I've found when trying to convince, it's often best to show where you agree. They've been conditioned to knee-jerk when they come across a 'denier', because you are the enemy of mankind and everything good and cuddly. They will assume you doubt the whole thing, and when they find out your area of disagreement is a 'mere detail' (to them, a value of sensitivity, a small amount of warming, a technological waste of money are all just 'details'), they are much more happy to listen and accept. It's lip-service, and a little dishonest, but you sort of have to prove your credential as one of the 'good guys' first, then you can start attacking it and they will listen.

It's a religion. It's a mass delusion. Take it or leave it.

That is all you can do.

What an intelligent but uninformed person will do is weight up the provenance. They will say on the one hand "97% of scientists" versus this bloke in the pub. Unless they are willing do to the research themselves, it's a reasonable strategy for them to go with the consensus position. I don't blame any of them for it.

At that point it all hangs on the personalities.

On the one hand, how do they rate you the teller as a credible source. Are you always banging on about conspiracies, are you well known for being something of a crank on many wide ranging areas. This can damage the provenance, if the listeners are the sort of people who usually dismiss conspiracies out of hand.

One their side, are they the sort of personality who is interested by the idea of an underdog, that perhaps things aren't always as they are being fed on the media. The redefinition of who the good guys are can sometimes appeal to certain types of people. But there will be some who cling to the establishment because to abandon it would be to abandon their sense of security.

So I don't believe there is a one-size-fits-all killer argument that you can make to a varied set of people. If they are lazy (and let's face it, most people are) then pointing to a graph isn't going to cut any ice, because then they'd need to take the time to understand the graph. If they are establishment types, then they will assume even if there are inconsistencies, then they have been decided by our betters to be ignored, and it doesn't change the headline.

Ask them how much they believe it. Ask them how big they want their bills to be (with no increased salary). How much reduction in lifestyle they are prepared for – smaller home, no flying, less possession, less grandkids, no pets, vegetarian diet, etc. Whatever they like to do, chances are they’re using too much energy. Current renewables won’t come to their aid. Ask them if they’ve even bothered to calculate their CO2 footprint (which has to be step one of acting on CO2). Ask them how close to the 2 tonne and falling sum they get. Anything above that is too much. The last time we were at that level of emission it was about 1850, walking was our main form of transport and the light bulb hadn’t been invented.

Ask them why, if AGW is so significant they know almost nothing about it and care even less. Why is it the only major area in their lives they hand over all decisions and responsibilities to people they nothing about.

If you were about to be condemned to a lifetime of poverty and hardship, wouldn't you want all the facts about your guilt to be examined and argued?

SimonW

Regarding 'All the ice is melting', there are 2 points:
1 - We've only been watching it from space since the mid 70s and measuring accurately since 79/80. There is some evidence that this was pretty much the peak of Arctic ice extent, and that it had been similarly low in the 1930s and (iirc) the 1880s
2 - Antarctica isn't following the same path, and has been setting record high extent and area over the last couple of years.

Regarding 'Hurricaines are getting stronger', there are four points:
1 - There hasn't been a major Atlantic hurricane make landfall in the US for a record period (since 2008?)
2 - Historically, the strength of hurricanes was only determined at landfall (or occasionally if a ship was unfortunate enough to have to go through one, which is something they tended to avoid), and the strength decreases very rapidly once the storm hits land. Now we are getting measurements at sea, where the storm is still being fed by the warm ocean water
3 - We are hearing more about tropical storms hitting very remote parts of the world. There's more reporting rather than more or bigger storms. ACE numbers generally support this, showing that the amount of cyclone energy varies fairly randomly.
4 - A warming climate does not necessarily lead to larger storms. The jury is still out on this one, but it is a reasonable hypothesis that because gorebull warming has a stronger effect in colder regions (temperate / polar), the decreased thermal gradient will actually reduce hurricanes in both number and intensity.

As for other points, it's probably worth finding out what your drinking buddies know, and particularly 'what they know that just ain't so'

1 - What the temperature rise from pre-industrial levels to present
2 - What the atmospheric concentration of CO2 is, and what it has been historically
3 - Do they know we are in an ice age? (OK, an interglacial, but it's still quite cold from an Earth history perspective).
4 - Where the evidence for large scale future warming comes from...

I find pointing out that approximately one third of all man-made CO2 emissions have taken place in the last 20 or so years, during which period (give or take) the satellite measurements say that no warming has taken place.

If that plays well, I then move onto an explanation of UHI, and how the land-based figures are being fiddled the wrong way.

If they're still with me, I point out that it's a $1Tr dollar industry annually, and we have nothing to show for it but an unreliable energy supply, danger of winter energy blackouts, higher energy bills, a visual environment polluted by wind turbines which don't work well (and which arguably have the effect of increasing CO2 emissions), and we've exported our jobs (and our CO2 emissions to China).

By then, we're onto our 5th pint, and we're usually talking about football instead.

If I was a believer curious about all this denier stuff, and open to being talked around, not sure anything I've seen here is a killer argument yet. Which is unsurprising, because I don't think there is one.

The arguments are subtle, usually criticisms of scale, speed and confidence levels. Yes, CO2 could in theory do this or that, but we don't see much of it actually happening in the world, or that the amounts they predicted 20 years ago have not happened, and this has consequences for other dire predictions etc.

Most of it requires the listener to get off their bums ad understand the science, which for most people is a step too far.

I don't think there's much chance of us reducing CO2 to dangerous levels, any time soon, so not sure that's an argument for convincing anyone.

If the words "Reverse Global Warming/Climate Change" are used, I usually ask How Far, 50-60 years, to pre-industrial times, 20,00years? Then add Winter of 1962/63, Little Ice Age, proper Ice age.

Apart from that lots of good things pointed out here already.