(UPDATE: Glen says he is interested in betting - see comments.)
Blogger Glen Raphael, another denialist of anthropogenic global warming, posted a comment here on my blog saying he "would have been willing to take your bet" over at Longbets, and it was too bad that Longbets was having problems. I emailed Glen saying maybe we can work something out - LongNow is based in San Francisco, not far from me, and if we can arrange a bet then I can show up at LongNow and force them to do their job.
Glen replied, withdrew his willingness to take my bet, declared himself a natural warming proponent, and made a counteroffer (even odds that temps won't increase above .2C in 20 years). I accepted, provided that the bet amount be real money, not the token amount he suggested. Glen now seems to have lost interest in the conversation. To be fair though, it's only been several days, so I'll post an update if I hear from him.
Not the first time this kind of thing has happened, but something useful did come out of it. Glen claimed, incorrectly, that temps warmed 1 degree C over the last century (it's .6C). Since that's supposed to be just a rebound from the Little Ice Age, I think one would expect the increase to slow down or stop entirely, but let's generously give to the natural warmer perspective that temps will continue to increase at the same rate of .6C per century. The result is .06C for 10 years or .12C for 20 years. By contrast, the mid-range of the consensus position is that temps will increase .15C for 10 years or .3C for 20 years. Mid-way between the two positions is 0.105C for 10 years and 0.21C for 20 years. While the mid-way point is above the bottom end of the consensus range of expected increase, it's close enough to the bottom to be acceptable for betting.
So that's my newest bet offer - even odds that future temperature increases will accelerate in 10 or 20 years, and will come closer to that predicted by the IPCC than the warming that ocurred over the last century.