The current global imbalances, at least those between the US and China, are only possible because China is currently saving a historically high share of its income. Various theories have been advanced to explain this surge in the savings rate: 1) Economic reform has increased household-level uncertainty and thus precautionary savings. 2) Forces have shifted from consumption-oriented households to savings oriented businesses. 3) Demographics and the life-cycle combined with the growth in income lead currently to high savings rates because savings change through the life cycle and thus fluctuations in the dependency ratio become important.
As Carl Bonham and Calla Wiemer point out, the savings rate has not been uniformly high and is in fact consistent with the changes in the dependency ratio. The savings rate increased through the 1980s to peak at 41.9% in 1995, then "bottomed" at 37.7.% in 2000, before surging back to 51.4% in 2008. The current global imbalance occurs in part because, unlike before, investment rates are restricted by policy, and stand at 43.5%. A modest decrease in the savings rate can rebalance things.
To test the three theories against these staggering numbers, Bonham and Wiemer use a structural VAR and determine the latter one is the most important, while the others cannot be dismissed. I am not particularly fond of VARs to test theories, they should rather just describe the data, but the evidence is quite compelling in this case. Of particular interest is that one can forecast the savings rate, as the dependency ratio is quite predictable. And this forecast shows that Chinese savings rates have peaked last year and will decrase quite significantly over the next decade. If true, this should reduce considerably the pressure on China to do something about current imbalances.