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Climate Confusion

Posted on 27 June 2022 by Evan

Climate Confusion

I periodically see the phrase, "when we reach net-zero emissions," as though it's a foregone conclusion. It is not. What if the best we can do over the next 100 years is no better than stabilizing CO2 concentration. What then?

Current climate models indicate that future warming is a function only of future emissions, and not current atmospheric CO2 concentration (read here). However, if CO2 stabilization is the best we can do, then the minimum warming we will experience is defined by current CO2 concentrations. These two views are compatible, because to stabilize CO2 concentration at current levels and hold it there over the next 100 year requires some level of continuing emissions. CO2 stabilization therefore implies some level of future emissions that would be unavoidable. A world where the best we do is to stabilize CO2 has, for all intents and purposes, "warming in the pipeline", something that does not occur if and when we reach net-zero emissions.

Some people seem so confident that we will achieve net-zero emissions that they no longer consider current CO2 concentrations to represent a minimum commitment temperature. This is dangerous. Considering that as of 2022 CO2 is still accelerating upwards, it is prudent to consider what happens if the best we can do is CO2 stabilization.

Here is the specific event that prompted me to write this piece.

I recently used Fig. 1 in one of my posts. The top curve shows the expected warming corresponding to measured atmospheric CO2 concentrations for an Equilibrium Climate Sensitivity (ECS) = 3ºC/doubling CO2. The bottom curve shows measured temperature anomalies. The dotted line labeled "Ocean Time Lag" indicates that the oceans delay the warming because of the time required to heat up the top layers of the oceans. This plot shows measured data only: there are no modeling results, other than showing expected warming based on ECS = 3ºC/doubling CO2

Graphs of expected warming for ECS = 3 and another graph showing measured warming up to 2021

Figure 1. Top curve (solid orange points) shows expected warming corresponding to atmospheric CO2 concentration (shown by the open circles) and an ECS of 3ºC/doubling CO2. The bottom curve shows the GISS measured Land-Ocean temperature anomalies (read here).

In response, a reader commented

No... although the ocean lag is plausible and is still often cited, it was questioned a decade ago and is now much in doubt...

I believe the commenter was well intentioned, because they cited a credible source by Zeke Hausfather (read here), but drew the wrong conclusion about what it says about climate science. There are three important physical principles that I would like to emphasize. No modeling study I'm aware of has modified the efficacy of the following.

Principle 1: For given CO2 concentration, there is a corresponding equilibrium temperature that indicates when the Earth is in energy balance.

Principle 2: If the current temperature is lower than the equilibrium temperature, Earth will warm until the two temperatures are equal.

Principle 3: The oceans delay the time to achieve energy balance due to the time required to warm the oceans.

Principle 3 is often embodied as the concept of "warming in the pipeline" associated with the time to warm the oceans. For ECS = 3ºC/doubling CO2, the relationship between atmospheric CO2 concentration and equilibrium temperature, ΔTeq, is ΔTeq=3log(CO2/280)/log(2). Table 1 summarizes some typical values of ΔTeq vs CO2.

Table 1. ΔTeq vs CO2 concentration, rounded to the nearest 0.1ºC.

CO2 [ppm] ΔTeq [ºC]
350 1.0
400 1.5
445 2.0
500 2.5
560 3.0

Figure 2 shows one way to visualize these three physical principles. According to recent climate models (read here), if and when we achieve, and indefinitely maintain, net-zero emissions, the situation is straightforward: atmospheric temperatures stabilize at that point and there is no significant change in temperatures for centuries. The more complicated situation occurs if we do not achieve net-zero emissions, but that the best we do is to stabilize CO2 at some level. Even though stabilizing CO2 at current levels is "easier" than achieving net-zero emissions, stabilizing CO2 is itself very difficult. By writing about these two pathways, I am not implying anything about the likelihood that either will be achieved.

Figure 2 shows the hypothetical situation where CO2 is stabilized at 2022 levels for about 100 years. To stabilize CO2 concentrations, Hausfather indicates that GHG emissions must initially drop about 70%. To maintain stable CO2 concentrations, GHG emissions must decrease to 0 over about 100 years and then remain at net-zero thereafter. Indefinitely. The exact profile by which emissions must decrease to maintain stable CO2 concentrations is complicated and not important for this discussion. What matters is that if our emissions over the next 100 years result in stable CO2 concentrations, then for all intents and purposes, there is "warming in the pipeline" of a magnitude represented by the difference between the equilibrium and current temperatures. Think of this temperature difference as a spring, pulling the current temperature up to the equilibrium temperature.

Warming in the pipeline due to difference between equilibrium and committed temperature anomalies

Figure 2. Temperature trajectory assuming atmospheric CO2 stabilization near 2022. To achieve this trajectory, CO2 emissions must first drop about 70% and then continually decrease until they reach net-zero emissions about 100 years later. About 100 years are required for the temperature to stabilize because of the time required to warm the oceans.

Dangerous Confusion

The problem is that many people, including, I believe, the commenter to my post, believe so strongly that we will achieve net-zero emissions, that any talk about levels of "warming in the pipeline" due to current atmospheric CO2 levels is old science and incorrect. The path where future emissions allow us to cap warming at current temperatures is very difficult. Although we can talk boldly about what future we will "choose", this is not like choosing what clothes to wear or what to have for dinner. A much more likely emissions pathway is one where current equilibrium temperature anomalies represent minimum, committed temperatures.

The pragmatic point is this. As long as CO2 concentrations are increasing, by any amount, for all intents and purposes, there is warming in the pipeline. Even if we manage to stabilize CO2 at some level, there will still be warming in the pipeline for at least 100 years. And to maintain that level of CO2 indefinitely, we will have to reach net-zero emissions at the end of that 100-year period.

If we do not achieve net-zero emissions, there will always effectively be "warming in the pipeline", delayed by the time required to warm the oceans.

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Comments 1 to 18:

  1. Confusion over "warming in the pipeline" reminds me a bit of the general  confusion over the so-called "hiatus" observed in certain temperature records during whenever-to-whenever (1998-...?) any particular study showed a deceleration or halt of temperature rise.

    There was never and could never be a "hiatus" in overall planetary warming short of a vast and mysterious disappearance of various GHG species, or some other impossibility. What appeared to be a slowdown or stall in warming to the extent this showed up in our metrics was (had to be) simply lack of perception on our part, incomplete instrumentation. There was no implausible change in radiative balance, sudden (and oddly unobserved) global albedo change or any other physical means of actually reducing the amount of energy accumulating on the planet. The energy was simply going where certain means of measurement couldn't see it. 

    But "hiatus" means a specific thing in the minds of most people, an actual pause in action. 

    "Warming in the pipeline" and "hiatus" are both examples of hastily conceived, poor terminology, sharing the feature of being mental pitfalls for information consumers of the normal, average variety. 

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  2. Doug, do you have a suggestion for better terminology that reflects the warming delay due to the difference between the current and equilibrium temperature anomalies?

    I like the mental concept of "warming in the pipeline" from a pragmatic viewpoint. If atmospheric CO2 concentrtions are increasing, then there is additional warming to come. If CO2 concentrations are stable or decreasing, but there is a difference between the upper and lower curves in Fig. 2, then there is also "warming in the pipeline.: This is consistent with the statement that future warming is due to future emissions, because if CO2 concentrations are increasing it implies continued emissions. But whereas the average person cannot easily get a handle on global GHG emissions, they can readily follow what the Keeling Curve is doing. So even if the phrase "warming in the pipeline" is flawed from a purely scientific viewpoint that says that all future warming is due to future GHG emissions, I find the concept of "warming in the pipeline" appealing from a purely pragmatic viewpoint.

    From Fig. 2, if and when we manage to achieve net-zero emissions, then the upper curve will come down towards the lower curve, the springs will relax, and the amount of "warming in the pipeline" will also decrease. But as long as these two curves are separated, there is effectively "warming in the pipeline".

    But I am open to a better way to phrase this. Comments?

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  3. I don't know the graphs above are meant to be or if I am reading them right. But..

    The ocean time lag is 30 yrs?

    The current temperature anomaly is 1.2C?

    The current CO2 concentration is 420ppm?

    30 yrs ago the CO2 concentration was 350ppm?

    pre industrial CO2 concentration was 280ppm?

    So 350-280 is a 70ppm rise has resulted in a 1.2C increase in temperature?

    420-350 is also a 70ppm rise so what temperature anomaly are we expecting in 2050?

    Is the ECS of 3C for 280ppm rise overly optimistic?

    I know I am being extremely simplistic here, but?

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  4. From the article, "EMISSIONS 29 April 2021 15:00
    Explainer: Will global warming 'stop' as soon as net-zero emissions are reached?.   
    "To stop these impacts may require reducing global temperatures through net-negative global emissions, not just stopping temperature from rising by reaching net-zero."
    Negative net-zero seems intuitive to me and necessary as a goal to promote, rather than "net zero." It's a wicked problem and negative net-zero may sprout its own wicked problems; we'll never know.
    I'm stumped.

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  5. wayne@3, thanks for your comments.

    The ocean time lag is a complicated function of the difference between the Equilibrium and Current temperature anomalies. Currently it is about 30 years for the current, specific CO2 profile, but this could change in the future. Currently temperature is increasing about 0.2C/decade, but hopefully this will decrease if and when we begin to aggressively cut GHG emissions.

    An ECS of 3C is a reasonable estimate, and is about midway between the range of low and high estimates used by the IPCC.

    EddieEvans@4, it's easy to write about the need for net-zero or net-negative emissions. Realizing them is quite another matter. The reason I focus on showing the CO2-stabilization scenario depicted in Fig. 2 is that by definition, we must achieve this much "easier" goal before we can ever hope to achieve the more ambitious net-zero or net-negative goals. So think of Fig. 2 as kind of a necessary first goal, first step. Just doing what Fig. 2 depicts would already be a huge success and would be a necessary precursor to more ambitious action.

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  6. There is the idea that a sudden end to CO2 emissions will result in the reduced forcing from continued CO2 draw-down balancing the pipe-line warming such that there is no extra warming beyond the end of emissions. As a theoretical exercise it is roughly correct but there is more to AGW than CO2 and a worldwide end to CO2 emissions (tomorrow morning, 0930 hrs GMT - set your watches) is but theoretical. But there it is, and folk do check it is a valid interpretation of what would happen (as per the lt blue trace below - graphic from this CarbonBrief item).

    CarbonBrief warming after zero CO2 graph

    But realistic zero-CO2 scenarios will not react like this. The IPCC AR6 SPM shows temperature peaking under SSP1-1.9 before zero CO2 is reached in 2050. And note its Fig10 which attempts to set AGW ΔT as a function of cumulative CO2 emissions. If you scale that graph, you'll find +1.5ºC equals to 2,960Gt(CO2). Note this is Gt(CO2) not Gt(C). And as of today June 2022 we have managed 2,510Gt(CO2).

    IPCC AR6 SPM fig 10

    But what is less well known is that post-2050 the SSP1-1.9 scenario expects negative emissions which according to the graphs in Meinshausen et al (2020) total 1,100Gt(CO2). That means we maintain the +1.5ºC (or a statistical chance of maintaining it) by extracting and storing out of harms way all our emissions from now to zero-CO2 as well as all the emissions back to 2008.

    That's quite a task to prevent pipeline warming from messing up the +1.5ºC limit. And the SSP1-1.9 scenario also shows (as does any logical analysis of what the 2,960Gt(CO2) budget implies) global CO2 emissions halving by 2030. And 2030 is not now very far away.

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  7. Love the balance acknowledgements. I dont hear this much yet it covers all of nature. By nature I extend to include the universe. Balance to me is like gravity. It is everywhere and will drop the apple on your head for lunch or speed you to demise when you step off the ledge. Orbits, plantlife, rivers and mineral cycles; even the milky way is in a 350M year orbit around our galaxy group. Balance. Co2 is a close brother of oxygen, and even though we draw up old reserves of that goo, Ox too is captured in the limestone and will require storms and erosion to bring it back up. Ox is in a steady decline for a M years in another cycle. I am watching for Co2 to balance with the 20% increase in foliage (Nasa) since 2000, 5% each last couple years, and the evaporation and cooling and added clouds and albedo this brings. Until once again there is balance, as this author references. There are millions of cycles interacting and the only constant is change and a desire to balance, without regard to one species or intent (see apple and falling above). Earth balanced after the big one (which sequestered the co2 and ox in the calcium and carbon slew), back from 4k ppm co2. If we consider balance, then warmer and erosion and trusting gravity and balance could mean the bigger picture just has us hubristically interjecting ourselves in to something, well, that might be needed later. Involving ourselves in something, not past our understanding, but past our paygrade. Interjections we are too important to get understanding just from an apple or acknowledging we know truly little, and that we can and will fall when we go past the edge.

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  8. Regarding the ideas of getting to 'net zero' and going beyond this perhaps getting back to pre industrial levels of CO2. There is a school of thought and some science that says atmospheric concentrations of CO2 are already high enough to stop or limit another ice age, so would it actually make sense to suck too much CO2 out of the atmosphere?

    That said, obviously we need to cut emissions fast and at least reach net zero.

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  9. Nigelj,

    The last time CO2 was this high the sea level was over 20 meters higher.  Most major cities are located at sea ports.  If the level of CO2 was reduced the final sea level will be lower.  

    I am skeptical that large amounts of CO2 can be removed from the atmosphere.  Who will pay for it?

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  10. nigelj@8, interesting thoughts.

    From what I understand, the ice anchors ocean and atmospheric currents. We might avoid the next ice age, and completely mess up the currents that sustain life by thinning the ice too much.

    Could humans ever hope to "adjust" the level of CO2 for a particular purpose, such as preventing the next ice age? Although I have no data nor science to back me up, I am sure that the best we can do to stabilize the atmosphere will leave us without any looming ice ages, but will leave us with whacky weather.

    The reason I wrote this piece is that I continually here this kind of talk about "how far we should go with NET technology," as though we will have the ability to deploy it at any arbitrary scale. I don't mean this in response to what you're writing Nigel, but to me this represents just one thing.


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  11. It may be possible to scale carbon capture and storage up enough to reverse the trend of GMST, but it will surely require a lot of energy. It would hardly make sense to power CCS with fossil fuels, nor to build dedicated renewable or nuclear energy capacity for CCS when fossil carbon is still being burned elsewhere.  At best, CCS must wait until the global carbon-neutral economy is built out.

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  12. nigelj,

    You have brought up a great example of "discourse of climate delay or denial" (refer to "Skeptical Science tackles 'discourses of climate delay' and 'solutions denial'")

    The focus on a small part of the big picture can look appealing as a justification for delaying doing, or deny the need to do, what is understandably required to limit the harm done to future generations of humanity. And limiting the harm done is the first step in 'developing sustainable mprovements' (harmful developments can appear to be helpful, as long as the focus is only on the 'good looking bits').

    The following Carbon Brief item from 2016, "Human emissions will delay next ice age by 50,000 years, study says", indicates that without the damaging human climate change impacts the next ice age would have been expected in about 50,000 years. It indicates that the current rapid increase of CO2 has created a long lasting condition that would 'delay' the ice age onset by an additional 50,000 years. Note that the ice age still happens. And this more recent Carbon Brief item, "Explainer: How the rise and fall of CO2 levels influenced the ice ages" provides more details regarding CO2's role in ice ages.

    The current high levels that would delay the ice age by 50,000 more years were not needed to offset the ice ace until 50,000 years from now. Wouldn't it be great to have well known reserves of fossil fuels that are kept buried and accessible until they were really needed? Maybe the entire next ice age could be offset by timely thoughtful use of those fossil fuels.

    In addition to finding and keeping the fossil fuels for that important future use (and 50,000 years is a reasonable amount of time for future humans to figure out how to effectively use the fossil fuels to do that), it is important for current day humans to reverse (clean-up, undo) the current massively harmful excess CO2. Expecting the next generation of humans to figure out how to live with the harm done (or correct things) is callous and irresponsible. There are many harmful results of keeping CO2 levels higher, not just sea level rise mentioned by michael sweet @9 (btw, michael I agree that if the systems of profitability and profit continue to be the governing systems more damage will continue to be done, and not just climate impact harm).

    The following CBC News item "Analysis reveals how climate change is influencing extreme weather" and BBC News item "Japan swelters in worst heatwave ever recorded" are added examples. But there are even more harmful consequences of the current excessive CO2 levels, harms that are irreversible, harms that will not be undone by reducing the current CO2 levels. And those harms are made worse as the CO2 is pushed higher -— even if pushing it higher today could be claimed to delay the next ice age by even longer.

    The best way to deal with high heat conditions is not the actions described in the most recent SkS repost of the Yale Climate Connections item "How to stay cool in hot weather". What would be best is leadership actions that rapidly limit the peak CO2 levels and rapidly bring them down (done in ways that still improve the lives of all those who are not yet living basic decent lives - but not caring if the higher-status harmful living ways get chopped down a few notches). The Joy Riding Party Bus humans who denied the undeniable understanding of how harmful they were being through the past 30 years and want to push CO2 even higher because they don't want their Good Time Harmful Fun ways of living to be limited or scaled back deserve to be severely disappointed (no matter how angry that makes them - like I, as a professional engineer, have had to tell clients they could not get what they wanted, no matter how angry it made them. And my MBA education helps me understand their anger and know what they want and why they want it. But I have maintained my engineering responsibility to Do No Harm rather than be tempted to personally benefit by letting them have what they want and reward me for allowing - and make me to blame if it turns out bad).

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  13. In my comment @12, the following wording probably makes more sense.

    (btw, michael I agree that if the systems of popularity and profit continue to be the governing systems more damage will continue to be done, and not just climate impact harm)

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  14. M Sweet @9

    Thank's for the info. That 20 metres of sea level rise at current CO2 concentrations / warming  is deadly serious although my understanding is it will be gradual over millenia. An ice age will also be serious and gradually emerge over millenia from what I've read. I'm not sure which is worse. Its a bit mind bending. But by then global population might be a lot smaller due to the trend towards smaller families,  and this will help with adaptation to either eventuality.

    I tend to agree sucking huge volumes of CO2 out of the atmosphere will be expensive or impractical. The best shot we have is reducing emissions. I think the whole sequestering carbon idea is just delaying reducing emissions, unfortunately.


    OPOF @12

    "Wouldn't it be great to have well known reserves of fossil fuels that are kept buried and accessible until they were really needed?"

    Yes this would be prudent. Lubricants, plastics, fertilisers, medicines etc.

    "Maybe the entire next ice age could be offset by timely thoughtful use of those fossil fuels."

    I've contemplated that idea myself. Might be a useful idea, but its geoengineering, and would acidify the oceans and would have other downsides and other challenges.

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  15. nigelj,

    I will clarify my point regarding the next ice age being offset. 49,000 years from now humans start using fossil fuels to keep CO2 levels nominally higher to stop the northern hemisphere ice growth.

    Right now humans have to focus on ending the increase of CO2 and focus on rapidly bringing CO2 levels down.

    And ending the production of unnecessary plastic from the fossil fuel resource would leave more for that valuable ice age offsetting.

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  16. This comment was prompted by:

    • michael sweet’s comment @9 “I am skeptical that large amounts of CO2 can be removed from the atmosphere. (because) Who will pay for it?”
    • Mal Adapted’s @11 “At best, CCS must wait until the global carbon-neutral economy is built out.”

    Those are both examples of ‘discourses of climate (action) delay’.

    And examples of the diversity of degree of leadership being harmfully compromised by the popularity and profitability of ‘discourses of climate (action) delay’ include the following two recent reports related to leadership actions to effectively limit the harm of climate change impacts:

    My responses to michael’s and Mal Adapted points include:

    • Who should pay for it? Obviously the people who benefited most from causing the harmful result should “pay the most to clean up the mess and repair the damage done”. This is why I used the analogy of Harmful Party People. Who should clean up and repair the damage done by a Harmful Party Crowd? Similarly, who should clean up litter? Those questions raise the more relevant questions “Why is harmful activity tolerated?” and “Why do people who are aware of the harm being done, the people who have to put up with or try to clear up or repair the damage done, not stop the harmful activity before it is gets too bad?” If the harmful people are the party crowd and they have the power, or ability to threaten and intimidate, to keep others for limiting the Fun They Are Having, then everyone else suffers the consequences and has to try to limit the harm done and try to clean up the mess made and repair the damage done - while the Party Crowd fight for the Freedom to be more harmful.
    • Why is technological development considered to be the only possible way to reduce Carbon levels? Indeed, in addition to significant reduction of energy consumption by humans, the remaining essential energy consumption needs to rapidly become net-zero. But many corrections of what has developed, and new developments that will reduce carbon, do not require any new technology to be developed. Check out Project Drawdown for many examples of non-technical human actions that would significantly drawdown carbon. Many of the ‘solutions’ are changes of regional food production to pre-industrial ways that are more sustainable regional ways of growing food. What needs to happen is ‘un-learning of the belief that technological developments are improvements by default’.
    • Why do people believe in and excuse systems developed by pursuits of Popularity and Profit that are undeniably harmfully compromised by persistent misunderstanding that excuses understandably harmful actions? Many harmful unsustainable systems have develop due to the collective of humanity inadequately limiting pursuits of power and personal benefit. Harmful winners can be expected to create harm through Authoritarian Rule, Dictatorship, Free Market Democracy or any other system that fails to effectively limit their Freedoms of Belief and Action. Any system can be less harmful and more helpful. It just depends on how harmfully compromised the people with the most power in the system become.

    Looking that the BBC and NPR news items with that understanding, the leadership of some of the 27 nations in the EU are more harmfully compromised. But, collectively, they were able to advance the development of helpful policy. The EU appear to be making advances in reducing harmful leadership influence. However, in the USA, the Supreme Court is now harmfully compromised in a potentially long lasting way. The USA leadership of global sustainable development efforts has always been questionable (The belief that Americans did not have to change how they lived, and the related leadership refusal to accept the understanding at the root of the Kyoto Accord that those who benefited most from the harm done so far must lead the rapid correction, even if it reduces their status – and competitive advantage - relative to Others). The USA being able to provide a helpful leadership example appears to be more questionable today than it was a decade ago.

    My closing point relates to Evan’s statement “Although we can talk boldly about what future we will "choose", ...”. That is also a tragically common misleading way of stating what is happening. The current day people are allowing the harmful among them to do more harm to the future generations of humanity. Current leadership is allowing harmful party crowd to make a bigger mess and do more irreparable damage to the ‘only known to be viable home for everyone now and in the future’. Another way to say that is “Although we can talk boldly about how much we will benefit from the harm our actions and inaction will impose on Others and the Future Generations of Humanity ...” (note that saying it that way makes it harder to continue saying anything).

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  17. Evan @ 5

    If we stabilize at 420ppm. At .2C per decade and a 3 decade lag we end up with 1.2 + 0.6 = 1.8C but the change from 280 to 350 resulted in 1.2C so there is still another 0.6C to consider which would bring it to 2.4C. I know its not a linear relationship but I doubt its going to break in our favour. The numbers just dont seem to match up in my mind. Land use is obviously a big factor but that doesnt seem likely to go our way in the near future either

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  18. wayne@17

    Let's separate the time lag from the equilibrium temperature. If we stabilize at a particular CO2 concentration and hold there for a sufficiently long time, the temperature will rise to a level that corresponds to the radiative forcing associated with that particular CO2 concentration. The relationship is something like this.

    • 350 ppm CO2 leads to 1C warming
    • 400 ppm CO2 leads to 1.5C warming
    • 450 ppm CO2 leads to 2C warming
    • 500 ppm CO2 leads to 2.5C warming

    And so on. So if we stabilize CO2 at 420 ppm and hold it there for 100 years, we will eventually warm to about 1.7C. The time lag to get to that temperature depends on a lot of complicated interactions in the biosphere. Under current GHG emissions, there is about a 30 year delay, but that delay could increase or decrease depending on how our emissions change. But in any case, the final warming is linked to the CO2 concentration.

    The reason we would lock in the current temperature anomaly if we were able to achieve net-0 emissions today, is that under net-0 emissions the atmospheric CO2 concentration would slowly decrease to a level that corresponds to the current warming. Considering we are at about 1.2C today, if we achieved net-0 emissions today, and stayed at net-0 emissions for a sufficiently long time, then presumably CO2 concentration would eventually drop to something like 370 ppm, a concentration that corresponds to 1.2C warming.

    Hope that helps, and hope the real climate scientists in the room don't find too much wrong with my description.

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