Michael Mann and Lawrence Torcello have an article in the Conversation about the philosophy and science of limiting global warming to 2oC. This caused some controversy on Twitter because it wasn’t clear if the article referred to the Northern Hemisphere only, or to the whole globe. It also cause some controversy because 2036 seems very soon for us to reach the 2 degree limit (self-imposed limit, at least).
However, if – as the article assumes – the ECS is 3 degrees and we follow a high-emission pathway (RCP8.5) then I think 2 degrees by 2036 is plausible. An ECS of 3 degrees suggests that feedbacks amplify the warming by a factor of about 2.7 (3/1.1). This tells us that the feedbacks must be about 2.2Wm-2K-1. If we follow a high emission pathway then we will increase anthropogenic forcings by about 2Wm-2 by 2036. Given that we have a planetary energy imbalance of around 0.6Wm-2 today, if we did not warm at all, we’d have a planetary energy imbalance of 2.6Wm-2 in 2036.
To reach 2 degrees by 2036, we’d need to warm by 1.1 degrees from today (1.1 + 0.9) which would produce a negative feedback of 3.7Wm-2, and positive feedbacks of 2.4Wm-2 (2.2 x 1.1). This would then leave a planetary energy imbalance of 1.3 Wm-2 (2.6 + 2.4 – 3.7) which may actually be a little high, but not implausible. So, 1.1 degrees from today seems entirely possible, especially as we might expect it unlikely that the planetary energy imbalance could grow much larger than around 1Wm-2.
This also seems broadly consistent with a post by Ed Hawkins which seems to suggest that 2 degrees by around 2040 is plausible if we follow an RCP8.5 emission pathway. So, I’m not sure I quite get what the fuss is all about. If the ECS is indeed 3 degrees (which is close to the expected value) then reaching 2 degrees by 2036 is indeed quite possible, if we choose to follow a high emission pathway. Of course, if we do reach 2 degrees by 2036, this will not be where warming stops, since we’d still warm by about another degree or so, so as to reach equilibrium. Of course, I’m not suggesting that the exact date would be 2036, simply that reaching 2 degrees by that time is quite possible if we continue along a high emission pathway. I guess we’ll know soon enough if this is indeed possible or not; at which point we can all collectively say “shit, Michael Mann was right!”.
...and Then There's Physics 
Anders, first, your link for the Conversation article actually goes to an article by Ed Hawkins.
Kevin Cowtan’s two box model run with RCP 2011 forcings plus ENSO estimates a TCR of 1.65 and 2 C in 2044 on RCP 8.5. 2036 is on the early side, but well within the likely error range of the estimate. (Kevin does not calculate the error range of his estimates, but it is very unlikely to be more restricted than Lewis and Curry’s likely range of -0.27, +0.47 on which I base my assertion.) Curiously, the Ed Hawkins article also shows a temperature transition around 2043 based on the CMIP5 multi model mean for RCP 8.5, with the earliest transitions being around 2028.
Based on that, I would be inclined to say that Mann’s estimate is pessimistic, but not absurdly so.
Even mentioning ECS seems strange for a period this short. TCR is clearly the sensitivity to use in this case.
Pekka, Manne made his estimate using an energy balance model with tunable ECS. That being the case, he is constrained to make his estimate from estimates of ECS.
It is worth noting that he writes, ” The curves for an ECS of 2.5 degrees and three degrees C fit the instrument readings most closely.” That being the case, and using his model to estimate the time to 2 C under RCP 8.5, he should give the range across which he obtains the best emperical fit, and hence have a central estimate of 2036 (3 C ECS) to 2046 (2.5 C ECS) with of course, some additional uncertainty on either side of that.
I would further note that the earlier part of the estimated time is the most policy relevant because the most potentially harmful. Even with the estimates above, I think policy is best based on an assumption of time to transition of 2036, or even 2030 because the cost of getting being too optimistic is greater than the cost of being too pessimistic within a reasonable range.
Just a comparison of various observations versus various climate forecasts (including Mann’s) from 1980 to 2036.
I find short term discussions disconcerting. “Oh look, Hawaii exploded global warming also appears to have stopped.”
Speaking of such a prospect on this sort of time scale throws sand in the gears of the analysis paralysis preferred by some.
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Of course the ECS is operative. That is what the land temperature will reach with very little lag! Land has no thermal sink to sequester the heat, and besides that it will receive latent heat from the oceans.
I like the trillionthtonne website which lets you experiment with different levels of warming in an easy-to-understand interface.
If you select 2C of warming per trillion tonnes of CO2, then it will tell you at what date we can expect to emit the trillionth tonne based on emission trends over the last 20 years. The date is currently Sunday, 27th November 2039. Although I realise it’s not saying that we’ll be at 2C by this date, just that we’ll be locked into it.
Tom,
Maybe Rachel fixed the link, but it seems fine now.
Pekka,
Tom’s right, the ECS is mentioned simply because it is a parameter in the model. One could also have referred to the TCR (as Tom does when discussing Kevin C’s model) which would be something like 1.7.
I must admit, off the top of my head I would have said that 2 degrees by 2036 was highly implausible, but Paul Williams’ graph above alone shows that it really isn’t. I do wonder how much influence the care people are taking to avoid charges of exaggeration is having on our perceptions.
Rachel –
Looking at that site, I suspect that even if we had a politically impossible moratorium on new fossil fuel infrastructure – No new coal power stations, no new oil or gas wells – we’d still be committed to 2K.
I still wonder if some of the surface temperature ‘pause’ is down to large scale aerosol emissions from China and we’ll see a temperature jump as soon at they get around to fitting flue gas desulphurisation. No doubt we’ll see.
ATTP
Really? Not being a weeny bit tongue in cheek? 🙂
It is the shrieking of denial. Amplified beyond even the usual frenzy because it’s aimed at Michael Mann.
Andrew Dodds
At least one fairly high-profile research group thinks not (Neely et al. 2013), but if Karsten is about, perhaps he will be able to say more.
I always like naked graphs, without references. It’s a reliable indicator of disinformation.
Paul Williams graph appears to be sourced from WhatsWrongWithThis, http://s23.postimg.org/fbw6reefv/IPCC_Warming_Forecasts_vs_Actual_Feb14.png
“I am gradually teaching my spam filter to automatically send to spam any and every comment that contains the words “warmist”, “alarmist”, “Al Gore” or a link to Watts. A comment that contains any of those is, by definition, not posted in good faith. By definition, it does not provide additional information relevant to the post. By definition, it is off-topic. By definition, it contains erroneous information. By definition, it is ideologically motivated, thus not scientific. By definition, it is polarizing to the silent audience. It will go to spam as fast I can make it happen.”
— http://blogs.scientificamerican.com/a-blog-around-the-clock/2013/01/28/commenting-threads-good-bad-or-not-at-all/
I forgot to include the link to the post to WitlessWondersWanderingThither, Here ’tis, http://www.donotlink.com/c6fk. A classic case of “I saw it on the internet, it must be true.”
BBD –
That’s interesting. I thought they there has been relatively little Volcanic contribution since 1992.
But – admittedly using Wikipedia as a source – it does seem like we’ve had a constant stream of VEI-4s in the 2000s, more than the 1990s. And even then VEI is an inexact measure.
So perhaps refine that to ‘When we have a lull in Volcanic activity for a couple of years..’
One factor that may contribute to the result many (including me) consider a little surprising is the definition of preindustrial temperature as the temperature has varied enough to allow for different choices. I tried to find out, what AR5 tells about that, but almost all uses of the word preindustrial were related to anthropogenic forcing, not temperature. For anthropogenic forcing the arbitrariness is much smaller that for the temperature. Finally I found one place in Figure 12.46, where the preindustrial temperature is used as point of reference. Combining that with what we know about temperature history (with the hiatus) seems to indicate that we are now about 0.8 C above the preindustrial, a value that sounds familiar to me from other contexts as well.
Mann chose, however, the point of reference so that according to his graphics 1.0 C was reached in the peak of 1998 and that the warmest years have reached 1.2 C and the latest point is close to 1.1 C. It does make some difference, whether the required warming from present to 2 C is 0.9 C or 1.2 C.
Pekka,
That’s clearly a factor, I agree. I would add, though, that if we do follow a high emission pathway and increase anthropogenic forcings by 2 Wm-2 in the next 20-30 years, then that would imply a similar amount of warming during the next 20-30 years as we’ve seen in the past 100 years. Consequently, we will probably be warming at a rate exceeding 0.2 degrees per decade, so a few tenths of a degree would simply correspond to a difference of a decade or so – not hugely comforting.
Hiatus? http://www.ncdc.noaa.gov/sotc/global/2014/9
The past 12 months—October 2013–September 2014—was the warmest 12-month period among all months since records began in 1880, at 0.69°C (1.24°F) above the 20th century average. This breaks the previous record of +0.68°C (+1.22°F) set for the periods September 1998–August 1998, August 2009–July 2010; and September 2013–August 2014.
Some hiatus. Words are important.
Pekka,
Having looked at Figure 12.46 it appears to suggest that we would cross the 2 degree threshold in about 2040 if we follow a high emission pathway. So, about the same as the article by Mann and Torcello suggest.
jsam,
If you refer to my use of hiatus, I mentioned it as it affects interpretation of the Figure 12.46 that presents only model projections that do not follow the known history of the years since 2000.
AndThen,
Yes, I did it. I got up early this morning to get to the comments in pending from overnight before you could go and approve them all 🙂
Andrew,
Yes, it seems that way. But I find hope in something James Hansen said which is that if we stopped all emissions by 2015, then we’d be back to 350ppm by the end of the century. If we wait 40 years before we stop emissions, then it’ll take a few thousand years to return to 350ppm. This is also the best argument for immediate action.
Here’s where Mike Mann did his calculations….
http://www.scientificamerican.com/article/mann-why-global-warming-will-cross-a-dangerous-threshold-in-2036/
All the MATLAB source code is available here:
http://www.meteo.psu.edu/holocene/public_html/supplements/EBMProjections/
ATTP,
Yes. The figure has also a relatively high prediction, but the question is, whether the recent deviation below the model projections like that should be given any weight. I would consider that figure together with Figure 11.25 when we are discussing, what can be expected over the next 35 years. The “hiatus” cannot be completely dismissed, when the period is so short. Figure 11.25 is in the chapter of projections to 2050, Chapter 12 considers longer term projections.
Pekka,
Okay, I see what you mean. Yes, that’s a fair point. Of course, if the hiatus is mainly internal variability, it may not actually influence the trends over multi-decade timescales.
tg,
Thanks. Yes, I had seen those. Haven’t looked his code though.
Irrespective of the scientific credibility or where on a probability density function the 2degC by 2036 might be the use of such claim along with the a number of other assertions looks like warmist alarmism to the majority people with little interest or knowledge of the climate debate.
It also confirms the worst fears of the AGW rejectionists. that AGW is a trojan horse for political change, signaled by this sentence.-
“As of yet, however, the world has largely failed to move beyond moral, political, and economic parochialism.”
Followed by a list of assertions about the ‘unfairness’ of BAU.
That seems rather contradictory, if you regard the political world system to be morally, politically and economically parochial then anti-parochial moral and economic arguments are unlikely to have much traction in changing the behavior of such institutions however much that is your apparent intention.
It is another inverted causal chain. While the science is explicit enough to indicate that BAU is an unwise path at the global level the reality is that the world lacks the global systems of governance to react appropriately. It is stuck in moral, political and economic parochialism. For both the developed nations ‘guilty’ of a generating most of the CO2 emissions so far, and the developing nations who see little alternative to exploiting fossil fuels along with renewables and greener tech to raise their poor up to the wealth level of the West.
This is the problem with the global moral, political and economic response to AGW. The deniers are correct in claiming that the ‘warmists’ are wanting political change. Whether intended or not, advocating reducing emissions inevitably requires significant political change because such changes are not in the interests of the parochial systems of governance we have.
The parochialism of world morality and politics will have to change to ensure any effective response to climate change and probably will. But however convincing the assertion that 2degC warming by 2036 means it MUST change is to the fellow-travellers, it is seen as advocacy for political and economic change threatening those with parochial interests.
The reason that carbon pricing agreements do not work as a means of controlling carbon emissions is that there are parochial economic and political interests that are harmed by them. The least effective argument to change the parochialism is to invoke the very thing it ignores, the wider picture either globally or over time. All that is ‘seen’ by the parochial interests is a claim that they MUST surrender to the new forms of governance and economics because of external and future threats they fail to recognise. And that failure to abdicate their power over this policy area is immoral, ignorant and selfish.
Even if true this is not an approach that is likely to convince those powerful parochialists. But perhaps the message is mainly for those that already believe it.
The ‘trick’ will be to make the changes required to reduce CO2 emissions away from BAU and into a less climate destabilising regime attractive and advantageous to the parochial interests.
Asserting that the politics MUST change NOW because it will be 2degC warmer in 21 years is not an effective way of doing that.
izen,
I think William Connolley is making a similar argument in his most recent post.
izen
Nothing is likely to convince vested interests to act against their own vested interest. They will ultimately have to be compelled. By regulation.
ATTP,
Speculating, how the influence of the internal variability affects the future seems to allow for many views. One on the “cold side” (note, however, the last sentence) was presented by (the late) Tom Crowley in the interview just published in the PAGES magazine as the last story of this issue (pp. 114-115):
BBD,
But who is going to decree that regulation?
And, who can tell, what’s a wise enough way of formulation that regulation?
We come always back to the point that declaring that strong action is required, helps little, if the political system ends finally up in choosing something that does not lead to the right outcome – whatever that is.
Related to the problems of achieving real changes I quote myself from 15 years ago:
This is the last paragraph of the Executive summary of a book I edited (many authors contributed to the chapters): Climate Change, Socioeconomic Dimensions and Consequences of Mitigation Measures. I don’t think that you can find that book in many places outside Finland.
The work was sponsored by a power company, where people apparently had realized that climate policies are actually not contrary to the interests of a power company that acts proactively, and that owns nuclear and hydro power (also some coal). The bought more hydro from others, who had not realized as well, what was to be expected. Opening of the electricity markets lead to losses for such a company, but emission trading helped in cancelling that change. (Finland did not follow the path of Germany in renewable energy policies, that path has hit very hard the power companies.)
“Of course, I’m not suggesting that the exact date would be 2036, simply that reaching 2 degrees by that time is quite possible if we continue along a high emission pathway. I guess we’ll know soon enough if this is indeed possible or not; at which point we can all collectively say “shit, Michael Mann was right!”.”
The political 2 degree limit is defined for the globe and that will be later.
I am reasonably sure that a considerable part of the mitigation sceptics will never say: “shit, Michael Mann was right!” Even if it were 10 degrees. Some of them might say that we are to blame because we did not communicate clearly that there was a problem.
Victor,
From what I’ve seen it’s plausible that it could be in 2036 and the most likely date (assuming RCP8.5) is just after 2040. So, not that much later – unless I’m misunderstanding something.
[Mod : If someone can’t respond, then it’s only fair that they don’t get mentioned] and Geoff Chambers who normally turn up at The Conversation to stalk Stephan Lewandowsky have heavily trolled Torcello and Manne’s article with the usual nonsense. (They managed to slip in some Lewandowsky bashing via a reference that a paper of Torcello’s had to one of Lewandowsky’s papers.)
[Mod : Again, if someone can’t respond here, then I’ll redact their name]
If Richard is reading this, I would be interested if it is still his position.
“Most climate scientists* do not subscribe to the 2 degrees “Dangerous Climate Change” meme (I know I don’t). “Dangerous” is a value judgement, and the relationship between any particular level of global mean temperature rise and impacts on society are fraught with uncertainties, including the nature of regional climate responses and the vulnerability/resilience of society. The most solid evidence for something with serious global implications that might happen at 2 degrees is the possible passing of a key threshold for the Greenland ice sheet, but even then that’s the lower limit and also would probably take centuries to take full effect. Other impacts like drought and crop failures are massively uncertain, and while severe negative impacts may occur in some regions, positive impacts may occur in others. While the major negative impacts can’t be ruled out, their certainty is wildly over-stated.”
http://bishophill.squarespace.com/blog/2011/11/9/dangerous-climate-change.html
@Andrew Dodds and BBD:
Thanks BBD! Neely III et al were testing whether increased Asian anthropogenic aerosol emissions have contributed to the observed increase in stratospheric background aerosol. Turns out they didn’t. The increased stratospheric background aerosol is therefore down to recent moderate volcanic eruptions such as Nabro in 2011 and other earlier ones. Definitely a small (and non-negligible) negative forcing.
Most research on anthropogenic tropospheric (Asian) aerosols suggest that (1) their increase was partly counterbalanced by decreasing emissions elsewhere, and that (2) the high Black Carbon fraction led to less surface cooling as it otherwise would have if only sulphate aerosols were involved. So no detectable anthropogenic aerosol forcing in the last decade. Some warming contribution in the 1990’s though (global brightening), after the massive aerosol cooling contribution in the 1960’s and 1970’s (global dimming).
The temperature slow-down is almost entirely due to ENSO, flavoured with a bit of solar and volcanic cooling contribution. The distinct Warm Arctic Cold Continent pattern (WACCy) in NH winter led to an additional detectable temporary cooling contribution in the last 5 years. Whether it’s down to the Arctic sea ice retreat or pure coincidence, we don’t know yet. I am with Cohen et al 2014 who argue for a strong sea ice feedback.
Okay, you know best. I had expected it to be clearly later. The Southern Hemisphere has much more ocean and the Arctic warms faster than the Antarctic.
Any thoughts on this paper which seems to be suggesting that the radiative forcing due to black carbon may be lower than previously thought?
VV –
Yes, it will be all our fault for not doing enough advocacy.
But, hell, if the WAIS floated off its bedrock tomorrow they’d call it natural…
Andrew,
That’s exactly what I think will happen. In the coming decades we will start seeing a move from “it’s not happening or is not dangerous” to “if only climate scientists had been more trustworthy”. It will always be someone else’s fault.
KarSteN –
Thanks. Next big El Nino will be interesting.
Karsten
Thanks – much appreciated. I try not to write your name too often… 😉
@AATP:
The paper tackled some of the issues in Bond et al. 2013, mainly the BC overestimation over remote (ocean/high latitude) areas. Some earlier work by Wang et al 2014 (different Wang though) pointed in a similar direction: http://onlinelibrary.wiley.com/doi/10.1002/2013JD020824/abstract
It’s no surprise that Bond et al. 2013 is biased high. Their relevant numbers in terms of forcing were those where they included co-emitted species anyway. Went unnoticed by many, particularly by those who argued that we should put a lot more effort in BC removal as an appropriate mitigation strategy.
ATTP
It will always be their fault, and I for one will make damned sure nobody ever forgets this.
Karsten,
Thanks. So, does that suggest that the net anthropogenic RF could be lower by a few tenths of a Wm-2?
ATTP,
I wouldn’t guess so. Overestimation over remote areas is an issue for all aerosol species to some extent. You often find the combination of either high (neg) sulphate (scattering aerosols) and high (pos) BC (absorbing aerosols) forcing or low (neg) sulphate and (pos) BC forcing. The end result is similar. A bit of a scaling issue if you like. If you happen to only publish the high BC forcing, you can’t infer the total forcing. The same applies if you publish a very high sulphate forcing (what many people did before the BC hype).
Bottomline: IPCC AR5 current central (aerosol) forcing estimate should be fairly robust. I tend to think that the uncertainty range could be reduced quite substantially though (except for the aerosol forcing – i.e. it’s temporal variability – over the course of the 20th century).
KarSteN,
Okay, I’m with you. Thanks.
Karsten,
One thing which strikes me about the HIPPO profiles being used to indicate overestimation of radiative forcing is that the data were all collected in the middle of the Pacific during a period of apparently abnormal Pacific variability (lovingly named “the hiatus”). Is there any possibility these might not be representative of typical aerosol transport behaviour? I note in the recent Wang et al. paper Figure 2 that profiles collected during the 2010 El Nino were the best match to modelled profiles.
Very good question, Paul! The answer is blowin’ in the wind I guess 😉
In other words, I’m afraid I have no answer for that one at the moment.
My earlier comment now does not make sense. Apologies if I stepped over a line. I will stick with keeping the discussion civil here at least. 🙂
My question was directed to Richard Betts re his 2011 comment on 2C and “dangerous” global warming. He has subsequently expanded on his view here.
http://www.twitlonger.com/show/n_1sdbl34
Mike, I wouldn’t call that an expansion so much as a substantial reversal. The Greenland bit is ironic, no?
Mike,
Not really your fault. It just seems easier to not mention people who then can’t comment. I guess I could relax my ban on certain people, but I’m not sure I have the energy to deal with the resulting comment streams.
I think there’s a lot to disagree with in Richard’s first comment, I think his speed limit analogy and accompanying comments are quite reasonable.
I think of the 2C target a bit like eating your “5 a day”. There’s no scientific basis for that particular threshold, and to be really healthy we probably need to eat more than that, but in general eating more fruit and vegetables is beneficial and having that target does focus some people’s minds and encourages them to eat more healthily. And, importantly, for most people it is achievable.
ATTP
Please don’t.
🙂
“I guess I could relax my ban on certain people”
Definitely not on my account. If you want to discuss climate science allowing more climate trolls is not the way to go. I have heard all their arguments. Many times. If they ever come up with something new, I am sure I will hear about it.
My beef with The Conversation is that they have built a great business on the back of contributions from academic authors but due to lazy, inconsistent and also IMO cowardly moderation, they frequently allow climate trolls free reign to trash the discussion. The cyberstalking of Lewandowsky, no matter what you think of his research is an attempt to intimidate and it is a disgrace that it is allowed by TC.
Sorry to raise moderation. It is a boring subject. I appreciate your blog and the comments and I am glad your hiatus was short lived.
Mike,
I tend to agree with you. There are certain sites on which I will rarely comment simply because the moderation is largely non-existent. I also find it a little frustrating when you comment on a blog and the post author doesn’t really bother interacting below the line. Having said that, I do understand why many may not want to do so – it is a rather thankless task 🙂
It has probably been covered in the comments above. It seems reasonable to speculate that fossil fuel burning will be reduced prior to 2036 in response to growing pressure when the global warming and it’s effects become plain. But reducing fossil fuel burning will also reduce aerosol pollution which might accelerate global warming, at least in the short term. So 2C by 2036 seems plausible to me.
Mike Hansen, 10:22 am, well said!
Harry –
It was covered above (and I was wrong.. it doesn’t seem as big an effect as I thought..)
2036 is only 22 years away, if we have noticeably reduced global fossil fuel use by then I’ll be surprised..
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