Basically there seem to be two versions of the "decoupling" thesis knocking about. The first of these (which is now very definitely going out of fashion very fast) was based on the idea that the global economy was finally decoupling itself from the US one due to the fact that key global engines among the G7-type economies - and in particular Germany and Japan (and following in both cases lengthy periods of structural reforms) - were finally coming out of a long period of sub-par economic growth and achieving "home grown", domestic-demand-driven, sustainable recoveries in a way which would enable them to take more of the global strain during what was perceived as being a period of inevitable US "correction".
Claus Vistesen and I never actually bought this story, in particular we didn't buy it since we never thought that domestic demand would recover in countries like Germany, Japan and Italy in the way in which many were expecting, essentially for age-related demographic reasons. I think history has, more or less, borne us out on that one.
But there is another sense of "decoupling" (which is the one Claus and I prefer to call "recoupling", although this is not recoupling in the way in which Nouriel Roubini uses the expression, which seems to refer to a renewed coupling to a US economy which is on its way down) and this is to do with the way in which certain emerging market economies (the EU 10, Ukraine, Russia, China, India, Turkey, Brazil, Argentina, Chile etc) are now accounting for a very substantial proportion of global growth (Claus and I have yet to do the detailed numbers on this, but suffice it to say that India, China and Russia alone will account for over 30 % of the growth in the global economy in 2007). This is a far cry from the central role which the US economy was playing in global growth in the late 1990s. So in this sense something fundamental has changed, and this is what Claus and I are calling "recoupling".
This situation can be observed quite clearly in the two charts which follow, which are based on calculations made from data available in the IMF October 2007 World Economic Outlook database. Now, as can be seen in the first chart the weight of the US economy in the entire global economy has been declining since 2001 (and that of Japan since the early 1990s). At the same time - and again particularly since 2001 - the weight of the soc called BRIC economies (Brazil, Russia, China and India) has been rising steadily. This is just one example - and a very crude one at that - of why Claus and I consider that demographics is so important, since it is precisely the population volume of the BRIC countries (and the fact that they start their development process from a very low base, ie they were allowed to become very poor comparatively, for whatever reason) that makes this transformation so significant.
Again, if we come to look at shares in world GDP growth we can see the steadily rising importance of these economies in recent years and the significantly weaker role of "home grown" US growth. The impact of the collapse of the Tech stocks/internet boom in 2001 is clear enough in the chart, as is the fact that everyone went down at the same time, and this is the old form of "coupling" wherein the US economy due, to its size (and hence specific weight) and "above-par" growth potential played a key role, and, as can be seen, when the US went down, then god save the rest. The present debate is really about what will happen if the rising dollar cost of oil and the ongoing difficulties in the financial sector caused by the sub-prime problem leads the US into recession in 2008. Will everyone else follow this time? In 1999 the US economy represented 30.91% of world GDP, and in 2007 this percentage will be down to 22.4% (on my calculations based on the forceast made by the IMF in October 2007). In 200 the US economy accounted for a staggering 40.71% of global growth, and by 2007 this share is expected to be down to 6.43%. So there are prima-facie reasons for thinking that this time round the impact of any US slowdown will not be as acutely felt in some parts of the globe as was the case in 2000, but which parts of the globe will be more affected and which less so?