Hi, > If emissions of CO2 could be reduced to zero overnight, would the global > temperature continue to rise due to the 400+ ppm CO2 in the atmosphere?
Some models indicate temperature may increase a bit after zero emissions (up to 0.5°C in the GFDL model, but that is the exception, doi:10.1088/1748-9326/10/7/075002), but most suggest it doesn’t (DOI: 10.1175/2007JCLI1905.1, Fig. 5, or DOI: 10.1038/NGEO1047, see also IPCC for further refs). See also doi:10.1088/1748-9326/9/12/124002. It’s more complicated though. The above is for CO2 only. If you set all GHG emissions to zero it would cool more strongly mostly because methane has a shorter lifetime. If you eliminate aerosols that would give a bit of warming on top of that (see also IPCC WG1 AR5 FAQ 12.3). CO2 and non CO2 are coupled both through technology and through markets. See below for results based on MAGICC tuned to CMIP (unpublished figure). Note that this goes out much longer to 2500. Again, as I said before, there is no evidence for strong continued warming after zero emissions. But sea level will rise will continue, as Mike pointed out. Reto [cid:[email protected]] From: John Nissen [mailto:[email protected]] Sent: Donnerstag, 17. November 2016 15:16 To: Knutti Reto <[email protected]> Cc: Michael MacCracken <[email protected]>; David Lewis <[email protected]>; geoengineering <[email protected]>; Kevin Anderson <[email protected]>; [email protected]; Greg Rau <[email protected]>; Peter Wadhams <[email protected]>; Sev Clarke <[email protected]>; Alan Gadian <[email protected]>; Kevin Lister <[email protected]>; Adam Rutherford - Science <[email protected]>; Hugh Hunt <[email protected]> Subject: Re: [geo] Negative Emissions: Arrows in the Quiver, Life Preserver, and/or Moral Hazard? Hi again, Let me put a simple question to you. If emissions of CO2 could be reduced to zero overnight, would the global temperature continue to rise due to the 400+ ppm CO2 in the atmosphere? John On Thu, Nov 17, 2016 at 9:48 PM, John Nissen <[email protected]<mailto:[email protected]>> wrote: Hi Reto, Let us continue to focus on the CO2 (and not be diverted by El Nino humour or aerosol cooling) and consider the scenario in diagram which I attached earlier. Suppose we can tell from the black line that the temperature is rising at 0.3C per decade when CO2 is 400 ppm and 0.4C per decade by the time it reaches 500 ppm. So far so good. Then at 2050, CO2 net emissions are suddenly reduced to zero. That is the "experiment". Nothing else changes. You claim that the temperature levels off quickly after 2050, as indicated by the red line. My argument is that the temperature will continue to rise after 2050, with a rate of temperature increase gradually falling from 0.4C per decade to 0.3C while the CO2 falls slowly from 500 ppm to 400 ppm. (It will reach 400 ppm some year after 2500, see red line in first graph.) The forcing from that level of CO2 (400-500 ppm) will remain for those hundreds of years so temperature will continue to rise accordingly. There is no reason for a sudden change in some parameter like your Q at the year 2050, to negate this CO2 forcing, just because net emissions have suddenly fallen to zero. Why would heat suddenly go into the ocean because CO2 emissions had stopped? It simply does not make sense. You are correct that there will be a gradual rebalancing of the system, but it won't happen suddenly. Regards, John On Thu, Nov 17, 2016 at 8:26 PM, Knutti Reto <[email protected]<mailto:[email protected]>> wrote: Dear John, Thanks. I was planning not to spend more time on this debate, but it gets increasingly nonsensical and funny. > but we've had a 0.2C rise between 2015 and 2016 according to WMO, see > attached. So one must expect the rate of temperature rise at 500 ppm to be > much greater than 0.2C per decade. Have you ever heard of El Nino? Interpreting the difference from one year to the next as a forced underlying anthropogenic trend is just as meaningless as all the claims that the hiatus would invalidate climate change. If 2017 is colder than 2016 (which is very likely) we won’t conclude that the next ice age is coming. That is interannual variability. > So that if CO2 reaches 500 ppm and stays at that level, its climate forcing > will stay at that level, and the global temperature will continue to rise > accordingly. So you argue that when you light a candle in a tent, that will produce runaway warming in the tent? I hope we agree it doesn’t. Once the system gets warmer it will radiate out more energy and come into a new equilibrium. The claim that a finite constant forcing will continue to warm a system forever is nonsense, unless the system is closed, which it is not. I’ll try again to explain the global energy balance to prove that your argument is wrong. The difference between the additional forcing F (essentially what is coming in) and what is additionally emitted (lambda*T, with lambda being approximately constant, the inverse of climate sensitivity) is the net uptake of the system Q, and is largely going into the ocean. So Q=F-lambda*T. That is not just a hypothesis but conservation of energy in a simple energy balance model, and it can be confirmed with data (see IPCC AR5 WG1 TFE.4, p. 67). Please tell me if you disagree so far. Today F~=2.3 Wm-2 and Q~=0.9 Wm-2. If you keep F constant then Q approaches zero, and therefore T (after some warming as discussed to compensate for the decrease in Q, about 0.5°C over 200 years) *must* become constant. If, as you argue, T were to increase as before or more, then so would Q (the ocean heat uptake to first order is proportional to T). So in our equation Q=F-lambda*T the right side of the equation decreases, but the left side increases, which is impossible. That is, indeed, plain physics, is called conservation of energy and is rather fundamental. Best regards, Reto From: John Nissen [mailto:[email protected]<mailto:[email protected]>] Sent: Donnerstag, 17. November 2016 11:21 To: Knutti Reto <[email protected]<mailto:[email protected]>> Cc: Michael MacCracken <[email protected]<mailto:[email protected]>>; David Lewis <[email protected]<mailto:[email protected]>>; geoengineering <[email protected]<mailto:[email protected]>>; Kevin Anderson <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]>; Greg Rau <[email protected]<mailto:[email protected]>>; Peter Wadhams <[email protected]<mailto:[email protected]>>; Sev Clarke <[email protected]<mailto:[email protected]>>; Alan Gadian <[email protected]<mailto:[email protected]>>; Kevin Lister <[email protected]<mailto:[email protected]>>; Kevin Lister <[email protected]<mailto:[email protected]>>; Adam Rutherford - Science <[email protected]<mailto:[email protected]>>; Hugh Hunt <[email protected]<mailto:[email protected]>> Subject: Re: [geo] Negative Emissions: Arrows in the Quiver, Life Preserver, and/or Moral Hazard? Hi Reto, I'll just focus on CO2. In the diagram I attached to my previous email, the red line in the temperature diagram suddenly becomes flat when CO2 reaches 500 ppm. This is just contrary to plain physics, and nobody has shown that I am wrong in my physics. The basic physics is that the rate of global temperature increase rises as climate forcing rises. So that if CO2 reaches 500 ppm and stays at that level, its climate forcing will stay at that level, and the global temperature will continue to rise accordingly. The rate of temperature increase was projected as 0.2C per decade in AR4, but we've had a 0.2C rise between 2015 and 2016 according to WMO, see attached. So one must expect the rate of temperature rise at 500 ppm to be much greater than 0.2C per decade. It is difficult to comprehend how IPCC could have made such a blunder, but that seems that they have. As a result, COP is suggesting that achieving zero emissions will halt climate change which is simply not true. Governments around the world have been misled. We need aggressive CO2 removal in addition to drastic cuts in CO2 emissions, to bring the CO2 level down close to its pre-industrial level. Kind regards, John -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]<mailto:[email protected]>. To post to this group, send email to [email protected]<mailto:[email protected]>. Visit this group at https://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/geoengineering. 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