Reassessing the RCPs

From Judith Curry’s Climate Etc

Posted on January 28, 2019 by curryja |

by Kevin Murphy

A response to: “Is RCP8.5 an impossible scenario?”. This post demonstrates that RCP8.5 is so highly improbable that it should be dismissed from consideration, and thereby draws into question the validity of RCP8.5-based assertions such as those made in the Fourth National Climate Assessment from the U.S. Global Change Research Program.

Analyses of future climate change since the IPCC’s 5th Assessment Report (AR5) have been based on representative concentration pathways (RCPs) that detail how a range of future climate forcings might evolve.

Several years ago, a set of RCPs were requested by the climate modeling research community to span the range of net forcing from 2.6 W/m2 to 8.5 W/m2 (in year 2100 relative to 1750) so that physics within the models could be fully exercised. Four of them were developed and designated as RCP2.6, RCP4.5, RCP6.0 and RCP8.5. They have been used in ongoing research and as the basis for impact analyses and future climate projections.

AR5 does not provide probability assignments for any of the RCPs, and yet many impact assessments utilize RCP8.5 to declare consequences of inaction. For example, while RCP4.5 and RCP8.5 are utilized for the Fourth National Climate Assessment (NCA4), the majority of its assertions are based in RCP8.5. The NCA4 states, “RCP8.5 implies a future with continued high emissions growth, whereas the other RCPs represent different pathways of mitigating emissions.” (Executive Summary, p.7). The reader is left with the impression that, although “high” is not defined, it is the present state of things and RCP8.5 delineates how it will grow higher. Further, the statement portrays the other RCPs as mitigation scenarios that are not being acted upon. Therefore, RCP8.5 has been portrayed as the “business as usual” scenario, and impact assessments continue to spread this falsehood.

This article employs some quantitative analysis and the original RCP documentation to demonstrate how the use of RCP8.5 is misleadingly wrong and a lower, narrower range of future CO2 atmospheric concentrations can be identified.

A Long-Range Forecast Based in the Evidence

The “C” in RCP is for concentration (and not emissions), to emphasize that greenhouse gas (GHG) concentrations are the primary product of the RCPs and inputs to climate models. The Earth’s radiative balance responds to the net result of GHG sources, sinks, and sub-processes as expressed in atmospheric concentration levels. CO2 is by far the dominant GHG contributor and therefore the subject of this analysis.

Long, rigorous ongoing CO2 measurement data sets are available from the South Pole since 1957 and from Mauna Loa since 1958. The values are reported with very small measurement uncertainties, and they reveal a consistent positive trend over the past 60 years with a slightly concave-upward shape. While their annual CO2 values were similar in the late-1950s (at 315 ppm), Mauna Loa data have been increasing slightly more than South Pole data and both now exceed 400 ppm (Fig. 2). Other measurement stations subsequently added to global CO2 monitoring comprise a marine surface data set with values between the South Pole and Mauna Loa series. South Pole and Mauna Loa data are employed for this analysis since they are the longest time series and they bracket other data.

figure-3

Figure 2. History and forecasts of CO2 concentration. RCP8.5 is defined by 936 ppm in 2100.

Increasing CO2 is a long-term substitution process as it transitions to a larger fractional share of atmospheric concentration. If well underway, such a process can be studied utilizing a logistic function as described by J.C. Fisher & R.H. Pry in their landmark forecasting paper, A Simple Substitution Model of Technological Change. The methodology provides a top-down appraisal of an ongoing transition assuming continuity in evolution of its contributing elements into the future. The method has been successfully employed in thousands of long-range forecasting applications across many fields of study. Its form is shown in Figure 1.

Figure 1. Fisher-Pry formulation of a logistic substitution model.

If sufficient historical data is available, the differential equation in Figure 1 can be readily solved through minimization of a rigorously constructed Chi-Square function. A solution reveals the ceiling value, process mid-point and rate constant; and it thereby has predictive power. The early portion of the S-curve is approximately exponential, followed by a transition towards the inflection point at which growth rate peaks, thereafter declining as the cumulative curve approaches its long-term ceiling.

For the case of CO2, the cumulative S-curve rests upon the pre-industrial starting level of 270-280 ppm. The rate of change in CO2 concentration is presently still increasing (Fig. 3), so the inflection point has not been reached; and second-difference calculations show no acceleration, indicating we are beyond the early exponential phase. The current substitution level should therefore lie between 15% and 50%, and this is found to be the case for the solutions shown in Figures 2 & 3.

Figure 3. Rate of change in CO2 concentration. RCP8.5 abruptly deviates from the historical trend.

The logistic CO2 forecasts project South Pole reaching 587 ppm and Mauna Loa reaching 654 ppm in the year 2100 (Fig. 2). The 90% confidence limits are calculated from variance of observations relative to the logistic fit and as a function of substitution level reached (Mauna Loa 24%, South Pole 33%). The result is well-constrained limits, and the slight divergence between data series continues into the future. RCP4.5 and RCP6.0 are similar to the South Pole forecast until mid-century, when RCP4.5 plateaus under mitigation assumptions and RCP6.0 increases towards the Mauna Loa forecast. RCP6.0 eventually reaches a ceiling below the Mauna Loa logistic ceiling. Results are detailed in Table 1 along with the values defining the RCPs.

Table 1. Atmospheric CO2 concentration projections.

Figure 3 displays the rate of change in CO2 concentration for the historical record, the logistic forecasts, and what is required to attain the defined RCP concentrations. The 60 year histories have a consistent upward trend, although with year-to-year variability. The highest transients above the trend are attributable to strong El Niño years (most recently 1998, 2016), which impair global vegetative response forming the seasonal CO2 cycle so that the annual value is temporarily elevated. The logistic rates-of-change are projected to attain their maximums (50% substitution) around 2037-2051 for South Pole and 2060-2080 for Mauna Loa. RCP4.5 and RCP6.0 rates bracket the South Pole forecast until mid-century, with transitions thereafter.

But what is glaringly apparent is the excessive rate-of-change required to attain RCP8.5’s 936 ppm in the year 2100. The rate would have to immediately depart from the historical pattern towards more than double any other forecast or RCP. In fact, since the RCPs were developed several years ago, it should have already transitioned to a very high trend to support an RCP8.5 expectation. This has clearly not occurred, and ongoing measurements show it is not happening. Other mathematical formulations were attempted for 936 ppm, but no logically consistent one was found. Even if it were assumed we remain in the early exponential phase of a substitution process the numbers do not support such a high expectation. RCP8.5 is a mathematically flawed projection for the future and clearly not the “business as usual” case. Rather, something similar to RCP6.0 should be assigned that designation, although with some modifications as to how it will evolve.

Revisiting the Origins of RCP8.5

The RCPs were presented in detail in a set of papers published in Climatic Change in 2011, and are worth reviewing. Recall that there was a desire to perform climate modeling over a wide range of forcing values – to fully exercise them from 2.6 W/m2 to 8.5 W/m2. This is understandable from an exploratory research standpoint, but says nothing about the likelihood of specific future outcomes. But, the papers do shed some light upon that.

RCP8.5 is described by the van Vuuren et al.  The representative concentration pathways: an overview  as a very high emissions scenario required to attain the desired forcing level. “RCP8.5 is a highly energy-intensive scenario as a result of high population growth and a lower rate of technology development.” Figures published in the paper identify where each RCP’s assumptions lie within the literature available at the time they were developed. Those taken for RCP8.5 lie at limits of 90th or 98th percentile bands (1% to 5% probability). The population projection is at the high limit of United Nations scenarios. Its primary energy consumption projection lies at the 99th percentile through most of this century. Energy intensity of the economy (energy/GDP) aligns with the 99th percentile from the literature. Improvement in RCP8.5’s carbon factor (CO2/energy) is minimal and at the 95th percentile, reflecting heavy reliance on fossil fuels. Coal comprises nearly 50% of RCP8.5’s energy mix, something which has not been seen since early in the last century. RCP8.5 has consequently been called a “return to coal” scenario (Why do climate change scenarios return to coal?, ). This is inconsistent with natural long-term sequential evolutions of energy technologies that project a declining share of the energy mix for coal.

It should come as no surprise then that a concatenation of very low probability assumptions yields a highly unlikely CO2 concentration at end-century. This result is given by van Vuuren et al. and shown in Figure 4. The RCP8.5 curve exits the literature envelope. The logistic forecasting exercise above confirms the most likely CO2 level that van Vuuren reported several years ago in the vicinity of 600 ppm in 2100 (Fig. 4). Their graph also serves as guidance for what might constitute a “worst case” CO2 scenario, which could be assessed to be in the range of 700-750 ppm.

Figure 4. Graph from van Vuuren et al. 2011 (Fig.9, p.23), the RCP CO2 concentrations. Gray areas indicate 90th and 98th percentile bands (dark/light gray) of referenced literature. RCP4.5/6.0 is centered; RCP8.5 exceeds the upper limit.

So, since it was documented years ago that RCP8.5’s CO2 concentration has a vanishingly small probability of actually occurring, then why has it been promulgated for impact assessments and to inform climate policy? And why have researchers who realize that a true “business as usual” future lies closer to RCP6.0 found that when they go to the climate model library the RCP6.0 model runs do not exist? Have they been purposefully directed to RCP8.5, or is anything less than RCP8.5 unable to force a hypothesized impact?

Conclusions

The 60-year records of rigorous CO2 concentration measurements provide valuable forecasting information that is highly amenable to logistic growth modeling. It is clear that a substitution process is well underway that can be quantified to provide constraints upon expectations of future concentrations. The consistent concave-upward CO2 trend, rising rate-of-change, and well-bounded variance about the logistic solution provide confidence in the resulting forecasts and rejection of significantly inconsistent projections such as RCP8.5.

CO2 concentrations in 2100 will likely fall in the 565-680 ppm range and well short of 936 ppm indicated by RCP8.5. In preparation for the next IPCC assessment report, RCP8.5 has been redefined at even higher CO2 concentrations [link]. Modifications to inconsistent assumptions in minor-GHGs cause CO2 in the new RCP8.5 to exceed 1000 ppm in 2100 through even more coal consumption to retain 8.5 W/m2 forcing. RCP8.5 requires a CO2 rate of change inconsistent with the observed record that will be worsened by higher concentrations.

The RCP reference literature documents how RCP8.5 was based on low probabilities and questionable assumptions. It is not “business as usual” or even a worst case scenario. Consequently, the findings of any impact assessment based in RCP8.5 should be critically reviewed, as they reflect a highly unlikely, if not impossible, outcome.

The NCA4 (Executive Summary, p.22) states “The observed increase in global carbon emissions over the past 15-20 years has been consistent with higher scenarios (e.g., RCP8.5) (very high confidence).” This statement suggests either dismissal of observational evidence or that carbon budget model calculations from emissions to concentration are unable to replicate the historical CO2 measurement record. As evident in Figure 3, the recent record does not support an RCP8.5 pathway, and the statement is false.

Unfortunately the compulsion towards exaggeration can be stronger than duty to facts, and without them it will be impossible to make progress towards preparing for the future. The RCP6.0 pathway is the scenario coming closest to the forecast presented above and therefore a more realistic expectation of the future, and mitigation actions could evolve it towards RCP4.5.

Acknowledgements. The author thanks his colleague, Theodore Modis (growth-dynamics.com), for conducting the logistic forecast calculations. For those interested, the methodology is well-documented in his book Natural Laws in the Service of the Decision Maker (2013).

61 thoughts on “Reassessing the RCPs

  1. “But what is glaringly apparent is the excessive rate-of-change required to attain RCP8.5’s 936 ppm in the year 2100. The rate would have to immediately depart from the historical pattern towards more than double any other forecast or RCP. In fact, since the RCPs were developed several years ago, it should have already transitioned to a very high trend to support an RCP8.5 expectation. This has clearly not occurred, and ongoing measurements show it is not happening. Other mathematical formulations were attempted for 936 ppm, but no logically consistent one was found.”

    That is the weakness of the silly RCP8.5 claim, since it isn’t showing up at all, not only that even the 6.0 level isn’t being reached either.

    • It appears that CO2 will fall into a small range around 540-640 range by year 2100, but temperature warming rate has not kept up with the models. Thus RCP >4.5/<6.0 range, but temperature below the modeled 4.5 range for temperature warming rate.

      A modeling failure in the making.

    • Why split hairs just put a straight line thru it and it will be somewhere around there and that is where the world is going and every country has accepted that by their actions. It is 80 years off and only a small minority care or buy the scare stories the majority voted.

    • Kym, can you name any study or paper that is using the RCP2.6 scenario?

      On the other hand pretty much every alarmist paper uses the RCP8.5 scenario despite the fact that it has no basis in reality.

    • Kym,
      You are wrong about the “aircraft carrier” accelerating. The article clearly states that the second derivative shows no acceleration in CO2 rates. It is currently at a steady rate heading towards the inflection point, at which time it will start decelerating.

  2. The panicmongers love RCP8.5 because of the scary outcomes. Crying wolf is much less ominous if the probable threat is a coyote at the worst, and is maybe only a chihuahua.

  3. “AR5 does not provide probability assignments for any of the RCPs”
    No, and nor should they. Scenarios describe possible decisions, and CMIP5 shows the outcome of those scenarios. They can’t attach a probability to what we might choose to do. You never know, it might even be influenced by what the CMIP5 modelling shows.

    It may well be right that 6 or 4.5 is a more likely scenario. That doesn’t detract from the value of calculating what would happen with no real restraint.

      • We need restraints where I am. Of the leather and canvas type, with fastening round the back. Applied to those who write the law and have incorporated RCP 8.5 in the law. I actually managed to get it removed in 2012 and it was put back again a year later.

    • Nick, that’s not the point. A highly improbable outcome is being used by the media and less than honorable members of the government and scientific community to promulgate extreme policy responses when they are not warranted. Geeesh.

    • Do you really trust the CMIP5? It is useless to predict any outcome, including the real world.

    • Nick is right. You can’t infer a probability from using statistics with confidence intervals because the statistician chooses the confidence intervals. Amazing how many scientists do not understand statistics.

    • There is a value in calculating what would happen with no real restraint on a really highly suspect forcing model .. only a statistician would say that 🙂

    • Every rational decision is based on the probability of occurrence and the expected outcome. If the different scenarios have different probabilities and different consequences, these must be taken into account. Not reporting them is deceptive.

  4. From the point of view of the plants a so-called “worst case” CO2 scenario, which could be assessed to be in the range of 700-750 ppm. would be highly desireable for the plants’ well being. A return to 280 ppm. would be a disaster. Unfortunately apart from some mushrooms, there are no plants in the IPCC.

  5. CO2 is by far the dominant GHG contributor and therefore the subject of this analysis.

    The only way that statement can be taken as true is if you put on a whole bunch of conditions.

    The dominant greenhouse gas is water vapor. link In the range where the Earth emits IR, water vapor is by far the most important absorber. CO2 absorbs in a band centered around 15 um. It overlaps with water vapor.

    The above link is really good because it shows the spectrum of the downwelling visible light and the upwelling IR as well as the absorption spectra of the main greenhouse gasses.

  6. All this dancing on a pinhead and for what?

    CO2 is essential for life, it matters not that it is 400 or 1000ppmv, as long as it is above 200ppmv.
    Life — all life — on the surface and under oceans of this planet need CO2, it is not toxic, and harms nothing even at 1000ppmv.

    The rate of growth of CO2 has been slow since 1750. Slow! If only we all could burn fossil fuels like China then we might make a small impact on the rate.

    • Totally agree the world voted with it’s actions we are going onward and upward and if it becomes a problem we will have to deal with it and no that won’t be by emission control but real hard science in action.

  7. Missing completely from this paper is any effect. It matters not one iota that CO2 increases in the atmosphere if there is no harmful effect. So let’s go with this analysis and assume for a moment that CO2 actually reaches 670 ppm by the year 2100 – what effect does this have?

    Well, I could start listing all the positive effects it might have, but let’s ignore those for a moment. The theory (or whatever they are calling AGW this year) says it should warm by some amount…how much? The further up the curve you are, the less warming the substitution model predicts. Now we have two unknowns – how much CO2 will be in the air and how far it is on the curve already. Its kind of pointless to keep guessing at this point without more data.

    If its 50% up the curve, then half of the possible heating has already occurred – and so the IPCC estimates can be cut approximately in half assuming they have predicted warming correctly (and they haven’t). I don’t know about you, but 1 to 2 degrees C of warming as averaged other the entire Earth sounds good…more temperate climate overall. More rain is possible. We can adapt to that. Greenland won’t melt, and neither will Antarctica. Who cares if the Arctic ice melts? It doesn’t do anything but allow for more fishing and industry to be built. Good and Good.

    Now this assumes we (humans) will continue to burn fossil fuels, but EVENTUALLY we will wake up and start producing most of our electricity from nuclear fission (NOT fusion which will still be 50 years away). With new technologies that lower power use and new batteries that actually store enough energy per volume, actual green energy sources that work (for say 20% of the total electricity required peak), and a few good-old standby gas-powered electricity power plants, we will just not need to keep growing our fossil fuel use. It’s going to happen in the West in the next 20 to 30 years because it’s efficient and clean and will become cost effective.

    So why does anyone care how much CO2 is in the air? It isn’t hurting anyone, it isn’t going to hurt if we just adapt a little, and the little plants love it! <–(that was an attempt at humor)

    We should dump all of the RPC guess work and actually prove that CO2 is harming us. If someone can provide that proof, I am on board to reduce CO2 emissions. Hand waving, personal attacks, screaming fits, and poorly written pseudo-science papers just don't convince me.

    • Robert of Texas
      Of course the amount of CO2 that stay in the air is highly dependent on what get dissolved in the oceans. At any given time it is at equilibrium for the local ocean temperature and atmospheric pressure.

      CO2 more or less follows Henry’s Law (Henry’s Law: At constant temperature, the amount of gas dissolved in a liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.) to get into the oceans but once there stays a very long while due to the ionization and chemical reactions encountered.

      Colder oceans more CO2 dissolved, warmer oceans less and perhaps some out-gassing.

      • t)m,
        You need care with Henry’s Law calculations. In the lab, the conversion factors are deduced from a fixed volume of solution and air space. In nature, the solution (the oceans) are constantly mixing and exposing new conditions to the calculations as new water at the surface can be diminished or enriched in CO2 relative to the Henry’s Law amounts. Geoff.

        • In nature, the solution (the oceans) are constantly mixing and exposing new conditions to the calculations as new water at the surface can be diminished or enriched in CO2 relative to the Henry’s Law amounts.

          You’re both right. Henry’s Law in action. Atmospheric CO2 mainly results from ocean temperature changes, which inherently includes all the factors Geoff mentioned.

  8. Nick – the point of the article is that 8.5 is inconsistent with observational evidence (see fig. 3). NCA4 states that the evidence is consistent with the higher scenarios, which is wrong.

    • “the point of the article is that 8.5 is inconsistent with observational evidence (see fig. 3”
      Well, Fig 3 doesn’t show that. Firstly, it is showing rates of change, not levels. The levels are the integral of that, and diverge much more gradually.

      But more significantly, Fig 3 shows the divergence of scenarios only after about 2015. So there is nothing that could be said to be inconsistent with observational evidence. The difference between scenarios on that basis is not observable. Actually, I’m not sure who made Fig 3, and I think they may have the dates wrong. But that is what it says.

  9. Therefore, RCP8.5 has been portrayed as the “business as usual” scenario, and impact assessments continue to spread this falsehood.”
    RCP8.5 was utterly intended to be used as a scare story, to go to the furthermost limits of possible scenarios in order to create alarmism stories far and wide in the sciences.

    Everyone gets in on the climate scam. Everyone from glaciologists to biologists can to use BAU RCP8.5, because the IPCC labeled as the BAU scenario, even though extremely implausible. To then allowed researchers far outside of climate studies to juice-up the impact of their findings for publishing success and grants success. The more non-climate scientists who participate in the hustle with their own work, the more vested interests the climate hustlers will have to silence dissent within the university science departments.

  10. The rate of increase of CO2 in the atmosphere has been nearly constant since 1990 while the rate of our emissions tripled in about 2002 then plateaued in 2012. Atmospheric CO2 is not responsive to human emissions (https://tambonthongchai.com/2018/12/19/co2responsiveness/). Not only is the temperature not controlled by CO2, CO2 is not controlled by humans. The whole effort of estimating RCPs to feed to the models to guess at the future so we can cut back on our gas consumption is so much meaningless hand waving. Unfortunately nearly no one is willing to investigate this relationship rather than discuss the legitimacy of the RCP scenarios in the prediction of future temps. Human emissions are lost in the noise of the huge natural flows. Reductions of emissions cannot be detected in the evolution of the atmospheric content.

    • In the Antarctic ice cores CO2 concentration is correlated with temperature. But CO2 concentration lags temperature by about 800 years.
      800 years ago was the Medieval Warm Period.
      QED current CO2 concentration changes must be dominated by anthropogenic emissions… That’s so obvious the IPCC doesn’t even need to explain how they know that.

      • Sorry, M Courtney, but your QED and “so obvious” claims are unfounded because you have failed to eliminate (rationally) every other possible cause that might explain the rapid rise of CO2 as compared to the ice-core lead/lag relationship with global temperature.

        For example, disprove the conjecture that atmospheric CO2 levels have increased significantly in the last 200 years due to primarily to an increase in CO2 venting from ocean-floor rifts and hydrothermal vents. I think you will have difficulty doing such due to lack of objective scientific data on the amount of such venting prior to, oh, about 30 years ago.

        According to Wikipedia, “white smokers . . . form . . . carbonate deposits” and “White smokers emitting liquid rich in barium, calcium, silicon and carbon dioxide at the Champagne vent, Northwest Eifuku volcano, Marianas Trench Marine National Monument.” (photo caption)

        • As important as it may be to learn the cause of the recent rise in atmospheric CO2 it is not necessary for the conclusion that it wasn’t fossil fuel combustion. The work of Salby, Harde and others shows this to be factual but it is not known to the consensus crew or ignored based on Kohler’s lame review. This whole charade of attempting to control the climate is based on the assumptions that CO2 can control it and all the new CO2 is human generated. When will the science community seriously review these works and definitively show them as erroneous or take them into account in future scientific work? If Salby is right, none of billions spent on controlling our emissions had any effect or value. All of the science accepting the premise that we are causing warming must find its value in the science alone not in any support for policy making.

  11. Unlimited CO2 concentration is impossible as at some point geologically oolitic carbonate will spontaneously precipitate in shallow ocean shelves again as it has in the past and currently does today in three places, one in Qatar, another is Bahia Lagoon, Baja, and a third I don’t remember off hand.

  12. The NCA4 (Executive Summary, p.22) states “The observed increase in global carbon emissions over the past 15-20 years has been consistent with higher scenarios (e.g., RCP8.5) (very high confidence).”

    The authors of NCA4 most assuredly know that RCP8.5, created in 2011 in preparation for IPCC AR5, was not consistent with any realistic emission scenario by 2018.
    It’s not even a good deception it is so demonstrably wrong (as shown here by Kevin Murphy (and many others through the years)). Claiming is consistent with the past is itself a deception, since RCP8.5 stupidity all lies in the future decades. Using RCP8.5 is just an outright lie from the NCA4 authors. A lie made by some of the supposedly most respected climate scientists in the US. Apparently they’ll do anything, including sell their integrity, for a grant.

    So with that statement (in italics above) that they all signed to by putting their names to the NCA4 report, they themselves are nothing but liars. Everyone of them, IMO.

    My list of unethical Science liars on NCA4 Volume 1:
    Science Liar #1: Donald J. Wuebbles, National Science Foundation and U.S. Administration Global Change Research Program, University of Illinois
    Science Liar #2: David J. Dokken, U.S. Global Change Research Program –
    Science Liar #3: Thomas K. Maycock, Cooperative Institute for Climate ICF and Satellites – North Carolina
    Science Liar #4: David W. Fahey, National Oceanic and Atmospheric
    Science Liar #5: Brooke C. Stewart, Cooperative Institute for Climate and Administration Satellites – North Carolina
    Science Liar #6: Kathy A. Hibbard, National Aeronautics and Space
    Science Liar #7: Dorothy Koch, Department of Energy
    Science Liar #8: Russell S. Vose, National Oceanic and Atmospheric Administration
    Science Liar #9: Benjamin DeAngelo, National Oceanic and Atmospheric
    Science Liar #10: Jack Kaye, National Aeronautics and Space Administration Administration
    Science Liar #11: Wayne Higgins, Department of Commerce

    The NCA4 report with their names on it will be a case study in failed scientific integrity one day. Let the authors know that now.

  13. CO2 is by far the dominant GHG contributor and therefore the subject of this analysis

    Is that a fact? What about water vapour?

    • When you push that point on the Alarmist climateers, they fallback and claim they are only talking about non-condensing GHG’s. Of course water vapor is a condensing GHG. They use that line knowing 99% of the science-illiterate population does not realize water vapor is the dominant GHG in climate.

  14. The latest IPCC report states that RCP8.5 is broadly comparable to the previous SRES A2/A1FI scenario and that ‘storyline’ from AR3 was summarised as ‘a future world of very rapid fossil fuel intensive economic growth global population that peaks in mid-century declines thereafter’ and that sounds like business as usual to me.
    There are two relevant variables, the atmospheric CO2 concentration and the global average temperature.
    The IPCC scenarios and ‘storylines’ are a load of bureaucratese gobbledygook indented to discombobulate the uninitiated.
    IPCC bureaucrats are trying to sidle away from their previous dire predictions as they fail to materialise, despite the best efforts of activist temperature ‘adjusters’.

  15. The best fit equation for net CO2 = 0.013 t^2 + 0.518 t + 310.44 where t = no. of years since 1950. Solving the equation for CO2 = 560 which is a doubling of the CO2 in the air since the year 1750 gives t = 120. That is 1950 + 120 = the year 2070. That is still 51 years away. Since most studies put the climate sensitivity to less than 1C, what in the hell are we worried about?

    • After looking at Kevin Murphy’s graph it seems that RCP6 does indeed match the quadratic equation above almost exactly.

  16. This would appear to be a very optimisitic article. As I understand it RCP 8.5 is false because humans will develope substitutes for fossil fuels and therefore CO2 levels will stop increasing and level off. I don’t actually know how the author makes the claim that CO2 levels will start decreasing using a logistic model since in such a model CO2 levels are monotonically increasing.

  17. Regardless of emissions levels, predicting future CO2 concentration is effectively a work of fiction if they don’t even try to accurately model ocean absorption.

  18. t)m,
    You need care with Henry’s Law calculations. In the lab, the conversion factors are deduced from a fixed volume of solution and air space. In nature, the solution (the oceans) are constantly mixing and exposing new conditions to the calculations as new water at the surface can be diminished or enriched in CO2 relative to the Henry’s Law amounts. Geoff.

  19. The fallacy in RCP 8.5, as described in the post, is in taking say 95th centile positions in several input variables. What you get from that is not a 95th centile scenario, but a vanishingly unlikely scenario. You are basically saying ‘This goes bad, and this goes bad, and this goes bad, and this goes bad…’ If ‘bad’ is a 5% scenario, then the composition of four is a 10^-5 scenario if everything is uncorrelated, and perhaps more with some correlation. But essentially not something even a prudent man has good reason to fear.

  20. Fit’s Stephen Schneider’s ‘make up scary scenarios to grab public attention’ description.

  21. To the author: “The highest transients above the trend are attributable to strong El Niño years (most recently 1998, 2016), which impair global vegetative response forming the seasonal CO2 cycle so that the annual value is temporarily elevated.” This is at best an assumption with no reliable data. The balance between uptake of CO2 and increased decomposition as a function of temperature is not known at this time. It is also an order of magnitude greater than human-caused CO2 production. Have you looked at the outgassing of CO2 from the ocean during an El Nino? Perhaps the new CO2 satellite can measure this during our next large El-Nino or La Nina.

    • Please look at my link posted directly above. It shows observational evidence that step-like changes in sea-surface temperature anomalies (on inter-annual to decadal timescales) that indicate that ocean outgassing may play a role.

  22. As I have been asking for a long time: after 31+ years of research and observation, why are the range of scenarios not narrower?

    There should be only one or two variables still needing to be nailed down under “setyled science”. pCO2 obviously is an emergent figure but limited in range and NOT going down in the 80 year range. So the range of scenarios should be small.

    Bizarre.

  23. Figure 2 and Figure 3 are duplicates for rate of change. Figure 2 should be concentration. Figure 1 after Figure 2?

  24. Do we have so much carbon at all?
    One ppm(v) CO2 equals 7.5GT, that again equals 2Gt pure carbon.
    It means that 1900ppm(v)-400ppm(v) should mean burning of 1500*2Gt = 3000Gt pure carbon.
    And so far only half the amount burnt seems to stay in the air, we need to burn 6000Gt of pure carbon.
    Do we have so much available?

    • I found a figure of known coal reserves in the amount of 1000Gt. Coal alone can not do it, and the other fossil fuels are less and has a lower carbon content, so it looks difficult to raise the CO2 contend to more that 1000ppm.

  25. Its only the “Western”countries which appear to believe in Fairy Tales”. It will make no difference to the other countries, who according to the likes of the Paris conference are just catching up, and who all are still waiting for the “Promised” money from the Western countries, for all the wrong” that we of the West have done to them over the years. .

    MJE

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