There is a wide range of results from climate models - http://www.ig.utexas.edu/people/staff/charles/uncertainties_in_model_predictio.htm - not simply carbon trajectories.
Climate seen as a dynamically complex system is theoretically determinant (as an initial value problem) but practically incalculable and I doubt that there is any value in these 'boundary value' projections at all. Complex systems theory - and real world data - suggests that abrupt change is the norm for climate at all timescales from ENSO to ice ages and beyond. Theory suggests that small changes in initial conditions (e.g. greenhouse gases) trigger climate fluctuation with climate then settling into a new state. Climate could be either warmer of cooler in 100 years and there is absolutely no way of meaningfully predicting what it will be. Tsonis et al (2007) – (https://pantherfile.uwm.edu/kravtsov/www/ downloads/GRL-Tsonis.pdf) used a relatively new network approach to analysing complex systems. They used 4 ocean/climate indices - the Pacific Decadal Oscillation (PDO), the North Atlantic Oscillation (NAO), the El Niño/Southern Oscillation(ENSO), and the North Pacific Oscillation (NPO) and show that climate behaves on multidecadal timeframes as you would expect it to - as a complex system in terms of complex systems theory. Major climate shifts occurred around 1910, the mid 1940’s, the mid 1970’s and 1998/2001. While complexity theory shows the futility of ambitious projections of average future climate – it suggests that there are other ways of approaching the problem. I have been reading a recent article by Vasilis Dakos and colleagues: ‘Slowing down as an early warning signal for abrupt climate change Abstract In the Earth's history, periods of relatively stable climate have often been interrupted by sharp transitions to a contrasting state. One explanation for such events of abrupt change is that they happened when the earth system reached a critical tipping point. However, this remains hard to prove for events in the remote past, and it is even more difficult to predict if and when we might reach a tipping point for abrupt climate change in the future. Here, we analyze eight ancient abrupt climate shifts and show that they were all preceded by a characteristic slowing down of the fluctuations starting well before the actual shift. Such slowing down, measured as increased autocorrelation, can be mathematically shown to be a hallmark of tipping points. Therefore, our results imply independent empirical evidence for the idea that past abrupt shifts were associated with the passing of critical thresholds. Because the mechanism causing slowing down is fundamentally inherent to tipping points, it follows that our way to detect slowing down might be used as a universal early warning signal for upcoming catastrophic change. Because tipping points in ecosystems and other complex systems are notoriously hard to predict in other ways, this is a promising perspective.’ – the article is downloadable from PNAS. It occurred to me that it might be possible to apply the autocorrelation technique of Schaffer et al to ENSO and Vostok ice core data and take at stab at predicting ENSO and ice ages. Complex systems theory suggests that abrupt climate change is the norm at any time in the history of the planet. Climate is complex and dynamic and fluctuates wildly between extremes on all sorts of timescales. Any projection - including my own I am afraid - is nonsense. On Jan 1, 8:56 am, Alastair <[email protected]> wrote: > On Dec 31, 12:06 pm, James Annan <[email protected]> wrote: > > > And what happens if you divide the total by 280 and take the log to > > work out the forcing? > > > James > > I was leaving that to you :-) You are the mathematician! > but in case you haven't noticed the glaciers, Antarctic ice and Arctic > sea ice are all melting much faster than your log of the forcing would > imply. > > 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
