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Is global warming in a hiatus?

On September 27 2013 the 5th Assessment Report by the Intergovernmental Panel on Climate Change (IPCC) will be released. One part of this report will address the so-called “warming hiatus”. This is the…

With low solar activity, a double-dip La Nina and more particles in the air, it should be much colder than it is. Les Chatfield/Flickr

On September 27 2013 the 5th Assessment Report by the Intergovernmental Panel on Climate Change (IPCC) will be released.

One part of this report will address the so-called “warming hiatus”. This is the argument that warming has stopped, with the further assertion in some quarters that we therefore have nothing to worry about in the future.

It is a fact, based on observations of air temperature, that the rate of global warming measured as surface air temperature has slowed over the past 15 years. The last decade is still the warmest in the past 150 years.

If you measure global heat content then global warming has not slowed. If you measure other indices including sea level rise or ocean temperatures or sea ice cover global warming has not slowed.

However, the warming trend in air temperatures has slowed over the last 15 years. There is a great deal of interest in this “hiatus” in the sense of whether it points to some fundamental error in climate science.

The 5th Assessment Report by the IPCC explains the slowing in the rate of global warming in roughly equal terms as the consequence of reduced radiative forcing (the difference between radiative energy that hits the earth and energy radiated back to space), increased heat uptake by the oceans and natural variability.

The reduced radiative forcing (the amount of energy available to drive the climate system) is due to the recent solar minimum (a period of low solar activity), and volcanic and anthropogenic aerosols (these are particles such as sulphur and soot, which block some radiation from hitting the earth).

The slowing in the rate of warming over the last 15 years is not in the least surprising. We have seen a combination of the solar minimum, anthropogenic aerosol emissions and back-to-back La Niñas.

What is surprising - and what is deeply concerning to me and almost entirely missed in the media commentary - is that we have not cooled dramatically over the last 15 years.

Below is the global surface temperature graph – this comes from a NASA site but any other reputable temperature reconstruction makes similar points. Note that there were periods through the 20th century where combinations of aerosols from volcanoes and human sources, solar variability and natural variability led to very significant cooling.

Figure 1: Global surface temperature. NASA

Between about 1880 and 1890, temperatures cooled by about 0.4C. Between 1900 and 1910 temperatures cooled close to 0.3C. Between 1945 and 1950 temperatures cooled about 0.35C. Between 1962 and 1965 temperatures cooled about 0.3C. There are other examples, but these were decade-scale cooling of 0.3C to 0.4C.

The most recent period of similar relevance starts with the extremely hot year, 1998. Since 1998, through to 2012, the temperatures cooled by 0.03C. However you choose to view the figure you simply have to conclude that natural variability, aerosols and solar variability have caused global cooling in the past of a scale that dwarfs anything that has occurred in the last 15 years.

So, here is what I think we should be genuinely concerned about.

Given the double-dip La Niña, coupled with the solar minimum and coupled with the high aerosol output from some developing nations, the question in the minds of some climate scientists is not “why has it cooled?”, because it has not cooled in any significant sense and the climatologically significant trends (calculated over 30 years) remain upwards.

Indeed, despite a suite of forcings that should have led to cooling, we still had the warmest decade in the observational record.

So, the question is, given it did cool several times in the historical period under broadly parallel circumstances in terms of the forcing, why has it not cooled since 1998 by 0.3C or 0.4C, and how come we broke the records for the warmest decade?

There has been time (its 15 years while previous cooling occurred in 10 years) for cooling of 0.3C or 0.4C to have occurred. There really is a case to argue that we should have cooled to close to the values measured in around 1990 and definitely not broken the record for the warmest decade on record.

A plausible answer is that we have underestimated the climate sensitivity.

We know, for certain, that aerosols, natural variability and solar variability have cooled the climate in the past. This time, they have not.

One way that this makes sense is if climate scientists have underestimated how dominant CO2 and other greenhouse gases are in warming the climate. In other words, CO2 and other greenhouse gases are countering the cooling effects of natural variability by much more than we anticipated.

If correct, this means that the capacity of CO2 and other greenhouse gases to accelerate warming - once natural variability, solar variability and aerosols decline in influence - has been underestimated.

A second possible explanation is that the warming by CO2 has led to a sufficiently different climate system that natural variability now functions differently. This seems extremely unlikely but is certainly anything but comforting.

If you see the slowing of warming over the last 15 years as a hint that climate scientists might have been wrong and that global warming is less of a problem than predicted, you are very likely being lulled into a false sense of security.

The lack of cooling of 0.3C or 0.4C since 1998 is most easily explained by the effect of increasing CO2 and other greenhouse gases masking the cooling that would otherwise have occurred.

It follows that when we next see an El Niño, and the solar cycle is more average, or if developing countries clean up their aerosol emissions, we will see an acceleration of warming rates observed prior to 1998.

In short, the slowing of warming rates since 1998 is not a good news story. It is very likely a hint that climate scientists have underestimated the sensitivity of climate to increasing CO2 and the slowing of warming is lulling us into a very false sense of security.

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    1. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to David Arthur

      I think Rupert may have had in mind the 2007 prediction by WIESLAW MASLOWSKI reported on by the ABC at the time that "the northern polar waters could be ice-free in summer by 2013". I see that the current graphs of sea ice extent show about 5 million square kms. "Missed by that much!" as the saying goes.

      The ABC's hopelessly uncritical piece still available for your reading pleasure. The dire warning at the end of the report by ABC's reporter a real belly slapper.

      http://www.abc.net.au/am/content/2007/s2117573.htm

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    2. David Arthur

      resistance gnome

      In reply to Marc Hendrickx

      If Citizen Rupert had Maslowski's purported prediction, perhaps he should have addressed his tweet to Dr Maslowski?

      Perhaps you could pass on some advice to Citizen Rupert, that "sea ice minimum [area] was only one measure of ice levels.

      "Observations from the Cryosat mission released last week by the European Space Agency showed the VOLUME of sea ice in the Arctic falling to a new low over the last winter.

      "Last March and April – typically the time of year when the ice floes are at their thickest – there was just 15,000 cubic km of ice. There would have been 30,000 cubic km, or TWICE that volume, at the height of winter 30 years ago, scientists said."

      (http://www.theguardian.com/environment/2013/sep/18/how-fast-is-arctic-sea-ice-melting)

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    3. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to David Arthur

      So we have one climate cycle worth of good data. So what!

      Gee and how is the South pole looking, Just like those climate models suggested?????

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  1. David Arthur

    resistance gnome

    Thanks for this, Dr Pitman.

    Perhaps the divergence of response times for various heat reservoirs to climate forcings render the concept of "climate sensitivity" somewhat problematic - it may have been of moderate value when introducing otherwise ignorant economists to the issue, but beyond that it is of little value?

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  2. Comment removed by moderator.

  3. Andrew Vincent

    Marketing . Communications . Multimedia

    "So, the question is, given it did cool several times in the historical period under broadly parallel circumstances"

    Andy - could you please expand on this?

    How were these other periods similar? The counter argument to your article is - well, they're obviously not similar.

    I agree with the thrust of the article but this seems to be a crucial point.

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    1. Michael Wilbur-Ham (MWH)

      Writer (ex telecommunications engineer)

      In reply to Andrew Vincent

      Though further information is welcome, I suspect that there is still going to be a fair bit of 'we don't know'.

      The deniers take hold of this uncertainty to try to convince people that climate change is no longer a threat.

      And sensible person bears in mind that this uncertainty leave open the possibility that CO2 sensitivity might be masked by this cooling and that in a few years we might suddenly find temperatures rising at a much faster rate than we predicted.

      It deciding how to act so secure the future prosperity of our children and our grandchildren, which view is sensible?

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    2. Paul Richards

      integral operating system

      In reply to Michael Wilbur-Ham (MWH)

      Michael Wilbur-Ham (MWH) wrote; "The deniers take hold of this uncertainty to try to convince people that climate change is no longer a threat." Interesting comment and a good observation. Some here even log in with this as their primary focus.
      There are very strong emotions involved, as some have had a career built on the perception exponential growth and use of finite resources is no problem.
      We all find it hard to admit any central premise in our values could be flawed. Generally it causes…

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  4. Juan Vesa

    student

    you're right, the fact that it's slowed and not reversed is indeed not conforting. so, now the 10-15 year "pause" (in replace of a cooling) has occurred can we see another 0.5° rise in temps over the next 20 years as has been witnessed in the past? i certainly hope not, i'm not a summer person.

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  5. Marc Hendrickx

    Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

    For the benefit of others the NIPCC released its latest report today which counters much of Pitman's points above.

    The complete report is available via...

    http://climatechangereconsidered.org/ccr-2013/

    Perhaps The Con's curators could request the NIPCC authors provide a piece for comment? Or is asking for some balance from this site going to far?

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    1. David Arthur

      resistance gnome

      In reply to Michael Wilbur-Ham (MWH)

      Fair point Michael.

      The evidence for human impact on climate is so overwhelming, we can no longer be certain of the loyalty of any Australian (including Citizen Rupert's "The Australian") to this nation who persists in Denying it.

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    2. Andrew Vincent

      Marketing . Communications . Multimedia

      In reply to Marc Hendrickx

      The problem with publications like the NIPCC is that they blow over with the merest puff of logic.

      That's not what this site is about.

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    3. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to Andrew Vincent

      "That's not what this site is about."

      What's Pitman's piece doing here then? one puff of reference to lower climate sensitivity and its gone!

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    4. Andrew Vincent

      Marketing . Communications . Multimedia

      In reply to Marc Hendrickx

      He's putting forward a theory ... "A plausible answer is that we have underestimated the climate sensitivity."

      This is true. It is plausable.

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    5. Mike Hansen

      Mr.

      In reply to Marc Hendrickx

      The NIPCC report is produced by the pro-tobacco, fossil fuel funded conservative climate change denial thinktank, the Heartland Institute.

      Apparently Australia's own Bob Carter gets about $1550 of fossil fuel money per month to help produce it.

      "Confidential documents leaked from inside The Heartland Institute, a wealthy think tank based in Chicago and Washington, detail strategy and funding for an array of activities designed to spread doubt about climate change science, paid for by companies that have a financial interest in continuing to release greenhouse gases without government interference."

      "Professor Carter did not deny he was being paid by The Heartland Institute, but would not confirm the amount, or if the think tank expected anything in return for its money."

      http://www.theage.com.au/environment/climate-change/scientist-denies-he-is-mouthpiece-of-us-climatesceptic-think-tank-20120215-1t6yi.html

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    6. Mark McGuire

      climate consensus rebel

      In reply to Andrew Vincent

      All very good putting forward theories after the fact.
      But the fact is, we have already begun transforming our world economies on what some people claim is a law, like gravity, which, at very least from Pitman's post above, appears to be a failed thesis, which requires more theories after observation proves it wrong.

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    7. Andrew Vincent

      Marketing . Communications . Multimedia

      In reply to Marc Hendrickx

      There are many studies on sensitivity - some higher, some lower. It's not necessary for each study to consider every outcome.

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    8. Mark McGuire

      climate consensus rebel

      In reply to Andrew Vincent

      Quote: "Temperature rise does not go in straight lines."

      Better tell that to Al Gore, the UN-IPCC, and Mike Mann, all of the Hockey Stick fame.

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    9. In reply to Mike Hansen

      Comment removed by moderator.

    10. Andy Pitman

      Director of the ARC Centre of Excellence for Climate System Science at UNSW Australia

      In reply to Mark McGuire

      I do not think any of these ever suggested temperature rise goes in a straight line.

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    11. Andy Pitman

      Director of the ARC Centre of Excellence for Climate System Science at UNSW Australia

      In reply to Mark McGuire

      Not sure what you are saying here.

      The physics that forces temperatures to rise as a consequence of more energy is a Law of Physics.

      Nothing I said hints that there is any science that contradicts the need to rapidly cut emissions of greenhouse gases.

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    12. Andrew Vincent

      Marketing . Communications . Multimedia

      In reply to Mark McGuire

      "Better tell that to Al Gore, the UN-IPCC, and Mike Mann, all of the Hockey Stick fame."

      Of course.

      um... because Al Gore and Hockey Stick.

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    13. Andrew Vincent

      Marketing . Communications . Multimedia

      In reply to Andy Pitman

      He's saying that because the temperature anomaly does not fit the IPCC projections this is "proof" that "the theory" is wrong. So you - being part of the great conspiracy, are making up new theories so nobody will question your taxpayer funded grants.

      Or something like that.

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    14. Geoffrey Henley

      Research Associate

      In reply to Mike Hansen

      "Apparently Australia's own Bob Carter gets about $1550 of fossil fuel money per month to help produce it."

      So what about the $180,000 per year Tim Flannery was getting paid to promote climate alarmism? Al Gore and David Suzuki have charged exorbitant amounts for speaking assignments.

      There is a lot more money to be made in promoting alarmism!

      Good to see Tim Flannery and the Australian Climate Alarmist Commission getting the chop. That money can now be spent on something useful.

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    15. Mark McGuire

      climate consensus rebel

      In reply to Andy Pitman

      Greetings Prof. Pitman, thank you for your time. Sir, I can only link an image of the infamous hockey stick with a straight line going up with no prediction of a hiatus.
      I don't doubt the law of physics. Matter of fact, I would be interested in your description of the physics mechanism that helps the heat travel down to the deep, cool depths of the ocean, as we all know surface tension emphatically rejects heat when applied from above, and this heat as a result of "more energy" is not detected at the surface.
      And though you do not contradict the need to cut ghg emissions, that is not the point. It is the hiatus, despite the continuing, relentless rise of dangerous carbon (sic) which you are addressing here.
      http://www.theguardian.com/environment/2010/feb/09/hockey-stick-graph-ipcc-report
      Again, thank you for attempting to help me understand this complex debate.

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    16. Michael Wilbur-Ham (MWH)

      Writer (ex telecommunications engineer)

      In reply to Marc Hendrickx

      It seems that I'm breaking community standards by posting my opinion that some of the deniers here are lobbyists as my post which mentioning this got removed by the moderator.

      Yet posting a link to a non-science report by well known anti-climate change lobby group The HeartLand Institute, as Marc Hendrckx did above, and him claiming that this report "counters much of Pitman's points" in the article here is acceptable.

      Clearly the management want the Conversation to be a platform for climate…

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    17. Mark McGuire

      climate consensus rebel

      In reply to Andrew Vincent

      Hi Andrew. No conspiracies need. If the science is settled as we have been assured and acted upon, than why the need to now produce new theories when observations don't match? Scientific method says time to admit failure, not claim you were wrong but, using the same science will be correct in the distant future.

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    18. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to Michael Wilbur-Ham (MWH)

      I am not a lobbyist for anything other than the scientific method. Here's a great video of how it works...

      http://www.youtube.com/watch?v=b240PGCMwV0

      Compare the theory to observations. If it disagrees with experiment its wrong. Now lets see how this applies to the climate models....

      http://opinion.financialpost.com/2013/09/16/ipcc-models-getting-mushy/

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    19. Matthew Parton

      Project Manager

      In reply to Geoffrey Henley

      People on both sides of the debate are profiteering, 'Lord' Monkton anyone?

      In terms of "following the money" I would suggest that it is pseudo-independent think tanks like the Heartland Institute that are to be most questioned. In the same way as the tobacco industry of the 70s and 80s did their best to use it to create doubt about cigarette dangers they are doing the same for anthropomorphic climate change.

      Do you think scientists chasing research grants or the fossil fuel industry has more to lose here?

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    20. Robert Tony Brklje
      Robert Tony Brklje is a Friend of The Conversation.

      retired

      In reply to Marc Hendrickx

      Why, is paying for junk science something to be recommended. How about the 'N' in NIPCC standing for nongovernmental as if that is something to be special (we know it is by the crazy US right wing, who want to pollute and waste like there's no tomorrow because 'God' will fix and that's not a joke, that serious US commentary).
      Why nongovernmental because of course everyone can trust those corporations who fund the heartland institute and the non-independent report, after all those corporations only goal is profits for themselves and by the own admission that is their only goal, profits, regardless of consequences to others.
      Balance requires balance in the input, not science on one side and propaganda on the other, science is not by popular vote, science is not by politics and most definitely science is not by public relations marketing pretending to news or science.

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    21. Andrew Vincent

      Marketing . Communications . Multimedia

      In reply to Mark McGuire

      It's the same theory. Andy's article explains another facet of it.

      Surface temp anomalies don't chart in straight lines so will invariably diverge from projections. Andy is explaining why.

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    22. Mike Hansen

      Mr.

      In reply to Mark McGuire

      "as we all know surface tension emphatically rejects heat when applied from above"

      We all know? No we do not as this is scientific gobbledegook from the same man who linked a temperature graph full of wiggles and declared it a straight line.

      Mark - it is the sun that in the first instance heats the earth. If the sun's rays were unable to penetrate the surface tension of the oceans, the oceans would be at absolute zero temperature. And when you stick your head under the waves, it would be pitch black.

      You are a climate denier troll of the worst sort - entirely clueless about science but determined because of your ideological fixations that it is wrong. Do us all a favour and take up bowls or whatever.

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    23. Mike Hansen

      Mr.

      In reply to Marc Hendrickx

      The lobbyist for the scientific method links to the opinion pages of the conservative Financial Post. Not to an article by a climate scientist but one by conservative economist Ross McKitrick.

      McKitrick is a signatory to a statement from the conservative creationist Christian Cornwall Alliance that declared that global warming was not happening because God would not allow it.

      "We believe Earth and its ecosystems – created by God’s intelligent design and infinite power and sustained by His faithful providence – are robust, resilient, self-regulating, and self-correcting, admirably suited for human flourishing, and displaying His glory. Earth’s climate system is no exception. Recent global warming is one of many natural cycles of warming and cooling in geologic history."
      http://en.wikipedia.org/wiki/Cornwall_Alliance

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    24. In reply to Mike Hansen

      Comment removed by moderator.

    25. Paul Richards

      integral operating system

      In reply to Michael Wilbur-Ham (MWH)

      Michael Wilbur-Ham (MWH) wrote; "... time to switch off notifications and put my energies elsewhere." Good strategy, there is no risk management conversation here. Just an adversarial mindset and that makes for poor conversion.

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    26. Felix MacNeill

      Environmental Manager

      In reply to Marc Hendrickx

      Marc, are you able to reference Zig and Zag's comments as well? Personally, I prefer honest clowns.

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    27. Felix MacNeill

      Environmental Manager

      In reply to Marc Hendrickx

      Or maybe they realise we all have better things to do with our trime than waste it chasing rabbits down holes.

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    28. Felix MacNeill

      Environmental Manager

      In reply to Marc Hendrickx

      I see the hysteria is building now, Marc and your natural spleen and abuse is beginning to bubble up as it always does.

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    29. Peter Turner
      Peter Turner is a Friend of The Conversation.

      Thinker

      In reply to Mark McGuire

      Whoops Mark - there's a difference between settled and extremely high probability, which is where the agw science is. Scientific method continually refines - sort of like the small adjustments we make to steering a car to keep it going straight. We are now at the stage of understanding where 97% of climate scientists agree we have a serious problem - are you betting on the 3%? - lousy odds, mate!

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  6. Marc Hendrickx

    Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

    I see the censorship of comments critical to the piece has begun.

    Quick put your heads in the sand!

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    1. David Arthur

      resistance gnome

      In reply to Marc Hendrickx

      Fair point Marc, except that the evidence for human impact on climate is so overwhelming, we can no longer be certain of the loyalty of any Australian (including Citizen Rupert's "The Australian") to this nation.

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    2. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to David Arthur

      No disagreement on the evidence of impact. It is the level of that impact and the comparative costs that is the critical question.
      Once again you are doing battle with your own preconceived ideas and generalizations.

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    3. David Arthur

      resistance gnome

      In reply to Marc Hendrickx

      Degree of impact? Start with

      NATURE CLIMATE CHANGE | LETTER
      Mapping vulnerability and conservation adaptation strategies under climate change
      James E. M. Watson, Takuya Iwamura & Nathalie Butt
      Nature Climate Change (2013) doi:10.1038/nclimate2007

      Then read "Great Barrier Reef Vulnerability Assessment" http://www.gbrmpa.gov.au/outlook-for-the-reef/climate-change/how-climate-change-can-affect-the-reef/great-barrier-reef-vulnerability-assessment

      Colberg, F. and K. L. McInnes (2012), The impact of future changes in weather patterns on extreme sea levels over southern Australia, J. Geophys. Res., 117, C08001, doi:10.1029/2012JC007919 might be worth a look, too.

      Comparative costs ie cost of change relative to continuing as we are at present? What is the replacement value of Australia's entire built infrastructure at altitudes less than 20m relative to the cost of commencing going to alternative energy right now?

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    4. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to David Arthur

      Well you would be wrong then.

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  7. Paul Richards

    integral operating system

    Andy Pitman wrote; "What is surprising – and what is deeply concerning to me and almost entirely missed in the media commentary – is that we have not cooled dramatically over the last 15 years" Appreciate the worldview and the comment is definitely accurate.
    With a caveat from this perspective; vested interest and their value systems create another view on every piece of scientific data. Put in one word, 'motive' for declaring opposition to new knowledge.
    Our media is affected by many human values…

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    1. David Arthur

      resistance gnome

      In reply to Paul Richards

      The word "Australian" is an adjective; so what is the noun missing from the name of News Corp's national newspaper?

      My guess is "Quisling", as in "The Australian Quisling"; little wonder, then, that climate science is so persistently misrepresented in its pages.

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  8. Marc Hendrickx

    Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

    Andy Pitman claims he and the rest of the modelling community has underestimated climate sensitivity to CO2. According to recent press accounts of leaked IPCC reports even the IPCC is winding back its sensitivity dial. I can't help but think that a few recent papers indicating lower sensitivity somehow failed to pass the good professor's review.

    In correspondence to me in 2009 Dr Pitman asked: (b) which key physical processes **that affect climate on timescales of decades** are missing from climate…

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    1. Mike Hansen

      Mr.

      In reply to Marc Hendrickx

      Marc attempts to muddy the waters by throwing out a huge list of references implying that they support a lower climate sensitivity.

      Marc knows that he is lying because some of those papers have been discussed here previously.

      On Otto el al. Here is an interview with the author
      "... when it comes to the longer term picture, the authors say their work is consistent with previous estimates. The IPCC said that climate sensitivity was in the range of 2.0-4.5C.
      This latest research, including the…

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    2. Marc Hendrickx

      Geologist: The Con is a bad Monty Python sketch, for climate sense see: http://www.thegwpf.org/

      In reply to Andy Pitman

      Those studies that point to higher CS values are generally model derived, those with less dramatic values are generally based on observation. Your focus on the high end CS figures is looking increasingly desperate and your bias is showing (and yes mine to) in emphasizing those values that concur with your alarmist worldview (as opposed to those arguably more robust studies that support my lukewarm view of the way climate is changing in response to human influences). You claim you did not cherry…

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    3. Matthew Parton

      Project Manager

      In reply to Marc Hendrickx

      On vested interests I would suggest that scientists have much less to lose than oil companies in this debate.

      Also, the scientists I know are less driven by money then the bankers, business people and actuaries I know which means that I'm more likely to come down on the scientists side too.

      On the NIPCC versus the IPCC reports again I would say that governments naturally have the interests of citizens at heart more than corporations however I will dedicate some time to the former's report.

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