> I see no sign, or even hint, or even hypothesis, which supports the > claim of "a step change in the rate of global warming" at 440ppm or any > other level, which is the quote with which I started this thread. But > maybe in 1000 years, Greenland will be green and Londoners will have > gills.
You provided a convincing argument for your beliefs, but I must confess that I have found by beliefs in error in the past. I believed that the Big Bang Theory was rubbish and I was completely convinced that the expansion of the Universe was the result of continuous creation. I also believed that the Younger Dryas (YD) stadial began when the pro-glacial Lake Agassiz burst out through the Gulf of St. Lawrence. That seems untrue now as well. A HINT The evidence shows that over the last 120,000 year the climate of the northern hemisphere has changed abruptly. When the last glacial maximum ended 20,000 years ago, that was an abrupt climate change to conditions warmer than today. This was followed by a severe blip, then later the climate deteriorated in two steps back to glacial conditions of the YD stadial. When the YD ended, temperatures in Greenland rose by 20F in as little as three years. This is more than a hint that climate alters in step changes, not smoothly. Of course it is argued that the rapid changes all happened went he NH was covered in ice, but there is still ice in the NH. There is the ice sheet in Greenland and the sea ice in the Arctic Ocean. Thus whether it is land or sea ice which is responsible for those abrupt changes, the potential for yet another rapid change is still there. And of course, rapid changes are not restricted to cooling. From LGM to Holocene, there were 3 major rapid changes only one, entry to the YD, of which was a cooling, although that is the one best known. . NO SIGN In my example of a tipping point there is no sign of the scales tipping, until the threshold is exceeded, therefore there will be no sign. This is one of the dangers of abrupt climate change - it will happen without warning! A HYPOTHESIS Your argument that since CO2 will slowly increase then so will temperature does seem to make sense, however have you considered what happens when ice melts. The temperature remains steady at the melting point until all the ice has gone then it starts to rise. The disappearance of the ice is a tipping point when the temperature start to leap. Unlike my example of the scales, this is directly applicable to climate. It seems that the NH ice is a cause of rapid climate change. In fact the hypothesis that sea ice causes rapid climate change is expounded in this paper: http://www.deas.harvard.edu/climate/eli/reprints/Gildor-Tziperman-2003.pdf 440ppm ? Of course that leaves the question "Why is 440 ppm the magic number?" Well I don't believe it is. The Greenland and Arctic sea ice is already melting and because of the ice albedo effect, the melting can only accelerate. We have already passed one tipping point, and we are sliding faster and faster towards the next! 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 -~----------~----~----~----~------~----~------~--~---
