 10% of current emissions."
Hi Keith:

Thanks for your response to mu post.

Regarding the quote about reducing emissions, the assumption of ending all FF burning bypasses this requirement.

There is also an additional complication to ocean dissolving CO2. Plants convert CO2 to carbohydrates, some of which are not eaten and then reconverted back to CO2 by its eaters when they metabolize carbs. One aspect of this complication is another human problem regarding the accelerating destruction of forests.

Regards,
Buzz
 
  • #15
sophiecentaur
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But even if we turn off all FF
I believe there is a significant contribution from food production as well as the more obvious 'Energy Use'. I can't remember how the figures compare but the digestion mechanism used by ruminants produces a lot of methane.
 
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  • #16
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A fusion reactors releases a lots of energy.
Most of this energy will end up as thermal energy after it has been used by the consumers.

This is happening now. It doesn't depend on which source of energy we humans use. It just depends on how much energy we humans use.
 
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  • #18
berkeman
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Thread will remain closed. The OP's question has been answered well. Thanks folks! :smile:
 

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