They calculate that, despite buying from major central banks like the ECB, there will be a $840 billion reduction in bond demand in 2020 against a $375 billion decrease in bond supply.

"This implies upward pressure on bond yields next year, particularly if our estimates of bond fund demand and G4 (US, Eurozone, Japan, UK) commercial bank bond purchases for 2020 prove correct," JPMorgan's analysts wrote in a note.

Next year should also break a four-year trend of rising global bond supply.

The $375 billion reduction predicted by JPMorgan reflects both a decline in net government supply in the United States and a reduction of corporate issuance. Companies globally are trying to rein in their debt having pre-financed on the back of record-low interest rates in recent years.

This year has seen bond supply rise to just over $3.1 trillion, the highest level since 2009. Over the past four years, annual global bond supply has gone up by almost $1 trillion.

On the demand side, the two surprises this year have been the strength of bond fund demand by retail investors and the extent of bond purchases by G4 commercial banks. The former saw close to a record high annualised pace of $850 billion this year, while the latter at $640 billion hit its highest level since 2009.

"We believe that both of these levels are unsustainable and we look for some normalization in 2020," they added.

(Reporting by Marc Jones; Editing by Christina Fincher)