Comments 1 to 25:

1. pjmattheis at 05:10 AM on 12 September, 2016

   The cartoon of the week has layers of meaning - I have a CO2 monitor, and know how to use it, but I do not have a bell jar like the one pictured. However, a lone person in a standard SUV, with windows closed and no other ventilation, will quickly drive CO2 levels to 3-5 times outdoor 400+ppm. At those levels, cognitive function is heavily impacted, and in no good way. For a human with extended time in such an environment, "CO2 as plant food" gains new meaning, since vegetative brain function may be all thats left. This might could explain some of the crazy...

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2. Tom Curtis at 09:17 AM on 12 September, 2016

   In the video, at 4:08 , Coral Davenport says (with ums, ahs and other redundancies and interjections excluded):

   "The specific marker that a lot of scientists and scientific institutions have put forth is the warming atmosphere beyond 3.7 degrees farenheight [2^o C] on average.  That is the point at which a lot of scientists say we will be irrevocably locked in to a future of these climate impacts, and we're at the point right now where scientists say a lot of that is already baked in.  There was a point in the climate debate when it was about how do we keep from getting there.  At this point, in terms of the emissions that are already out in atmosphere, and the rate of emissions being produced today, scientists are saying we are probably set to go past that tipping point, and the debate is really about how do you keep it from getting far, far worse.  How to you keep the planet inhabitable by humans."

   That is inaccurate on several counts.  First, it is not clear that we are past the point where a realistic global emissions policy will prevent an average rise of temperatures above 2^o C.  We may be past the point were the political process will get us a policy that will achieve that, but we should distinguish what is technically feasible and what is simply a matter of inertia and unwillingness to treat the issue with sufficient seriousness by politicians internationally, lest we justify the inertia of the policians based on that inertia itself.

   Second, neither 2^o C nor 1.5^o C (which a substantial body of scientists believe is the relevant limit) is a known tipping point.  Nor are either the point where it is known with certainty that there will be significant harmful impacts from global warming.  Rather, both are reasonable estimates of the temperature beyond which it is likely the impacts of global warming will by significantly harmful, and likely that we will may pass any tipping points.  If we keep below those thresholds, on the other hand, it is most likely that we will not have passed any tipping points, and that harms will be small relative to the range of climate impacts from a stationary climate (ie, on in which temperatures have not been rising).

   Third, however, and most significantly, there is no possibility that the emission of fossil fuels and cement will bring the planet to a point at which it is uninhabitable by humans.  That is not great news.  At around 10^o C above preindustrial temperatures, part of the tropics will become uninhabitable to humans without specific protection (cooling suites, or significant respites in air conditioned areas for significant periods, etc) for several weeks a year on average.  That is a circumstance well worth avoiding.  Somewhere between 4^o C and 10^o C we will pass a point where the burden of global warming is likely to bring about a collapse of our civilization, with a consequent loss of life in the billions due to the collapse of global trade.  But the debate is not, or should not be about these outer limits which we will explore only if we do effectively nothing about AGW (something that would require a reversal of current policy and technical trends).  Rather, it is about how close to the 2^o C (or 1.5^o C) we can keep the rise, and how quickly can be bring global temperatures back below those limits, given that we overshoot.

   Coral Davenport is wrong to suggest that human inhabibility is in anyway a plausible consequence of global warming (except as restricted to specific areas at the outer limits of potentical temperature increase); and wrong also to suggest that once we go past 2^o C the debate is suddenly about keeping below a much higher limit that essentially lets poluters of the hook.

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   Moderator Response:

   [JH] Please share your oncerns with Coral Davenport. Climate change is one of her beats.

3. chriskoz at 14:37 PM on 12 September, 2016

   Tom Curtis@2

   At around 10^o C above preindustrial temperatures, part of the tropics will become uninhabitable to humans without specific protection...

   You made a typo, that is important to explicitly corrrect here. Should be "around 4^o C" I think.

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4. Tom Curtis at 17:56 PM on 12 September, 2016

   chriskoz @3, Sherwood and Huber (2010) (SkS discussion here) state:

   "Peak heat stress, quantified by the wetbulb temperature T_W , is surprisingly similar across diverse climates today. T_W never exceeds 31 °C. Any exceedence of 35 °C for extended periods should induce hyperthermia in humans and other mammals, as dissipation of metabolic heat becomes impossible. While this never happens now, it would begin to occur with global-mean warming of about 7 °C, calling the habitability of some regions into question. With 11–12 °C warming, such regions would spread to encompass the majority of the human population as currently distributed. Eventual warmings of 12 °C are possible from fossil fuel burning."

   Their estimates of regions effected are based on areas that have at least one five hour period with T_w (wet bulb temperature) equal to or greater than 35 C in a year.  They are slightly pessamistic about the survivability of such temperatures, given that mine workers routinely work 10 hour or longer shifts with T_w up to 32.5 C.  Wet bulb temperatures of 35 C are survivable with no work, no sunlight, plenty of hydration, and cooler conditions after the five hours.  That is, provided you are healthy and acclimatized.  Such temperatures will result in significant death tolls among the elderly, but do not necessarilly render the areas uninhabitable.

   As the extent of such 35plus T_w areas increases, however, the prospect of Tw significantly greater than 35 C, or extending through most of any given 24 hour period increased, and that will render the areas uninhabitable for practical purposes, and certainly by 12 C, large portions of the Earth's surface will be uninhabitable in the summer (or for the tropics, spring and autumn) seasons.  10 C represents a convenient intermediate benchmark to express this idea more simply.  If you want to insist on the 7 C value, however, I will not object - but there is no basis for a claim of uninhabitability at 4 C.

   Note, even at 12 C, a significant part of the Earth will remain inhabitable, and much more of it on a seasonal basis; which by it self is sufficient to refute Coral Davenport's claim. 

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   Moderator Response:

   [JH] Coral Davenport is a journalist for one of the world's most influential newspapers. Therefore, it would be extremely beneficial if you could communicate your concerns to her. The more journalists know about the science of climate change, the better off we will all be. 

5. chriskoz at 18:50 PM on 12 September, 2016

   Tom@4,

   Now I undesrtand that you really mean homo sapiens uninhabitability threshold be 7-12^oC based on Sherwood and Huber (2010). It's higher than I imagined previously & I thought it (erroneously) be a typo. Thanks for your explanation.

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6. John Hartz at 23:38 PM on 12 September, 2016

   Manmade climate change is already directly impacting humans in ways we are just now beginning to understand...

   Blame Global Warming for Your Bad Attixtude by Eric Roston, Bloomberg News, Sep 8, 2016

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7. One Planet Only Forever at 01:00 AM on 13 September, 2016

   Tom,

   A scientific assessment of the regional temperature change that "human beings" could live with is, like all such science, just the evaluation of a bit of the whole.

   Human survivability is actually only able to be properly assessed on the whole, not by a bit. That means that the survivability of the robust diversity of life which human beings are only a part of needs to be understood.

   That is a much more complex matter to figure out. It would seem likely to only be well understood when it becomes apparant that the warming was too much too fast, when it is too late to practically mitigate the created and unavoidably obvious damage done.

   It would seem that the practical sustainability of human life as a sustainable part of the robust diversity of all life far into the future on this amazing planet could be challenged by a significantly lower amount of temperature change than the change that 'Human Beings evaluated in isolation of other life' could tolerate. And any created challenge for future generations deserves to be acknowedged as a fundamentally unacceptable thing for a previous generation to do to a future generation (it is fundamantally unjust to consider the opportunity perceived to be lost by a portion of a current generation to be able to be balanced against the challenges created for future generations - as percieved by those in the current generation who would be giving up their opportunity for more personal benefit).

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8. nigelj at 07:49 AM on 13 September, 2016

   Tom Curtis @ 2 and 4.

   All your points are well made, and seem technically correct to me, and are informative for a non climate scientist like me. I agree it's important people are accurate in descriptions, and avoid hyperbole.

   However you might be falling into your own trap in one regard. You make the valid point that too much concentration on the 2 degree limit and unproven claims that its been breached, gives climate sceptics an excuse to claim its too late to do anything.

   However you then give a description of research that heat stress only becomes a problem at 35 degrees or more at 100% humidity and this requires 7 - 10 degrees of warming. This in turn gives the climate sceptics breathing space, as they would argue we will never hit such large temperature increases!

   I also recall India has just had a massive, record setting, extended and dangerous heatwave with temperatures of 35 - 50 degrees. This may not be at 100% humidity, and as concerning as the definition in the Sherwood research, but its still very stressful. The last IPCC report stated that theres already evidence of increasing heatwaves, so this is already a problem in some regions.

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9. nigelj at 08:07 AM on 13 September, 2016

   One Planet Only @7

   You seem to make the point that too many people are putting their selfish short term concerns and personal benefit above the concerns and rights of future generations. I agree with this, and it’s not a viable long term plan for the planet.

   Part of the reason is just selfishness. However part of the reason may be how we process information. Humans are evolved to be good at processing information on short term risks, but struggle to get to grips with long term risks, especially complicated ones. There is some psychological research on this, and I can't remember where, but probably easily googled. There is thus a temptation to just ignore the long term future as being too hard to contemplate.

   Of course experts and long term thinkers have tried to do the job for us. The Stern report looks at long term issues and costs of climate change and costs of mitigation, and shows that reducing emissions can be done at an affordable cost to society. However the media have suspiciously avoided much discussion of this research, and it is dismissed by climate sceptics with a wave of their imperious hands.  What a surprise.

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10. Tom Curtis at 08:09 AM on 13 September, 2016

    OPOF @7, you need to draw a distinction between conditions under which humans can continue to live as a biological species; and those underwhich we can sustain our current population and civilization.  If, biologically, only a million humans are able to continue ekeing out an existence near the polar caps, reduced to the state of hunter gatherers than Earth is still inhabitable by humans.  Under those conditions, we know it is inhabitable because humans continue to inhabit it.  

    The level of ecological complexity needed to sustain such a life is minimal compared to that which exists today.  All that is required is the existence of some prey animals, and some (perhaps wild) fruits for sustenance.

    You also need to understand the type of robustness found in ecological systems.  It is relatively easy to knock an ecological system out of kilter - to remove a key species so that a large number of other dependent species will also be lost with the result that the surviving system can sustain only a far more limited total number of species, and total biomass.  But the ecosystem as a whole will survive (will predictably survive) the loss of 90% or more of species.  We know that because it has happened at the Permian mass extinction.  More importantly, we know that because the most difficult factor any living thing has to deal with in its environment is other living things.  The range of nearly all plants could be greatly extended were it not for the competition of other plants more suited to particular conditions.  Likewise with animals.  The effect of a mass extinction, consequently, is to remove the most fearsome impediments to survival of the surviving species.  That loss of competition itself allows the survival of species not specifically dependent on particular other species for survival.

    That last condition is most easilly met by generalists - those species not adapted to any particular condition but found across a wide range of conditions across the planet.  Among these, preeminent among large animals are humans.

    So, except for two caveats, humans will survive the coming ecological collapse.  I say the coming collapse because if global warming does not do it (and temperature increases of 4 C may well bring it about), species transfer by trade will; and if not that over fishing will.  The two caveats are that global mean surface temperatures do not rise by more than 10 C, and that we do not spark intense enough wars as a result of the collapse so as to exterminate ourselves.  Even if we do that later, after a few years the Earth will be uninhabited by humans, but still habitable.

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11. Tom Curtis at 08:20 AM on 13 September, 2016

    XKCD has an interesting cartoon on global warming, which is unfortunately too large to place here.  Quote:

    "[After setting your car on fire.]  Listen, you car's temperature has changes before."

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12. Tom Curtis at 08:34 AM on 13 September, 2016

    Moderator inline @4, the only contact information for Coral Davenport that I can find is her twitter account.  As I do not, and will forseeably, have a twitter account that does not help me.  I would be quite happy, however, for somebody else with a twitter account (or other contact details) to advise her of this dicussion.

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    Moderator Response:

    [JH] Try: coral.davenport@nytimes.com

13. Bob Loblaw at 09:07 AM on 13 September, 2016

    For some reason, in Tom's comment 11, the link to the XKCD cartoon has extra junk at the start. This one should work. The cartoon is definitely worth it - thanks, Tom.

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14. One Planet Only Forever at 09:24 AM on 13 September, 2016

    Tom Curtis@11,

    The main point of my comment remains.

    It is unacceptable for a current generation to impose any challenges on future generations. And it is even less than unacceptable for a portion of a current generation to be benefitiing at the expense of others in the current generation as well as at the expense of future genrations. This is a combination of depletion of non-renewable resources and acumulated impacts of human activity.

    Also, the full understanding of the robustness of other life required to sustain human life will likely only become well understood when it is too late to reasonably mitigate the impacts and created challenges. The current generation is already faced with a many bigger challenges to mitigate because of the "lack of restraint and lack of concern for the future" of previous generations.

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    Moderator Response:

    [JH] You could do us a great service by rolling-up your comments into an article for posting on SkS.  

15. chriskoz at 11:17 AM on 13 September, 2016

    It's worth noting that even though habitability of Earth by homo sapiens (as defined by Sherwood and Huber (2010) and promoted by Tom Curtis here) does not change much with even very pessimistic AGW scenarios, the life expectancy of all homo sapiens individuals will be curtailed severely, as Tom himself asserts:

    Such temperatures will result in significant death tolls among the elderly

    I would love to see the life expectancy metric quantified for various RPC scenarios & various regions, because this is far better metric of AGW direct impact on homo sapiens species, rather than Sherwood and Huber (2010) metric. However, I don't know if anyone tries such quantification; I guess there is not enough historical data for the very moderate warming so far and any data is hidden behind the influence of technology and improved hygiene which prolongs life expectancy.

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16. Zoli at 19:26 PM on 13 September, 2016

    @Tom Curtis

    "First, it is not clear that we are past the point where a realistic global emissions policy will prevent an average rise of temperatures above 2o C."

    Why? As I understand we have accumulated GHGs equivalent of 487 ppm CO2 so far. http://www.esrl.noaa.gov/gmd/aggi/aggi.html

    487/280 (pre industrial) =1,74

    So we almost doubled the GHG amount.

    Climate sensitivity estimates are about 2,5-3 Celsius.

    0,74×3 = 2,22

    0,74×2,5 = 1,85

    So we achieved the requirements for 2 Celsius rise. The only question is the time the world needs to accumulate enough heat, melting ice etc.

    There is a chance the climate sensitivity estimates or my simple calculations are wrong of course.

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17. chriskoz at 07:55 AM on 14 September, 2016

    Zoli@16,

    You are wrong in thinking that the "GHGs equivalent of 487 ppm CO2" must stay in the atmosphere while Earth is warming in equilibrium (next 40+ years). The GHGs breakdown:

    

    indicate that some 30% of the GHG forcing is from CH4, which increased since 1750 by about 1ppm. But CH4 has the lifetime of only 10y (the image is wrong in labeling CH4 as "long-lived") after which it oxidises to CO2. The forcing of the resulting 1ppm increase in CO2 is negligible compared to the existing CO2 forcing from 400/280 ppm. All we need to do is stop emitting CH4 and that part of forcing quickly goes to essntially zero.

    Secondly, if CO2 emissions ceased today, it would not stay at 400 ppm forever but would slowly equilibrate with ocean reservoir over the next few decades or so, while the temperature is, hopefully still reaching the equillibrium. Read e.g. Archer 2005 for details. The bottom line is: current CO2 amount of 400ppm is not "locked". Only about 15-25% of the 400/280 in crease (i.e. 30-40ppm) will stay in the atmosphere for 100s thousand y (essentially forever).

    So currently, the amount of "locked CO2" is 310-320 ppm only. Of course realistically, it will be more because of continued emissions and science denial by FF interest groups, but cetainly not yet as high as you claim (487ppm).

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18. Tom Curtis at 10:19 AM on 14 September, 2016

    Zoli @16, I will add a few points to Chriskoz's excellent response.

    First, the estimate of CO2eq concentration you use is for greenhouse gas concentrations only.  It does not incorporate all anthropogenic impacts on Global Mean Surface Temperature.  Once you include the impact of other factors, in particular that of aersols, the CO2 eq emissions as of 2014 (ie, the most recent year for which data is available) was 440.6 ppmv CO2eq.  For comparison, the 2014 value from your linked source was 481 ppmv CO2eq, with a most recent value (2015) of 485 ppmv CO2eq.  I take it your 487 ppmv CO2eq represents an estimate of the additional increase in the half year since the end of 2015.  Similarly estimating the approximate trend increase of for all anthropogenic factors gives 446 ppmv CO2eq, or 1.6 times the preindustrial average (compared to the GHG only estimate of 1.74 times the preindustrial average.  Therefore the GHG only estimate is a substantial overestimate for estimating future climate impacts.

    Second, the IPCC AR5 does not give median or mean estimates of the Equilibrium Climate Sensitivity (ECS).  From the estimates they do give, and a reasonable assumption about the shape of the Probability Density Function (PDF) of the ECS, it is possible to estimate that while the mean value is in the order of 3- 3.4 C, the median value (ie, the value such that we have a 50% chance of an ECS less than that) is in the order of 2.4-2.7 C.  Therefore, based in the IPCC AR5, even at a CO2eq concentration of 600 ppmv, there is a 50/50 chance that we will not exceed a GMST of 2 C.  (Based on mean values of the ECS, we need to keep CO2eq concentrations below 525 ppmv.)

    I consider a 50/50 chance to be a "realistic chance", and also consider it a very realistic possibility that we will limit total CO2 emissions to double the 2014 increase over preindustrial values or less, ie, about 600 ppmv CO2eq.  That by itself is sufficient to justify my claim.

    I should note that this is little comfort to AGW deniers and those wanting a slow reduction in CO2 emissions.  That is because, assuming a linear increase in damages with increase in temperure the relevant value of ECS is not the median, but the mean; and damages are likely to increase more than linearly with increased temperatures.  That is why estimates of the emissions reduction task are based on values which are likely (66.6% probability) to keep GMST below 2 C, where the value minimum value which is likely to achieve that is just slightly higher than the mean estimate.

    Third, based on a current CO2eq concentration of 446 ppmv, and a requirement to stabilize it at no higher than 525 ppmv by 2050, we can increase it by no more than 79 ppmv over 34 years, or in other words to limit the average increase over that period to 2.33 ppmv per annum, and with a current average increase 3.5 ppmv per year (approximately).  If we reduce the increase on a linear basis, by 0.1 ppmv per annum, the average emissions over the 34 years will be about 1.8 ppmv, well below the threshold.  That is clearly a physically, and technically feasible reduction program, although other reduction programs will probably be better.  The reasons for pessimism, and they are reasons for grave pessimism, are entirely political.  Will the leaders of the nations of the Earth have the collective will to pursue an emissions reduction program of that magnitude.

    Finally, these are not my only reasons for my statement.  I think it is more important that the ECS will not be achieved for many years after a stable CO2eq concentration is reached, and that with zero net emissions, the CO2eq concentration will be drawn down by the ocean fairly rapidly up to a limit.  That limit is about 25% of the current CO2 concentration, which will be drawn down much more stably.  That means if net emissions can be reduced to zero (and certainly not more than 5% of current values), CO2eq concentrations will fall rapidly such that by the time ECS is reached, the CO2eq concentration will result in a temperature rise approximately equal to the Transient Climat Response to the peak CO2eq concentration.  That gives us significantly more leeway than calculations based on the ECS allow, as indicated by Chriskoz.  

    Note, again, the decision to drop down to zero net emissions is a political one, and it is far from clear that the politics will result in that decision.  The approach favoured by many economists of putting a social price on CO2eq emissions and then allowing emissions to stabilize where they will will certainly result in ongoing emisisons.  Indeed, it will likely result in ongoing emissions greater than 10% of peak emissions which would mean the eventual stable temperature will be in excess of that estimated from ECS, and would continue slowly rising into the future for as long as net emissions were greater than zero.  However, if sensible policies are pursued, ie, any policy that secures measured reductions in global emissions, achieving net zero emissions by 2050, or net negative emissions at a slightly later date has a good chance of keeping GMST below 2 C (except in El Nino years), and a reasonable chance of keeping it below 1.5 C above preindustrial levels.

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19. chriskoz at 13:09 PM on 14 September, 2016

    Interesting what's going on with nuclear in Alabama:

    For sale: Multibillion-dollar, non-working nuclear power plant

    I'm posting it here because there were discussions about advantages of nuke over renewables. Now the renewable ulitily company is placing a bid on this nuke site were $6b have been completely wasted.

    I'm not going to argue about advantages of renewables over nuke, but I note that this 647ha site was meant to be generating 1.2GW of nuke power. If you covered such are with PV panels (this is what the prospective renewables buyer is likely to do) in the range of 10% efficiency, which is ~200W/m², you will get 647,000,000*200W = 1.3GW of peak power. The same capacity as the ill-fated nuke, surely at the small fraction of the investment cost ($50m) and essentially free running to some 20y.

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20. Tom Curtis at 13:54 PM on 14 September, 2016

    chriskoz @17, CDIAC (or TJBlassing, at least) gives an exponential time constant for CH4 of 12.4 years, meaning it will take about sixty years for CH4 to drop to natural concentrations, following the cessation of all anthropogenic emissions (and ignoring changes in 'natural' emissions as a result of feedbacks on changes in temperature and/or precipitation).  Just saying that it has a lifetime of 12.4 years (or 10 years) may mislead some into believing essentially all CH4 will be gone in about a decade, which is false.

    Further, when you use CO2eq, particularly when using all anthropogenic forcings, aerosols also have a low exponential time constant so that the rapid fall in CO2eq concentration will be, at least roughly, balanced by a rise in CO2eq concentration due to the reduction in aerosol concentrations.  That is not relevant in discussing Zoli's figure which is based on greenhouse gases only, but it is relevant when discussing the more appopriate European Environment Agency figure I discuss above.  The initial relatively rapid fall in CO2 concentration, given zero net anthropogenic emissions still quickly reduces the CO2eq concentration in that scenario, and sustains your very important point.

    As a side note, "long lived greenhouse gases" by convention are any greenhouse gas which does not condense out of the atmosphere, ie, any greenhouse gas other than H2O, which has an exponential time constant measured in hours.

    r @19, peak generation capacity is probably not the best measure given that mean generation capacity of solar is significantly less than nuclear, and that even peak generation capacity requires cloud and haze free skies on only a few days in the year, and then only around noon.  More typically, daily peaks will be 10% or more less than that, and will represent a minority of the days output.  Fossil fuel and nuclear power unquestionably require less space than renewables for a given generation capacity.  Your example, however, certainly provides andecdotal evidence that economically solar trumps nuclear. 

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21. scaddenp at 14:21 PM on 14 September, 2016

    I hectare is 10,000 m2, so I think your area is off by factor 10. Since solar incoming is 1367W/m2, I dont your solar panel is going to give you 200W/m2. NREL puts Alabama available solar input at 5kWh/m2/d

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22. chriskoz at 16:15 PM on 14 September, 2016

    Tom@20,

    Thanks for your clarifications to what I agree.

    Your posts always have very precise meaning, allowing easy and clear discussion, a benchmark of quality blog commenting.

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23. chriskoz at 18:50 PM on 14 September, 2016

    scaddenp@21,

    A typo crept into my comment@19.

    I ment to show, that if you could have PVs that collect 200W peak power per m² in AL, and jam-pack that site with such PVs, then your peak power output from that site would be (647ha = 6,470,000m²) * 200W = 1.3GW.

    Obviously I see now, that 200W peak power is incorrect and not correct metric. With the more reasonable metric you pointed out (5kWh/m2/day) we and up with average insolation of just 200W over 24h. With 10% PV efficiency, the energy yield would then be 0.13GW averaged over 24h - 10 times less than planned nuke yield. Needless to say the yield would be intermittent, unlike nuke. With the best available commercial PVs  approaching now 20%, the yield would still be five times less than nuke.

    However I did not underestimate the cost of jam-packing that site with PVs. The latest estimate of PV cost is at $0.3 per 1W capacity.

    

    So I the total cost of such project is $0.13Giga*0.30 = $39m

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24. Zoli at 00:51 AM on 15 September, 2016

    @chriskoz

    @Tom Curtis

    Thank you. So climate change isn't that big issue as I thought.

    And IPCC authors are alarmists because they didn't count the quick CO2 drop.

    [img]http://i67.tinypic.com/vddces.jpg[/img]

    Long term changes, page 1104

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25. Tom Curtis at 02:22 AM on 15 September, 2016

    Zoli @24, I don't know how big an issue you thought it to be, but AGW is one of the biggest, indeed probably the biggest policy issue facing humans today.  That is because, while there is a reasonable chance of a soft landing* (climate sensitivity in the lower half of the probability range, damages at a given temperature in the lower half of expected range, rapid reduction in net global emisisons), there is a significant risk of absolutely catastrophic outcomes (climate sensitivity in the upper half of the PDF, damages in the upper half, and very limited reductions in net emissions).  Thinking that the former makes AGW a non-issue is like thinking that Russian Roullette is safe because there is a five in six chance that you will not blow your brains out.

    Second, the IPCC is fully aware of all the factors discussed here.  The image you provide an URL for shows the outcomes of specified scenarios with prescribed emissions history, and concentrations calculated from those emissions history using carbon cycle models that take into account all the factors we discuss.  Most of those scenarios do not achieve net zero emissions in this century, and hence show ongoing temperature increases. Remember, for CO2 concentrations to be drawn down naturally, CO2 emisions have to fall to less than 10% of their peak values - something that does not even occur in RCP 2.6 until late in the century, and not at all in the other scenarios this century.  So, no.  The IPCC are not "alarmists".  Rather they are realistic and well informed.

    

    (* Note:  Even a soft landing will involve many individual climate caused catastrophes - just not a global catastrophe. 

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