Arguments
The 97% consensus on global warming
What the science says...
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97% of climate experts agree humans are causing global warming. |
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Climate Myth...
There is no consensus
The Petition Project features over 31,000 scientists signing the petition stating "There is no convincing scientific evidence that human release of carbon dioxide will, in the forseeable future, cause catastrophic heating of the Earth's atmosphere ...". (Petition Project)
Science achieves a consensus when scientists stop arguing. When a question is first asked – like ‘what would happen if we put a load more CO2 in the atmosphere?’ – there may be many hypotheses about cause and effect. Over a period of time, each idea is tested and retested – the processes of the scientific method – because all scientists know that reputation and kudos go to those who find the right answer (and everyone else becomes an irrelevant footnote in the history of science). Nearly all hypotheses will fall by the wayside during this testing period, because only one is going to answer the question properly, without leaving all kinds of odd dangling bits that don’t quite add up. Bad theories are usually rather untidy.
But the testing period must come to an end. Gradually, the focus of investigation narrows down to those avenues that continue to make sense, that still add up, and quite often a good theory will reveal additional answers, or make powerful predictions, that add substance to the theory.
So a consensus in science is different from a political one. There is no vote. Scientists just give up arguing because the sheer weight of consistent evidence is too compelling, the tide too strong to swim against any longer. Scientists change their minds on the basis of the evidence, and a consensus emerges over time. Not only do scientists stop arguing, they also start relying on each other's work. All science depends on that which precedes it, and when one scientist builds on the work of another, he acknowledges the work of others through citations. The work that forms the foundation of climate change science is cited with great frequency by many other scientists, demonstrating that the theory is widely accepted - and relied upon.
In the scientific field of climate studies – which is informed by many different disciplines – the consensus is demonstrated by the number of scientists who have stopped arguing about what is causing climate change – and that’s nearly all of them.
Authors of seven climate consensus studies — including Naomi Oreskes, Peter Doran, William Anderegg, Bart Verheggen, Ed Maibach, J. Stuart Carlton, and John Cook — co-authored a paper that should settle this question once and for all. The two key conclusions from the paper are:
1) Depending on exactly how you measure the expert consensus, it’s somewhere between 90% and 100% that agree humans are responsible for climate change, with most of our studies finding 97% consensus among publishing climate scientists.
2) The greater the climate expertise among those surveyed, the higher the consensus on human-caused global warming.
Expert consensus results on the question of human-caused global warming among the previous studies published by the co-authors of Cook et al. (2016). Illustration: John Cook. Available on the SkS Graphics page
Scientific consensus on human-caused global warming as compared to the expertise of the surveyed sample. There’s a strong correlation between consensus and climate science expertise. Illustration: John Cook. Available on the SkS Graphics page
Expert consensus is a powerful thing. People know we don’t have the time or capacity to learn about everything, and so we frequently defer to the conclusions of experts. It’s why we visit doctors when we’re ill. The same is true of climate change: most people defer to the expert consensus of climate scientists. Crucially, as we note in our paper:
Public perception of the scientific consensus has been found to be a gateway belief, affecting other climate beliefs and attitudes including policy support.
That’s why those who oppose taking action to curb climate change have engaged in a misinformation campaign to deny the existence of the expert consensus. They’ve been largely successful, as the public badly underestimate the expert consensus, in what we call the “consensus gap.” Only 16% of Americans realize that the consensus is above 90%.
Last updated on 8 May 2016 by BaerbelW. View Archives
To all posters:
Moderator DB posted data that shows klmartinson's claim that
"last winter in continental USA was the coldest in 110 years. I don't understand how we can have "record heat" and yet have "record cold seasons"
was simply made up. I note that several informed posters replied to this claim as if it were actually correct. This shows how difficult it is to argue with deniers: they simply lie about data to support their wild claims. No-one can know all the data so all of us can be fooled. data that is numerical and very specific ("coldest in 110 years") is genrally aclcepted as from a reliable source.
My questions to klmartinson: who told you this deliberate lie? Why do you believe them?
Michael, the claims of Klmartinson are in the category of "amusing".
I am reasonably sure that even he himself doesn't believe them.
For a follow up to my post at 851 on being fooled by lies:
While I do not know all the data and can be fooled by deliberate lies, I find that between my friends Eclectic, DB, Bob Loblaw and the other posters here at SkS, someone recognizes the lie and links to the actual data. All of us have different interests and are knowledgable about different facets of climate change. We have strength in numbers to fight deliberate propaganda.
@Postkey
Are those peer-reviewed articles publicly available maybe?
And I also wonder if there is any conclusion (concensus) about how significant actually is AGW (what percentage of "global warming" is contributed to humans)?
Thanks!
"I also wonder if there is any conclusion (concensus) about how significant actually is AGW (what percentage of "global warming" is contributed to humans)?"
In the early 20th century human activities caused about one-third of the observed warming and most of the rest was due to low volcanic activity. Since about 1950 it's all humans and their activities.
https://journals.ametsoc.org/doi/10.1175/JCLI-D-18-0555.1
https://onlinelibrary.wiley.com/doi/full/10.1002/wcc.522
Further, the detection of the human fingerprint in the observed tropospheric warming caused by the increase in atmospheric concentration of greenhouse gases like CO2 has reached 6-sigma levels of accuracy.
https://www.nature.com/articles/s41558-019-0424-x
Hi All. I think it's essential that we all think for ourselves on this topic. I wanted to do that, and I started recently by looking at the scientific consensus.
I now have lots of problems with the information on this page, which I think is misleading in several different ways. From what I can see, this is an argument between the people who think that doubling CO2 will raise the world temp by about 1C (which they think will not be a major problem) and those who think that doubling CO2 will raise the world temp by about 3C (which, they think, would be a major problem). So it is very misleading to say, above, that "97% of climate experts agree humans are causing global warming", because both sides agree on that.
Secondly I have a lot of problems with the way that the consensus is reported both here and in eg Wikipedia. I decided to look at the data. I looked at what seemed to be the most recent paper on this, by Bart Verheggen and colleagues, called Scientists’ view about attribution of global warming.
https://pubs.acs.org/doi/abs/10.1021/es501998e
In the light of my first point above, the only question that you really want to hear about is their Q12, "How concerned are you about climate change as a long-term global problem?". What is quite extraordinary is that Bart and colleagues don't mention this question, or the responses to it, in the whole of their article. How could that happen?
Fortunately they have published a summary of the responses:
https://www.pbl.nl/en/publications/climate-science-survey-questions-and-responses
Now we discover that only 33% of climate scientists are more than "somewhat concerned", and 8.5% are "not very concerned" or "not concerned at all".
That doesn't really look like a consensus.
The main argument in the abstract of Bart's paper is that the authors who publish a lot on climate science are more likely to agree that anthropogenic gasses are the dominant driver of recent climate change. John Cook's graph, above, makes a similar point. Given that scientists, such as Judith Curry, who take a "contrarian" view of climate change complain that they can't get their work published, this doesn't see like a very good argument.
With the best will in the world, none of this looks good for the consensus.
Would it be possible to change the information on this page to encourage people to look at the original data in Bart's report? And also to highlight areas of agreement - such as that most contrarians are "lukewarmers" who agree that human activities cause some warming? That way lay-people such as myself would be in a much better position to think about this for ourselves.
PatrickSS @856,
You say that there is "an argument between the people who think that doubling CO2 will raise the world temp by about 1C ... and those who think that doubling CO2 will raise the world temp by about 3C ..." Do you consider the folk saying that Equilibrium Climate Sensitivity (from 2 x CO2) is about +1.0ºC to be more than just a few contrarians and that their supporting evidence is well-founded? And if you do consider them to be thus, providing a serious scientific position, perhaps you should name their leading members so their position within the 'consensus' can be properly adjudged along with showing how numerous they are and how well-founded their arguments.
Just a minor point - anyone saying "they cant get their papers published" - in any field, let alone climate science, - ask them to publish their reviewers comments. I will bet that most wont, largely because I think the "papers" are mythical and simply a rhetorical point, but others would be embarrassing. If they are prepared to do so, then sure, you can read the comments and see whether you think the reviewers have a point.
As to sensitivity, someone who thinks ECS is 1 degree is frankly a denier not a skeptic. This requires the existance of unobserved negative feedbacks and really only "exists" in the statistical evaluation of error not in the physics. Against this is the overwhelming evidence of net positive feedback.
You need speculative processes to drive the ice-age cycles with a sensitivity of 2.0 or less. On the other hand, an ECS of 2.5 or higher fits well with known physics, observations and models. That is where the evidence is pointing. Lukewarmers are generally trying frantically to magnify unquantified uncertainties to support a ideologically or identity based positions. Wishful thinking not evidence-based thinking.
A further comment. I see most "lukewarmers" as too honest as to deny physics, but unable to imagine a policy response that is compatiable with their values/identity, hence work hard to try and deny the need for action. A pity because coming up with an acceptable and effective response is something the right wing badly need. The political debate should be about best policy not science denial.
However, I also acknowledge that there are people who frankly see the threats posed by climate change as an excuse to beat a different political drum and like the hard right, they are more interested in pushing their ideology than science. Most scientists dont appreciate being lumped with them simply because they do exist.
A good question to ask, "if we knew for sure that ECS was 2.0, then would you still be arguing for same policy response as if we knew for sure that ECS was 4.5?" My answer would be no way. Yes, it is still highly desirable to get off FF if no other reason than they are limited and sooner or later will run out anyway, but the urgency of the time frame is different and the scope for damage much less.
Reality is that we dont know ECS with certainty and evidence would have it closer to 3 than 2. Reducing the uncertainty is extremely difficult so the precautionary principle applies.
Anyone else notice that while climate scientists come in all political colours, climate science deniers seem to be overwhelmingly right wing?
Why my comment wasn't published?
[PS]There is no sign of a deleted comment from you in our moderation database. Last comment showing up from you was 12 Dec and it is visible (no 854). If you have posted since then I suspect a technical glitch. Sorry about that. Try again.
scaddenp @859: You asked:
Actually, many are Russian BOTs.
Thx so much for your replies.
It’s incredibly unfortunate that climate science has become political – on both sides IMO.
Actually I don’t feel that any of you have really engaged with my main argument: does this page give a fair summary of scientists’ views? E.g. does sticking up the percentage “91%” give a fair summary of Vergehhen’s data? (Obviously not.)
Science is IMO very subject to fashions. When authors, reviewers and the people who award grants all have the same point of view it can all go wrong. E.g. a few years ago almost everyone believed that fat in the diet was a kind of poison – which we now know is nonsense.
What I notice is that most scientists who are contrarians are either old and retired, or else somehow supporting themselves on private means or as consultants. That doesn’t seem like a good situation. It could mean that only crazy old men and women believe this nonsense, or it could mean that young climate scientists would damage their careers if they expressed contrarian views. MA Roger @857, I've listened to Freeman Dyson, Richard Lindzen and William Happer on youtube and none of them seem crazy, they seem to be good scientists. Judith Curry said that she couldn’t get her work published. I’ve just checked what she said – in fact she did publish one reviewer’s comment:
“Overall, there is the danger that the paper is used by unscrupulous people to create confusion or to discredit climate or sea-level science. Hence, I suggest that the author reconsiders the essence of its contribution to the scientific debate on climate and sea-level science.”
Hmm. That’s definitely a very dangerous argument. In fact it's very worrying indeed.
Scaddemp, most lukewarmers that I've listened to (including Judith C and Matt Ridley) definitely want to protect the environment, and they propose the expansion of research into new energy systems, but they worry about taking it to an extreme.
But . . . . although the process looks bad, there could be a real problem here. I find it incredibly hard to know. Unfoortunately we all have this thing called confirmation bias, and that makes everything tricky.
[DB] Sloganeering snipped.
Patrick$$ @862,
It is well established understanding that expanded awareness and improved understanding are easily compromised by misleading marketing that is based on carefully prepared fictions that are based on minimal factual evidence and designed to appeal to a person's developed preferences.
There is a massive diversity of evidence supporting the climate science consensus understanding that human activities, particularly fossil fuel use, are significantly impacting the global climate in ways that are detrimental to the future generations.
Revisit the claim-making by the people you list from the context of that understanding. They may sound reasonable. But are they Really helping expand awareness and improve understanding?
Apply the same context of understanding to the criticism of Currie's story, and any 'concern' about her 'concern' is likely just another part of the fiction she is making-up in an attempt to appeal to learning resistant believers who are easily tempted to prefer poor excuses for harmful behaviour rather than expand their awareness and improve their understanding in ways that would require them to change their mind about how they like to live.
DB, can't I say that it's incredibly unfortunate that climate science has become political?
One Planet, when I listen to “consensus” climate scientists, they say that sunlight comes in, heats the Earth, and the heat escapes from the Earth via IR. Increased CO2 absorbs and blocks more IR, so the Earth gets warmer.
When I listen to Richard Lindzen he says that CO2 and H2O already absorb all the IR emitted at the Earth's surface, and that the IR that escapes is actually emitted high in the atmosphere. Increasing CO2 causes the IR to be emitted at slightly greater altitude. This warms the surface because the temperature at which the emission takes place is the same, so when the lower atmosphere is chaotically mixed the air reaching the surface is hotter (because it gets compressed as it comes down).
That seems to me to be "expanding awareness and improving understanding". He seems to be a good communicator and a good scientist. It seems unlikely that he invented the whole thing.
Then I watched Richard Alley on youtube. He is a very good communicator, and at first I found his argument very convincing. He said that the ice ages were driven by cycles of the sun at 100,000, 41,000, 23,000 and (I think it was) 19,000 years. Then he said that the sun cycles (periodically) released CO2, and the CO2 drove temperature. So we have sun -> CO2 -> temp. But the sun can only act through temperature. So we have sun -> temp -> CO2 -> temp. Suddenly it seems much less plausible. What's wrong with sun drives temperature?
One Planet, I don't get your point about Curry's reviewer. Surely we can agree that his or her comment was extraordinary, and showed dishonest thinking? Curry's other reviewers may have been good and rational, but one at least was not. Of course she could have made that comment up – but I have no reason to believe that. It seems more likely that she is sincere because she has put her career on the line.
None of this means that the “consensus view” is wrong. But it makes it very difficult to know who we should listen to.
[DB] Moderation complaints snipped.
PartickSS @864,
Expanded awareness and improved understanding are based on all available evidence, not bits of it.
A person who makes a solid sounding science statement but then also makes an unscientific claim that is contrary to aspects of 'all of the available evidence (makes an illogical leap that is happily followed by someone who was impressed by the earlier Sciency Show and likes where the leap takes them thought-wise), is not helping to expand awareness and understanding. They are potentially corrupting efforts to expand awareness and improve understanding by the use of misleading marketing.
Seek out detailed explanations of the incorrect aspects of the claims made by Lindzen, Alley and Curry. There are many sources for the corrected expanded understanding (and a vast amount is available right here on the SkS site).
You should find many explanations that are 'even more compelling than the claim made that you liked', unless you choose not to become more aware (don't seek out the expanded awareness and improved understanding), or not want to develop improved understanding (do not wish to accept that fossil fuel burning has to be rapidly ended).
That understanding should clarify my comment regarding Curry.
PatrickSS @862,
You present three names in response to my request @858 for the scientists you tell us "think that doubling CO2 will raise the world temp by about 1C," a position you appear to set as equal in importance to "those who think that doubling CO2 will raise the world temp by about 3C." It's not much of a list. Do note that two of these are not climatologists and further, I do not see that any of them present substantive reasons to support their bold claims. This is evidently not two sets of scientists arguing. It is sadly science under attack from a handful of swivel-eyed lunatics.
In support of my own rather bold statement, I would share with you my view of the one climatologist you name - the veteran climate denier Richard Lindzen. He has been at this game so long that he has lost entirely his grasp on the science he is supposed to be practising and now resorts to bare-faced-lies/deluded-foolishness [delete as applicable]. He has certainly ventured far beyond the science of climatology with his nonsense. See his 2017 version here and tick off the numerous examples of untruth he presents. (And to keep us on-topic, note his first attempt to refute AGW is "The 97 Percent Meme".)
I note you cite Dickie Lindzen when you say "Increasing CO2 causes the IR to be emitted at slightly greater altitude. This warms the surface because the temperature at which the emission takes place is the same, so when the lower atmosphere is chaotically mixed the air reaching the surface is hotter (because it gets compressed as it comes down)." I am not sure where Lindzen explaining this mechanism but the way you phrase it is subject to vast misinterpretation.
You add that Judy Curry has had difficulty getting published yet if she has anything worth publishing she only has to post it on her website to get it into the scientific/public domain. Yet there is complete absence of any substantive comtribution from Curry, an absence that speaks volumes.
@862 you say you do not feel your "main argument" has not be "really engaged." You appear to be arguing that the scientific view of AGW is not truly reflected in the 97% consensus and specifically that Verheggen et al (2014) is 'obviously not' fairly summarised by the 91% value. I find this difficult to accept. Perhaps we are reading a different paper.
I don't make many posts but as far as my knowledge of Lindzen, he's always been a luke warmer who believes the doubling of CO2 will only produce a temperature rise of 1 degree celcius, ignoring any type of feedbacks. We've already risen 1 degree and we've increased CO2 less than 50% of a doubling.
In addition, his Iris effect theory, that as temperature increases they'll be less moisture and fewer clouds that will cause more infrared radition to escape has been shown by several studies since then, to not be the case.
Estoma I will check out the Iris Effect
Rodger, did you read the summary of the raw data that I pointed you to? Here's the link again:
https://www.pbl.nl/en/publications/climate-science-survey-questions-and-responses
What do you think of the responses to Q12?
Isn't it very odd that Bart V and colleagues didn't mention Q12 in their paper?
And do you realize that the "91%" quoted on this page includes Lindzen, Happer, Dyson, Curry and Ridley?
Thx for all your responses. I'm going to the "It's the sun" page.
PatrickSS @868,
My appologies for not spotting @856 your referencing of Question 12 in the Climate Science Survey which sets out the data used within Verheggen et al (2014). Your complain was that this Q12 was not featured within Verheggen et al (2014). Were the responses to Q12 as you set out up-thread @856 it may perhaps be considered an omission. You wrote:-
This is completely incorrect. The more than "somewhat concerned" figure (so "very concerned") is not 33% but 67%. More exactly, if the data for the "respondents with more than 10 climate-related peer-reviewed publications" reported by Verheggen et al is gleaned from Figure 12.2, it is 71% who are 'very concerned', 22% 'somewhat concerned' and just 7% who are less concerned than this. To me, here is a 93% concensus.
Those who may be inclined to peel off the 22% 'somewhat concerned' from this concensus should consider how the question would be answered in 2012. "How concerned are you about climate change as a long-term global problem?" For a climatologist in 2012, a 'somewhat concerned' response could result from a belief that mitigation measures will arrive to to prevent AGW becoming a serious crisis for humanity, or that in the "long term" AGW is not a serious crisis because, whatever the damage through the next century, in the "long term" humanity will survive, the natural world will survive. We are not taking about a humanless or lifeless planet by the end of the millennium.
The additional comment @868 that various swivel-eyed denialists would have been included in the headline 91% result of Verheggen et al (2014) is firstly incorrect as three of them are not qualified as authors and secondly, while Dickie Lindzen & Judy Curry sometimes try to argue that they would be part of such a consensus gathered from such surveys, their position is not entirely sincere and they surely could not honestly feature in the Q12 result.
PatrickSS - WRT those three you mentioned:
Dyson is a brilliant physicist - but not a climate scientist. Lindzen, who has worked at the CATO Institute, is well known in the field for a series of papers claiming a strong negative feedback; he has never actually addressed actual (and numerous) criticisms of the first 'Iris effect' paper, simply repeating his claims over and over. In the last version I'm aware of he directly invoked 'cloud forcing', when clouds are, rather, a short lived (hours) feedback to temperature and humidity. And as for Happer (also not a climate scientist), he has been documented as writing climate science for pay, with fossil fuel money routed through nonprofit organizations for anonymity. Happer is more properly a lobbyist, not a researcher.
You might want to look for better references.
Well he's some denier comments that seem misinformed...especially the bit about funding. How do deniers know how funding works in the academic setting?
However I do think this denier has a point in that many countries are never going to agree to lower carbon emissions.
Not all climate scientists agree with the current CO2 modeling being used. Academics and other grant seekers are producing what the government wants to market. No agreement no funding. Universities don't lift a finger unless they get a grant.
If the US went dark it would not change or reverse the climate dynamics on a global scale.
Certainly China, India, Africa, et al, will not comply with the Paris agreement or any other agreement in the next 12 years or next 5 generations. So what are you going to do today? Support countries like China and India, buy vinyl siding, heat your home, drive a car? Logic and common sense have been left behind and the only way to run a government is with the aid of a propaganda machine to create a false reality.
The more I see what is occurring worldwide with respect to climate change and all the dreadful news we are seeing now in Australis and the Amazon, how can anyone feel hope for this situation?
Cheer up, TVC15. Put a smile on your face, and know that things will get worse before they . . . er . . . stop getting worse.
It sounds like your denier friend is a quitter ~ he gives up, just partway into the battle to do the right thing. I wonder what his great-grandparents would have thought of his lack of moral character?
Sure, most countries are dawdling on carbon emission reductions ~ and there's no realistic hope of limiting world temperature rise to merely 1.5 degreesC. The question is, will we collectively take enough action to hold things to a 2 degreeC rise (or will it be much more)?? Already we are seeing problems & extremes cropping up more intensely . . . with only the (so far) rise of 1 degreeC. A full 2 degrees or 3 degrees will give our great-grandchildren some very "interesting times" indeed !
Eventually there will be no choice ~ almost all nations will have to (rather desperately & expensively) take belated major action against emissions. Common sense tells you that the ground-swell from voting citizens will simply get stronger and stronger. And future politicians will become increasingly nervous about "the alternative use of lamp-posts" !!!
The denialist's thinking is crazy if he reckons the upper echelons of government want to fund truth-speaking science researchers ~ in reality, most politicians want the the whole AGW thing to disappear as an election issue. They'd rather not hear about it. (It sounds like his brain is switched to stand-by mode.)
Such people as your denialist, who think that humans mostly just do stuff for money . . . well, the psychologists would say that these denialists are "projecting" their own trashy money-grubbing attitude onto everyone else.
TVC 15 @871, Building on Eclectic's response.
The Delayer you have encountered is attempting to distract attention from expanded awareness and improved understanding of the current day and future problem.
The current day and future problem is the result of the highest per-capita impacting people, and the nations they controlled, in the 1980s failing to responsibly lead the correction of economic activity.
Instead of doing the harder less popular and less profitable work of correcting the incorrect direction of development, the populations of those nations willingly accepted leadership messages that encouraged them to continue to over-develop in the Unsustainable Damaging direction they were headed in. When and where did one of the most absurd opposites of responsible correction, Hummers, become a popular expression of Winning? The same nation that spawned the misleading marketing attacks against climate science.
The Kyoto deal included nations like China and India agreeing to be tied into restricting their development to the 'per-capita' impact levels that the higher impacting nations were showing leadership towards by lowering their per-capita impacts (while sustainably improving the living conditions of their poorest).
China and India are still 'developing up to the per-capita levels' of the USA and its correction resistant hangers-on. And they have every right to develop up to the per-capita impacts of the highest impacting nations.
Some portion of the current day global population clearly deserves to be blamed today. And it is the highest per-capita impacting people and the nations they try to hide in and get defended by. And many of them deserve to be penalized for how they behaved through the past 30 years, and they know it.
That fundamental understanding can be applied to a diversity of claim making by the Delayers.
Tell the Delayer that everyone has the right to benefit by behaving as badly as the worst behaving cheating Winner they see. And everyone should compete to be an even worse Winner in everything they do (including Sports). Then tell them you personally disagree with that attitude, you understand it to be incredibly destructive and that any perceptions of Wining that way are unsustainable, but you understand that it is an accurate description of the actions of the Delayer you are dealing with. Finish the point by stating that you know everyone continues to have the ability to learn to behave more helpfully no matter how old they are and hope they choose to learn to behave better, to be more helpful, to be less harmful.
Thank you Electric,
I try to not focus on things that make my soul sad for all living creature and plants on this earth but when I look at the denial machine and how humans are so divided by over climate change due to science illiteracy, anti-science folks, confirmation bias, political stances etc....it can be quite discouraging. Especially knowing we are in the midst of a very serious mass extinction event. I sometimes wish I was not a biological/medical scientist. I would be just as clueless as most of the planet with respect to human impacts on earth.
Thank you One Planet Only Forever for offering great insightful suggestions.
TVC 15,
In response to the point about everyone having the right to be as bad as Others, you may face a further angle of denial claiming that population is the problem. And you may preempt that by sharing a version of the following rather than waiting to see if it comes up.
The consensus understanding is that human impacts are causing significant negative climate changes to occur. And it is the total global impact that matters.
A good way to argue against the simple claim that 'increased population is the problem' is to point out that each person's impacts add up to the total impact, and though total population is a concern it is the impacts of the highest per-person impacting portion of the population that needs to be reduced (along with the point that every person has the right to be as harmful as Others).
A related item to point out regarding total impacts is that the impacts that developed more fortunate circumstances in the national regional environment that a person is born into should also be counted as impacts of that person. That was part of the Kyoto understanding. It was recognised that the current more fortunate population of the more fortunate nations owed a debt for the impacts caused by the development of their more fortunate circumstances.