'So, do you accept that (having removed natural variability) we have externally forced climate signal, which is monotonic, accelerating warming during the 20th century?'
'Viewed in this light, the lack of modelled compared to observed interdecadal variability (Fig. 2B) may indicate that current models underestimate climate sensitivity. Finally, the presence of vigorous climate variability presents significant challenges to near-term climate prediction (25, 26), leaving open the possibility of steady or even declining global mean surface temperatures over the next several decades that could present a significant empirical obstacle to the implementation of policies directed at reducing greenhouse gas emissions (27). However, global warming could likewise suddenly and without any ostensive cause accelerate due to internal variability. To paraphrase C. S. Lewis, the climate system appears wild, and may continue to hold many surprises if pressed.' http://deepeco.ucsd.edu/~george/publications/09_long-term_variability.pdf - same publication outside of the paywall There is a simpler procedure for extracting natural variability due to ocean cycles by averaging over a whole cycle of variability - the residual increase is about 0.08 degrees C/decade. As I pointed out in my E&E commentary - An Additional Physical Mechanism for Global Warming Between 1976 and 1998. Which is about what you get from Swanson et al. I am not sure that either is a valid procedure for complex systems. That is small changes result in abrupt change through spontaneous internal reorganisation of climate systems. This is what is meant by 'climate sensitivity' in the Swanson et al article rather than X amount of warming for CO2 doubling. I am not sure either that the variability originates in the oceans. ENSO is a physical system involving a sun warmed surface layer and upwelling of frigid subsurface water. A delicate balance that is influenced by the state of ocean warming which in turn is influenced by Earth albedo. See Figure 2 - http://deepeco.ucsd.edu/~george/publications/09_long-term_variability.pdf - climatologically very significant cloud changes that switch sign after 1999. There is a need to think in terms of total systems - difficult as there are so many gaps in understanding and lack of data - rather than trying to isolate a specific factor in a causative chain. It is useful to think in terms of climate shifts rather than global warming necessarily. I think it is helpful to have some understanding of complex systems theory - as a metatheory, an organising principle, for ideas about abrupt climate change. Greenhouse gases should be thought about as changes in initial conditions after which the climate system takes over in a 'cascade of powerful systems' which determines the climate trajectory - until the next climate shift. But it seems that this is an idea you either get or you don't. Cheers Robert -- 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
