Prof. Stefan RahmstorfNuclear #fusion will not only come too late to help solve the #climatecrisis. Even in the long run it will not be the unlimited energy source that some are dreaming of. The reason is basic physics, and anyone can do the back-of-envelope calculation. 🧵1/
The problem is that all human energy use ends up as heat. That's no problem now: our current global energy use corresponds to 0.04 Watt/sqm (that's per square metre of Earth surface). The human-caused CO2 increase has a far stronger warming effect: 2.1 W/sqm, following IPCC. 2/
But our energy use (here also in W/sqm) is growing exponentially by 2.3 %/year, 10-fold per century. What does this mean for the future? The Master thesis by Peter Steiglechner @PIK_Climate investigated this in 2018 using a global climate model. Figures taken from his work. 3/
But first, back of envelope: a 10-fold increase in energy use from the current results in a heat flux of 0.4 W/sqm.
With the standard IPCC climate sensitivity that results in 0.3 °C global warming. Oops, now this is a problem, coming on top of greenhouse warming! 4/
With the standard IPCC climate sensitivity that results in 0.3 °C global warming. Oops, now this is a problem, coming on top of greenhouse warming! 4/
Here's two scenarios to 2100 Peter studied (black lines): 2% increase per year, and a more moderate IPCC scenario called SSP5. That’s less than a ten-fold increase. BUT: the heat release is not globally uniform. Unlike for CO2, it is concentrated where we live, on land. 5/
That is why the (admittedly rather coarse) climate model shows warming concentrated over Northern Hemisphere land, reaching 0.2 – 0.4 °C warming there by 2100 (not even yet in equilibrium). And we’re already struggling to prevent every 0.1 °C of further warming! /6
In terms of heat release, nuclear power (fusion or fission) is just as bad as coal.
Renewables are different: they use energy from wind, sun, tides or geothermal which is already in the climate system and will end up as heat anyway, whether we use it or not. /7
Renewables are different: they use energy from wind, sun, tides or geothermal which is already in the climate system and will end up as heat anyway, whether we use it or not. /7
(In case you want to say now: but extra heat is radiated into space! This is of course already taken into account. The Earth must get warmer to radiate more, that is what the climate sensitivity describes.) /8
The bottom line is: if humanity wants to use a lot more energy in future, nuclear power can't be the solution. Not just not for the next decades, but also in the long run renewable energies are the only sustainable solution. /9
These technologies we already have, they are growing exponentially and are safe and cheap. (And don't tell me the sun doesn't shine at night - energy system experts already account for that, believe it or not.) /10
---
RT @scienceisstrat1
The @IEA’s bombshell new report on renewables has incredibly good news.
For example, solar is undergoing a mega boom & may surpass coal by 2027
Below is a 🧵 on genuinely good news on green ener…
https://twitter.com/scienceisstrat1/status/1601650724852895744
Science Is Strategic on Twitter
“The @IEA’s bombshell new report on renewables has incredibly good news. For example, solar is undergoing a mega boom & may surpass coal by 2027 Below is a 🧵 on genuinely good news on green energy from the IEA & beyond (1/22) Cc: @Noahpinion @JesseJenkins @ramez @dwallacewells”
A similar argument regarding waste heat was recently made in a peer-reviewed paper in Nature Physics as well. Check it out if you like. /11
https://www.nature.com/articles/s41567-022-01652-6
https://www.nature.com/articles/s41567-022-01652-6
FelipeSo, perhaps I'm misunderstanding something, but not all human energy consumption ends up as heat, does it?
What about LED lights? What about motion? Sure, there is friction in motion but that doesn't account for all the energy, or does it?
As an engineering guy, I'm genuinely interested in this concept. If you could clarify it, that would be great.
Jim Hughes ☢️@FelipeW @rahmstorf light gets absorbed, gradually heating up the item which then radiates it out
Seriously? LED light, which doesn't contain much infrared waves, heats up all the objects around?
I am not saying that's impossible, but it doesn't sound right to me...
That would mean that moonlight (a very blue light) would also heat up the earth - though it's much less than the sun of course...
@FelipeW @rahmstorf tiny amounts, but the light gets absorbed and the energy has to go somewhere. All of it eventually ends up as useless heat
But the color white reflects almost all light, right?
But then it hits other surfaces which aren't white... I get it, I guess!
I didn't get yet how motion is completely turned into heat, though.
@FelipeW @rahmstorf friction. With air, any mechanical components etc.
Oh wow. Now I get it!
Motion is infinite in space because of a lack of friction. Any object on earth that is put into motion, stops eventually due to friction - this friction is of course generating heat, even though it's usually very little.
Sometimes it's really a lot though, thinking of car brakes!
So all motion ends with friction and all friction ends with heat and now I get it.
But back to LEDs: those 2 W of electricity going into the diode = 2W heat! Right?