The gathering was originally due to be held in Glasgow last year but the global health crisis forced organizers to put it back by 12 months.

A delay would be a setback for Prime Minister Boris Johnson’s ambitions to demonstrate political leadership of the climate change agenda, and a blow to campaigners’ hopes of securing a deal to reduce greenhouse gas emissions.

Holding the event with no changes to the format is “unlikely,” and so is a fully-virtual conference, according to Yamide Dagnet, who is in close contact with COP participants as director of climate negotiations for World Resources Institute. Several options are being considered, including a short delay or some kind of hybrid meeting that would have fewer people present. She expects more information in mid-April.

“We cannot derail the progress that needs to be made,” Dagnet said Wednesday.

Read more: The Dangers of Turning High-Stakes Climate Talks Into a Zoom Call

The U.K. government said it was still keen to hold the summit this year as planned.

“We are working on the basis of COP26 being held in person this November, while closely monitoring the Covid situation,” the government said in a statement. “The summit team is working closely with all partners and exploring what different scenarios might mean for COP26 and how we plan for that, whilst putting the health of the participants and the local community first.”

–With assistance from Will Wade.