TBYJ, I'll try another tack.
You haven't even made it clear what the question is.

"..alarmed at Climate Change?"

Throw me a bone, please. Should I focus on what "climate change" is, or just focus on what, might, alarm me?
And before you throw me a bone, at least acknowledge that you are asking a political question.

Your worrying trend of 1.4C/century is doubtless well meant. I don't understand why HADCRUT3 should be a reference and not 4 (I didn't realize 3 was still maintained) and I don't understand where the two trend values come from. How did you detect a change point? In this Real Climate article no such point is shown. The implication is that the trend is and has been 1.7/century and that you should perhaps set your worry point target to 1.7 in 2020 (a sterner test).

There are reasons, but HADCRUT4 it is then, I'm not snobby. I've plotted a new WFT graph here. The pink line is the overall trend across the 1965-2015 half century. I've done two more trends: green for pre-pause and blue for pause. As you can see I've been generous with the ranges, and tried not to cherry pick the start year for the pause to the large El Niño year - I could have gotten a much more marked change if I had) - I've overlapped the two trends by a couple of years.

So as a rough eyeball:

Overall trend = 1.6 degrees / century
Pre-pause = 1.4 degrees / century
Pause = 0.9 degrees / century

I'm quite happy to stick with my 1.4 degrees, even though it is a tougher target for me to hit, and would require the pause to continue / the first derivative to continue dropping. If the rate of change from 1965-2020 is 1.4 or above then I'll be concerned. I'll be alarmed if it's as much as 1.7.

A 1.4 degrees / century rise would give us another 1 degree by 2100, making it about 1.8 degrees since pre-industrial. Since we're told the magic number is 2 degrees, you can understand why I am not concerned if we are at or near that figure. At 1.7 (the headline rate you gave supported by the overall HADCRUT) this would give us 1.3 degrees, making us 2.1 degrees warmer than pre-industrial by the end of the century. Again, very near the 2 degree magic number, so even by official standards, not particularly alarming.

For us to move into the official scary territory of 2 degrees plus by end of century, then the trend will need to go up substantially, to well over 2 degrees per century. So I hope you can agree my 1.4/1.7 range is basically an affirmation of my gut feeling/belief/hunch/hope that these sorts of rapid trends are not going to happen any time soon.

So there you go.

michael hart

And before you throw me a bone, at least acknowledge that you are asking a political question.

Well, I'm not sure what you mean by political question. If you mean the original meaning of politics, as in the art or science of influencing people, then almost everything we say here is meant to influence someone, or why bother saying it. So I will admit that I am trying to influence people to come out of their tribal foxholes, and re-iterate the basis of their beliefs. I think this is healthy, we are something of an echo-chamber in here, and whilst it might be nice to have the back-slapping of people who agree with you, these are not the people we hope to convince.

If you mean political in terms of trying to get you to admit to something you would rather not admit to (which alas seems to be what politics means these days) then I am asking for your genuine beliefs. Hardly anyone from the alarmist side reads BH, and an even smaller percentage of them venture deep into a thread like this. You can speak here. It's not a sign of weakness to reconsider your position - it strengthens your position if you can look at the evidence afresh and still come to the same conclusion. It is a sign of weakness to avoid looking at it, it shows you might be afraid you have made a logical faux pas somewhere which you might feel ashamed to see.

Now, back to your question. I am not asking you to define what Climate Change is or might be. I'm assuming for this thought experiment that Climate Change is how it is described by the popular alarmist press - a rise in global temperature accompanied by changes in weather systems and hydrologic cycles which will be in part detrimental to human life. I'm not arguing the likelihood of this coming to pass in reality, just imagining that these predictions turn out to be true as a thought experiment.

So the question is, at what point in the process from here until there would you personally accept that you have been mistaken. That is it.

The silence from the climate committed about what it would take to change their belief is telling.

Geronimo,

That's dodging the bullet. I'm not asking at what point you suddenly believe climate models are accurate. I'm asking at what point the evidence of your eyes would convince you that it is happening.

Big Yin,

I've been generous with the ranges, and tried not to cherry pick the start year for the pause to the large El Niño year - I could have gotten a much more marked change if I had

Sure you could, but it wouldn't mean anything. Just like the pre/post trends mean nothing. Add error margins and they might, but what you have plotted is just not how statistical analysis is done.

If the rate of change from 1965-2020 is 1.4 or above then I'll be concerned. I'll be alarmed if it's as much as 1.7.

That is a stick in the ground, but as 2020 is so close, I doubt it is meaningful. All the same, I hope you don't get to be alarmed.

Michael Hart, it is really simple. What would it take for you to change your mind about climate change?

Hunter, if you search, you'll find some scientists saying what it would take for them to question their current understanding. For example a fall in global average temperature sustained for a decade with no proximate cause or a sustained rise in stratospheric temperatures.

Geronimo,

What this hypothesis is saying that unless we eradicate CO2 emissions there will be catastrophic results.

No it isn't. For someone who takes such an interest in climate change it is remarkable that you don't even know that.

So if it not a climate crisis you are concerned about, Raff, exactly what is it you want us to believe?

Sure you could, but it wouldn't mean anything. Just like the pre/post trends mean nothing.

Well, not 'nothing', that's a bit harsh, they are only indicative of a temporary change in the first derivative. In a very noisy signal, it's just a visual clue, not evidence of anything. It was merely me re-stating the pseudo-existence of the 'pause', I wasn't including it in my projection for 2020 which is based on the overall trend.

That is a stick in the ground, but as 2020 is so close, I doubt it is meaningful. All the same, I hope you don't get to be alarmed.

Well, you asked me to quantify the sort of evidence that might satisfy point (1) of my original four points. Five years isn't long enough, ten isn't. Climate scientists themselves have been a bit wavering on exactly how long a trend has to last to be significant, moving the goalposts when their earlier estimates were overtaken. So you have to put your thumb in the air and at least make a binary decision at a cut-off, and that's what I've done. We can return to it in 5 years.

"Geronimo,

That's dodging the bullet. I'm not asking at what point you suddenly believe climate models are accurate. I'm asking at what point the evidence of your eyes would convince you that it is happening."

It isn't dodging a bullet, although by and large I believe dodging bullets is a good thing. What you're asking is impossible to answer because I haven't the faintest idea what will construe "evidence" of catastrophic global warming. Catastrophes? What like Krakatoa? Or the Tsunami? The Sahara "greening". I'm not Doubting Thomas, there is no evidence I know of that could persuade me that there will be "catastrophic climate change" 50 to 100 years from now. If that makes me a "Bad Sceptic" so be it. I'm not making the forecasts, the environmentalists and their scientific friends are, I don't feel obliged to tell them what evidence would make me believe them, nor do I have any reason to believe they're right.

Let us instead take a look at what's actually happened in the era of rising CO2:

No climates have changed, I am assuming that climate change means we move from one of the present classifications into another. The classifications are: Arid, Mediterranean, Temperate, Tropical, Snow and Polar. Have any of the current classifications changed for any area of the world. So, I'm drawn to the conclusion that 0.8C increase hasn't had much effect.

No weather has changed.

Food supply has increased.

People have prospered more than any time in their history on the planet.

The biosphere has increased by 14%

Now you want me to imagine something that would persuade me of catastrophic global warming? Catastrophes? They happen all the time. Climate changes? They happen all the time.

The theory is not falsifiable, because of which I can't produce a condition under which the theory is true.

"What this hypothesis is saying that unless we eradicate CO2 emissions there will be catastrophic results."

If Raff could tell me what the hypothesis really is, I might be able to give a set of conditions that would persuade me that it is true.

I'm not Doubting Thomas, there is no evidence I know of that could persuade me that there will be "catastrophic climate change" 50 to 100 years from now.

Ah I see where we have crossed wires. I'm not asking you to say at which point you would believe Climate Change will happen in the far future, I'm asking you what evidence you would need to believe it was happening now or in the immediate future. Forget about predictions and models, taking people's guesses on faith. The question is simply about actual evidence:

What actual measurements and observations would convince you that there is an immediate problem with climate*

*Let's leave 'catastrophic; out of it for now, my other points about human adaptation would influence how catastrophic things would get if it ever happened. The idea of catastrophe is predicated on us all sitting around doing nothing if it happens, which simply isn't going to happen. So let's prise apart the idea of significant climate change from a catastrophe, you can have the one without the other.

I believe climate change is happening now. I believe humans contribute to climate change. I don't need evidence that would convince me the Earth is turning on its axis anymore than I need to be convinced that he climate is never in a stable state.

Geronimo,

Again that's moving the pea. We all agree climate changes naturally, and we all agree we're not sure how much it changes naturally on the decadal scale because most of the proxies we have smooth these out and we haven't been measuring long enough. And most of us agree that human activity will have some effect on these natural fluctuations, but not sure how much. Let's not re-iterate the actual problem, this is a thought-experiment.

The question was: at what point (i.e. what would you personally need to see) would you consider that our influence is moving it out of the natural fluctuations into something else which might conceivably be harmful to us. Mild examples would be a sharp increase in the temperature or extreme weather trends (my personal level) or for others it might be more physical, such as major low-lying cities becoming flooded, or crop failures in the temperate zone causing food shortages. But I re-iterate - if you have no point at which you would be convinced, then your position is ideological, not rational.

The wriggling from you and others on this is interesting to me. There is a lot of tribalism in this debate, and people retreat into their foxholes. The debate gets polarised, people start to emotionally dislike the arguments and thoughts of the other side. What starts off as a gut-feeling that something is wrong becomes a dogma which must be protected. The idea of this thread was to work out the spectrum or rationality. I fully expected some people to say there would be NO set of circumstances where they would recant their scepticism. It's not a judgement, there are plenty on the other side who will be exactly the same - they'd be shouting about global warming as the glaciers squashed their houses.

TBYJ. I've explained myself to you as best I can, I'm not moving any peas, and don't expect to be told I'm acting in bad faith. Because you've somehow got it into your head that a "good" sceptic should have a position which falsifies his/her view of the world, doesn't make it true, or indeed, virtuous.

I've been told a fairy tale, I can see that from the evidence in front of my eyes, and the boy at the top of the class has asked me what would make the fairy tale true for me because he's decided what? That there is a purity in being to state what would falsify your opinions of the evidence you've seen?

I don't have a theory that there is no climate change, nor do I have a theory that there will be catastrophic outcomes to climate change, so I don't have to say what would falsify my non-theories. It should be obvious, clearly the notion that a body in space fed energy by another body in space which it revolves around , in a galaxy that itself is moving around the universe is not a prime contender for a stable climate. Catastrophic outcomes can only be falsified by no catastrophes, and my view that it's horse-shit can only be falsified by catastrophes, even then it's not as though there've been no catastrophes historically.

In the event I've had my say, and you've had yours I'm out of here.

Nobody has to do anything, this is a voluntary discussion. Why are you getting angry and feel insulted by my insistence that you answer the question I asked, and not the one you wish to answer? What is it about answering this question which cuts to your very core?

Let's play with it by moving to a less emotional area.

Me: "What evidence would you need to believe there were green men on the moon?"
You: "I don't need to answer that"
Me: "This is just a thought experiment, you don't need to answer."
You: "I don't believe predictions that there will be green men in the moon in 100 years"
Me: "I'm not talking about 100 years. What evidence would convince you now?"
You": What you're asking is the reverse of Popper. I don't have to believe a hypothesis that has no known falsifiable state, and I don't have to provide a state which would make me believe such a hypothesis."
Me: "I'm not asking you to falsify a prediction, I'm asking what you personally would need to see."
You: "I have no idea what would constitute evidence of little green men on the moon."
Me: "OK, what about seeing them through a telescope, seeing their buildings, hearing their conversations"
You: "That's it, I'm out of here"

Something is absurd here, but I don't think it's the question.

TheBigYinJames
I think you can only say after the event, perhaps decades or centuries after the event that there has been a shift outside previously experienced extremes. For me as the previous 3 interglacials were warmer than current then it is unlikely that I will be alive when the GAT moves into uncharted territory for the current climate regime. If you're talking other events ice free Arctic, farming on Greenland, Rivers flowing in the Western Sahara and so on I'm not sure local events like that would be significant in themselves as they, or something similar have occurred during this interglacial without looking back further.

So I'm not sure that anyone can answer your question, because if it happened in the past without human input but for unknown or unmeasurable reasons we can't assign a cause with 100% certainty now.

Reasonable response Sandy. You think we can't detect it in advance, which may well be true.

Game theory at least would say that we spend money in preparation according to the chance of an outcome. It would recommend that even if you guesstimate that damaging climate change is only 10% possible, we should still spend 10% of the adaptation costs in advance. As it becomes more certain, you can add to this. If it becomes less certain, then you've lost your stake money to a certain extent, but over multiple instances you will maximise wins.

I think what you are saying (and Geronimo was saying in a roundabout way) is that there are no climate events which have not happened in the past, so any one or more of them happening now cannot be evidence of a change.

I think this is wrong, because although these single events may have happened before, it's the frequency and size which are important. If they can start growing grapes in Scotland every year, then the fact that there's a book saying they tried it once in 1286 does not mean that the current phase is the same as then. They may have only managed it for a couple of years back then and gave up when the weather got colder.

In a noisy signal, everything will have happened at least once, it's naïve to expect brand new unprecedented events to happen as a prerequisite to becoming concerned. Instead we need to see if the frequency is increasing.

White furred bears, and brown furred bears, fishing in Scottish rivers, would be cause for alarm.

Would they get on? Any fights would disrupt the flyfishing and cash flow for the International community of Scottish Landowners.

Big Yin,

Well, not 'nothing', that's a bit harsh...

No, starting your interval at a peak that stands out is nonsense statistics. And this nonsense works in both directions; you might just as well say you could start your trends in 1976 or 1985 - they are notable troughs in your graph and would give bigger trends. But that too would mean nothing.

Your five year horizon is brave - especially given that nobody else here can bring themselves to address your question seriously. My guess is that it won't make you any friends.

TheBigYinJames
Taking your example of growing grapes in Scotland, there are a couple of points which come to mind to make things like that difficult to assess. Firstly could grapes have been grown in Scotland in the previous three interglacials at their warmest? Probably yes. Has Viticulture progressed the hardiness of grapes in the last 700 years? Again probably yes. Has viticulture itself progressed in the last 700 years? Again yes. Does this mean we're comparing like with like? No.

You're probably as aware as I am that there was a climatic/environment (with a possibly unknown and unquantifiable human input) change in Scotland, Ireland and elsewhere in NW Europe, when climate began wetter and cooler encouraging blanket bogs and killing native forest/woodland. If there is a return to a warmer drier regime which produced a return to woodland, sheep and deer permitting, would that be climate change with a human input or totally natural in your opinion?

Raff, I'm used to saying the unsayable here, but I rely on veritas to protect me. I don't mind if people don't like what I say, as long as they can't prove it's wrong. I try not to dislike people I disagree with, and I hope they extend the same effort.

Sandy,

If there is a return to a warmer drier regime which produced a return to woodland, sheep and deer permitting, would that be climate change with a human input or totally natural in your opinion?

Well, let me start by saying I have given my main criteria for concern/alarm - rapid upward trends in temperature and extreme climate.

I'd only be worried by a change in regional climate if it was rapid. As you say, we don't really know the extent which human deforestation since the Neolithic led to the creation of moorland and bogs, and how much was environmental, so we can't really use that sort of thing as a barometer of changing regional climate.

My example of the grape growing was more to illustrate that a one-off event happening in history cannot be used to proxy the temperature, because we need the frequency of these events not the existence of them.

What might persuade me to change my mind - and worry?

Successful non-trivial predictions from global warming theorists. Too many have failed. Two failures come to mind: ice-free Arctic by 2014; temperature increasing by 0.3C per decade. No doubt there are others (examples welcome). Also welcome would be examples of suitable predictions which await verification.