The European Central Bank would need to buy assets worth €1 trillion ($1.4 trillion) to lift inflation by as little as a fifth of a percentage point, according to an internal assessment of quantitative easing.
The estimate, first reported by Frankfurter Allgemeine Zeitung newspaper but confirmed by a person familiar with its contents, comes a day after the ECB gave its strongest hint yet that it is prepared to embrace bond-buying to prevent the euro zone from sliding into deflation, or even a long period of low inflation.
The estimate, which is based on just one of a number of options for QE that policy makers are considering, shows that €1tn of purchases of euro-denominated securities over the course of a year, or €80 billion a month, could add between 0.2 and 0.8 percentage points to inflation in 2016.
The ECB is expecting a figure of 1.5 per cent in two years meaning QE could also potentially take inflation above the central bank's target rate of just below 2 per cent.
The vast scale of purchases required and the uncertain effect on prices could add to concerns about the merits and risks of QE, particularly in Germany if a substantial chunk of the central bank's funds are used to buy the debt of weaker euro zone sovereigns.
The fact that the assessment was leaked to FAZ, a bastion of German economic orthodoxy, has reignited suspicions by some ECB insiders of a campaign to foment German public opposition to QE as European parliamentary elections loom at the end of May.
At 0.5 per cent, inflation is now only a quarter of the central bank's target. ECB president Mario Draghi said on Thursday that rate-setters were united in supporting more radical action, such as QE, should price pressures even become more subdued.
While Jens Weidman has signed up to the central bank's pledge to use unconventional measures, including QE, to counteract a "too prolonged period of deflation", the Bundesbank president is unlikely to sanction any further action until at least June and has indicated he would prefer purchases of private sector debt if the ECB was forced to resort to buying assets.
A person familiar with the matter said several scenarios have been presented to the ECB's executive board and members of the rate-setting governing council over recent months.
The central bank is yet to finalise how it would conduct QE, which is a much trickier exercise, both politically and operationally, for the eurozone's central bank than its counterparts in the UK and the US, which have already bought government bonds.
"There are obviously different preferences about which QE would be more effective, and we will continue working on that in the coming weeks," Mr Draghi said on Thursday.
The FAZ quoted a source labelled as a central bank insider as saying: "The question would be whether the private debt market in Europe is big enough for QE."
A spokesperson for the ECB said: "As the governing council said [on Thursday], it is unanimous in its commitment also to use unconventional instruments. The relevant committees of the Eurosystem will continue their reflections on the various scenarios that will be made."
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