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Why global emissions must peak by 2020

Filed under: — stefan @ 2 June 2017

(by Stefan Rahmstorf and Anders Levermann)

In the landmark Paris Climate Agreement, the world’s nations have committed to “holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels”. This goal is deemed necessary to avoid incalculable risks to humanity, and it is feasible – but realistically only if global emissions peak by the year 2020 at the latest.

Let us first address the importance of remaining well below 2°C of global warming, and as close to 1.5°C as possible. The World Meteorological Organization climate report[i] for the past year has highlighted that global temperature and sea levels keep rising, reaching record highs once again in 2016. Global sea ice cover reached a record low, and mountain glaciers and the huge ice sheets in Greenland and Antarctica are on a trajectory of accelerating mass loss. More and more people are suffering from increasing and often unprecedented extreme weather events[ii], both in terms of casualties and financial losses. This is the situation after about 1°C global warming since the late 19th Century.

Not only will these impacts get progressively worse as warming continues, but our planet also runs a growing risk of crossing critical tipping points where major and largely irreversible changes to the Earthsystem are triggered (see Fig. 1).

Fig. 1 Tipping elements in the Earth system, in relation to past global temperature evolution since the last Ice Age 20,000 years ago as well as future warming scenarios[iii]. The Paris range of 1.5 – 2 °C warming is shown in grey; the bars show increasing risk of crossing tipping points from yellow to red.

The West Antarctic Ice Sheet (WAIS in Fig. 1) has likely already been destabilised, committing the world to at least three meters of global sea-level rise in coming centuries[iv] – an outcome that scientists have warned about since the 1970s[v]. The Greenland Ice Sheet – holding enough ice to eventually raise global sea levels by seven meters – may likewise be destabilised below 2°C[vi]. Coral reefs have suffered pan-tropical mass bleaching in 2016 and are doing so again in 2017 as a result of warming oceans, and only if global temperature stays well below 2°C some remnants of the world’s coral reefs can be saved[vii]. The Gulf Stream system (THC in Fig. 1) appears to be already slowing[viii] and recent research indicates it is far more unstable than previously thought.

Because overall global temperature rise depends on cumulative global CO2 emissions, the Paris temperature range can be translated, with some uncertainty, into a budget of CO2emissions that are still permissible. This is the overall budget for the century and it lies within the range of 150 to 1050 Gt of CO2, based on updated numbers from IPCC[ix]. At the current global emission level of 39 GtCO2 per year, the lower limit of this range would be crossed in less than four years and is thus already unachievable without massive application of largely unproven and speculative carbon dioxide removal technologies. Even the CO2 budget corresponding to the mid-point of this uncertainty range, 600 GtCO2, is equivalent to only 15 years of current emissions. Fig. 2 illustrates three scenarios with this budget and different peaking years for global emissions. It makes clear that even if we peak in 2020 reducing emissions to zero within twenty years will be required. By assuming a more optimistic budget of 800 Gt this can be stretched to thirty years, but at a significant risk of exceeding 2°C warming.

It is still possible therefore to meet the Paris temperature goals if emissions peak by 2020 at the latest, and there are signs to show we are moving in that direction as global CO2 emissions have not increased for the past three years. We will need an enormous amount of action and scaled up ambition to harness the current momentum in order to travel down the decarbonisation curve at the necessary pace; the window to do that is still open[x].

In summary, declining carbon emissions after 2020 is a necessity for meeting the Paris temperature limit of “well below 2 degrees”.

Fig. 2 Three illustrative scenarios for spending the same budget of 600 Gt CO2, with emissions peaking in 2016 (green), 2020 (blue) and 2025 (red), and an alternative with 800 Gt (dashed).

Note: This article first appeared in the report 2020 The Climate Turning Point


[i] World Meteorological Organisation. WMO Statement on the State of the Global Climate in 2016 (WMO, Geneva, 2017).

[ii] World Meteorological Organisation. Weather extremes in a changing climate: hindsight on foresight (WMO, Geneva, 2011).

[iii] Schellnhuber, H. J., Rahmstorf, S. & Winkelmann, R. Why the right climate target was agreed in Paris. Nature Climate Change 6, 649-653 (2016). doi:10.1038/nclimate3013

[iv] Feldmann, J. & Levermann, A. Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin. Proc Natl Acad Sci U S A 112, 14191-6 (2015). doi:10.1073/pnas.1512482112

[v] Mercer, J. West Antarctic ice sheet and CO2 greenhouse effect: a threat of disaster. Nature 271, 321-325 (1978).

[vi] Robinson, A., Calov, R. & Ganopolski, A. Multistability and critical thresholds of the Greenland ice sheet. Nature Climate Change 2, 429-432 (2012). doi:10.1038/nclimate1449

[vii] Frieler, K. et al. Limiting global warming to 2 degrees C is unlikely to save most coral reefs. Nature Climate Change 3, 165-170 (2013). doi:Doi 10.1038/Nclimate1674

[viii] Rahmstorf, S. et al. Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation. Nature Climate Change 5, 475-480 (2015). doi:10.1038/nclimate2554

[ix] Peters, G. How much carbon dioxide can we emit?  (2017)

[x] A Roadmap for Rapid Decarbonization. Science, March 24, 2017: Johan Rockström, Owen Gaffney, Joeri Rogelj, Malte Meinshausen, Neboja Nakicenovic, Hans Joachim Schellnhuber

210 Responses to “Why global emissions must peak by 2020”

  1. 101
    Michael says:

    So I recently asked for clarification on the graph but my question seems to have been deleted. My question (very sincere) didn’t apparently make it through moderation.

    Here’s Clara Jeffery (Editor-in-Chief, Mother Jones), making the same general point: we the public want to understand but we need some help.

    Asking again:

    Does THC = thermohaline circulation ?

    Does ENSO = El Niño Southern Oscillation ?

    Does Sahel = desertification of the Sahel region of Africa ?

    Thanks again.

  2. 102
    Gorgon Zola says:

    BPL 88

    What kind of Philosophy minor doesn’t include coverage of logical fallacies?

    Addressing ‘science’ in your reply, is indeed a straw man. But I will answer your silly question regardless: What we need in stead of science is a proper response to the knowledge gained, by scientists as well. Which is what most of this thread is all about.

    What we see instead is researchers constantly underplaying the situation and a systemic compartmentalisation in presenting the relevant facts and implications.

    Not that any of it matters anymore at this point in time..

  3. 103
    Charles Hughes says:

    Thomas says:
    9 Jun 2017 at 8:19 PM

    I agree with Hank @ 100. Thomas needs to get a private room where he can be alone.

  4. 104

    gc 99: given that CO2 is at best a weak driver of temperature

    BPL: That’s wrong, sir. Where did you get that idea?

    gc: a cooling of 2 K is just as likely.

    BPL: Not even remotely possible, unless we have a nuclear war or an impactor hit about that time.

  5. 105

    M 101: Yes, all those are correct.

  6. 106

    GZ 102: What kind of Philosophy minor doesn’t include coverage of logical fallacies?

    BPL: What did I ever post that said I didn’t understand logical fallacies? Look again. Here’s my tutorial on formal logic. Part 3 is a long list of logical fallacies.

    It’s always best to research these things before posting.

  7. 107
    MA Rodger says:

    Michael @101,
    Your original question still sits @95, but with no responding comment appearing so far.

    Within the text of the OP, “THC” is described as meaning “the Gulf Stream system”, not the most technical description of the thermohaline circulation (indeed technically it is inaccurate), but the description does set “THC” as being an ocean thing and thus sensibly must be the thermocline circulation.
    In the original version of the OP here, the caption of Fig 1 contains the explanation “ENSO = El Niño Southern Oscillation” although I would myself consider “ENSO” as being an adequate description.
    “Sahel” is actually the opposite of desertification; a greening which results from changes in the West African Monsoon.
    These “tipping elements” set out in Fig 1 are a bit of a mixed bag. Some, like the Greenland ice sheet which will destroy itself as the top of the ice drops down to warmer altitudes, are “tipping elements” that are irreversable, in the case of Greenland without a return to ice age condidtions. Some like the melting of the permafrost and resulting release of GHGs from the thawed grond will bring on an amplification of global warming. And some will be slow processes taking millennia so the “tipping point” under discussion refers to the level of global temperature rise rather than the timing. Others, like the loss of coral reefs, will be quite sudden ecological disasters rather than climatical ones and again will not be reversed by a simple return to temperatures below the “tipping point.”

  8. 108

    I like your effort to put the numbers in to perspective and words. Nice blog.

    If anyone is interested in the environmental blogs please visit

  9. 109
    Jim Eager says:

    The galloping dromedary wrote: “given that CO2 is at best a weak driver of temperature a cooling of 2 K is just as likely.”

    Only fools make such ignorant pronouncements with such certainty.

  10. 110
    Mal Adapted says:


    You lunatics imagine CO2 emissions going to zero between 2035 and 2050.

    Ggc goes on to imagine he can predict the trajectory global fossil carbon emissions through 2060 better than you lunatics. By imagining that CO2 is at best a weak driver of temperature, he imagines that “cooling of 2 K is just as likely” as a warming of the same amount.

    I’ll say this for Ggc: he may be wrong, but at least he’s sure. He’s obviously no scientist, but I wonder if he’s a professional politician? He’s pretty good at staying on message!

  11. 111
    MikeN says:

    All of these charts reach 0. Is this the actual required goal for stopping global warming, and not the 80%(now closer to 90%) cut called for on a regular basis?

  12. 112
    Digby Scorgie says:

    Michael @101, Barton @105, MA Rodger @107

    I thought the Sahel was the region just south of the Sahara, sometimes subject to greening and sometimes to desertification, depending on global climatic conditions. Have I got it wrong?

  13. 113
    Thomas says:

    100 Hank Roberts, maybe jealousy is a curse? Or maybe too many refs with direct quotes to papers and scientists talking? Or maybe Hank, you have nothing worth saying or contributing? Or, maybe you never ……….? (shrug)

    Now some really important questions for you Hank and other adhominem critics: Do have any idea what Tom Bjorklund just said, what he has done and why he did it?

    Do you have any insights backed by evidence on this matter Hank?

    Any ideas at all?

    Can you comprehend and realise (and then explain to other readers here with clarity) what both Tom Bjorklund and the authors of the RC article are in serious error and why that is so?

    Come on. I dare you to put up something more concrete than crying in a hankerchief!

    Mindful that neither you or anyone needs to read me unless they want to! Logical Hank, it’s logic not a fallacy. Enough of your et al fallacies please. :)

  14. 114
    Thomas says:

    #106 BPL: What did I ever post that said I didn’t understand logical fallacies?

    Well that #106 post is the latest example of not understanding logical fallacies.

    This is another: BPL: So something taxed is NOT produced in smaller quantity? You can produce the same amount even if your cost of production goes up and demand stays the same?

    A: Yes. In fact things can be taxed and production continues to rise. That’s not only logical it’s factually correct and backed by hard evidence. For some strange unknown reason BPL seems obsessed with denying reality and venturing off into logical fallacies and untruths.

    There has been a constant stream of logical fallacies contained in just about every response he has ever made to one of my comments here. That’s a very clear entrenched pattern of not understanding logical fallacies by continually committing them himself.

    Another classic example of BPL posting comments which shows beyond doubt that he does not understand logical fallacies was his multiple posts about the USSR economics a while back.

    It’s logical to assume that the moderators are not concerned at all about PBL repeatedly embarrassing himself in public. Otherwise those USSR posts would have ended up in the bore hole where they belonged.

    Tips for BPL: Stick to astrophysics. Drop the haughty attitude.

  15. 115
    Dennis N Horne says:

    @ Thomas. Good work. One “counter-argument” I had from a professor at Cambridge and former government adviser (also associated with the GWPF):
    No Certain Doom: On the Accuracy of Projected Global Average Surface Air Temperatures. Patrick Frank, Stanford.

    Which reinforces a conclusion I came to many years ago: Man is a mad animal. I claim no exemption, by the way.

  16. 116
    Ric Merritt says:

    Tom Bjorklund —

    I’m just catching up after traveling, so apologies for not hewing to the usual internet standard of instant replies.

    You appear to be making predictions about future global temperatures at odds with mainstream climate science. If not, please say briefly and plainly that you endorse mainstream climate science, to at least the extent of expecting continued warming over decades, absent huge changes to human activities or very large volcano eruptions. If so, please discuss with me a public bet. Not one of these namby-pamby $100 to charity things. I want to bet a mortgage-sized amount, based on decadal comparisons. Details of proposal on request. There’s nothing like a rooting interest to involve the public in an issue. Let’s go public. Offer open to anyone. (I’ve said this for probably 10 years on blogs, but never get a nibble. It’s almost as if the “contrarians” don’t actually believe what they’re writing!)

  17. 117

    gallopingcamel at #99 has his hump in a twist:

    That Figure 2 is absurd. You lunatics imagine CO2 emissions going to zero between 2035 and 2050.

    Reality will be a little different. CO2 emissions will rise at an accelerating rate thanks to the BRIC countries regardless of what the rest of the world does…

    Oh, well, if we’re all ‘lunatics’ that settles it, then.

    But I had this really cool hallucination about how Chinese emissions have been stable for three years and are actually projected to drop this year:

    Hmm… what does BRICs stand for again? Brazil, Russia, India, and oh yes, China… the biggest emitter…

    What about the other four?

    Who is dreaming ‘lunatic’ dreams here? The obvious reality is that the primary foot dragger on climate action is the good old USA.

  18. 118
    Mike Roberts says:


    “The safest approach is to assume that all of the fancy solution ideas will never come to fruition…” This is pretty gloomy view of the world.

    No, it has nothing to do with a gloomy view. I said it’s safer to assume this than to assume that some fancy solution will save us. It seems that you are “bet[ting]” on the fancy approach and, therefore, not advocating other actions?

  19. 119
    Tony Weddle says:

    There were many comments to this which suggested much of the post was unrealistic. Yet there have been no responses from the authors. Shame.

    I seem to recall that the last IPCC report gave a range of values for future emissions that might still provide a chance of staying below 2C. Those ranges started at zero. And that was 5 years ago (or the science it was based on was 5 or more years ago). Yet we still get commentary on its being possible to avoid 2C. But, given the uncertainty, isn’t it also possible that 2C is now unavoidable? If so, what is that possibility? If it is a substantial possibility (say 10-20 percent) shouldn’t that narrative also feature prominently in scientific discussion?

    Of course, when we add in the likelihood of global economies wanting to take serious action on climate change or, to be more specific, the likelihood of action being taken (rather than just “wanting” to), doesn’t the possibility of limiting warming to 2C take a further dive?

  20. 120

    DS 112,

    Yes, I think you’re right about that. The Sahel is the region you describe.

  21. 121

    Th 114: A: Yes. In fact things can be taxed and production continues to rise. That’s not only logical it’s factually correct and backed by hard evidence. For some strange unknown reason BPL seems obsessed with denying reality and venturing off into logical fallacies and untruths.

    BPL: Th has “wrong on an issue” confused with “logically fallacious.” He’s not even right about the issue. Of course things can be taxed and production continue to rise; the question, to put it technically, was whether adding a tax shifts the production curve.

    Th: There has been a constant stream of logical fallacies contained in just about every response he has ever made to one of my comments here.

    BPL: Give a specific example. The one above doesn’t count, as I showed.

    Th: Another classic example of BPL posting comments which shows beyond doubt that he does not understand logical fallacies was his multiple posts about the USSR economics a while back.

    BPL: Again, specifics, please.

    Th: Tips for BPL: Stick to astrophysics. Drop the haughty attitude.

    BPL: If anyone here has a haughty attitude, it’s you. You insult and belittle anyone who disagrees with you on any issue at all. You assume you know better than everyone else here. You think when you fail to communicate that everyone here is just too stupid to understand you.

    Tip for Th: Get some therapy. You don’t relate well to others and it shows.

  22. 122
    MA Rodger says:

    Digby Scorgie @112,
    The Sahel is roughly as you describe, a region south of the Sahara with a very sensitive climate. The droughts of the 1980s have been blamed on air pollution from Europe/USA impacting ocean temperatures enough to reduce rainfall. Some who didn’t like such a message (for reasons you can probably guess at) blame it on overpopulation and too may goats. The link to ocean temperatures is well established, perhaps with the caviat set out in Park et al (2016) which identifes the influence of the Mediterranean.

  23. 123
    tegiri nenashi says:

    “I want to bet a mortgage-sized amount …”
    Oh, you are so brave [and, therefore, must be right].
    There is no question somebody like Leo, or Bloomberg can bet 1M over any issue — it is a pocket expenses for them. So as Larry Ellison, who openly says that solar energy program in California is a scam.

    When speaking of “global temperatures”, what averagist/adjuster do you have in mind and why should we trust them? How about betting about temperature at one state of the art facility:
    Certainly, if polar amplification is a thing, then this would be the best blace to look for? Then, what is your prediction for that particular spot in 10, 20 and 50 years?

  24. 124
    Elaxminn says:

    #48 – The toll of the decline of psychoanalysis caused psychological suffering ignoring climate change and its potential amelioration will cause physically obvious problems like sea level rise, agricultural disruption (starvation), and species decline.

  25. 125
    Thomas says:

    117 Kevin McKinney: “The obvious reality is that the primary foot dragger on climate action is the good old USA.”

    Good point Kevin. It has been since the 1990s despite all beliefs PR to the contrary. Right behind it are the other anglophone/5 eyes nations being UK, Canada, Australia and less importantly NZ. These 5 nations are also prima facie the homeland for the most egregious levels of climate science denial on the planet.

    Others include nations like Saudi Arabia (who fought like hell over the AR5 summaries wordings), all the others FF nations in the Gulf and north africa. Russia is another FF exporting nation who has been foot dragging on seriously acting to minimise emissions etc, but they are far less well placed than the US/EU/Gulf or even China to make major inroads.

    Why? a nation with almost half the US population their GDP peaked @$2Trillion a few years back and now sits about $1.5Trillion. That is the same Australia’s GDP atm with only 21 million people. So Russia may be 1st world with nuclear arms, missile defense, and mil aircraft but it is distinctly a 3rd world level economy due to severe trade/finance sanctions and the drop in global FF prices.

    There is a strong theme in Russian politics also that AGW/CC is overstated – but one thing is sure it is not a priority issue there which (for obvious reasons) is perfectly sane and rational from their pov given geopolitical realities, bias and so on.

    Oh Iran is also a bit of a foot dragger on AGW/CC for similar reasons, a GDP of only $440 billion with a large growing population of 80 million, and very high ratio of college degrees, it struggles to grow the economy to service the people due to major sanctions and being barred from oil/gas exports by it’s competitors and their allies.

    While such geopolitical realities remain on the ground with various entrenched positions and distrust, in my view nothing truly significant or lasting will or could possibly come out of the UNFCCC that adequately addresses the urgency of action today.

    Or as Dennis T Horne said above – “Man is a mad animal.” – on which I concur completely based on the historical evidence and today’s reality, I find that truth undeniable. Any and all exceptions merely add more proof that rule is correct.

  26. 126
    Thomas says:

    115 Dennis N Horne says: “@ Thomas. Good work.”

    Thank you for saying so Dennis. Appreciated. Frustrating isn’t it? :-(

  27. 127
    t marvell says:

    #79 – Thanks for answering my question (that the lag between CO2 change and temperature change is thought to be 25-30 years).
    Now, is there good information about the lag between temperature changes and sea level changes? I estimate that it at least another 25-30 years. If so, it is baked in that the sea level rise will continue for 50-60 years and will exceed the rise that has already occurred.

  28. 128

    tm 126,

    When I do the analysis, I find an extremely high correlation (R ~ 0.9) between CO2 and temperature in the same year, for the last 167 years.

  29. 129
    Gorgon Zola says:

    BPL: Not addressing that which was addressed, seems to be a game of choice to you. So be it. I generally agree with your posts and enjoy reading them, but there seems to be an ego thingy going on here. Writing about something and being able to apply the implications of those writings, are of course two different things. Weird it needs pointing out.

    And @ all who criticise Thomas: Even if verbose, at least he’s providing the total picture and not some compartmentalised CO² emission blather, which really is but one out of many an issue, all relevant, which are rarely presented in tandem.

  30. 130


    What the cake said to Alice.

  31. 131
    Hank Roberts says:

    > …. verbose, at least he’s providing the total picture

    Illustrating the classic problem one gets from trying to have everything: where do you put it?

    Trying to put full text of everything important eveywhere so everyone will see it is self-defeating.
    Yes, he’s echoing a lot of information and links familiar to those familiar with other sites for political/economics discussions.

    Please help him set up a blog where he can save his contributions, and then point to them in brief posts elsewhere.
    He’s getting upset with people who ask him to make his stuff more accessible and easier to find and read. That bug needs fixing.

  32. 132
    Thomas says:

    Re Cakes, bares repeating the obvious “Tips for BPL: Stick to astrophysics. Drop the haughty attitude. Please? If at all possible?

  33. 133
    Thomas says:

    Hank, please, you have no idea what me life circumstances are. What I do where and when is my business. Not yours. I have told you multiple times I have no interest in creating a blog. Could you please just drop it?

  34. 134
    Dennis N Horne says:

    Talking about Barton Paul Levenson … I don’t sense an inflated ego. I sense a man who knows what he’s talking about and knows it. I call that confidence.

  35. 135
    nigelj says:

    Thomas @133, I have read some of your posts, and you are obviously well educated and smart enough, and seem on the right side of the climate debate, and make some good points. I also very roughly agree with your general world view.

    However your posts are repetitive, and are very long for what they really say.Could you please appreciate this is very frustrating for readers? Remember commenting here is a privilege.

    You also have a tendency to be very thin skinned and defensive. It’s like you are constantly trying to prove you are smart, and it generates a lot of sarcastic, empty rhetoric. I like barbed humour, but endless pages of sarcasm get tedious to wade through.You are lucky you don’t get banned form this website.

    I actually quite like the fact you see the big picture, and I’m interested in this, partly because I did such a wide range of stuff at university in my first two years. But if you want to “join the dots” you have to do this extremely well, or it comes off as all over the place. And remember climate scientists are entitled to have a website that discusses the nitty gritty detail of climate change.

    And please stop the silly feud with BPL. It’s just weird, like childish, and off topic. BPL is an entirely logical chap and pretty polite, and non provocative, and I see nothing wrong in essence with his comments on the history of Russia, climate science etc and I don’t see any “logical fallacies” in his comments. I do occasionally see things I disagree with for other reasons.If you have a disagreement, point to something specific that can give people something useful to talk about.

  36. 136
    Brian Dodge says:

    “If so, it is baked in that the sea level rise will continue for 50-60 years and will exceed the rise that has already occurred.” Let’s do a thought experiment. Imagine a pile of ice that represents the Greenland ice sheet when it is in equilibrium, neither growing or shrinking. At high elevation in the middle of the sheet, the average annual temperature must be low enough for snowfall to accumulate, in order for balance to be maintained against the losses from melt and calving which will inevitably occur around the edge of the pile at lower warmer altitudes. It’s a state of dynamic equilibrium between accumulation at higher cooler and ablation at lower warmer altitudes; The elevation at which the change from net loss to net accumulation(the firn line) is surface temperature dependent, since the lapse rate will always be between the moist and dry adiabatic .lapse rate. Now, envision a warmer surface moving the elevation where ablation changes to accumulation higher; this will reduce the area where accumulation occurs, and increase the area where ablation occurs, resulting in a negative mass balance, as has been observed in Greenland. This loss of mass will lower the surface of the ice sheet, which has the same effect on reducing accumulation and increasing loss areas as surface warming raising the firn line. An increase in snowfall over the accumulation area will tend to compensate for the reduction in area, but “”The best fitting estimate for the acceleration in ice sheet mass loss for the observed period is 30 ± 11 Gt/yr2 for Greenland and 26 ± 14 Gt/yr2 for Antarctica. This corresponds to 0.09 ± 0.03 mm/yr2 of sea level rise from Greenland and 0.08 ± 0.04 mm/yr2 from Antarctica.”
    “To verify that the improvement obtained with the quadratic model is significant we used an F-test [e.g., Berry and Feldman, 1985]. The F-test show that the improvement obtained with the quadratic fit is statistical significant at a very high confidence level.”
    Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE; I. Velicogna; GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L19503, 2009; doi:10.1029/2009GL040222
    see also – “Prominent in Greenland is the strong thinning of the entire western ice sheet, as well as the southeast and northwest ice sheet margins (Fig. 11). The dynamic thinning of Jakobshavn Isbræ in particular has penetrated deep into the ice sheet interior…”

    The positive feedback from melting causing more melting is causing some of the observed acceleration of melting. The continuing increase in CO2 forcing is causing some of the acceleration. The additional energy being absorbed by increasing ice free areas of the Arctic ocean is making a contribution also. More absolute humidity in the air, an observed consequence of global warming, will increase snowfall in the accumulation zone, but also more rainfall induced melting in the ablation zone. The details of water flowing into moulins, transporting heat into the ice and weakening it, and lubricating the base of the ice, are areas of current study( But unless temperatures fall from current levels, the ice will continue to melt, and likely continue to accelerate because of the positive feedback from melting.

  37. 137
    t marvell says:

    128 – a simple regression will give no information about the lag. The regression just tells you whether the variables are trending together, and the standard error is wildly understated. Must do it with change (differenced) variables.

  38. 138
    Hank Roberts says:

    For Thomas:

    sometimes you just want to throw your latest project up quickly and be done with it — at no cost to you.

    Sound familiar? But throwing it up here in huge long posts isn’t helping you get the attention worthy of some of your material

    If that sounds like your situation, you’re in luck. take an in-depth look at the top free (and nearly free) hosts on the market.

    Collect your text files. Post them in full, with pointers spread around the web to attract attention to your work.

    Please. Be effective.

    ‘Nuf said.

  39. 139
  40. 140
    Mal Adapted says:

    Dennis N Home:

    Talking about Barton Paul Levenson … I don’t sense an inflated ego. I sense a man who knows what he’s talking about and knows it.

    Yep, pretty much, although even BPL can fool himself if he doesn’t try hard enough not too ;^).

  41. 141
    t marvell says:

    #136 – but what is the lag between temperature change and sea level change? It is probably very large because, for example, it takes a while for higher temperatures to heat up the body of ice in Greenland and Antarctica. That is, surface melt increases, in part, because the surface starts out warmer when the body of ice is warmer.
    I calculate that the lag impact is spread through 10 to 50 years.

  42. 142
    Larry Edwards says:

    What troubles me in this post is not the conclusion presented in its title and its final sentence – that an emissions peak by 2020 and a decline thereafter. That is old news (but still important) for those who have followed Kevin Anderson’s work in recent years.

    These things do trouble me:

    1. The analysis presented has an inherent but undisclosed probability that the recommended 600 GT Peak-2020 pathway will fail to keep the temperature increase below 2oC. What is the magnitude of that probability? Same question for the 600 GT Peak-2025 pathway and the 800 GT Peak-2020 pathways.

    2. The curves in Fig. 2 for the above pathways imply average annual percent reductions in emissions, post-peak. How much are those average annual reductions?

    This post prompted my to revisit RealClimate’s 2009 post “Hit the Brakes Hard” (4/29/09). It is a commentary on the then-new “Trillionth Tonne” papers and the proposal for a carbon budget approach instead of a percent-reduction by 2050 approach. It was an enlighted approach, and the post underscored that and went a step farther in saying:

    “We wonder why we were not advised to adapt to crash curtailing CO2 emissions …”

    However, at the time I found the papers as well as that post very troubling in their unquestioning acceptance of the 2oC target and — even then as now — a 2020 emissions peak. At that time there still was a chance for a smaller target. Please see my comments #159 and #424 (neither of which got a response). I think some here will find them prescient. Too bad we can’t turn the clock back 8 years and proceed differently for an earlier peak and, as the 2009 post’s last sentence put it: “We wonder why we were not advised to prepare to adapt to crash curtailing CO2 emissions?”.

    So, the third thing that troubles me about the present post is that the conclusion in its last two sentences doesn’t go even as far the above 2009 question. It says:

    “We will need an enormous amount of action and scaled up ambition … declining emissions after 2020 is a necessity…”.

    It is a bland conclusion to a portentous chart, using the kind of diplomatic language that has led the COP conferences astray. If a crash curtailment of CO2 emissions was needed in 2009, why is the 2017 post not clear that we need to “hit the brakes” even harder now? We still need – even more so now – a crash curtailment of emissions. And at this point I think this means that many lifestyles have to change in addition to the on-going shifts to renewable energy and better efficiency.

  43. 143
    Glen Koehler says:

    To t marvel #64
    From footnote in Hansen et al. 2016 (draft)
    Young People’s Burden: Requirement of Negative CO2 Emissions
    Earth Syst. Dynam. Discuss., doi:10.5194/esd-2016-42, 2016 Manuscript under review for journal Earth Syst. Dynam. Published: 4 October 2016

    Footnote on page 16:
    “We use the “intermediate” response function in Fig. 5 of Hansen et al. (2011), which gives best agreement with Earth’s energy imbalance. Fractional response is 0.15, 0.55, 0.75 and 1 at years 1, 10, 100 and 2000 with these values connected linearly in log (year), cf. Fig. 5 of Hansen et al (2011).”

    Hansen et al 2011 = Hansen, J., Sato, M., Kharecha, P., and von Schuckmann, K.: Earth’s energy imbalance and implications, Atmos Chem Phys, 11, 13421-13449, doi:10.5194/acp-11-13421-2011, 2011

    Another key figure in Hansen et al 2016 footnote on page 3:

    “IPCC (2013) finds that 2×CO2 equilibrium sensitivity is likely in the range 3 ± 1.5°C, as was estimated by Charney et al. (1979). Median sensitivity in recent model inter-comparisons is 3.2°C (Andrews et al 2012; Vial et al 2013). “

  44. 144
    Glen Koehler says:

    To those with expertise in tipping points:
    The temperature ranges shown in Figure 1 seem absurdly high for all systems to the right of Coral Reefs for when those systems will reach abrupt, self-sustaining, or irreversible change, i.e. a “tipping point”.

    Winter Arctic sea ice has already shown extreme losses, yet Figure 1 implies no problem until we hit 5C.
    THC has already shown ca. 30% decline, yet Fig. 1 shows that impact beginning at 3.5-4C.
    Ditto permafrost, Fig 1 shows it kicking in at 5C. Multiple studies show permafrost thaw already adding to CO2 load, and that by 1.5-1.7C, permafrost up to 60N at risk of thaw.
    One more, while EAIS not as advanced as WAIS, it too is showing signs of disruption at our current 1-1.2 C above 1880-1920 average.

    (If 18809-1920 is close enough for Hansen to use as a proxy for preindustrial, it is good enough for me. Hansen argues going earlier such as 1850-1900 doesn’t change the value anyway, about 0.1C, and that by going earlier you get into the problem of poor measurement record as the foundation, whereas NASA GISS record starting in 1880 is a reliable record)

    Am I the only one who sees Figure 1 as ludicrous?

  45. 145
    Thomas says:

    134 Dennis N Horne, so if you received a response that went “Eat Me!” or worse, you’d be fine with that?

    Or if you wrote “ABC” and got a Strawman response falsely claiming you had said “XYZ” which was ridiculed and you were ridiculed for saying something you did not say, or mean, then you’d be fine with that too, or see it as an example of “confidence”?

    Despite them being 100% wrong? I guess thus far you’ve been lucky Dennis. :-)

  46. 146
    Thomas says:

    138 Hank Roberts says: “huge long posts”

    There’s only in the last several months — this one

    A very specific on topic reply to 89 Tom Bjorklund’s long post on the very website where he posted it.

    I am not looking for “attention”. I do not seek popularity or praise, nor to be well known. I am not here to “entertain” or “please” anyone.

    I am doing what I want and what I choose to do and say for my own good reasons and purposes. I do not need, or seek, nor ask for anyone’s “approval” for that, bar the Moderators.

    If anyone, even only one person, finds value in any comment or ref link I submit then that’s a bonus.

    I do not want your advice, I did not ask for your advice and I do not need your approval either. This equally applies to all. Genuine compliments and expressions of thanks / gratitude are of course welcomed.

    Genuine queries for clarification about what I “meant” if confused or I as not clear enough, are always treated respectfully by me. Genuine respectful dialogue equally so, if/when time permits.

    It’s not rocket science, is it? :-)

  47. 147

    Th 132: Re Cakes, bares repeating the obvious “Tips for BPL: Stick to astrophysics. Drop the haughty attitude.

    BPL: “bears.” I ain’t takin’ off my clothes for you, pal.

  48. 148
  49. 149

    Thanks, Nigel.

    I am capable of reacting in anger and I frequently do, although I’m trying, with great difficulty, to train myself out of it. All I can do is say the Lord isn’t through with me yet.

  50. 150
    nigelj says:

    BPL @149

    Here’s a perspective on anger,off the top of my head,for what its worth: Clearly reacting with anger can sure create problems, and needs some degree of control. People that are constantly angry scare the hell out of me. Just being nice really is actually quite a good thing.

    But I think we all react in anger sometimes, and I do. It’s pretty normal and obviously its an emotion we have evolved with, so I’m not going to say its entirely unhealthy or pointless. You actually don’t seem too bad, but maybe I have missed some posts, but at least you don’t seem to go looking for trouble.

    Obviously its a case of trying to control the anger, or reserve it for when really justified, and to not go around hitting people. Apparently the latest terrorist in Britain that killed some Moslems with a van, had major anger issues, possible depression, and work and relationships problems.

    However this is interesting:

    This theory that swearing is good for us has been doing the rounds recently so the article is not just the opinion of one isolated guy. Im not suggesting swearing online as it becomes a huge distraction, but Im suggesting that rather than suppressing all anger it may be a case of directing it and diffusing it in various ways and that attempting to never be angry at all might actually be as psychologically damaging as too much anger!