Today I tweeted that global average temperatures will stop rising when global CO₂ emissions reach zero.
I have tweeted this before & it is a well-known result, but this time I got a lot of people saying it was not correct!
A thread on some papers...
I have tweeted this before & it is a well-known result, but this time I got a lot of people saying it was not correct!
A thread on some papers...
The relationship between global warming cumulative & cumulative CO₂ emissions came to prominence after three papers in 2009:
Allen et al nature.com/articles/natur…
Meinshausen et al nature.com/articles/natur…
Matthews et al nature.com/articles/natur…
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Allen et al nature.com/articles/natur…
Meinshausen et al nature.com/articles/natur…
Matthews et al nature.com/articles/natur…
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It is not necessarily 100% correct to say temperatures will stop rising when net CO₂ emissions reach zero, there may be some 0.x°C change from the time emissions reach zero, & non-CO₂ also effects temperature.
But, warming from time of zero & non-CO₂ are second order.
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But, warming from time of zero & non-CO₂ are second order.
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IPCC AR5 highlighted the near-linear relationship between warming and cumulative CO₂ emissions.
Headline statement: "Cumulative emissions of CO₂ largely determine global mean surface warming by the late
21st century and beyond."
Headline statement: "Cumulative emissions of CO₂ largely determine global mean surface warming by the late
21st century and beyond."
IPCC SR15 had a very nuanced sentence, perhaps too nuanced...
I am not sure of the literature which supports "sustained net negative global anthropogenic CO₂ emissions ... may still be required to prevent further warming due to Earth system feedbacks"
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I am not sure of the literature which supports "sustained net negative global anthropogenic CO₂ emissions ... may still be required to prevent further warming due to Earth system feedbacks"
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Gasser et al for example shows that the carbon budget is smaller (you have to get to zero earlier) because of permafrost feedbacks, but that is different to maintaining negative emissions to offset continued (& strengthening feedbacks)
nature.com/articles/s4156…
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nature.com/articles/s4156…
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IPCC SR15 Chapter 1 supports the statements in tweet #3, & you can read the details there ipcc.ch/sr15/
As the figure shows, give or take 0.1°C or so (& constant non-CO₂), zero CO₂ emissions leads to stable temperatures.
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As the figure shows, give or take 0.1°C or so (& constant non-CO₂), zero CO₂ emissions leads to stable temperatures.
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IPCC SR15 Chapter 2 uses the relationship extensively, & even derives carbon budgets from it. This is the scientific consensus. ipcc.ch/sr15/
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Matthews & Caldeira 2008 "We then show that to hold climate constant at a given global temperature requires near‐zero future carbon emissions. "
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Cao & Caldeira discuss at length, and show the effects on CO₂ concentrations. iopscience.iop.org/article/10.108…
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Matthews et al again nature.com/articles/nclim…
There are dozens of paper on this (I just picked ones that show also concentrations and other GHG emissions)
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There are dozens of paper on this (I just picked ones that show also concentrations and other GHG emissions)
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Tanaka & O'Neill basically make the case that GHG emissions do not need to be zero (as in the Paris Agreement), but zero CO₂ emissions are probably sufficient depending on non-CO₂ emissions.
nature.com/articles/s4155…
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nature.com/articles/s4155…
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If you think my statement in the original tweet is wrong, then can you back that up with literature?
Channeling @Knutti_ETH, @KenCaldeira, @damon_matthews, @KatsuTanaka, @oneill_bc, @kasia_tokarska, @JoeriRogelj, who know better than me...
11/11
Channeling @Knutti_ETH, @KenCaldeira, @damon_matthews, @KatsuTanaka, @oneill_bc, @kasia_tokarska, @JoeriRogelj, who know better than me...
11/11
