Alice-
I think the uncertainties have been readily available, and I don't understand why people bang on about this so much, unless it's just that they disagree with the assessment of uncertainty. It's odd to me that IPCC cops so much flak, because most climate scientists these days regard its statements as having been too conservative, particularly on potential sea level rise.

You can endlessly quote snippets out of context, but you always have to look at how statements are qualified in context to get a reasonable measure of the reliability that's attributed to conclusions.

You can be purist about how to present uncertainty about future events, but IPCC chose to use probability statements because they thought they would be the best way to communicate their assessments. That was their judgement, and others have other judgements.

If you want to be smart, or purist, then I can say you can't prove the sun will rise tomorrow. You can't put any probability on it. You can't even make an informal statement about reliability. Most people would say, however, that it's a reasonable projection, based on the millions of times it's happened before.

Alice-
Regarding "denialist", I think those who dismiss a data set or finding without properly examining it, or who attack or disparage the messenger, or can only sneer and make contrary assertions, earn the description.

Perhaps also my patience isn't infinite on this web site. I invite you to count the number of insults, ad hominem slurs, disparaging remarks etc directed at me or James Hansen on this thread alone, and the amount of sarcasm and derision more generally, versus my one (I think) possibly unnecessary label. You can start with good old rpg's go at my motives in the post before this. I don't want your sympathy, I'm here by choice, but perhaps some of you could notice your own level of imperfection. Some here seem to be only interested in slanging, but still they have very thin skins.

On balance, Alice, you have conducted a not-unreasonable discussion. However your opening tone seemed to be one of derision, and you still sign off with the "in Warmerland" barb.

btw I don't debate in these threads because I think any posters are open to actual arguments and likely to change their minds. I do it for those (few?) who might be following, so they might see some balance in the discussions. Anyone still out there?

Re Denialists.

There are many questions which remain controversial among scientists, but the existence of human-caused climate change is not one of them. Over 97% of publishing climatologists (Doran and Zimmerman, 2009), virtually 100% of peer-reviewed studies (Oreskes, 2004), and every scientific organization in the world (Logical Science, 2006) agree that humans are causing the Earth to warm. As Donald Kennedy, former editor-in-chief of the prestigious journal Science, says, “Consensus as strong as the one that has developed around this topic is rare in science.”

Oh and Alice, I notice you used the term "alarmist" in your very first post here. And the pervasive derision.

I take back some what I said about you being reasonable, and I note your thin skin.

Thanks Geoff

Uncertainty and its treatment is surely critical here.

Many climate modellers find themselves in a CATCH-22 about modelling and just appeal to the Precautionary Principle.

"The other option is to communicate only what we are confident about. But being conservative (ie: not being wrong by not saying anything) may be dangerous in this context; once we are SURE about certain THREATS, IT MAY BE TOO LATE TO ACT." [p4660, Phil.Trans.R.Soc. A (2008)

How convenient. "Climate model projections are admittedly an issue"; but, "they are unlikely to be the limiting factor that prevents us from making a decision and acting on, rather than talking about, the climate change problem."

Translation: We don't know whether there really is a 'climate change problem' (and may never know?), but if (let's assume) there is one and if humankind does not act now, it will be TOO LATE. Catch-22. How do we know it will be "too late", if we really don't know whether there is a CC problem, and so on?

As Judith Curry lamented last year while reflecting on uncertainty (from inside the modeller tent):"there is circularity (in the argument) that is endemic to whatever reasoning logic is used".

As for my use of the term "alarmist", how else should one describe your closing comparison?

"After the extreme weather of Black Saturday, Australia added the “Catastrophic” category of bush fire danger above the previous highest “Extreme” category.

The danger from global warming may have moved from “Extreme” to “Catastrophic”."

Do you really believe it is legitimate to use such a (local/global/unrelated) comparision - and the word "catastrophic" - given our present state of knowledge about this controversial issue?

[You are not suggesting the "extreme weather" that caused the Victorian bushfires was a direct result of "climate change"/local warming/etc, especially after the "extreme weather" of the wet summer there this year?]

If you do, you run the risk of attracting not only "pervasive derision", but also being grouped with the countless "the-end-is-nigh"/"Godot-is-coming" folk down the centuries who (so far, at least) turned out to be false prophets.

Alice (in Warmerland)

Alice-

Scientists (including me) who appeal to the precautionary principle do so as ordinary people, not as part of their science. It is not a scientific conclusion, just something that seems a sensible way of proceeding, like buying insurance, or not getting on a plane that has a 10% chance of crashing.

If you say scientists should stick to science, well I don't agree. We are people too, with as much right as anyone else to argue for a policy.

On models, the case does not depend just on models, Alice, that's one of the main points of this article. And the models *do* have some level of reliability, despite your repeated claims to the contrary.

On "alarmist": if the news is alarming, that doesn't make the messenger an alarmist. Simple distinction Alice. An alarmist is someone who raises the alarm when there is no relevant threat. I (and many others) certainly think there is a relevant, alarming threat. The consequences of global warming could indeed be "catastrophic". That is the implication of the bushfire warning: it is a warning of potential catastrophe. Only with global warming the potential is for *global* catastrophe.

As I have said many times on threads and in articles on this site, the resistance to reducing our greenhouse gas emissions only makes sense if it would be a big burden on our society. But it wouldn't. Even mainstream economists are now agreeing that the net cost to the economy would be small, less than 1% reduction in GDP growth. It's not a large insurance premium to pay. Some industries would phase out and others would grow, but we've had plenty of such "restructuring" over the past 30 years. So why all the kicking and screaming?