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Is global warming linear in the sense that doubling the emission of Greenhouse gases will result in a doubling of global warming. Is there a threshold, i.e. is there are certain concentration of GHG where global warming is triggered and additional gases do not lead to a faster global warming?

Mark
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    Definitely not linear. You should take a look at section 7.3 here: http://acmg.seas.harvard.edu/people/faculty/djj/book/bookchap7.html – f.thorpe Feb 27 '18 at 03:56
  • Your definition of linear is wrong. In linear system y = kx and you propose it to be y = x. – Communisty Feb 27 '18 at 08:45
  • @Communisty No, I don't – Mark Feb 27 '18 at 08:49
  • Well if doubling emissions leads to tripling warming, the system is still linear. At least you seem to imply a linear relationship with a factor of 1. – Communisty Feb 27 '18 at 09:03
  • @Communisty That's not true. If you have y = kx and you double x you still get double y, no matter what the value of k is. – bon Feb 27 '18 at 12:35
  • Um, I'll just crawl under a rock if thats ok with you. – Communisty Feb 27 '18 at 12:54
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    @Communisty Yes, that's perfectly fine :) – Mark Feb 27 '18 at 12:58
  • By "doubling the emission" do you mean the rate of emission or the cumulative amount in the atmosphere? Also, I assumed you were referring to the persistent GHGs (predominantly CO2) - is that correct? – Keith McClary Feb 27 '18 at 18:00
  • @Keith McClary I mean doubling the amount of GHG emission from mankind e.g. in a year: will that rise the the global temperature x2 in comparison to the "normal" emission – Mark Feb 27 '18 at 19:38
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    If we held CO2 emissions constant then the CO2 concentration (and temperature) would continue to rise for a long time until an equilibrium is reached. Is it that equilibrium temperature you mean? I think we would run out of fossil fuels before that, though. – Keith McClary Feb 28 '18 at 00:55
  • My other question was, are you asking about persistent GHGs (predominantly CO2) that accumulate in the atmosphere over decades, or water vapor, which is not cumulative, but fluctuates in the short term depending on temperature? – Keith McClary Feb 28 '18 at 19:02

2 Answers2

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No. Consider water vapor. Water vapor is a greenhouse gas. As the temperature increases, more water is evaporated. Since water vapor is a greenhouse gas, the temperature will increase. Clouds, however, form from water vapor, reflect sunlight.

The earth is not as linear as people would like.

BarocliniCplusplus
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  • @BaroclinicCplusplus - Can you add a description in terms of the Math i.e. what is linear and non linear ? –  Feb 27 '18 at 02:58
  • You've described a feedback loop, which is not really what the question is about. Perhaps you could try to answer the question in terms of a long-lived GHG? – f.thorpe Feb 27 '18 at 03:55
  • @gansub I interpreted OP as asking if $\bar{T}=f([GHG])$ (linear) or if $\bar{T}=f([GHG],T) $ (nonlinear)?. – BarocliniCplusplus Feb 27 '18 at 14:51
  • @BarocliniCplusplus - That makes sense to us but I am not sure of OP's background. If you could add an English version of that mathematical relation maybe that would help –  Feb 27 '18 at 14:56
  • @farrenthorpe The equations governing the evaporation, condensation and precipitation of water are nonlinear, therefore it answers OP's question. Even neglecting the feedback loop, or even GHGs altogether, the primitive equations are nonlinear, due to advection, But to address longer lived GHGs consider this loop- GHGs increase the temperature. In response, humans consume more electricity on air conditioning, which increases the $\ce{CO_2}$ concentration.... – BarocliniCplusplus Feb 27 '18 at 15:12
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No, it is logarithmic. Each doubling of CO2 concentration will result in a constant increase in temperature which is called the equilibrium climate sensitivity, estimated to be 1.5C to 4.5C. Wikipedia.

Keith McClary
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