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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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How the IPCC is more likely to underestimate the climate response

What the science says...

Select a level... Basic Intermediate

The IPCC lead authors are experts in their field, instructed to fairly represent the full range of the up-to-date, peer-reviewed literature. Consequently, the IPCC reports tend to be cautious in their conclusions. Comparisons to the most recent data consistently finds that climate change is occurring more rapidly and intensely than indicated by IPCC predictions.

Climate Myth...

IPCC is alarmist

"Unquestionably, the U.N. Intergovernmental Panel on Climate Change (IPCC) was formed to build the scientific case for humanity being the primary cause of global warming. Such a goal is fundamentally unscientific, as it is hostile to alternative hypotheses for the causes of climate change." (Roy Spencer)

One characterisation of the IPCC is that it is politically motivated to exaggerate the dangers of global warming and the level of human influence on climate change. When IPCC predictions are compared to observed data, the opposite is shown to be the case.

Conservative Greenhouse Gas Emissions Scenarios

For example, the acceleration in fossil fuel CO2 emissions is tracking the worst case scenarios used by the IPCC AR4 (Copenhagen Diagnosis 2009). Consequently, atmospheric CO2 is increasing ten times faster than any rate detected in ice core data over the last 22,000 years.

Figure 1: Observed global CO2 emissions from fossil fuel burning and cement production compared with IPCC emissions scenarios. The coloured area covers all scenarios used to project climate change by the IPCC (Copenhagen Diagnosis 2009).

Conservative Attribution of Global Warming to Humans

While the IPCC first made statements attributing global warming to humans in 1995, Cook et al. (2013) found that there has been over a 90% consensus in the peer-reviewed scientific literature that humans are causing global warming since at least 1991.

consensus over time

Figure 2: Percentage of papers endorsing the consensus among only papers that express a position endorsing or rejecting the consensus.  From Cook et al. (2013).

Additionally, the 2007 IPCC report stated:

"Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations"

However, the body of scientific research has consistently shown that human greenhouse gas emissions are responsible for more warming than has been observed over the past half century (because aerosols and other non-greenhouse gas temperature influences have had a net cooling effect).  Wigley and Santer (2012) found that this IPCC greenhouse gas warming attribution statemt is far too conservative.

"Here, the probability that the model-estimated GHG component of warming is greater than the entire observed trend (i.e., not just greater than ‘‘most’’ of the observed warming) is about 93%.  Using IPCC terminology, therefore, it is very likely that GHG-induced warming is greater than the observed warming.  Our conclusion is considerably stronger than the original IPCC statement."

In fact their central estimate is that humans are responsible for 100% of the observed global warming for the 1950–2005 timeframe, with greenhouse gases responsible for 160% (Figure 3).

contributors 50

Figure 3: Percent contributions of various effects to the observed global surface warming over the past 50-65 years according to Tett et al. 2000 (T00, dark blue), Meehl et al. 2004 (M04, red), Stone et al. 2007 (S07, green), Lean and Rind 2008 (LR08, purple), Huber and Knutti 2011 (HK11, light blue), Gillett et al. 2012 (G12, orange), and Wigley and Santer 2012 (WS12, dark green).

As Figure 3 shows, the body of scientific literature is still very consistent in finding that grenhouse gases have most likely caused more warming than has been observed over the past half century, and thus that the IPCC has been too conservative in this respect.

Conservative Sea Level Rise Projections

Satellite and tide-gauge measurements show that sea level rise is accelerating faster than expected. Rahmstorf, Foster, and Cazenave (2012) compares the historical sea level tide gauge data from Church and White (2011) and recent satellite altimetry sea level data (orange and red in Figure 4, respectively) to the 2001 and 2007 IPCC report  model projections (blue and green in Figure 4, respectively).  The observational data in Figure 4 are aligned so that extending the satellite best-fit line (red) back to 1990 will match the IPCC projections at that date, where the IPCC TAR model runs begin.

RFC12 Fig 2

Figure 4: Sea level measured by satellite altimeter (red with linear trend line; AVISO data from (Centre National d’Etudes Spatiales) and reconstructed from tide gauges (orange, monthly data from Church and White (2011)). Tide gauge data were aligned to give the same mean during 1993–2010 as the altimeter data. The scenarios of the IPCC are again shown in blue (third assessment) and green (fourth assessment); the former have been published starting in the year 1990 and the latter from 2000.

The authors conclude as follows.

"The satellite-based linear trend 1993–2011 is 3.2 ± 0.5 mm yr-1, which is 60% faster than the best IPCC estimate of 2.0 mm yr-1 for the same interval"

The IPCC future sea level rise projections also appear to be too conservative, primarily because they do not account for dynamic ice melting processes.

Conservative Arctic Sea Ice Decline Projections

Summer-time melting of Arctic sea-ice has accelerated far beyond the expectations of climate models. The area of sea-ice melt during 2007-2009 was about 40% greater than the average prediction from IPCC AR4 climate models. The thickness of Arctic sea ice has also been on a steady decline over the last several decades. September sea ice thickness has been decreasing at a rate of 57 centimetres per decade since 1987.

Figure 5: Observed (red line) and modelled September Arctic sea ice extent in millions of square kilometres. Solid black line gives the average of 13 IPCC AR4 models while dashed black lines represent their range. The 2009 minimum has recently been calculated at 5.10 million km2, the third lowest year on record and still well below the IPCC worst case scenario (Copenhagen Diagnosis 2009).

Accurate Global Surface Warming Projections

Rahmstorf, Foster, and Cazenave (2012) also found that the IPCC global surface temperature projections have been acccurate thus far.  The paper applies the methodology of Foster and Rahmstorf (2011), using the statistical technique of multiple regression to filter out the influences of the El Niño Southern Oscillation (ENSO) and solar and volcanic activity from the global surface temperature data, finding that when these short-term influences are removed, the IPCC projections accurately match the observed human-caused global surface warming trend (Figure 6).

RFC12 Fig 1

Figure 6: Observed annual global temperature, unadjusted (pink) and adjusted for short-term variations due to solar variability, volcanoes and ENSO (red) as in Foster and Rahmstorf (2011).  12-month running averages are shown as well as linear trend lines, and compared to the scenarios of the IPCC (blue range and lines from the 2001 report, green from the 2007 report).  Projections are aligned in the graph so that they start (in 1990 and 2000, respectively) on the linear trend line of the (adjusted) observational data.

Asymmetric Challenges to Science

A recent study (Freudenburg 2010) investigated what it calls 'the Asymmetry of Scientific Challenge', the phenomenon in which reports on science fail to evaluate all outcomes, favoring certain probabilities while ignoring others. In the case of the IPCC, the researchers found that the media steadfastly challenge the predictions on the basis that they are exaggerated, worst-case scenarios. What they fail to speculate on is whether the opposite is true; that it may be equally correct to suggest that things might be far worse. This is how the researchers summarised their findings:

" scientific findings were more than twenty times as likely to support the ASC perspective [that disruption through AGW may be far worse than the IPCC has suggested] than the usual framing of the issue in the U.S. mass media. The findings indicate that...if reporters wish to discuss ‘‘both sides’’ of the climate issue, the scientifically legitimate ‘‘other side’’ is that, if anything, global climate disruption may prove to be significantly worse than has been suggested in scientific consensus estimates to date".

While their study specifically addressed the relationship between the maintream media (MSM) and climate science, the overall conclusion they reached suggests that criticisms of the kind elaborated here may be highly inappropriate:

"If the intention is to offer true balance in reporting, the scientifically credible ‘‘other side’’ is that, if the consensus estimates such as those from the IPCC are wrong, it is because the physical reality is significantly more ominous than has been widely recognized to date".

Brysse et al. (2012) suggests that the IPCC and climate scientists in general tend to be too conservative in their predictions because they are "erring on the side of least drama" (ESLD).  However, they point out that an underprediction is just as wrong as an overprediction.  Climate scientists may be introducing bias into their predictions for fear of being called "alarmist," but this conservative bias may leave us unprepared for the magnitude of future climate change.

Intermediate rebuttal written by dana1981

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Additional video from the MOOC

Expert interview with K. Meissner 

Last updated on 6 July 2015 by pattimer. View Archives

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Denial101x video

Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial


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Comments 1 to 25 out of 138:

  1. While I understand the two first pictures, I dont get the last one (figure 4) to make sense. The observed trend starts to diverge from the IPCC models mean at latest in the end of the 1970's - so what were those models based on, pre-1980 data?
  2. We need some source for information about the IPCC. The denialist community has succeeded in marginalizing its public moral authority way beyond anything reasonable or acceptable. Something must be done to directly combat the denialist's lies concerning the who, what, where and how of the IPCC. Any thoughts or suggestions?
  3. The very best defense of the IPCC will be their next report. We've seen this movie before and we'll see it again; IPCC releases latest synthesis, doubters and impressionists pile on, no significant dent is made. The IPCC is undergoing a review of its processes with an eye to making its next report more useful and less susceptible to synthetic controversy. Learn about the review here at the InterAcademy Council website.
  4. citizenschallenge, Maybe the IPCC itself, has helped to diminish 'its public moral authority', by, among other things, purposely publishing outrageous predictions, even though two expert reviewers and the Indian government adviced them to withdraw the erroneous claim (e.g. the Himalayan glaciers). Recent news: The world's leading climate science body must "fundamentally reform" its organisation and how it operates if it is to regain the public's trust, according to a major review.
  5. There is a wonderful (in the sense of frightening) piece by Roy Spencer published by the George C. Marshall Institute. Put on your head clamp and read it carefully. He thinks we should dump the IPCC process, altogether. And why? He argues it was instigated by politicians who "saw a way to accomplish personal goals." The really frightening feature, to me, is that in this letter he doesn't even mention one of those putative goals. Whatever those "personal" goals might be (sustainable society, clean air, maintenance of biological diversity, survival of great grandchildren, ...) At the George C. Marshall Institute, apparently, that qualifies as analysis. And that institute doesn't support any actions instigated by politicians? I think it does from time to time. I assume that institute's standards really, implicitly, involve the evaluation of the goals of politicians. So the "bad" goals are implicit in Spencer's argument in this piece. Spencer is a coward because he will not explicitly pen his specific accusations. The George C. Marshall Institute, as a research institute, is made bankrupt by passing off Spencer's rant as anything like research. Anyway, this note by Spencer suggests to me he is grinding out some other agenda through his "science" rather than simply doing science. How crazy is our world? Spencer wants to shut down the IPCC, because the IPCC was created by politicians who wanted scientists to report their understanding of the science. Meanwhile Spencer reports to the George C. Marshall Institute. (I also learned in that piece that Spencer's boss at UAH is Christy. That was a surprise to me.)

    [DB] Hot-linked URL.

  6. Do you have a graph for how temperature matches up to the models? Just been in a few denialist arguments where they claim the temp is not up to the models and can't find a good source. Thanks
  7. The advanced version of this one gives the model and the 'match' for the most famous model of all. If they're not thrilled with reading there are good videos at Crock of the Week and Potholer 54 - often focused on the Monckton stuff. Fool Me Once is on that entirely - but fan. tas. tic. presentations anyway.
  8. Lancelot (question on other thread) The results this last week for Arctic sea ice - lowest ever extent, lowest ever area, lowest ever volume - tell us that the IPCC was nowhere near 'alarmist' enough on this particular topic. As for floods. Pakistan, Australia, several South American countries, USA, several African countries have all had exceptional events recently. Droughts, likewise. For the policy implications? The scientists can only be as direct as possible in their drafts for IPCC reports. When the international negotiations start on watering down those direct scientific statements, the scientists try to keep the statistical likelihoods as close to their results as possible. But the reports are always less 'alarming' in your words, direct would be my preference, than the original. I'd like to see the "director's cut" for the next IPCC report. Seeing what it looks like before the editors / negotiators got their hands on it might be instructive.
  9. Hello, I'm a newcomer in this field. I have read most of the arguments on all sides. This site by the way is really good. Keep up the good work The point of my question here is - OK, AGW is real, but for policy and decision makers, how much confidence can be placed in IPCC predictions, and how much weight should we attach to them? In Wikipedia article on IPPC the Chairman biography link is given here [] and the following is stated: 'On 20 April 2002, Pachauri was elected Chairman of the Intergovernmental Panel on Climate Change, a United Nations panel established by the WMO and UNEP to assess information relevant for understanding climate change. Pachauri has been vocal on the issue of climate change and said, "What is happening, and what is likely to happen, convinces me that the world must be really ambitious and very determined at moving toward a 350 target." 350 refers to the level in parts per million of carbon dioxide in the atmosphere that top climate scientists such as NASA's James Hansen agree to be a safe upper limit in order to avoid a climate tipping point.' AS the current CO2 levels are 385 ppm, in excess of 350 ppmv, my questions are; 1. Is thus is a misquote from either of the two sources? 2. If so, should the Wiki text be corrected? 3. If not, what are the consequences in terms of confidence in future IPCC predictions, for policy makers? This is not an idle question, it is a question which concerns me when having to make financial decisions on allocation of public resources. It would be great if any replies could be objective, rather than emotive.
  10. lancelot The warming from increased levels of CO2 is not instantaneous, the thermal inertia of the oceans means that it will take a century or so for all of the warming to which we are already committed to be fully realised. Thus even though we are now above the 350ppm figure doesn't mean that the "climate tipping point" should already have happened, but that if we stabilise at that level the tipping point may occur before the climate reaches its new equilibrium. Essentially there is no contradiction there. Just because we have reached a level of 385ppm doesn't mean we can't stabilise at 350ppm.
  11. lancelot - it's not a misquote or typo. Some argue that current CO2 levels are too high because as Dikran notes, we have not yet experienced the full climate effects of the CO2 we've emitted thus far. Looking at historical data from when CO2 levels were this high in the past, sea levels were significantly higher, for example. See this post. On the other hand, realistically it will take a major effort just to limit atmospheric CO2 to 450 ppm. Personally I think that should be our target, and in the future maybe we can find ways to reduce the level back down to 350 ppm. See this post about the global warming 'danger limit'.
  12. Hang on lancelot. The full quote reads "What is happening, and what is likely to happen, convinces me that the world must be really ambitious and very determined at moving toward a 350 target." He said it in 2009. The CO2 concentration was already blowing past 380ppm. The 350ppm target is really very, very ambitious because it requires us not to just cut emissions, but to reduce concentrations. I don't know what kind of policy/financial work you do. But if someone comes to you with a proposal to quarry, crush and distribute dusts & gravels of CO2 absorbing rocks, do the world a favour and set them to work.
  13. Adelady hello - I did give the full quote. You gave part of it. You omitted: '350 ppmv is a 'Safe upper limit... in order to avoid a "climate tipping point" There is no additional qualification to that statement such as give by dana1981. The consensus view here seems to be that there is no misquote. If that is correct, it worries me. 350 as a 'stable state' level is indeed very ambitious. In view of the ongoing rate of development in China, India and the rest of the developing world, it is also, I think, totally unrealistic. We are heading for at least 450 ppmv, possibly 500 ppmv. To get back to a stable level of 350 will take a very, very long time. And I am yet to be convinced that it is necessary. But my main point is that by apparently 'crying wolf' too often, the IPCC loses public credibility.
  14. lancelot It is dissapointing that so soon after writing that replies should be "objective rather than emotive" you are already using emotive rhetorical terms, such as suggesting the IPCC are apparently "'crying wolf'", when in fact they are doing no such thing and the confusion lies at your end, as I have already pointed out. Passing 350ppm DOES NOT imply that we should have already observed the tipping point to which the quote alludes. The quote refers to a stabilisation value for carbon dioxide, it refers to a long term objective, and hence the dangers it seeks to avoid are likewise long term. Not observing those tipping points on passing 385ppm does not mean that the danger has passed and the tipping point wont happen because of action we have already taken (unless we do something about it - such as stabilise at 350ppm). If you truly are in the position where you must "make financial decisions on allocation of public resources" then you are under an obligation to either understand the science more fully, or obtain trustworthy expert opinion. If you are going to accuse the IPCC of "crying wolf" based on a misunderstanding of the science then it is not surprising that you have a difficulty on your hands as you are dismissing the trustworthy experts without developing a basic understanding of the science.
  15. lancelot, so far as I can tell the "climate tipping point" quotation is the wording of the people who wrote the Wikipedia article rather than Pachauri or Hansen. It is not shown in quotation marks in the article, and does not appear in the link cited as the source. Thus, if you are accusing the IPCC of "crying wolf" with the 'tipping point' comment... it didn't come from either of the two scientists you are apparently conflating (improperly IMO) with the IPCC reports. Also note that there ought to be a difference between the carefully reviewed work of thousands of scientists from around the world in the IPCC reports and things Rajendra Pachauri happened to say off the cuff. You accuse the IPCC of losing credibility for promoting a target limit of 350 ppm... but that target does not appear in the IPCC reports. I also note that you give absolutely NO reason for believing that Hansen's 350 ppm limit is 'wrong'. You just take that as a given and then fault the IPCC for "crying wolf"... even though they didn't.
  16. Dikran and CBD, hello. I am quite familiar with the science. I did not 'improperly conflate' RKP and J Hansen with IPCC. Wikipedia does. Don't shoot the messenger! RKP, in his highly public position, should not say things 'off the cuff'. No-one in such a position should. How is whether the figure appears in IPCC reports relevant to the impact of public statements made 'off the cuff'? Have you heard of the 'Media'? CBDunkerson you wrote: "the 'tipping point' comment... it didn't come from either of the two scientists" I didnt say that it did. The Wiki article appears to. Safe upper limit: If an engineer says that 100 lbs per sq ft is a safe upper limit for loading an elevator, he means exactly that. He does not mean that is a limit 'just in case' someone were to walk in carrying another 100 or 200 lbs or whatever. He means it the safe upper limit as would be generally understood in any other field I can think of. If it is not that sort of limit in climate science, what exactly is it? - this seems to be turning into a game of words. I have simply pointed out how the Wiki quote could be (mis)understood by the average reader. Take that up with Wikipedia perhaps? In general: Do you think 350ppmv is a realistic global target? If so, when do you think it might be achievable?
  17. lancelot wrote: "I am quite familiar with the science. " Very clearly this is not the case, otherwise you would not have seen any contradiction in the idea that 350ppm is a "safe" stabilisation concentration yet not having observed a "tipping point" given that we had already past that level. The reason there is no contradiction has already been explained to you, and yet you have not accepted it, nor refuted it. This is not encouraging. A more realistic safe upper limit argument would be to say that the safe upper limit for dietary intake would be 2500 calories per day. However if on one day you eat 4000 calories at a banquet, the fact you didn't have a heart attack or stroke on that day does not mean that 2500 calories is not the long term safe upper limit. The 350ppm is a safe LONG TERM stabilisation figure, not a limit on the safe SHORT TERM transient concentration. If you think it is just that the Wikipedia article is badly worded, why are you discussing it here, rather than at Wikipedia (I suspect the chaps at Wikipedia would point out the error in your position much as I have)?
  18. lancelot wrote: "In general: Do you think 350ppmv is a realistic global target? If so, when do you think it might be achievable? " This is pretty off-topic for this article, if you want to discuss it in detail, please find a more appropriate thread. From a scientific perspective, the natural environment is currently taking about 1.6GtC per year out of the atmosphere. 40ppmv is about 19GtC, so it would take the natural environment at least 12 years to get back down to 350ppm if we cut emissions to zero today. That gives an approximate lower time limit. So of course it is achievable, however I am rather cynical about those in public office and those that elect them. Both are generally too focussed on short term self-interest to act for the long term good of us all. Thus 450ppmv is a more realistic stabilisation point (the politics being the limiting factor not the science), and we will have to put up with the consequences, which will generally be worst in those parts of the world least capabale of adapting and who generally will have been least responsible for creating the problem.
  19. lancelot, no the Wikipedia article does not attribute Pachauri's position to the IPCC. In any case, it hardly matters whether 'you' or 'your interpretation of the Wikipedia article' are incorrect... the position stated (by whomever) is not accurate. You also still haven't given ANY reason for the claim that 350 ppm is "crying wolf"... which is certainly your own claim rather than anything in the Wikipedia article. It needs to be understood that the primary difference between Hansen's 350 ppm estimate and the more common 450 ppm estimate of 'safe' CO2 levels is the timeframes involved. If we look only at 'fast' (e.g. within 100 years or so) feedbacks then we could likely go up to about 450 ppm. However, if you take the long term view then going over 350 ppm would eventually cause significant warming and flooding of major coastal cities around the world. The relevant questions then become how soon would major consequences from exceeding 350 ppm manifest, and would that allow us enough time to get back down below 350 ppm. Is 350 ppm a reasonable target to get back down to within 500 years? I'd say yes... if we switch away from fossil fuels in the next several decades and then work on technologies to pull CO2 out of the atmosphere that seems entirely possible. Could we get back to 350 ppm within 50 years? Certainly not... but then we shouldn't be seeing major problems (e.g. large sea level rises, major agricultural disruptions, millions of deaths) in 50 years unless we continue to push CO2 levels higher.
  20. The IPCC is a political organisation - they choose the revieweres, the policies, they review the reports and choose the board in plenary sessions. Politicians are also involved in the Summary For Policymakers.. This is from their very own website. "The IPCC is an intergovernmental body. It is open to all member countries of the United Nations (UN) and WMO. Currently 195 countries are members of the IPCC. Governments participate in the review process and the plenary Sessions, where main decisions about the IPCC work programme are taken and reports are accepted, adopted and approved. The IPCC Bureau Members, including the Chair, are also elected during the plenary Sessions. " The IPCC was setup by the UNEP - the United Nations Environment Program... (-Snip-)
    Response: [DB] Sloganeering snipped.
  21. Tell you what, krisbaum: I'll copy the reference list for the aerosols section of AR4 and post it on a neutral site dedicated just to that list. Will you then start looking through the literature? I don't care if the IPCC was formed by the Nevada State Clowns Association. That's no reason not to read the referenced literature. That literature was not peer reviewed by the IPCC; it was peer reviewed by the dozens of journals in which climate science is published. It was not summarized and interpreted by politicians. It was summarized and interpreted by scientists. If you have a problem with the credentials of any of the hundreds of scientists involved, let's have out with it. You are implying that these hundreds of scientists are colluding to construct a lie, and that the rest of mainstream climate science is in on it. A lot of greenpeace members? WTH? "a lot"? What sort of political stripe need a scientist be in order to gain your respect? Richard Alley is a conservative. Does he count? Or is he just a dupe of the secret leftist scientist coalition?
  22. krisbaum, the list of IPCC and their affiliations can be found here. Furthermore you can see what each said, and what the chapter authors did with there comment. To be a reviewer, all you basically need to do is request a draft and sign an NDA. It's pretty hard to see how you could set up a more transparent and fair way for governments to get a review of the state of climate science. Now what is your evidence for bias? Hopefully a little stronger than "I dont like their conclusions so it must be wrong". Where is your evidence that they failed to examine important papers that would result in a different conclusion? If you are so sure they are wrong about aerosols, then surely you must have a paper that forms that opinion?
  23. scaddenp; the review process does not work like that... yes, the material is sent out to people to review, but the lead authors collect the reviews and decide which ones are to be included and which arent. even the Interacademy Council recommends this extra step of transparency and scrutiny. there is no separate body that is responsible for reviewing and approving or scrutinising the end result of what the IPCC produce. the Summary For Policymakers is a combined political & scientific production - this is how the process works!! I am not making up anything here.
  24. This page lists the process; as you can see, the government chooses 'experts', a 'bureaux' selects authors.. tbose authors produce a 2nd draft which then goes to a combination of the expert panel & government officials and a final review!!! it is NOT a purely scientific publication / report. if it was, you would have absolutely no government involvement until the document has been produced. even better, you would have a group of people or committee completely divorced from the IPCC that would review what they had produced - and have the ability to deny publication pending changes or review. this does not happen. the SPM also gets written by the plenary. It is released BEFORE the main report.
  25. scaddenp - when i investigated the whole aerosol problem, i discovered that the IPCC dont have any solid science to base their estimates of forcing on. there are no solid papers on the aerosol effect - that definitively tell scientists whether aerosol levels have increased or decreased and by how much over the last 100 years. This is because we didnt record aerosols around the world until recently. Go find me one that has historial records. It does not exist.

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