The Archbishop of Canterbury has apologised after suggesting failure to act on climate change could be worse than the inaction of world leaders in the face of Nazi atrocities against the Jews.

Archbishop Justin Welby apologised "unequivocally" for the comparison, made in comments to the BBC as world leaders gather in Glasgow to discuss climate change.

The Archbishop suggested that a failure to commit to action at the COP26 summit could lead to "a genocide on an infinitely greater scale" than that perpetrated against the Jews by the Nazis.

He said it was possible that people in the future would speak of today's leaders "in far stronger terms than we speak today of the politicians of the 30s, of the politicians who ignored what was happening in Nazi Germany because this will kill people all around the world for generations, and we will have no means of averting it."

Failing to act, he continued, "will allow a genocide on an infinitely greater scale."

"I'm not sure there's grades of genocide, but there's width of genocide, and this will be genocide indirectly, by negligence, recklessness, that will in the end come back to us or to our children and grandchildren," he said. 

In other remarks, he suggested that world leaders attending the summit would be "cursed" if they failed to reach an agreement on addressing climate change.

After his words sparked a backlash, the Archbishop issued an apology on Twitter.

"I unequivocally apologise for the words I used when trying to emphasise the gravity of the situation facing us at COP26," he said.

"It's never right to make comparisons with the atrocities brought by the Nazis, and I'm sorry for the offence caused to Jews by these words."