It is very safe to say the Arctic Sea will be essentially ice free by 2030, and I’d personally bet on 2020 — any takers?
I think (and hope!) that's too pessimistic. When I saw it, I contacted Joe and cc'd William and James, figuring their interest in betting against climate skeptics might extend to this too, which turned out to be right. We hammered out the details (mainly that the ice is 90% gone, not 100% gone), and ended up with Joe betting $333 against each of the three of us. While the bets may be legally enforceable in theory, in reality it's a matter of trust, especially for the modest amounts involved.
I can't say that betting against over-alarmism is very important to me. I think we've done far too little about climate change, not too much, and so it's the skeptics/denialists who are the real problem. Still, it's interesting to me as something that brackets my climate expectations with the $9,000 bet I made with a climate skeptic. James, on the other hand, might consider this closer to what he hoped a betting mechanism would be in terms of showing what overall group expectations are for climate.
I think James, William and maybe Joe might blog about this, and I'll put in links if they do. (UPDATE: William's post is here, James' with an amusing put-down of me is here, and Joe's side of things is here.)
One thing I'd note: if the bet ended in 2050 instead of 2020 (and if I was interested in betting that far in the future, which I'm not) then I'd be on Joe's side in this bet. The question is how soon the climate catastrophe will start.
The other interesting psychological aspect: I was originally interested in just betting Joe a token amount. When William and James both wanted to bet far more, I suddenly became willing to up the ante. Following the herd....
MORE UPDATES: See crandles' comment - I haven't checked his math, but if it's right, then a 70% increase in the current rate of sea-ice retreat is necessary for me to lose the bet.