How to debate with a climate "sceptic"

I've just entered and won my second battle with a climate "sceptic". After the bruising experience of the first win (with an Emeritus Professor), I thought I would take a more intelligent approach. It worked, so I thought I would share.

The standard "sceptic" tactic is to bombard you with a barrage of nonsense to debunk - everything from the survival rates of polar bears to whether ice is melting on Mars. Most of this is irrelevant, cherry picked or simply made up and it takes for ever to go through each one - and then the sceptics have well rehearsed counter arguments or just pile more on. So you end up on the defensive.

Instead, define exactly what you will debate. The key issue (agreed by all) is climate sensitivity - usually defined as the amount of warming you will get from a doubling of CO2. The IPCC endorsed range for sensitivity is 2-4.5°C (most likely 3°C) which means we are in trouble if we keep emitting carbon at current rates. For the sceptics to be right and for this to be alarmism, sensitivity has to be in the region of 1°C or so.

Nobody can argue that this is not the key issue - even the "potty peer" Lord Monckton agrees it is. Once you have agreement on this, unleash your secret weapon: evidence. I used this review paper of climate sensitivities which assess a whole load of different methods of measuring sensitivity and shows they all point to the same result (and presents them in a nice graphical style). There are uncertainties, but they apply to the upper end of the range which doesn't matter for this debate.

Now here's the problem for the "sceptics" - only one peer reviewed paper gives them the sensitivity they need and it only considered the tropics where climate sensitivity is low. So you have lots of papers using a range of different methods converging on the IPCC range and one limited model dissenting.

The guy I was debating against refused to play anymore (he had goaded me into the debate), claiming it was a trap and he couldn't possibly check 100 papers. That was the point, I said, the evidence was overwhelming. He got very upset and took his ball home in a huff, saying he was "done with me". I chalk that up as a clear win.