Prime Minister Andy Burnham has warned that the consensus on both science and climate change has "gone".
Addressing other world leaders and delegates at the COP31 climate summit in Turkey, he said that despite this, the UK was ready to begin a "new era of British leadership" on the climate change issue.
But environmental campaigners at the summit said the PM had to back up his warm words with stronger actions.
In recent months, the UK government has announced policies which critics say have weakened its green credentials, such as reducing support for heat pumps, approving the Jackdaw gas field and doubling down on support for Heathrow Airport's expansion.
Burnham opened his speech on Thursday by talking about the heat experienced in the UK this past summer.
He said "it was not normal" - in fact it was the hottest on record, made 130 times more likely because of climate change, according to the Met Office.
Hundreds of schools were closed, cereal harvests were down 11%, and ambulance services were inundated with calls beyond levels seen during the Covid-19 pandemic.
As a result of the threat to people's health and homes, the PM said he was creating the UK, and the world's, first climate security envoy, Dame Madeleine Alessandri.
