[repolfx]

The IPCC, being a UN body of government appointed scientists, economists etc, consistently take an overly conservative view

No, IPCC predictions have been wrong/over-aggressive in the past. Their 1990 long range predictions can be compared against the present now and are 40% out:

http://joannenova.com.au/2012/05/the-ipcc-1990-far-predictio...

People have a tendency to cherry pick predictions that worked out or which assert a requirement for even more panic, whilst ignoring predictions that didn't work out (of which there are many).

Your argument is basically unfalsifiable: scientists must be listened to because they all agree (itself a dubious or false claim), but the internationally agreed consensus must not be listened to because it's "bland" and influenced by people who might disagree (but who in the end endorsed the report anyway).

It appears that evidence is only accepted as legitimate if it's more alarming than past evidence: how could this argument ever ramp itself down? And how can the argument both be argument by authority whilst simultaneously attacking the credibility of those authorities?

[NeedMoreTea]

That seems to be exactly what you are doing -- one cherry picked alleged mistake at your link as against 8 instances of under-estimate in that old Scientific American article, and the instances picked up by this NYT piece. A link I might add that is a highly dubious source[1] who is already demonstrably wrong on extent of current warming, and has written for the Heartland Institute[1][2], a bunch of extremist idiots -- notably with no scientific credentials -- who think CATO too moderate. All you need to know is revealed by their continued denial, even today, of the link between tobacco and health[3].

Her about page quotes proudly Matt Ridley and James Delingpole - two outright and consistent liars on climate and multiple other topics over decades. Both well known UK climate deniers who you absolutely don't want to be lauded by if you want a shred of credibility. Ridley, the man who brought down a bank (Northern Rock) in 08, then claimed the answer would have been less regulation and he was in no way to blame - the inquiries found him to blame and specifically criticised him for bringing Britain and British banking into disrepute.

So at the very least I would want independent confirmation from a reputable source that her outlying view of climate sensitivity and the IPCC's alleged error is even accurate. She can't even quote SkepticalScience accurately or honestly, but cherry picks part of what they wrote to try and paint them incorrectly as fools.

I'm not suggesting we do not listen to the IPCC either, just that they have on past performance been found to be consistently conservative in their estimates. That's borne out by their structure, their errors of omission, and that they give little to no consideration to tipping points and non-linear impacts -- which is understandable given that some are unknown and none are amenable to modelling. Both issues highlighted in that Scientific American piece. Put another way IPCC reports are the least impact we can probably expect, which the data is bearing out as years pass.

[1] https://en.wikipedia.org/wiki/Joanne_Nova

[2] https://en.wikipedia.org/wiki/The_Heartland_Institute

[3] https://en.wikipedia.org/wiki/The_Heartland_Institute#Tobacc...

[rayiner]

Without getting into who is a crank and who isn’t, I think the following point from the post you’re replying to really gets to the heart of my consternation:

> And how can the argument both be argument by authority whilst simultaneously attacking the credibility of those authorities?

If people are supposed to believe the IPCC because it’s a consensus statement, how can you then ask them to then assume the IPCC is wrong? Who is the scientific authority we’re supposed to trust more than the IPCC?

Your assertion that the IPCC “gives too little consideration to tipping points” highlights the issue. The IPCC seems to have considered runaway greenhouse gas effects and rejected them as “unlikely.” Why should we disregard those conclusions?

[NeedMoreTea]

I'm not suggesting to assume the IPCC is wrong - but that the reports have a conservative outlook. In some respects that's a good thing in that outlying and unclear studies and predictions will be omitted, yet some of those outliers may turn out to be accurate and the middle of the road view wrong. That's fine and expected, if frustrating at times.

In other respects, notably the structure of having a political approval stage for reports has, if that Guardian Saudi piece is to be believed, subsequently toned down those consensus views -- under pressure from home for political or economic reasons. There's also an awful lot of "he said, she said", meaning it's impossible to reach certainty from those reports. Without criticising any nation's scientific and economic representatives involved in the preparation phase, there are multiple representatives criticising that final political approval phase... Draw your own conclusions.

The upshot for those of us trying to make sense of it is IPCC tends to a very diligent presentation of the least contentious, which subsequent measurements have shown to have underestimated it on multiple occasions. Which leaves me thinking IPCC reports a best-case scenario: I believe them, it's the best consensus we have, but am not surprised if something crops up that turns out to be worse or more significant than projected. I still find that far better than had they been over-estimating impacts consistently. YMMV. :)

Specifically on tipping points, they're likely to always be something of an unknown before they actually tip. Once a threshold has been passed and an ice sheet thought safe for decades collapses, or permafrost tips into catastrophic melting it's clear the threshold was passed, and we know from hindsight. Predicting and modelling on the other hand will probably remain near impossible - we only really know after it's switched. Which is, of course, after it's too late and tipping them back effectively impossible.

That said, that old Scientific American article mentioned they would be including some consideration to threats from tipping points and non-linear effects from 2014.