"Climate is a national security issue," said Burnham, the only leader from a G7 country attending the meeting.
The newly appointed envoy, Madeleine Alessandri, is the former head of the Joint Intelligence Committee (JIC), which is responsible for overseeing Britain's intelligence services.
In a statement, Alessandri said she would work with partners in government and internationally to strengthen understanding of climate threats, build resilience and ensure that we are better prepared for the challenges ahead.
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