I cut straight to the economics. It is all about the RMB peg to the dollar. As long as the peg exists China will keep buying US paper. The peg will not go away anytime soon. However, it is correct to assume this is not a position China necessary likes to be in and it would like to diversify away from the dollar.
The situation remains - this is like two drunks holding each other up. One moves and they both fall over.
What the PBoC cannot do with its reserves [China Financial Markets]
Beijing is not Washington’s banker
If China runs a current account surplus, it must accumulate net foreign claims by exactly that amount, and the entity against which it accumulates those claims (adjusting for actions by other players within the balance of payments) ultimately must run the corresponding current account deficit. And as long as China ran the largest current account surplus ever recorded as a share of global GDP, and the US the largest current account deficit ever recorded, and especially since China also ran an additional capital account surplus (i.e. other non-PBoC agents ran a net capital inflow), it was almost impossible for the PBoC to do anything but buy US dollar assets. Given the sheer amounts, a substantial portion of these assets had inevitably to be USG bonds.
This was not a discretionary lending decision. It is the automatic consequence of China’s currency regime, in which it pegs the RMB to a foreign currency, in this case the dollar. Why? Because when the PBoC decides on the level of the RMB against the dollar, it does not do so by passing a law, and making it a capital crime for anyone to trade at a different price. What it does is far simpler. It offers to buy or sell unlimited amounts of RMB against the dollar at the desired price.
No one will sell dollars for less than what they can get from the PBoC, nor will anyone buy dollars for more than what they can pay the PBoC, so all transactions get done at that price. That is how the PBoC (or any other central bank that intervenes in the currency market) sets the foreign exchange value of its own currency.
This means that as long as it wants to set the exchange rate, then, it must take the opposite position of the market. Since the rest of the market is a net seller of dollars (China runs a current and capital account surplus), the PBoC has no choice but to be a net buyer of dollars, which of course it must then invest.
If it stops buying dollars, it must let the market decide by itself on the new equilibrium price of the dollar. In that case the value of the dollar has to plunge in RMB terms (or the RMB soar, which is the same thing) in order for buyers and sellers to match up and for the market to clear. The moment the PBoC stops buying, in other words, the RMB will rise in value – and so it cannot stop buying in anticipation of the RMB rising in value, as the FT article suggested.
Of course the PBoC must fund the purchase of these dollars. It does so primarily by borrowing in the domestic money markets, selling PBoC bills or entering into short term repos (although it also issues some longer-term bonds), or by “creating” money by crediting the accounts of the commercial banks who sell it the dollars.
This means, to simplify, that the PBoC has a balance sheet consisting on one side of dollar assets (and here “dollar” is short-hand for all foreign assets). Against this and on the other side it has a roughly equivalent amount of RMB liabilities (I say “roughly” because when you run a mismatched balance sheet, changes in the relative value of assets and liabilities will create losses or profits).
Here is where things get interesting. China’s reserves are often thought of as if they were a treasure trove available for spending. They are not. They are simply the asset side of the mismatched balance sheet. If the PBoC wanted to “spend” $100, say for example to recapitalize a bank, it could do so, but this would automatically create a $100 dollar hole in its balance sheet. – it would still owe the RMB that it borrowed originally to purchase the $100. To put it another way, the reserves are not a savings account, free for the PBoC to spend as it likes. Reserves are effectively borrowed money.