Except that the entire "humans are responsible for say n%" is the latest diversionary tactic by climate deniers to sucker rational people onto opposing policy that mitigates climate change.

The argument is akin to saying "your program slowdown is - and I'm making up a number out of thin air - 50% caused by systems outside of your control so you should definitely spend 50% less time optimizing the things you can optimize".

The logical flaws are blatant: the % is an invention, and the truth or otherwise of the premise has no bearing on the action you can and should take.

Let me get this right: you're saying that human emissions of CO2 need to be reduced in order to mitigate climate change regardless of whether CO2 emissions cause any warming?

If humans caused 100% of the change then we can stop causing it. If humans caused 0% of the change then we can't stop causing it and must adapt to it. If humans caused 50% of the change, then we can stop some of it but will have to adapt to the rest.

Obviously the premise has a huge bearing on the action we can and should take.

Firstly, I said it was in invention. It's an argument that has the benefit of never having to provide any sort of evidence to back it up.

But since I'm forced to attack the strawman: let me put it another way: if humans are responsible for less warming than 100%, then we're going to have to do more to mitigate our effects, because we have to mitigate more human behaviour for the same outcome.

Until we're making meaningful changes - yet to happen - it's utterly irrelevant if we've caused 50%, or 100%.

Suppose that it's significantly greater than predicted? Are you willing to bet your future happiness, and the health and wealth of the rest of humanity, that it isn't?

> Suppose that it's significantly greater than predicted? Are you willing to bet your future happiness, and the health and wealth of the rest of humanity, that it isn't?

Yes. Of course I am. We make those sorts of bets constantly, because Pascal's Wager doesn't work. We can't not make those sorts of bets.

When somebody says "the end of the world is nigh!" it is almost always worth waiting a bit to see if in fact the thing they're worrying about is actually a problem. Hindcasting is nice and all but the real test is: Does the warming trend actually continue as predicted and if so, once it does get warmer, do we actually see negative effects from it that significantly outweigh all the likely positive effects of warming?

The warming trend is continuing, and the insurance industry is already seeing significant negative effects. See for example [0], [1], [2], [3], all from a single search on "insurance industry extreme weather trends"

[0] http://www.theguardian.com/sustainable-business/extreme-weat...

[1] http://www.foxbusiness.com/industries/2014/02/14/allianz-sto...

[2] http://www.theglobeandmail.com/partners/advinsurancetrends11...

[3]

Even if it's still "warming" at all - whether it is depends on what timescale you look at and how you average the data points - it's certainly not continuing as predicted, but rather at a lower rate than expected. Breathless media stories notwithstanding, nobody thinks the amount of warming we've seen thus far is likely to have generated measurably "more extreme" weather. One of your links is about Sandy, but atlantic Hurricane activity has been unusually LOW over the last decade, with 2013 one of the lowest yet. You should perhaps balance your diet with more stories like this:

http://www.climatecentral.org/news/what-happened-to-the-2013...

(Regardless, even if there were measurable negative effects you would need to balance them against the measurable positive effects to determine if the NET externality was positive or negative. It's silly to add up just one side - even the IPCC doesn't do that.)