The spot market in European Union emissions permits may re-open next week following a cyber attack that resulted in nearly 30 million euros (£26 million) of carbon permits being stolen.
But carbon exchanges and registries doubted an early re-start.
Last week, the EU suspended spot trade in its carbon market, the bloc’s chief weapon for fighting climate change, after permits called EU allowances (EUAs) were stolen from accounts in the Czech Republic and Austria.
The European Commission said before registries could re-open, each member state had to provide an independent report confirming that minimum security requirements had been met.
The Commission’s spokeswoman Maria Kokkonen said the first reports had been received and were under review.Regarding the possibility of a registry re-opening next week, she said: "It depends on the length of the report, the time needed to assess it. Theoretically it's possible."
But the International Emissions Trading Association said all the main registries "must resume" business in the first week of February.
"While the safety of online banking has been scaled up, EU Member States have failed in protecting an 80 billion euro market, thereby undermining the EU's main tool to reach climate objectives," said Henry Derwent, head of IETA.
Registries and environment ministries were unable to confirm any deadline for re-opening as they ran security checks with the Commission. "We're not in a position to give timescales," said a spokeswoman for Britain's energy and climate ministry.
The Czech registry said it would be shut for at least six weeks, and expressed doubts about any wider re-opening. "I cannot imagine that European registries will open next week," said Jiri Stastny, general director of the Czech carbon market operator OTE.
All exchanges remained closed to spot trade.
ICE Futures Europe, which operates the largest European emissions exchange, said on Thursday spot carbon trade would be suspended until February 7.
Paris-based BlueNext, Dutch bourse Climex and Nasdaq OMX Commodities have all said their spot carbon trade was suspended until further notice.