The study, published by UK think-tank New Economics Foundation and backed by environmental activist group Greenpeace, urged the ECB to take companies' carbon footprint into account when choosing which corporate debt to buy as part of its multi-trillion-euro quantitative easing (QE) scheme.
Lagarde opened the door to this notion last week, saying the market had failed to correctly price climate risk and the ECB should consider addressing that failure as part of an ongoing review of its strategy.
The NEF researchers found the ECB could still draw from a pool of 1,829 corporate bonds worth a total 1.062 trillion euros if it excluded fossil fuel companies and those with relatively high carbon intensity, a spokeswoman said in a written response to Reuters' questions.
On both measures this equalled a reduction of just under 30% compared with the size of the ECB's current eligible bonds.
The authors estimated the ECB could even axe all bonds issued by carbon-intensive sectors apart from green bonds and still have 1.078 trillion euros worth of debt in which to invest if it included junk-rated paper.
"It is now time for Europe's most powerful financial institution to decarbonise its QE programme," said Yannis Dafermos, one of the authors of the study and a lecturer in economics at SOAS University of London. "Our data analysis shows how this can be done."
He and co-authors Daniela Gabor, Maria Nikolaidi, Adam Pawloff and Frank van Lerven said in the study the ECB's purchases had rewarded polluting industries such as oil producers, non-renewable utilities and car manufacturers out of proportion to their contribution to euro area employment and value added.
The ECB has bought 236 billion of euros worth of debt in the past four years under its Corporate Sector Purchase Programme, plus 52.4 billion euros in its Pandemic Emergency Purchase Programme, which also includes commercial debt.
It has bought those bonds in proportion to their outstanding amounts but this so-called market-neutrality principle" is now being thrown into question by Lagarde and board member Isabel Schnabel.
(Reporting By Francesco Canepa, editing by Larry King)