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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 sensitive is our climate?

What the science says...

Select a level... Basic Intermediate Advanced

Net positive feedback is confirmed by many different lines of evidence.

Climate Myth...

Climate sensitivity is low

"His [Dr Spencer's] latest research demonstrates that – in the short term, at any rate – the temperature feedbacks that the IPCC imagines will greatly amplify any initial warming caused by CO2 are net-negative, attenuating the warming they are supposed to enhance. His best estimate is that the warming in response to a doubling of CO2 concentration, which may happen this century unless the usual suspects get away with shutting down the economies of the West, will be a harmless 1 Fahrenheit degree, not the 6 F predicted by the IPCC." (Christopher Monckton)

 

Climate sensitivity is the estimate of how much the earth's climate will warm in response to the increased greenhouse effect if we double the amount of carbon dioxide in the atmosphere.  This includes feedbacks which can either amplify or dampen that warming.  This is very important because if it is low, as some climate 'skeptics' argue, then the planet will warm slowly and we will have more time to react and adapt.  If sensitivity is high, then we could be in for a very bad time indeed.

There are two ways of working out what climate sensitivity is. The first method is by modelling:

Climate models have predicted the least temperature rise would be on average 1.65°C (2.97°F) , but upper estimates vary a lot, averaging 5.2°C (9.36°F). Current best estimates are for a rise of around 3°C (5.4°F), with a likely maximum of 4.5°C (8.1°F).

The second method calculates climate sensitivity directly from physical evidence, by looking at climate changes in the distant past:

adapted fig 3a

Various paleoclimate-based equilibrium climate sensitivity estimates from a range of geologic eras.  Adapted from PALEOSENS (2012) Figure 3a by John Cook.

These calculations use data from sources like ice cores to work out how much additional heat the doubling of greenhouse gases will produce.  These estimates are very consistent, finding between 2 and 4.5°C global surface warming in response to doubled carbon dioxide.

It’s all a matter of degree

All the models and evidence confirm a minimum warming close to 2°C for a doubling of atmospheric CO2 with a most likely value of 3°C and the potential to warm 4.5°C or even more. Even such a small rise would signal many damaging and highly disruptive changes to the environment. In this light, the arguments against reducing greenhouse gas emissions because of climate sensitivity are a form of gambling. A minority claim the climate is less sensitive than we think, the implication being we don’t need to do anything much about it. Others suggest that because we can't tell for sure, we should wait and see.

In truth, nobody knows for sure quite how much the temperature will rise, but rise it will. Inaction or complacency heightens risk, gambling with the entire ecology of the planet, and the welfare of everyone on it.

Basic rebuttal written by GPWayne


Update July 2015:

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

Last updated on 5 July 2015 by skeptickev. View Archives

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Further reading

Tamino posts a useful article Uncertain Sensitivity that looks at how positive feedbacks are calculated, explaining why the probability distribution of climate sensitivity has such a long tail.

There have been a number of critiques of Schwartz' paper:

Comments

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Comments 376 to 386 out of 386:

  1. Penguin,

    In hte paper you cite they claim that climate sensitivity is derived completely from cliamte models.  That is false.  there are several ways to derive climate sensitivity from data includig paleoclimate data.  I note they provide no citations to support their claims.  They will only be read by skeptics.

    They assume that the change in cloud cover forces the change in temperature.  That is completely backwards.  Cloud cover is a response to the change i temperature and not the casue of the change.  In order to chage the temperature you have to add energy.  Changes in clouds do not add energy. 

  2. Penguin, the response to the JK&PM paper is huge laughter.

    A paper based on limited observations ( over just 25 years ) and giving a "calculated" climate CO2 sensitivity of 0.24 degreesC (transient sensitivity) . . . is laughable.

    Also amusing, is the paper title.  JK&PM themselves did no experiment !

  3. Penguin ~ some more details about the JK&PM paper you mentioned :-

    It is not a paper in a peer-reviewed scientific journal.  It has been described as a re-hash of an older (and non-peer-reviewed) paper from Energy & Environment journal (which is a social journal, not a scientific journal).

    It was based on a limited amount of information from old satellite data ~ which was subsequently found to be faulty.  You can find extensive criticisms of it, by various respected scientists, at the high-quality blog climatefeedback.org/claimreview/non-peer-reviewed-manuscript-falsely-claims . . . . (etcetera)

    Not only that, but JK&PM have made a number of other gross mistakes (such as saying that only a tiny portion of the 20th & 21st Century rise in atmospheric CO2 level derives from human influence).

    Penguin, the short version is: the "No experimental evidence (etcetera)" manuscript was authored by crackpots and is rubbish from beginning to end.  Laughable !

    Penguin, if you'd like to gain some climate knowledge in a relaxed easy-going way, then have a look at "Climate Change — the scientific debate" by youtuber Potholer54 (a science journalist) and the whole follow-up series of videos (most, fairly short!)      Not only very informative, but done in an entertaining & often humorous manner.

  4. Penguin @375,

    You specifically ask "Do we know what longer series or more recent data would show?"

    The paper (or actually the paper of 2014) uses alleged low cloud data for 1983-2008 without describing the source. The dates suggest ISCCP data which has been sourced by the denialists on the Climate4you website to provide identical data. (Elsewhere Exeter University's Richard Betts describes Kauppinen & Malmi's cloud data as "at odds with peer-reviewed papers.") The paper also plots relative humidity 1970-2010 as a proxy for low cloud, again without attribution. A previous paper describes this as 700mbar & 850mbar data but using NCEP reanalysis data it looks more 700mbar than 850mbar. (So that's 3,000m - not exactly low cloud.) The temperature data appears to be based on HadCRUT4.

    If you plot NCEP 700mbar data 1948 to date, it shows no change post-2010 while the global temperatures actually show significant rise. And pre-1970 there is a large Relative Humidity change 1948-60s which by Kauppinen & Malmi's grand theory would suggest a there was a rise in global temperature of +0.8ºC when, of course, global temperature was pretty-much flat as a pancake. The 850mbar data is a poorer fit 1970-2010 but also shows the same trends beyond the 1970-2010 period.

  5. I am an anthropogenic climate change denier because I have never found any scientific evidence that supports it. The theory is based upon modeling climate sensitivity to CO2 and as you state: “In truth, nobody knows for sure quite how much the temperature will rise”.

    We hear regularly from the media that 90+% of scientists believe in anthropogenic climate change but my question is how many scientists are actually trained and practice climate modeling?

    I’ve looked at the undergraduate and graduate curriculum for the top US environmental science universities and have found only one course on climate modeling. Penn State offered METEO 523 in Spring 2020 and only 6 of 30 seats were filled and the course has been since dropped. So what course is available in climate modelling so I can learn the science?

    Given the lack of curriculum on climate modeling it is apparent that all climate science curriculum is based upon the assumption of anthropogenic climate change without providing any scientific evidence or expertise. This isn’t science, it’s group think. So the opinion of those 90+% so called scientists is based upon blind faith rather than science. This isn’t science it’s a hoax.

    I remain interested in finding a quality course in climate modeling.

    Response:

    [DB]  Please start off by reading this thread and this thread.  Then proceed to this post, which discusses the empirical evidence for AGW.  Skeptical Science has dedicated posts on pretty much every point anyone would think to contend with the science of climate change on, just use the Search function to find the most appropriate thread, read it including the comments, and only then if you still have questions, post them there, and not here.

    Off-topic and Gish Gallop snipped per the Comments Policy, which you should also read.  As this is a moderated forum, you should also ensure that future comments are constructed to adhere to it.

    Moderation complaints and sloganeering are unacceptable.

  6. @381 Deplore This. Everyone has seen this argument. It was a well known published "merchant of doubt" argument full of logic fallicies and false premises designed to mislead people like you... which unfortunately it seems to have worked so far. However, if you are honestly seeking a University level course, I suggest you change your google search terms to "statistical modeling" and /or "statistical modeling of climate change" and you will find a whole lot of universities in the world can help you.

    And yes sensitivity is a factor in all of them. In some as a constant and in a few papers there are calls for sensitivity as a variable to fine tune accuracy.

    However, the statement, "The theory is based upon modeling climate sensitivity to CO2" is false. Called a false premise logic fallacy.

    Actually global warming is based on empirical evidence.

    Response:

    [DB] The user to whom you are replying has recused themselves from further participation here.

  7. Climate theory  is most certainly not based on climate modelling, but observation including the measurable increase in surface irradiation from increased CO2. If sun increased output by 4W/m2 then you would surely expect earth to warm (if not, what is your theory for seasons), but somehow increase from GHG wont cause warming. Climate models are our best guide as to how the future might look. Far from perfect but lightyears ahead of reading entrails or believing nothing will change. I remain stunned that people insist the consensus reported by the IPCC is wrong while obviously having never even opened it the WG1 reports.

  8. Interesting math, but it doesn't appear to be consistent with NASA, Berkeley, Hadley, World Meteriorlogic Organization, and Cowtan and Way global temperature datasets--every international real-time and long-term dataset for Global Temperature.

    Please bear with me as I focus on real data generated by hard working climate scientists over the past 6+ decades.

    Mauna Loa Observatory (MLO) began recording CO2 in Mar1958 and continues to be the longest real-time record of atmospheric CO2.

    The average temperature change of the above internationally highly acclaimed datasets for global temperature (Mar1958 through May2020), is 0.85 C {1.00, 0.92, 0.78, 0.72, 0.83} respectively.

    CO2, per MLO, rose from 315.71 to 417.07.

    If climate sensetivity for CO2 was 2 C (.85 C / ln[417.07/315.71] x ln(2 or a double) = 2 C), CO2 alone would explain 100% of all climate change! 

     

    1) The Sensetivity of all GHG combined > 2 C is not supported by real-time climate for the past 6+ decades.

    2) CO2 is not the only GHG and GHG is not the only thing causing climate change.

    Response:

    [TD] It appears that you did not read the Advanced tabbed pane of this post. Please do.

  9. Leehoe @383 ,

    please, the word is Sensitivity.  Remember the humorous old saying :-

    "Typo me once, error me twice".

    Yes, the past 6 decades have been a moderately good time for doing a back-of-envelope calculation of sensitivity, because of the fairly flat level of insolation ( around 1360 w/m2 ).  And with only a rather small change in non-CO2 / non-H2O greenhouse gas levels.

    Unfortunately, the last part of of your post was so abrupt, that your meaning is ambiguous.  Please expand your wording, to give a clear indication of your meaning.  Readers may be confused on your intention regarding ECS versus TCS.  And it is entirely unclear whether you were alluding to the industrial aerosols and volcanic aerosols during this 6 decade period.

    Please clarify !

  10. leehoe - do you understand the difference between Equilibrium Climate Sensitivity (often just climate sensitivity) and Transient Climate sensitivity? The box on pg 1110 of the IPCC WG1 has some explanation.

    Discussions around estimates of climate sensitivity from the instrument record here especially the Marvel et al paper. And also here for earlier work by Otto, Curry, Lewis

  11. The big news announced yesterday is the narrowing of equilibrium climate sensitivity (ECS) from a combination of paleoclimate and historical measurements and feedback modelling, a study which will feed into IPCC AR6. As I understand it, ECS is now very likely (90% likely) to be within 2.0‐5.7 °C, and likely (66% probability) to be 2.6‐3.9 °C, with a longer tail above 4.5 °C than below 2 °C. Anyone 'gambling' on low sensitivity would lose. Sherwood et al, "An assessment of Earth's climate sensitivity using multiple lines of evidence", Reviews of Geophysics, 2020. http://dx.doi.org/10.1029/2019RG000678

    The following long review tells me more than I need to know about feedbacks of all kinds: Heinze et al, "Climate feedbacks in the Earth system and prospects for their evaluation", Earth System Dynamics, 2019. https://doi.org/10.3929/ethz-b-000354206
    Although there may be 'black swan' events and earth-system feedbacks, the idea that climate scientists aren't including albedo or cloud changes in models is incorrect.

    More recent info on feedbacks in the latest CMIP6 models is in Meehl et al, "Context for interpreting equilibrium climate sensitivity and transient climate response from the CMIP6 Earth system models", Science Advances, 2020. https://doi.org/10.1126/sciadv.aba1981 and Zelinka et al, "Causes of Higher Climate Sensitivity in CMIP6 Models", Geophysical Research Letters, 2020. https://doi.org/10.1029/2019GL085782, the latter including a nice figure S7 showing the contribution of different feedbacks in different models.

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