With time ticking away for Europe to meet its targets for slashing greenhouse gas emissions, banks could end up securing massive amounts of debt to finance the transition to clean energy. Issuing "green bonds" is one mechanism they could use. European governments are staggering under the weight of public debt. That has injected some uncertainty into the European Union's plan to cut emissions 20 percent below 1990 levels by 2020. Private-sector financing and public financial markets will bear €2.9 trillion in debt financing needed to develop and roll out cleaner energy sources in a decade, according to a study by Barclays Capital and the consulting firm Accenture.