The unscheduled departure of Scott Pruitt, the head of the US's Environmental Protection Agency, was the talk of the first day of the two-day event, Xinhua reported.
There was no formal word on why Pruitt left the talks after participating in only a single negotiating session, posing for a group photo with other delegation heads, and holding one-on-one talks with his counterparts from Germany, Japan and Britain.
In US media, it was reported that Pruitt was "summoned" by US President Donald Trump.
Pruitt's departure comes just days after Trump announced the US would withdraw from the Paris Agreement, a global pact designed to fight against climate change.
Negotiations continued even after Pruitt left Bologna, with more junior US officials heading the US delegation.
Officials from other countries said they focused on negotiating a strong final statement, which is expected to cover not only climate but also energy policy, government incentives, deforestation, recycling and financial issues.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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