What say I put a truth from below at the top: "It is generally not in dispute that the AVERAGE planetary long term depth of ice in New York is measured in thousands of feet above current mean sea level. Ice level rise puts sea level rise to shame :-)." > > However, overall the probable inability of man to noticeably influence > > long term climate cycles in many manner at all will ensure that from > > some time in the next century onwards we will not need to be concerned > > about glacial retreat for about the next 90,000 years. > Let me get this straight - if we make it through the next 90 years, the > 90,000 after that will be easy? The concepts "not need to be concerned about glacial retreat ..." and "will be easy" need not be synonymous and, in the scenario I envisage, certainly aren't. Based on historical records (long term ice cores and much more) there is essentially unamimous agreement (no warmist/denialist/ ...disagreements here) that the earth undergoes long term temperature cycles of very large magnitide. About 90% of the time the temperature is much much colder than at present and these periods have the populist name "ice ages". Typically you get aboyt 90,000 years of ice age and about 10,000 years of temperatures roughly similar to what we have nlw. Some past periods appear to have been much hotter to much much hotter than at present. This is not an area of major argument in the broader scientific community. ie its not a warmist/denialist etc issue. Prediction of future cycles lengths based on past data is not quite as bad as predicting the stock market or subprime markets 10 to 20 years out, but is by no means a well understood art. however, significant indications are that we are rather long overdie for another 'ice age' - one may well have been expected to start at about the time of Christ. It's been argued that the "Roman warm period" was in fact caused by the Roman empire human effects on what would have been a raher unstable system at that stage and that we were "saved" from the onset of an iceage by their activities. There was another warm blip about 900AD and another around 1200-1400 - the magnitude and world wide extent of being questioned because if it can be seen to have been smaller or non existant then it makes certain other models look better - depending on what you want to demonstrate. That part is irrelvant to the main point here. But, IF we are on the cusp of another ice age, as well we may be, then any major factors that can tip the system over the edge are liabvle to be "of some interest." One such possible is solar activity of various forms and one indicator is sunspot activity. During the period from about 1650-1700 Sunspot activity virtually ceased. Over the same period general temperatures fell and winters became notably colder to the extent that the river Thames froze at London and people could skate across it at Tower bridge, and they held Winter ice fairs. This period has become known as the "Maunder minimum" http://en.wikipedia.org/wiki/Maunder_Minimum During the last sunspot cyle (#23) whicj peaked in about 2000, it became evident that 'something strange' was happening' and the descent and restart of sunspot activity turned instead into a long tail with no new cycle 24 activity until long long after forecast and, now that there is some cycle 24 activity it is very low and fitful, so much so that we are now out past the 100 year low and increasing by the month. Less than a year ago the official NOAA forecast was that the SSN should be about 50 by now and climbing towardas a peak of about 115 by late 2012. (I've taken the mean of the 2 sigma forecast range and dates). Instead it's around 8 to 10 and when I last checked a week or so ago is showing no sign of picking up. Now, NOBODY knows for sure if there is a correlation bewteen mini ice ages and SSN - and the fact that the suggested mechanisms are subject to lively debate, peer reviewed and other, allows that just maybe causality and correlation were not previously linked. It seems likely that the skaters on the Thames are a good indication that this is not so, but nobody is sure. One much touted and plasuible mechanism with some experimental proof, but far from wholly proven is that as low SSN leads to low solar field which affects gamma radiation inbound to earth 9all true enough so far) that atmospheric particulate formation is affected and more gamma rays lead to morecondensation points and more cloud of a certain type which leads to higher planetary albedo and lowering of net absorbed insolation so lower temperatures. this chain is no less plausible than many which are accepted as true and less crazy than a few which are currently holy scientific writ until their paradigms come to be overturned. I certainly wouldn't bet against the theory at this stage. SO - We may very likely be on the oscillatory crest of a plunge into a new ice age just because that's what happens, and one is overdue. - The sun may be causing or preparing to cause planetary temperatures to back off regardless of how this may be being hidden by entirely normal cariations caused by many interacting cycles. - Somewhat wide oscillatory swings (not unlike what we have been seing in the last decade or few) would not be inconsistent with all this. - Thus the glaciers may be about to come back with a vengeance. - If it does happen that the iceage cometh, then we may just be able to transform our environment enough to hold things large ly stable. if it does come to that it will be the greatest and most unifying challenge that personkind [tm] has ever been called to face. Failure to successfully face it together will lead to a few very very cold planetary future. - All this may be utter rubbish. We can hope. It is generally not in dispute that the AVERAGE long term depth of ice in New York is measured in thousands of feet above current mean sea level. Ice level rise puts sea level rise to shame ;-). > Because the most optimistic predictions I have heard of say the > (north)polar ice cap will be gone by 2030. What the ear hears depends in part which mouth's it hears from. They MAY be correct. I certyainly don't know, but I do know for certain that nobody else does either, and that the correlation between louness of voice and soundness of model is often bot great. If I presently had to bet on icecaps melting against glaciers starting to come back in uncomfortable excess, I'd be strongly tempted to support the glaciers. Hopefully we will see, one way or the other, within current lifetimes. A key thing is as honest and open a mind as possible, not rejecting true science for any reason, but also questioning the science underlying all and any assertions with the greatest of care. FWIW: Many people get excited about the 1st graph on this page. http://en.wikipedia.org/wiki/Current_sea_level_rise I have no problem with that. BUT I suggest that people also look at the SECOND graph on the page and see how exciting that appears, given what I said above. Notice the time before the present and what happened to sea levels about 10,000 years ago. Have an attempt at predicting the sea level 2000 years from now :-(. Russell -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist