Arguments
Talk to someone who rejects the conclusions of climate science and you’ll likely hear some variation of the following: “That’s all based on models, and you can make a model say anything you want.” Often, they'll suggest the models don't even have a solid foundation of data to work with—garbage in, garbage out, as the old programming adage goes. But how many of us (anywhere on the opinion spectrum) really know enough about what goes into a climate model to judge what comes out?
Climate models are used to generate projections showing the consequences of various courses of action, so they are relevant to discussions about public policy. Of course, being relevant to public policy also makes a thing vulnerable to the indiscriminate cannons on the foul battlefield of politics.
Skepticism is certainly not an unreasonable response when first exposed to the concept of a climate model. But skepticism means examining the evidence before making up one’s mind. If anyone has scrutinized the workings of climate models, it’s climate scientists—and they are confident that, just as in other fields, their models are useful scientific tools.
It’s a model, just not the fierce kind
Climate models are, at heart, giant bundles of equations—mathematical representations of everything we’ve learned about the climate system. Equations for the physics of absorbing energy from the Sun’s radiation. Equations for atmospheric and oceanic circulation. Equations for chemical cycles. Equations for the growth of vegetation. Some of these equations are simple physical laws, but some are empirical approximations of processes that occur at a scale too small to be simulated directly.
Cloud droplets, for example, might be a couple hundredths of a millimeter in diameter, while the smallest grid cells that are considered in a model may be more like a couple hundred kilometers across. Instead of trying to model individual droplets, scientists instead approximate their bulk behavior within each grid cell. These approximations are called “parameterizations.”
Connect all those equations together and the model operates like a virtual, rudimentary Earth. So long as the models behave realistically, they allow scientists to test hypotheses as well as make predictions testable by new observations.
Some components of the climate system are connected in a fairly direct manner, but some processes are too complicated to think through intuitively, and climate models can help us explore the complexity. So it's possible that shrinking sea ice in the Arctic could increase snowfall over Siberia, pushing the jet stream southward, creating summer high pressures in Europe that allow India’s monsoon rains to linger, and on it goes… It's hard to examine those connections in the real world, but it's much easier to see how things play out in a climate model. Twiddle some knobs, run the model. Twiddle again, see what changes. You get to design your own experiment—a rare luxury in some of the Earth sciences.
In order to gain useful insights, we need climate models that behave realistically. Climate modelers are always working to develop an ever more faithful representation of the planet’s climate system. At every step along the way, the models are compared to as much real-world data as possible. They’re never perfect, but these comparisons give us a sense for what the model can do well and where it veers off track. That knowledge guides the use of the model, in that it tells us which results are robust and which are too uncertain to be relied upon.
Andrew Weaver, a researcher at the University of Victoria, uses climate models to study many aspects of the climate system and anthropogenic climate change. Weaver described the model evaluation process as including three general phases. First, you see how the model simulates a stable climate with characteristics like the modern day. “You basically take a very long run, a so-called ‘control run,'” Weaver told Ars. “You just do perpetual present-day type conditions. And you look at the statistics of the system and say, 'Does this model give me a good representation of El Niño? Does it give me a good representation of Arctic Oscillation? Do I see seasonal cycles in here? Do trees grow where they should grow? Is the carbon cycle balanced?'”
Next, the model is run in changing conditions, simulating the last couple centuries using our best estimates of the climate “forcings” (or drivers of change) at work over that time period. Those forcings include solar activity, volcanic eruptions, changing greenhouse gas concentrations, and human modifications of the landscape. “What has happened, of course, is that people have cut down trees and created pasture, so you actually have to artificially come in and cut down trees and turn it into pasture, and you have to account for this human effect on the climate system,” Weaver said.
The results are compared to observations of things like changing global temperatures, local temperatures, and precipitation patterns. Did the model capture the big picture? How about the fine details? Which fine details did it simulate poorly—and why might that be?
At this point, the model is set loose on interesting climatic periods in the past. Here, the observations are fuzzier. Proxy records of climate, like those derived from ice cores and ocean sediment cores, track the big-picture changes well but can’t provide the same level of local detail we have for the past century. Still, you can see if the model captures the unique characteristics of that period and whatever regional patterns we’ve been able to identify.
This is what models go through before researchers start using them to investigate questions or provide estimates for summary reports like those produced for the Intergovernmental Panel on Climate Change.
Very good summary - thanks to Scott and Ars for allowing the reposting.
However, given how easy it is to be distracted by rhetocial misdirections, I think it might be helpful to add one bit of context. The skeptic claim quoted at the start
is false in both its first and second clauses. Our understanding of future climate is not all based on models. If we were to throw the models away as useless, we would still have a good idea of where we're going, because we can predict future climate on the basis of past climate over a whole range of timescales.
Like any Earth science, climatology has the problem of not easily being able to run experiments the way one can in, say, particle physics or chemistry. As expensive as it is to build and run a particle accelerator, it is simply impossible to "build" an alternate Earth, more-or-less perfectly replicating the real thing, and run it through decades or centuries or millions of years of change in a reasonable timeframe.
So you use a model.
In essence, a computer model of the Earth climate system is a laboratory experiment of the Earth's climate. One you can run through in a reasonable amount of time, at a reasonable cost, and can replicate at will (subject to time/cost/other resource constraints).
Yes, it's an approximation that will likely never be 100% accurate. But what matters is whether it's good enough to be getting on with, even as scientists work on developing better models and better understanding the Earth climate system.
Of course, some of the components of the Earth climate are amenable to simpler forms of experiment, such as (to the best of my lay knowledge) analysis of the radiative properties of greenhouse gases. And, as noted by Kevn C, such analysis (as well as research into paleoclimate), rather than modeling, is what has led to our current understanding of climate.
The bottom line is that our current understanding of the physics, of paleoclimate, and the current results of modeling, all are more than enough to be getting on with - particularly if what we are getting on with is coming to terms with the fact that we simply cannot continue to increase the concentration of long-lived greenhouse gases in the atmosphere if we want to avoid very unpleasant consequences.
This is a nice capsule summary of modeling and why models are useful.
An added reason for the development of models is short-term forecasting to help decision makers understand their likely conditions for near-term things like farming, shipping, off-shore operations, and weather related disaster relief planning.
It is important to note that climate models cannot reliable forecast the significant but random or irregular impacts like major volcanic eruptions and the ENSO changes. The models can have these items as input from past history and reasonably produce the historic results, but the models cannot reasonably forecast these impacts. However, these impacts are not "drivers" of long term change. So the models can reliably forecast the "norm" into the future with the understanding that random factors like major volcanic eruptions and ENSO changes will create departures from the norm.
The models are reliable even when they do not predict the long-term ENSO influence, because they are not able to predict the ENSO far into the future so they don't try to. However, as more is learned about the intricate behaviour of the ocean currents the models will be able to include reasonable long-term predictions of ENSO.
Prof. Inez Fung says in 2011-2-08 lecture on video there are ==>6,500,000 grid cells which are <1 degree apart with 50 air layers (max height 10-15km), 30 ocean layers (max depth not mentioned), 10 soil layers. I compute an 80km grid for 6,500,000 cells from these but 1 degree = 111km so it looks like they are using 90-100km grid. They are working (2011) on a finer 25km grid so perhaps that's in use now. Prof. Fung says it's a 15-minute time slice.
I'm a layman - no climate creditionals, no science degrees. I'm simply a voter (probably like lots of others out there) being asked to regulate CO2 footprints.
I don't have the expertise to understand the science - if I'm to trust others to do the science, I have to see that it's being done objectively. The Climategate emails showed me that there were (and probably still are) lobbyists masquerading as scientists out there. There's enough of them for it to take a decade for that fact to come out.
All that leaves is the models. If the models are accurate in predicting the future, then ordinary people like myself don't have to understand the science or trust the objectivity of others. We can judge for ourselves whether CO2 emissions are to blame.
It seems that there's been a disconnect between the what the models have predicted so far, and what has eventuated. It's understood that there are difficulties modelling a chaotic system. My question is though, how long is it expected for this disconnect to remain, and how long should we give the models before it is a fair conclusion that we don't yet understand what's going on in the climate enough to regulate CO2 footprints?
I[PW] Ironbark, this is a gentle warning: you've made unsupported accusations in your post, above, and on SkS, when this is done, we will insist that you supportithose accusations. Given you've openly admitted that you're not an expert nor a scientist, that admission does not, in and of itself, give you license to make statements of fairly suspect nature ("The Climategate emails showed me that there were (and probably still are) lobbyists masquerading as scientists out there. "). As such, you need to not argue from the fallacy of personal incredulity without a single source of relevant data with which to back it/them up.
I'd reference you to this link, which may help you address your misgivings about the veracity of climate models.
http://www.skepticalscience.com/climate-models.htm
ironbark, accusations of desception are a contravention of the comments policy, which I suggest you read before posting further. You comment is also essentially an ad-hominem as it suggests that you are prepared to disregard the opinions of scientists simply because of who they are, rather than the content of the scientific arguments they make. It is easier to keep the discussion productive if that sort of thing is avoided as far as possible.
Ironbark, you admit having no expertise, and then you point to "climategate" as evidence of fraud. Upon what basis do you interpret "climategate"? If you respond, respond on one of these threads. Your comment will be seen, since most of the SkS regulars follow the aggregate comment page.
As for models, what is your definition of "accurate"? Modeling has done remarkably well, with the exception of its massive underestimation of Arctic sea ice loss. Consider where the surface temp trend could have reasonably (from the perspective of someone naive of the science, like you) gone over the last fifty or twenty or ten years. Now look at the model projections. Surface temp is still within the bounds of the range described by 95% of the model runs, and that range isn't all that wide. So where and why have models failed--and failed to the point of uselessness? Respond here or on one of the many model posts.
Ironbark, as another scientific layperson, I can assure you that you do not need climate modelling to understand that (a) CO2 emissions are responsible for warming, or that (b) such warming, if unabated, presents a serious concern for our affluent societies.
To figure out (a) you just need to know some physics of radiative heat transfer and know enough to rule out other possible sources of warming (which, if you read through this site enough, you will find we can do, to an extremely high degree of confidence).
To figure out (b) you just have to work out the consequences of warming using some logic. Without modelling, of course, projecting the rapidity and severity of consequences is a lost cause, but as long as warming continues unabated, consequences will occur (and, indeed, have already occurred and are occurring as of this writing).
None of the above requires any fancy degrees. Just a willingness to follow the evidence where it leads you.
At 6, Dikran I'm raising a concern that's held by many ordinary people who don't have the time or expertise to read every science paper to check whether the claims are true or not.
Those ordinary people either have to trust that the science is objective, or find another way to inform themselves that isn't reliant on trust.
Yes there are probably climate scientists out there who are objective, and they should rightfully feel disappointed that their objectivity is questioned. I've read the Climategate emails and I don't belief that the hypothesis in those papers was tested without bias. (-snip-)
The beef of truly objective scientists shouldn't be at ordinary people who don't have the time or skills to tell who is objective, and who isn't, but rather at those peers who brought the overall climate community's reputation into disrepute. (-snip-)
My comments are reasonable discussions being had by ordinary people who just want to know whether we should restrict carbon footprints or not. Banning reasonable questions which seek to find the easiest way to determine the truth (matching predictions with observations) may keep the comment board 'clean', but doesn't deal with the concerns of ordinary people which was what I thought was the intention of this website.
[JH] You are now skating on the thin ice of sloganeering and excessive repetition -- both of which are prohibited by the SkS Comment Policy. Please cease and desist, or face the consequences.
[PW] Allegations of impropriety and ignorance removed.
Please note that posting comments here at SkS is a privilege, not a right. This privilege can and will be rescinded if the posting individual continues to treat adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.
Moderating this site is a tiresome chore, particularly when commentators repeatedly submit offensive or off-topic posts. We really appreciate people's cooperation in abiding by the Comments Policy, which is largely responsible for the quality of this site.
Finally, please understand that moderation policies are not open for discussion. If you find yourself incapable of abiding by these common set of rules that everyone else observes, then a change of venues is in the offing.
Please take the time to review the policy and ensure future comments are in full compliance with it. Thanks for your understanding and compliance in this matter.
You're not being reasonable, though, Ironbark. You've already admitted not knowing enough about the science to make a reasonable science-based conclusion, yet you uncritically accept interpretations of the work of Mann and Jones based on severely de-contextualized snippets of text. Worse yet, the interpreters you rely on cannot be identified. Their memes have been spread far and wide, but no one is stepping forth to defend those memes. No formal allegations were ever made, despite the extreme seriousness of the whispered claims. Nine investigations found the scientists not guilty of scientific misconduct. And you just want everyone to accept your understanding of "climategate" without question? I feel I should be more skeptical.
Ironbark, it doesn't actually matter whether the science is objective, what matters is whether it is correct. This applies to both sides of the argument. John Christy, for example, is far more of a lobbyist that Phil Jones - count up the number of times each has volunteered to speak before government hearings. Does that mean I can dismiss Prof. Christy's work because he is not "objective"? No, his arguments have to be evaluated on their own merits.
Now if you are not in a position to do that, a sensible approach would be to determine what the climate science research community think about this. Fortunately the IPCC WG1 report is intended to be a survey of the mainstream scientific position on this. There also have been surveys of the litterature, for instance The Climate Project (but there have been several others), which show that the skeptic position has very little support amongst the real experts.
So please, no more ad-hominems, that form of argument adds nothing to the discussion.
BTW, the comment "All the reviews that exonerated the people involved have made that perception worse." is a classic symptom ("incorrigibility") of delusional behaviour (intepreting evidence that contradicts a strongly held belief as support for that belief).
P.S. you might want to check my entry in the "Team" descriptions under the "About" tab on the blue bar immediately under the logo.
[PW] To eliminate the looming possibility of dogpiling on Ironbark, allow him/her to elucidate upon his/her accusations: Ironbark, you've now received a second warning, and you've yet to provide anything much beyond fairly typical denier memes and untruths. Your next warning may or may not be the 3rd, or your last.
Again, please review the Comments Policy, before making any more inflammatory remarks.
Moderator Response @11.
Ironbark did ask a valid quetion @5 although very heavily draped in denialist clothing. Perhaps this question of his ("My question is though, how long is it expected for this disconnect to remain, and how long should we give the models before it is a fair conclusion that we don't yet understand what's going on in the climate enough to regulate CO2 footprints?" ) should be directed to an appropriate thread rather than the denialist nonsense. Does the global warming 'pause' mean what you think it means? is a very recent thread and likely will quickly get to the nub of Ironbark's stated enquiry.
At Moderator - understood, appreciate the feedback and thanks for the link. I don't agree with one of it's conclusion though that 'we can’t wait for 30 years to see if a model is any good or not' - that is an opinion that people are allowed to have regarding their own perceptions of the costs vs benefits. That is a subjective comment though - I don't believe it's a scientific comment. Being subjective, my own perception is that there will be lots of needless suffering on the poorest if we are incorrect in regulating CO2 footprints (i.e. if CO2 footprints are to blame, we can't address the issue without preventing poor countries from improving their quality of life, since improved quality of life comes from fossil fuels). Is there a scientific position as to how long model predictions can deviate from observations without questioning the underlining inputs and assumptions?
At 12, MA Rodger - easy on the 'denialist' trigger. My conclusions on Glimategate correspond with Prof Richard Muller's lecture on youtube, who for what I can make out, appears to think that all the warming we've seen is caused by humans, yet says Climategate was 'scientific malpractice'. My point is that if it takes a decade for that to come out from the original papers, after the graph was used by the IPCC and Al Gore, what hope now do ordinary people have to take any study that's not older than 10 years on face value?
The link you've provided helps, though I'm not sure it gets to the crux of the question. The essence of the 'Does the global warming 'pause' mean what you think it means' thread, appears to be that there is no pause over a longer period. Whilst this is interesting and I would agree that to discern overall trends needs long time frames, the context of my question was that of someone who just wants to look at how predictions have gone against observations to make a decision. Why - because the reason to regulate CO2 footprints now is predicated on the assumption that we have no time to lose. Since models weren't making predictions 30 years ago, their performance over that time period isn't relevant to that question. The relevant time period is to match when models were predicting the future, against those now historical observations. From what I can make out those predictions appeared to start in the late 1990's (please correct me if I'm wrong). The link talks about the oceans switching to another warming cycle - how long would this be, if it's long, can that not support the position that we don't have to act imminently? How many years of no warming from when models started making predictions would it take for ordinary people to be able to say that there might be more going on here that we don't understand?
As an aside, I don't think the graph on that page comparing how 'realists' and 'skeptics' view climate doesn't helps the case. I haven't seen anything said by skeptics which would support such a graph - their overall argument in fact appears to be the opposite, that even 30 years is to short a trend - some are saying we need to look a trends over thousands of years. I don't know which one is right, other then that graph characterising the 'skeptics' view, doesn't correspond with anything I've read from them. Obviously it's up to this site to determine how it wants to reflect opposing viewpoints, however IMO I think it detracts from great work that's being done here as opposed to helping it.
[JH] Recommend that you insert "climategate" into the SkS search box and see for yourself how extensively it has been discussed over the years on this website. You might even take the time to read some of the articles.
Just so we keep our stories straight...
-- Climategate and MBH 98 have to do with models how?
-- Al Gore has to do with models how?
-- Poor people we're presently choosing not care for have to do with models how?
Would be nice if we could stay on topic. Distinguishing one topic from another is a skill that can easily be learned. Start by remembering that GCMs are are not policy, GCMs are not celebrities, GCMs are not paleoclimate reconstructions, GCMs are not archaic emails on unrelated topics.
At 10 - DSL, whether others agree with me or not on the Climategate issue is secondary to my overall question.
Unless the emails I've read, are not the emails commonly understood, the use of words trick, 'hide the decline', the attempts to control what Journals published to restrict dissenting papers shows clear bias. People objectively seeking the truth (which we're all keen to know) would have encouraged people trawling over their work. It would have been far more relevant and less damaging to the AGW hypothesis if the hockey stick had been displayed what the proxy data actually showed. Then others could have built on that. Humanity would be better off for those scientific papers. Instead those papers set back the cause of objective people who say the evidence substantiates AGW and the climate community is only making it worse by not calling a spade a spade. People like Professor Richard Mullins calling it 'scientific malpractice' are to me, the best hope of restoring integrity in the eyes of the ordinary person, though apparently his opinions are the minority here.
At 13 - Moderator, will do, thank you.
[JH] If you wish to discuss "climategate" further, please do it on the thread of an article about the subject.
At 14 doug-bostrom - thank you - on topic... the topic of the thread is trusting models.
Hindcasting sounds good, but if you went to the races with a someone who had a formula that predicted the winner of every race yesterday, but missed picking the winners in the first couple of races today, how much money would you keep giving him? This is how ordinary people think - people can judge that as simplistic, but I know a lot of people who think that way and AGW denial will only increase if there isn't an answer a layman can understand.
The question was if there is a scientific principle of allowable variance from observations, before the underlying assumptions are questioned. How long can the pause be expected to continue?
If there is a thread that explains model deviations from predictions since 2000, (not hindcasted predictions) that would be useful - and people such as myself, who aren't as intelligent as a lot of people on here can have a response to others when those reasonable questions are asked.
Ironbark writes @13:
S/he continues @15:
I am not going to discuss these comments in detail here, as they are off topic. If Ironbark wants a serious discussion on this issue, s/he should post on the topic here.
I will, however, point out that Michael Mann's graph as featured in the IPCC TAR, and in Al Gore's lecture series, movie and book does not hide the decline. Nor does it substitute real temperatures for proxy temperatures in any case. The suggestion that he did so comes from a blatant misinterpretation of something that Phil Jones says he (Phil Jones) did with another graph that has never appeared in any IPCC publication, nor been used by Al Gore (or anybody else so far as I know). Nor, for that matter, did Phil Jones do what Michael Mann actually did in his paper that produced the graph used by the IPCC and Gore.
This is typical of the whole "climategate" farce. Almost the entire basis of attack against the authors of the CRU emails has been on the misinterpretation of a few lines of text taken out of context. I strongly recommend that Ironbark not keep on spreading that misinformation until they have investigated the issue in detail here on an appropriate thread where more knowledgable people can point out, point by point, the nature of the misinterpretation involved. Alternatively, they can consider the possibility that many independent inquiries that have exonerated the authors of the emails of wrongdoing have all simply conspired to hide the truth. Absent such a conspiracy theory, it is absurd to keep on pushing the misinformation about the emails in the face of those multiple, independent exonerations.
At 18, Thanks Tom - I disagree with your comments regarding it being a spread of misinformation, but respect the moderator's wishes that this topic is not the area for such a discussion.
[JH] Tom Curtis has conveniently provided you with an appropriate venue for discussing climategate. If you cannot defend your stated opinions there, please cease and desist from stating them again. Sloganeering and excessive repitition are both prohibited by the SkS Comment Policy. Yes, your opinions on climategate are sloganeering.
Ironbark @19, your clearly believe, and have stated in effect that the hockeystick graph, ie, the graph from Mann, Bradley and Hughes 1999 both "hid the decline" and substituted real temperature data for proxy data to do so. Neither is true. How is spreading the contrary opinion not spreading misinformation?
"The question was if there is a scientific principle of allowable variance from observations, before the underlying assumptions are questioned. How long can the pause be expected to continue?'
If you read up some of the threads on so-called "pause", you will understand this better (in fact read the IPCC AR5 analysis), but as I understand it, the question is more philosphical. Firstly, the models can get some things totally wrong without invalidated climate theory. Things that would invalidate climate theory would be an end to the energy imbalance; LW spectral reading in violation of theory, total ocean heat content declining etc.
The question on models though is whether they have useful skill (do better than null hypothesis that tomorrow will like today or similar). The climate modellers would be the first to tell you that climate model has no skill at decadal level projection. They do not predict internal variability well. On the other hand, if add in internal variability (eg the Foster and Rahmsdorf paper or similar efforts), then do you expect them to "hindcast" pretty well. Thus if you get an El Nino year where there temperatures are lower than previous El Nino years of similar magnitude, (or for that matter La nina years compared to earlier La Nina years) without volcanoes or similar forcings then you would say something missing from the model.
Climate models to be useful have to predict climate so 30 year trends significantly smaller than predicted would also indicate an issue - with the models but not necessarily with climate science. I would note that Manabe's primitive 1975 model allowed Broecker to predict 2010 temperatures remarkably well.
The "models are unreliable" thread has much much more.
Moderator - apreciate that you have a difficult job here. I would have no problem with all my posts on this topic being deleted excluding comment 18 which I think represents an uncontroversial question relating to models (a question I think many people a keen to here answers on, from those who know more about it). I will take up the opportunity of discussing those other off topic areas on other areas at SKS which are more appropriate as you have suggested.
[JH] I will let your prior comments stand as is because they provide the background and context of this ongoing discussion. Perhaps you should spend more time reading and digesting the responses to your comments and less time posting new comments.
At 21 - thanks scaddenp, that is exactly what I'm referring to - appreciate the leads of where to head to next.
Ironbark, further to the moderators comment @19, your comments on "climategate" are not sloganeering because you make them. They are sloganeering because you make them but decline to provide evidence in support of your stated position. Where you to provide that evidence on an appropriate thread, they would not be sloganeering. Where you to provide that evidence here, they would still not be sloganeering, but would remain off topic.
Ironbark @13.
Your request that I ease up on the 'denialist' trigger would be more likely heeded if you ease up on the denialist argumentation. This you singlularly fail to do. In the very same paragraph as your request you tell us Richard Muller describes that the e-mail hacks from CRU demonstrated 'scientific malpractice' (he may well have done, he has a history of denial) and you then intimate that "the graph" (presumably the "hockey stick" from Mann et al 1999) used by the IPCC and Al Gore was also show after 10 years to be wrong. You cannot be serious!
I do not know where you get such deluded ideas from. Mann et al 1999 featured in IPCC TAR of 2001 and along with a whole bag full of other 'hockeysticks', also in IPCC AR4 of 2007. And if you bother to examine the final draft of IPCC AR5 WG1 Chapter 5 figure 5.7 you will see that Mann et al 1999 is now replaced by Mann et al 2008, within which the work of Mann et al 1999 remains all correct and ship shape being presented within figure 3(b) of that paper. There was no error, no malpractice attached to the 'hockeystick'.
Do you deny this to be so? Or will you accept that 'climategate' had zero impact on the science.
(Note. There is somewhere on video a UK climatologist (?) who delights in pointing to some minor adjustment to a global temperature record for part of a decade of the 19th century that was the sum total scientific impact of 'climategate', so perhaps "zero impact" is not entirely correct.)
Of course (as pointed out @24) this is off topic here. Indeed, to remain on topic, please do not present your detailed thoughts concerning a different SkS post in this comment thread. That other SkS post does have a comment thread of its own which is provided for such a purpose.
Ironbark #5 you say "All that leaves is the models" then later "whether CO2 emissions are to blame" but they are largely unrelated. The simulation "models" purpose is to get a reasonable picture of future climate, not to prove that CO2 is "to blame". "whether CO2 emissions are to blame" (are the primary warming agent) is determined by many means all telling a very similar picture. Physics of CO2 (adults do it & schoolkids do it on videos), hundreds of thousands of thermometers in the oceans over decades taking (must be millions) of measurements showing it's warming. The IPCC report even shows how much warming or cooling is attributed to each major factor each year, not just CO2. None of this science has anything to do the the simulation "models" that project the future climate, the only slight interrelation is that they also use the ocean part of the models to estimate accurately the water temperatures between the floats with thermometers in them, because that's far more accurate than just taking a straight line between them.
You say "ordinary people who don't have the time or expertise", "don't have the time or skills", so you say you have other life priorities and you imply strongly that you lack the mental equipment or life-conditioning or both that's required for logical analytical thought, so you base your opinions on the popular news. We all see that many humans are similar to that so they are easily led by the well honed techniques of those with power and intelligence well versed in advertising and the masses-manipulation techniques (that is, not naive obsessive scientist brainiac types). You must not be massively under the gun for time though because you've posted a few words so far.
The tree ring data goes back 2,000 years. It's not worth me lookiing back at the data for details (you can't even be bothered for a 2-minute look to asses it a bit and comment, you are so busy) but humans had pretty good thermometers last few decades and the tree ring data showed cooling but the thermometers reasonable warming. If you had a good thermometer outside your home and recorded temperature each day and chopped down your cherry tree after 10 years and found its rings showed it freezing outside when your thermometer log showed it warm would you throw out the thermometer readings you took and assume the tree rings were right ? It's ridiculous. The trees were poorly chosen at the treeline where they were bashed by the elements, instead of trees deep in the forest. Prof. Muller says the whole 2,000 years tree record should have been thrown out then rather than just throwing out the last bit, and he seems to have a point but that would not change the last decade of big warming record at all (as Prof. Muller has said that also) and there are other ways that were used to measure temperature back 650,000,000 years, not just 2,000 years, and they all show the same story as near as matters - it's getting warm very suddenly lately. The clever professionals in the human-based soft sciences lead the masses around by nose rings by any sparkly bit of trivium because the masses don't have the necessary mental equipment, have much bigger priorities (we are all selfish by nature) and prefer simple entertainments.
Me#26 I see there's earlier links to the dendochronology discussion that'll be more accurate than my ad hoc summary, that's likely misleading, so look there instead. Especially since I'm better sticking with the base climate model theme since I've written a simple simulation model in 2002 (elevator system , fat bods, thin bods, elevators) for company promo site and assisted on another time-slice simulation model in 1973 (big old computer).