On the eating of crow...

[GliderGuider]

12. Regarding climate sensitivity...

I've been thinking about the "slow feedback" term that falls out of the paleoclimate work of scientists like Hanson and Kiehle. In their assessment that term raises the climate sensitivity from +3C to +6C. On reflection, I think it probably only acts over geological time scales - too long to matter if the human shit hits the fan in 2050 or so

However, this has me thinking about methane feedbacks. We all seem fairly convinced that methane is going to start belching into the atmosphere any day now, and this process will only speed up as things get warmer.

The +3 curve I have drawn above takes into account only the CO2 released from burning fossil fuels, along with whatever feedbacks that has been generating up to now. For these effects +3C seens like an appropriate sensitivity - unless AR5 has a surprise in stoe for us. In order to account for positive feedbacks we are aware of but are only beginning to enter the picture, I propose to add a second temperature curve that branches off from the +3 curve right about now, and adds an increasing factor to the sensitivity to simulate the addition of methane (and other potential positive feedbacks).

What feels right to me is to gradually increase in the sensitivity from +3 today to +4 over the next 50 years. It won't make a hill of beans difference to what happens between now and 2050, but it will give an indication of what the methane could eventually do to the temperature.

In the process, the current +4.5 curve would disappear.

Any thoughts?