date: Tue Oct 24 16:55:59 2000
from: Mike Hulme <m.hulmeatXYZxyz.ac.uk>
subject: mitigation is not enough
Tim (and Melvin),
Thanks for taking time to talk to me last Friday. I found it useful to get a firsthand account of what you are doing.
I read your paper and note. My main comment about the note concerns the notion of what is safe and what is dangerous.
Since you are looking to long timescales, 4.7degC warming over 10 centuries equates to 0.5degC/century, the same rate we have experienced this century. Whilst one may argue that 4.7degC over 100 maybe 'dangerous', I doubt you can sensibly say that 4.7degC over 1000 years is equally dangerous. Indeed, given what society has adapted to this past century, we may well argue that 0.5degC/century over the next millennium is sustainable (given enhanced economic growth and continuing tech. change).
Of course, as you say, feedbacks and sensitivity may lead to T change larger than this, but this is not the thrust of your argument.
I think therefore you need to stress much more the adaptive potential is a world warming only at 0.5degC/century (you mention this towards the end, but it is buried).
0.5degC/century may well be a target worth aiming for and I think you would have a hard time demonstrating it is dangerous.