----- Original Message ----- From: "Tom Adams" <[EMAIL PROTECTED]> To: "globalchange" <[email protected]> Sent: Thursday, June 21, 2007 1:27 PM Subject: [Global Change: 1786] Re: Latest Hansen
> > On Jun 20, 5:44 pm, James Annan <[EMAIL PROTECTED]> wrote: >> Tom Adams wrote: >> > On Jun 20, 9:43 am, William M Connolley <[EMAIL PROTECTED]> wrote: >> >> On Wed, 20 Jun 2007, Tom Adams wrote: >> >>> In a book about the prehistory of Scotland "Beyond Scotland" it >> >>> mentioned that the sea level rose a meter or so (or was it a foot?) >> >>> in >> >>> a few days, causing a good bit of havoc for the humans living along >> >>> the coast of the land bridge between Scotland and Europe. Due to an >> >>> ice dam failing or a meteor impact hiting Canada's glacier or >> >>> something. If we have archeological data about impact of sea level >> >>> rise on humans, then, with all the other potential data, I'd think we >> >>> might be able to map it out in time pretty well. >> >> The meteor idea would suggest that palaeo analogues are even less >> >> useful! >> >> > I guess you are right that even if we could identify a rapid sea level >> > rise event in the paleo record we could no just assume it's due to >> > albedo flip. >> >> > But I was thinking that we might know more about the rate of the last >> > big thaw, the whole thaw, not just that one event that may have been >> > caused by a meteor or ice damn break. >> >> Don't forget that when you are looking at the paleo record (especially >> termination of the last ice age) you are talking about a time when there >> were large ice sheets at relatively modest latitudes, which can soak up >> a whole lot of rays. There simply isn't this ice to melt any more. >> >> I've spent some time looking at climate sensitivity and believe that I'm >> on solid ground there. I'm reluctant to wade in over Hansen and ice >> sheets because I know much less about them, but the argument seems to >> follow a similar meme: we "can't rule it out", so we should worry. I'm >> also a bit dubious about the language in any case: it's not as if people >> are going to be drowned in their beds. >> >> The time I would look for analogues is the last interglacial, when it >> was significantly warmer than today. > > Looking at the last few interglacials, I think I see evidence of the > lag: > > http://en.wikipedia.org/wiki/Image:Ice_Age_Temperature.png > > Look at all the temperature spikes. Some are narrow and some are > broad. Now look at the ice volume, the low ice volume minimums. The > ice volume minimums don't just reflect the maximum of the temperature > spikes, they also reflect the *width of the temperature spikes*. > That could only happen if there was a lag on the order of several > thousand years. > > If you take the temperature plot and put it through a low pass filter > tuned to around 10K years, you would get the ice volume plot. > > But that a kind of general lag. Our concern is the current > configuration of a particular ice sheet. What you are looking at there is the temperature in Antarctica. No one lives there. Not even William :-). Nearly everyone, including William and James, live in the Northern Hemisphere. For that you need the temperature record from the Greenland ice cores. Here it one since the last interglacial. It is the red oxygen isotope line at the top: http://www.ncdc.noaa.gov/paleo/pubs/blunier2001/sync.pdf I don't see many slow steady changes in that! Cheers, Alastair. > > > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
