RealClimate logo


Technical Note: Sorry for any recent performance issues. We are working on it.

The new IPCC climate report

The time has come: the new IPCC report is here! After several years of work by over 800 scientists from around the world, and after days of extensive discussion at the IPCC plenary meeting in Stockholm, the Summary for Policymakers was formally adopted at 5 o’clock this morning. Congratulations to all the colleagues who were there and worked night shifts. The full text of the report will be available online beginning of next week. Realclimate summarizes the key findings and shows the most interesting graphs.

Update 29 Sept: Full (un-copyedited) report available here.

Global warming

It is now considered even more certain (> 95%) that human influence has been the dominant cause of the observed warming since the mid-20th century. Natural internal variability and natural external forcings (eg the sun) have contributed virtually nothing to the warming since 1950 – the share of these factors was narrowed down by IPCC to ± 0.1 degrees. The measured temperature evolution is shown in the following graph.

Figure 1 The measured global temperature curve from several data sets. Top: annual values. ​​Bottom: averaged values ​​over a decade.

Those who have these data before their eyes can recognise immediately how misguided the big media attention for the “wiggles” of the curves towards the end has been. Short-term variations like this have always existed, and they always will. These are mostly random, they are (at least so far) not predictable, and the IPCC has never claimed to be able to make predictions for short periods of 10-15 years, precisely because these are dominated by such natural variations.

The last 30 years were probably the warmest since at least 1,400 years. This is a result from improved proxy data. In the 3rd IPCC report this could only be said about the last thousand years, in the 4th about the last 1,300 years.

The future warming by 2100 – with comparable emission scenarios – is about the same as in the previous report. For the highest scenario, the best-estimate warming by 2100 is still 4 °C (see the following chart).

Figure 2 The future temperature development in the highest emissions scenario (red) and in a scenario with successful climate mitigation (blue) – the “4-degree world” and the “2-degree world.”

What is new is that IPCC has also studied climate mitigation scenarios. The blue RCP2.6 is such a scenario with strong emissions reduction. With this scenario global warming can be stopped below 2 ° C.

A large part of the warming will be irreversible: from the point where emissions have dropped to zero, global temperature will remain almost constant for centuries at the elevated level reached by that time. (This is why the climate problem in my opinion is a classic case for the precautionary principle.)

Sea-level rise

Sea levels are rising faster now than in the previous two millennia, and the rise will continue to accelerate – regardless of the emissions scenario, even with strong climate mitigation. (This is due to the inertia in the system.) The new IPCC scenarios to 2100 are shown the following graph.

Figure 3 Rise of the global sea level until the year 2100, depending on the emissions scenario.

This is perhaps the biggest change over the 4th IPCC report: a much more rapid sea-level rise is now projected (28-98 cm by 2100). This is more than 50% higher than the old projections (18-59 cm) when comparing the same emission scenarios and time periods.

With unabated emissions (and not only for the highest scenario), the IPCC estimates that by the year 2300 global sea levels will rise by 1-3 meters. [Correction: the document actually says: "1 m to more than 3 m"]

Already, there are likely more frequent storm surges as a result of sea level rise, and for the future this becomes very likely.

Land and sea ice

Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent.

The Greenland ice sheet is less stable than expected in the last report. In the Eemian (the last interglacial period 120,000 years ago, when the global temperature was higher by 1-2 °C) global sea level was 5-10 meters higher than today (in the 4th IPCC report this was thought to be just 4-6 meters). Due to better data very ​​high confidence is assigned to this. Since a total loss of the Greenland ice sheet corresponds to a 7 meters rise in sea level, this may indicate ice loss from Antarctica in the Eemian.

In the new IPCC report the critical temperature limit at which a total loss of the Greenland ice sheet will occur is estimated as 1 to 4°C of warming above preindustrial temperature. In the previous report that was still 1.9 to 4.6 °C – and that was one of the reasons why international climate policy has agreed to limit global warming to below 2 degrees.

With unabated emissions (RCP8.5) the Arctic Ocean will likely become virtually ice-free in summer before the middle of the century (see figure). In the last report, this was not expected until near the end of the century.

Figure 4 The ice cover on the Arctic Ocean in the 2-degree world (left) and the 4-degree world (right).

Rainfall

The IPCC expects that dry areas become drier due to global warming, and moist areas even wetter. Extreme rainfall has likely already been increasing in North America and Europe (elsewhere the data are not so good). Future extreme precipitation events are very likely to become more intense and more frequent over most land areas of the humid tropics and mid-latitudes.

Oceans

At high emissions (red scenario above), the IPCC expects a weakening of the Atlantic Ocean circulation (commonly known as the Gulf Stream system) by 12% to 54% by the end of the century.

Last but not least, our CO2 emissions not only cause climate change, but also an increase in the CO2 concentration in sea water, and the oceans acidify due to the carbonic acid that forms. This is shown by the measured data in the graph below.

Figure 5 Measured CO2 concentration and pH in seawater. Low pH means higher acidity.

Conclusion

The new IPCC report gives no reason for complacency – even if politically motivated “climate skeptics” have tried to give this impression ahead of its release with frantic PR activities. Many wrong things have been written which now collapse in the light of the actual report.

The opposite is true. Many developments are now considered to be more urgent than in the fourth IPCC report, released in 2007. That the IPCC often needs to correct itself “upward” is an illustration of the fact that it tends to produce very cautious and conservative statements, due to its consensus structure – the IPCC statements form a kind of lowest common denominator on which many researchers can agree. The New York Times has given some examples for the IPCC “bending over backward to be scientifically conservative”. Despite or perhaps even because of this conservatism, IPCC reports are extremely valuable – as long as one is aware of it.

Update & Correction (28 Sept): The upper value of the sea-level range is 98 cm, not 97 cm – I overlooked the fact that IPCC corrected this between the final draft and the approved version of the SPM.

Some media wrongly report a rise of “only” up to 82 cm by the year 2100. That is a misunderstanding: 82 cm is the average for the period 2081-2100, not the level reached in 2100. Both the curves up to 2100 and those 20-year averages are shown in Fig. 3 above. Note that the additional rise of up to 16 cm in the final decade illustrates the horrendous rates of rise we can get by the end of the century with unmitigated emissions.

It is also worth noting that the 98 cm is the upper value of a “likely” range (66% probability to be within that range). As IPCC also notes, we could end up “several tens of centimeters” higher if the marine-based parts of the Antarctic ice sheet become unstable. Leading ice experts, like Richard Alley and Rob De Conto, consider this a serious risk.

Further Commentary:

Mike Mann: Climate-Change Deniers Must Stop Distorting the Evidence
Stefan Rahmstorf: The Known Knowns of Climate Change


133 Responses to “The new IPCC climate report”

  1. 51
    Tony Weddle says:

    As I understand them all of the RCPs assume economic growth ad infinitum. Is that true? If so, I don’t think it’s an assumption that would stand up to scientific scrutiny (given resource depletion and environmental degradation). Consequently, I see this report more in the way of explaining what could happen in a fictitious world that had any level of business as usual, rather than showing what actually could happen in the real world.

    Attempts to keep economic growth going will likely (it seems to me) get even more dirty fuels burned but that doesn’t look like it could go on until the end of the century. Extreme mitigation actions, along the lines of RCP2.6 also look highly unlikely (with 99% confidence), unless caused by societal collapse. This all makes me very uneasy about these RCPs, in that none of them would seem to be modelling any path that makes any sense in the real world.

  2. 52
    Julien Cochard says:

    Hi there,

    You might want to have a look at the latest reporting of The Economist on climate change:
    http://www.economist.com/blogs/babbage/2013/09/ipcc-climate-change-report

    The interesting pieces that deserve some response:

    About sea ice decline:
    “summer sea-ice minimum is shrinking by about 10% a decade, though this year’s summer ice melt was smaller than last year’s”
    Why they feel the need to mention this year’s extent when talking about decadal trends, I don’t know but they might have their reasons for that

    About ECS:
    “But recent work, partly influenced by the pause in temperatures, has suggested sensitivity might be somewhat lower.”

    “The IPCC also decided to scrap its central “best guess”. Perhaps this is meant to reflect uncertainty in the science. If so, some scientists argue, then perhaps it should not have increased its confidence that man is the main cause of global warming.”
    What the last 15 years have to do with the ECS, and what the ECS has to do with attribution, I have no idea but would be interested in learning…

    Cheers

  3. 53
    Archi3 says:

    I’m a little bit puzzled by how the > 95 % confidence has been calculated after reading Judith Curry’s blog.

    Is there an accurate statistical calculation that provided a value x > 95 % , or not? (it is of course unlikely that a p-value would just be equal to a conventional limit of 90 %,and then exactly equal to 95 % ).

    if yes, what is this value ?
    if not, how can we give a confidence interval ?

  4. 54
    Fred Magyar says:

    sidd @48,

    Tks for the reality check… >:-(
    I’m returning to my home in the greater Miami area in a few weeks. I’ve been on an eight month sabbatical in Brazil.

  5. 55
    Didactylos says:

    I can think of several ways that von Storch could get a result that makes him happy (while being uselessly wrong).

    The easiest way would be to define stagnation as no statistically significant positive trend over a fixed period of 15 years starting in 1997 or 1998.

    Then when he goes looking for such a thing in model simulations that have been free-running since way before this, he is all surprised when there doesn’t happen to be any ENSO events that line up neatly with his fixed period.

    2% sounds about right for this silly exercise.

    Other things he could do: use models that don’t include natural variation or generate ENSO events, use models that don’t include real-world forcings, and, of course, he can ignore statistical significance and call any trend over 0 “warming”.

    Dishonesty is really easy. I can’t imagine he will ever publish this.

  6. 56
    deconvoluter says:

    RE: ‘Balance’(cont.); Philip Machanick(#9),Rob Nicholls (#34)and me (#46)

    This morning BBC Radio 4′s 9AM news bulletin was , as usual, followed by an item consisting of a chat about to-day’s newspapers. It started with an item about the use of computer models by the police to optimise their crime prevention efforts; someone provided some support for this idea but appeared to warn that using computers for modeling the world’s climate might be a different matter because there were so many variables. So I postponed switching off until that item came up again. In the event one guest was impressed by an item in the Mail that Arctic researchers ‘had made an error of a million square km. of ice’. Next came an item from the Telegraph. Then someone mentioned the IPCC’s report but only in passing.

    I’m reminded when on another BBC chat show some years ago someone said that you could no longer trust the scientists, it was not just the politicians. But when was this show? It coincided with one of the long series of exonerations of the people at CRU after the ‘emailgate’ libel. If that exoneration received a mention , I must have missed it.

  7. 57
    Ray Ladbury says:

    Adam Gallon,
    von Storch’s contention is highly problematic because he doesn’t bother to even give enough data that his study could be replicated or even enough that his probabilistic reasoning could be tested. There are many ways in which one could phrase the problem that would yield dramatically different answers:

    1)What is the probability that a 15 year interval yields no significant rise? The probability here might in fact be low.
    2)What is that probability that some 15 year interval selected within a 50 year window would yield no significant rise? The probability here would be substantially higher.
    3)What is the probability of a 15 year interval beginning with a huge-assed El Nino and ending with two good-sized La Ninas would yield an insignificant rise? The probability here would be damn near close to 1.

    The significance of the event which the denialists trumpet as their one solid piece of evidence is really only evidence of their delusion.

  8. 58
    MARodger says:

    deconvoluter @55.
    I didn’t find BBC Radio 4′s Broadcasting House programme anything like as bad as you describe. The review of the papers section can be a bit more ‘interesting’ than an interview on a set subject as they probably do try to ‘balance’ political views and an individual’s views on the stories in the papers can occasionally be extreme.
    So we find Angela Ripon (ex-new reader) is sceptical enough about AGW to prefer to believe a Rail on Sunday headline than the IPCC AR5.

    Her fellow reviewers did quickly rally to the defense of truth and righteousness with Maggie Aderin Pocock saying there are “very very large warning bells and we should be doing something about” AGW. And Henry Dimbleby talking of our previously stable climate, so “why are we conducting this unprecedented experiment on our climate?” The only thing they didn’t do was confront their fellow reviewer over her antediluvian views.

  9. 59
    Moose says:

    It is clear. This IPCC is full of crap. So the sun does not contribute to any global temperature? Or change in it?
    Explain then: why it is cooler in the shade, when the sun goes under in the evening and its cooler at night?
    Explain why and how variations in earth orbit, thousands of km’s, output of the sun can not have any influence?
    Explain why CO2 greens the planet and has risen in level to 400ppm and the temperature stagnated and even dropped a bit?

    Moose

  10. 60
    Radge Havers says:

    Moose,

    Please explain: How is it that you are able to not pay attention and yet not be aware that you’re not paying attention.

  11. 61
    SecularAnimist says:

    Moose’s comment (currently #58) is a joke, right?

  12. 62
    Ray Ladbury says:

    Oh, Moose, sweetie, I can only hope you are satirizing the denialists, because if you really are that dim, CO2 might make you grow, too!

  13. 63
    Tokodave says:

    Moose @ 58. Dude, you’re serious right? You’ve stumbled onto the wrong website for that level of ignorance. I suggest you return to the RealClimate website and go to “Start Here” or go over to Skeptical Science (http://www.skepticalscience.com/) and click on “Newcomers Start Here”.

  14. 64
    jgnfld says:

    @58

    Yeah…In the immortal words of B O’R: “The tide goes in, the tide goes out. You can’t explain that!”

  15. 65
    Geoff Beacon says:

    Last year Professor John Mitchell OBE FRS, Principal Research Fellow, at the Met Office, kindly replied to my email about the feedbacks that were in climate models. The missing/incomplete ones…

    5. more forest fires
    5 we don’t do yet, but could be important for changing ecosystems response to climate.

    6. melting permafrost
    6a/b [GB - a:CO2, b:CH4] we don’t have in the GCM, but have some simple modelling of. Too early to show any results yet, but we plan to publish later this year. Bottom line is that both CH4 and CO2 will be released as permafrost thaws. The magnitude is uncertain, but likely to be significant.

    7. increased decomposition of wetlands
    7, we have in HadGEM2 but didn’t enable as a fully coupled feedback, but we can diagnose changes in wetland extent and CH4 emissions

    I would add that although these things may be important, they are not always easy to quantify, model, initialize and validate, especially 5-7. That is why is taking time to implement them.

    John

    Is this true for the CMIP5 models used for the current IPCC report?

    See the rest at Do you believe the European Commission on Climate Change?

  16. 66
    Mal Adapted says:

    Is it just my prejudice, or does the moniker “Moose” suggests a high-school football player who barely passed algebra? I wonder if that’s intended.

  17. 67
    Jim_S says:

    In answer to my own question @16 regarding the missing tables and figures, I’ve finally found them – If you scroll right down to the end of the document, they are all there in one lump, individually labelled as [FIGURE SUBJECT TO FINAL COPYEDIT]
    As this is the public release version, rather than a ‘for comments’ beta, I find this is a bit sloppy, but then that’s just me :-)

  18. 68
    Jim Larsen says:

    That’s gotta be Bullwinkle. Where’s Rocky when you need him?

  19. 69
    Fred Magyar says:

    @58, I call Poe! Come on, ‘Moose’!? That’s a dead give away.

  20. 70
    Tony Weddle says:

    Can anyone please explain how economic growth can continue for the rest of this century, as the RCPs assume. Anyone?

  21. 71
    tkette says:

    I am not a climate scientist, just a lowly HVAC guy.

    Let’s assume the surface temperature of land masses are increasing 0.5 deg. C (dry bulb) per century is true.

    If the world is “warming” that means an increase in “heat” (BTU/LB or KW/KG dry air).

    Using a psychrometric chart – provided for your convenience (http://www.google.com/imgres?imgurl=http://www.truetex.com/psychrometric_chart.gif&imgrefurl=http://www.truetex.com/psychrometric_chart.htm&h=987&w=1379&sz=75&tbnid=YuQ3WPg2gcAtSM:&tbnh=91&tbnw=127&zoom=1&usg=__ulclQrqna3y5wRQAUOyWnj6gPlo=&docid=qEafn0tBqO7VdM&sa=X&ei=TLpIUvfrO6GCyQG-s4HgAg&ved=0CC0Q9QEwAA)

    Please explain how we know the “heat” (i.e. BTU/LB dry air) at the surface of the earth is increasing if we do not know the increase (or decrease) in the corresponding WET BULB temperatures?

    Thanks,

    Please email me at tkette@bex.net

  22. 72
    Anonymous Coward says:

    Tony Weddle (#69),
    I could explain but this is kind of off-topic here.

    Perhaps you could look at the scenarios from this perspective: “The RCPs are not new, fully integrated scenarios (i.e., they are not a complete package of socioeconomic, emissions, and climate projections). They are consistent sets of projections of only the components of radiative forcing that are meant to serve as input for climate modeling, pattern scaling, and atmospheric chemistry modeling.” (RCP database)

    I generally agree with you regarding the plausibility of these scenarios. But if less oil and gas is burned and more coal is burned instead or if more fossil fuels are burned earlier in the century and less at the end of the century, as far as the climate is concerned the result would not be all that different as long as the amount of CO2 emitted is the same. There are differences of course (else the scenarios would be pointless) but there are much larger differences between the different scenarios you object to.
    So these scenarios provide a wide spread of possible outcomes that should be useful to you even if you do not care for some of the assumptions that underly them. If you think a likely scenario in terms of cumulative CO2 emissions would be in between RCP2.6 and RCP4.5 for instance, you could average the sea level projections for both of these scenarios to get a ballpark value for what your preferred scenario would yield (crude, yes, but preferable to having no idea what to expect).

  23. 73
    Retrograde Orbit says:

    I am wondering if Tony Weddle is in fact referring to “the limits of growth”. Many of the scenarios in the “limits of growth” study resulted in collapse of society by the mid 21st century. If they were right, then – I could argue – the effects of global warming at the end of the 21st century are somewhat of a non-issue.
    Then again, maybe not.

  24. 74
    Retrograde Orbit says:

    Hey, and what about the moral decay of society?
    That could easily preempt global warming as well …

  25. 75
    Russell says:

    The coincidence of the multidecadal decline from ~ 1840 to 1920 with the heyday of coal-fired steam energy is obvious, but insofar as these global estimates span the oceans as well as land one wonders about the effect of readings taken in sea lanes on the overall statistics.

    The aerosol and NOx optical depths over the sea lanes of today are still very high, and conspicuously visible in satellite imaging.

    in Victorian times the bulk of marine traffic clung to these narrow tracks and hence raw thermometric readings taken at sea may reflect travel along sea lanes often adumbrated by the sooty emissions of the ships traversing them

    Can anyone address howthe question of optical depth feedback from ‘marine heat islands’ was addressed in arriving at these graphs ?

  26. 76
    Joe says:

    Apologies if this has been answered before elsewhere, but do future climate simulations (and the publications that describe them) quantify the amount of heat that goes into the oceans? All I see are surface temperature projections.

    Somewhat related, the IPCC AR5 SPM says that 60% of the heat accumulated went to the top layers (0 – 700 m) of the ocean, and 30% went to the deep layers (below 700 m). Is this information currently used to calibrate or test GCMs?

    Thanks for all the work you RCers do!

  27. 77
    adelady says:

    Russell. Steamships were rather late to the party for the major long trading routes in the Victorian era. Certainly the wheat and wool trade from Australia was pretty well entirely sailing by fast clippers until very late in the 19th century. Some were still being used in the Edwardian era.

    Until later in the 19th century, steamships were used more in river trade and around coasts rather than as trans-ocean vessels.

    Anyway, with no buildings or hard paving or factories, it’s a bit hard to see how there could be anything remotely like an UHI in the middle of the Atlantic or Pacific, let alone the roaring 40s.

  28. 78
    Tony Weddle says:

    Thanks to Anonymous Coward and Retrograde Orbit for their responses. I guess the RCPs do serve a useful purpose as they allow some communication with our leaders and other members of our societies who all assume that it’s possible to grow the economy for ever (or at least until 2100).

    However, it doesn’t seem to be working as I just heard one of our leaders, here in New Zealand, say that we must balance the need for economic growth against the actions needed to mitigate warming. How stupid is that? Let’s compromise on the one thing that underpins all life and the whole economy so that something that is underpinned by the environment can continue to ignore it.

  29. 79
    Ed Barbar says:

    So what would present day temperatures be without the man made warming? Presumably natural variability sucked out the .4 degrees C out of the atmosphere? I think it would put today’s temps .4 degrees C below the “0″ baseline. That would put the earth back into Little Ice Age temperatures, would it not?

  30. 80
    MARodger says:

    tkette @71.
    I’m not sure your question has an answer, so it’s lucky meteorology concerned itself with measuring rainfall and the causes thereof. Thus your question remains purely theoretical.

  31. 81
    Timothy (likes zebras) says:

    “In the new IPCC report the critical temperature limit at which a total loss of the Greenland ice sheet will occur is estimated as 1 to 4°C of warming above preindustrial temperature. In the previous report that was still 1.9 to 4.6 °C – and that was one of the reasons why international climate policy has agreed to limit global warming to below 2 degrees.”

    Er, oops?

    So even if, miraculously, the world managed to cut carbon dioxide emissions quickly enough to keep temperatures below 2C, there would still be a roughly 1-in-3 chance that Greenland would completely [eventually] melt anyway. That’s pretty bad.

  32. 82
    Timothy (likes zebras) says:

    @ Geoff Beacon

    “Is this true for the CMIP5 models used for the current IPCC report?”

    In his reply it looks as though John Mitchell is refering to the set-up of the Hadley Centre model HadGEM2. This model is one of several that add so-called “Earth System” components to the previous generation GCMs, in particular land and ocean carbon cycle models. However, each model is different and some will have some processes while other will not, so it is pretty hard to give an answer to your question off the top of my head.

    One expects that the full WG1 report will summarise the differences between the models so you can find your answer. You’d hope that there would also be some discussion of known unknowns – those processes that are known could be important, but haven’t been incorporated into the models yet.

  33. 83
    Mal Adapted says:

    tkette:

    Please explain how we know…

    Start here

  34. 84
    Hank Roberts says:

    For those wondering about mentions of copyediting, click through and read what’s linked. It says there:

    Before publication the Final Draft will undergo copyediting as well as any error correction as necessary, consistent with the IPCC Protocol for Addressing Possible Errors. Publication of the Report is foreseen in January 2014.

  35. 85
    Doug Bostrom says:

    “I’m a little bit puzzled…after reading Judith Curry’s blog.”

    Confusion is the objective but puzzlement is an acceptable substitute.

  36. 86
    WDL says:

    Hog Wash, The collapse of the magnetosphere allows more solar and space whether “radiation” to warm our planet. Co2 are much higher and the correlation between co2 higher temperatures is n

  37. 87
    dan says:

    The greenland Ice sheet is composed of snow from the last 100,000 years. (wiki) When was the last time it melted completely? Is it the position of this blog that temperatures over the last 100,000 years have never been 1 or 2 degrees hotter than they are today?

  38. 88
    AIC says:

    What am I misunderstanding? The IPCC Website http://www.ipcc.ch/report/ar5/wg1/ has a button for Full Report, but what I am downloading has on the bottom of each page: “Do Not Cite, Quote or Distribute”.

  39. 89
    Hank Roberts says:

    AIC, you’re looking at the final draft. Always check the website (and clear your browser cache).

    Yesterday when I looked it said:

    . . . Before publication the Final Draft will undergo copyediting as well as any error correction as necessary, consistent with the IPCC Protocol for Addressing Possible Errors. Publication of the Report is foreseen in January 2014.

    The IPCC has last I heard a dozen paid staffers; now that the people creating that Final Draft have finally gone off to get some sleep, I expect the paid staff has some cleaning up to take care of.

    Just now when I looked it said:

    Disclaimer: The accepted Final Draft of the full Working Group I report, comprising the Technical Summary, 14 Chapters and three Annexes, has been released online in an unedited form. Following copy-editing, layout, final checks for errors, and adjustments for changes for consistency with the Summary for Policymakers, it will be published online in January 2014 (tbc) and in book form by Cambridge University Press a few months later.

  40. 90
    Steve Metzler says:

    @87 Dan:

    The greenland Ice sheet is composed of snow from the last 100,000 years. (wiki) When was the last time it melted completely?

    From the ‘Greenland ice sheet’ Wikipedia article (presumably the same one you got the 100,000 year old ice figure from):

    The ice in the current ice sheet is as old as 110,000 years.[4] The presence of ice-rafted sediments in deep-sea cores recovered off of northeast Greenland, in the Fram Strait, and south of Greenland indicated the more or less continuous presence of either an ice sheet or ice sheets covering significant parts of Greenland for the last 18 million years. From just before 11 million years ago to a little after 10 million years ago, the Greenland Ice Sheet appears to have been greatly reduced in size.

    So the ice sheet has been there for at least 18 million years. I can’t answer the question of when it was last 1 – 2C hotter than today, but it probably wasn’t in the last 100,000 years. It could have been during that period 10 – 11 million years ago when the Greenland ice sheet had melted considerably, but not completely.

  41. 91
    MalcolmT says:

    Ed @ 79 You’re in the right ballpark – see http://www.realclimate.org/index.php/archives/2013/09/paleoclimate-the-end-of-the-holocene/ for the longterm natural trend. I don’t know that anyone has studied this in detail, though.

  42. 92
    deconvoluter says:

    Re: #58 MARodger.
    Fair enough; two witnesses can be better than one.

    So what do you think about the drift of my main criticism of the BBC’s coverage of climate science research? It matters, especially when you consider that the UK’s Secretary of State for the Environment * may have acquired his views from the newspapers which share his politics and the BBC.

    (a) Too many conclusions combined with too little straight science, leaves a void to be filled by contrarians who pretend to dig deeper and provide a simple story e.g those in the BBC’s own Moral Maize and in Channel 4′s “Swindle”.
    (b) “Climate Wars” by Iaian Stewart spoilt by too much prominence given to so called ice age scare of the 1970′s, and by reference to a hot summer.
    (c) Sensational and muddled Horizon programme on global dimming.
    (d) Biologist, Steve Jones advised the BBC to drop the policy of balance,
    but it is unclear how much notice they have taken.
    (e) The one good programme in which Horizon’s “Science under Attack”
    allowed Paul Nurse to interview James Delingpole and Bob Carter, led to
    such severe political attacks on the BBC that they may have been a bit scared to put on any more like it.
    (f) Radio 4′s Moral Maize should have covered this issue, but its coverage has either been absent or dominated by contrarians.
    (g) Coverage of the leaked or stolen emails from CRU was sensational and biased against the CRU. The exonerations were either omitted or accompanied by interviews with Nigel Lawson, who was allowed to attempt to rubbish them.
    (h) I missed some of these, but have been told that the run-up to the release of the AR5′s SPM had multiple short items partially framed by contrarians.
    (i) The odd ‘balanced’ way of reporting the final release of the SPM was also remarked upon by Caroline Lucas, Green Party MP, in the evening’s ‘Any Questions’.
    (j) The overall impression is too often that there is a difference of opinion between two lots of honest people with a tendency to zealotry on both sides.

    Thats what I can remember of the last seven years. Many viewers/listeners can be excused if they know next to nothing about the roles of increasing water vapour and falling albedo etc. and and without these their knowledge has to be very impoverished.

    It is mainly climate science thats in the doldrums; parts of physics, cosmology and materials science have fared rather better while geology and especially evolution have been covered quite well.
    ————-
    * “The climate has been changing for centuries” says
    Owen Paterson

  43. 93
    Lennart van der Linde says:

    @Steve Metzler #90,
    During the Pliocene, about 3 million years ago, it was probably about 2-3 degrees Celsius warmer than now (or pre-industrial). Sea level was probably about 20 m higher than now. Greenland had probably no or very little ice, just as West-Antarctica. East-Antarctica probably also contributed significantly to the higher sea level.

  44. 94
    James Cross says:

    When do the Working Group II and III reports come out?

  45. 95
    MARodger says:

    deconvoluter @92.

    I would agree that the BBC has often in the past done badly when presenting the reality of AGW. And as you allude to, the UK still has at least one climate denier in the cabinet as well as some very vocal deniers who hold the ear of the PM & the boy George next door. And when push comes to shove, it is government that controls the BBC.
    I don’t consider BBC airing of denialism to be systematic, a decision to do the dirty deed good and proper (like say Channel 4 with the “Great Global Warming Swindle”) but a combination of the ‘balance’ problem (apparently revised in 2006 so scientists are no longer faced by a denier during interview) and of internal skeptics/deniers doing what they do naturally with nobody on hand to prevent it.

    My own bad memories are of presenters like John Humphries, Andrew Neil or Michael Portello bursting forth with denialism. I assume they know no better. My ‘favourite’ was Jeremy Vine (?) on Newnight. A report on German lowering of emission cut targets was followed by a chat with anchorman Vine in the studio which concluded something like – . Vine “So what does this mean?” Reporter “Well, if the scientists are right, this is very bad news.” Vine “So let’s hope the scientists are wrong then.” Reporter “Yes. Let’s.”

    But while the BBC’s coverage has caused me to make a few official complaints, they do also get it right. The denialist 1990 Channel 4 film “The Greenhouse Conspiracy” was a response to the BBC’s “After the Warming” documentary (Part One and Two I never did see it, myself). And just last week the entire Today programme the day the AR5 was to be released was well presented (No John Humphries that morning.)

  46. 96
    Lauri says:

    RE: >Tony Weddle says:
    >29 Sep 2013 at 5:17 PM

    >Can anyone please explain how economic growth can continue
    >for the rest of this century, as the RCPs assume. Anyone?
    This is easy. Economic growth is no longer equal to increased use of physical resources. More and more of economic activity is due to immaterial services, like playing your favorite game on your smartphone. It is the ingenuity of the humankind that creates more efficient ways of accomplishing the same things with less resources. The predictions of the “Limits of growth” have already proven misleading.

  47. 97
    Brent Smith says:

    Steve Easterbrook #6 – “The plan was to go with a higher scenario, RCP2.9, which, together with RCP4.5 bracket the lower 5% and upper 95% confidence interval for what can be achieved with strong mitigation policies.”

    Forgive my confusion, but does that mean there is only a 5% chance of staying on a RCP2.9 pathway even WITH strong mitigation policies? And that RCP2.9 doesn’t even keep us under 2C increase in global warming? So, what is the chance of a RCP2.6 scenario with strong mitigation? Even lower than 5% right?

    I appreciate the IPCC report, I know a lot of work went into it to make it clear, quantifiable, and accurate. Thanks to all of you who worked on it. I just wish there was a way to clearly and simply state the facts – “Global temperatures are going to increase MORE than 2C, that’s going to cause a LOT of problems for all of humanity. We need to deal with it now.” Of course, scientists will respond: “We’ve been saying that for YEARS!”

  48. 98
    Steve Metzler says:

    @93 Lennart van der Linde:

    During the Pliocene, about 3 million years ago, it was probably about 2-3 degrees Celsius warmer than now (or pre-industrial).

    Thanks for the info. Just goes to show that even as Wikipedia makes for a decent entry point if you know nothing/little about something, it isn’t a substitute for primary sources. Going to go read up a bit on the Pliocene now…

  49. 99
    Prem Nandlal says:

    Tremendous study for the attention of politicians ,sociologists ,economists and religios leaders.
    What is required now is for a correlation with diseases caused by the deterioration of the world climate on the world population

  50. 100
    Steve Metzler says:

    Yeah, so I accessed the Wikipedia article on the Pliocene, and it linked to Robinson et. al. 2008, which is where the 2 – 3C warmer than today figure for the mid-Pliocene comes from.

    Only… the paper is on NASA’s FTP server… which has been taken down due to the government shutdown :-( I managed to source the paper from elsewhere, but that’s not the point. I will refrain from partisan comment because this isn’t the right venue for it, but… ouch.


Switch to our mobile site