On Tue, 19 Jun 2007, [EMAIL PROTECTED] wrote: > - Over geologically long time times, CO2 content in the atmosphere > varies by ratios as large as 4:1, without human input.
no problem > - Current levels of CO2 are half or less than the average for the last > 500My. quite likely: http://en.wikipedia.org/wiki/Image:Phanerozoic_Carbon_Dioxide.png > - There is little correlation between CO2 levels up to 4 times current > levels and global temperature. not reasonable > - That a number of significant peaks in CO2 level coincided with lower > global temperature over extended periods of time (tens of millions or > years). don't think so. There is an RC post on this somewhere but I forget where > - That by itself, CO2 level is unlikely to be a significant driver of > global temperature. No (unless you mean, deliberately suppressing feedbacks). -W. > Does this make sense? > > Regards, > Philip > > > > On Jun 18, 4:39 am, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> > wrote: >>> That's entirely beside the point. We are moving into sustained rates >>> of change rarely if ever seen in nature, even in the rather >>> climatically erratic recent million years. It is indeed outlandish to >>> suggest that this is a good idea. >> >> I readily accept that the rates of change implied by a 3C temperature >> rise in 100 years are large compared to Earth historical precedents, >> except for a few pretty rare events like once in 60 million year >> meteorite impacts. >> >> Whether this necessarily implies a net negative impact on human >> welfare is another matter. However, I don't think this is an area >> where agreement is that important to me, I am much more worried about >> what the best policy response is. And I am quite happy to debate this >> policy response on the presumption that 2C extra is bad. >> >> http://scienceblogs.com/stoat/2007/05/more_hot_air.php >> >> I've been having a relevant discussion with William on the 2C target, >> where he left me quite confused indeed. >> >> He writes: >> >> "What if a 2 oC limit turns out to be necessary? ...And I don't think >> we can possibl[y] avoid 2 oC with 95% prob, given that its 2 oC over >> pre-ind, ie 1.[2] ish over now" >> >> "What if the science says we need to stick to this target? If that >> were so, ... qualms about difficult[]y become irrelevant. What it >> would mean ... then [would be] deciding what CO2 levels you need to >> stick to 2 oC" (sligthly edited by me for greater clarity) >> >> There are several interesting points here. Firstly, how to translate >> the 2C target into emissions targets? And how do propabilities figure >> in this? Are we going to aim for 95% probability of avoiding 2C? Or >> 50% probability? And on what basis? >> >> That 95% is "not possible"? And if so, what does "possible" mean in >> that context? Politically possible? >> >> --------- >> >> And then having decided the right emissions targets, and presuming for >> the moment that costs don't need to figure much in that, how do we >> decide how to operationalise these through actual policy measures? >> >> On the one hand, there are people who'll want to stop nuclear power >> and much large scale industrial development, they want to go for less >> impact through fewer people living a simple lifestyle. >> >> On the other hand, we can go for nuclear power or large scale >> development of renewables, and carbon sequestration through >> mineralisation, ie things that won't involve much lifestyle change. >> >> This is a big issue, because, well, I think for the majority of people >> the wider picture matters more than the climate specifics. So, nuclear >> power say won't be acceptable at all as an emissions reduction policy, >> and if that was the only major consequence of a law reducing >> emissions, they'd reject the law. > > > > William M Connolley | [EMAIL PROTECTED] | http://www.antarctica.ac.uk/met/wmc/ Climate Modeller, British Antarctic Survey | 07985 935400 -- This message (and any attachments) is for the recipient only. NERC is subject to the Freedom of Information Act 2000 and the contents of this email and any reply you make may be disclosed by NERC unless it is exempt from release under the Act. Any material supplied to NERC may be stored in an electronic records management system. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/globalchange -~----------~----~----~----~------~----~------~--~---
