Former Australian Prime Minister Bob Hawke said on Monday Australia should not give up if it is rebuffed at Copenhagen because the environmental cause is too important.

Hawke said the United Nations climate summit in Denmark appeared to be offering little hope, leaving Prime Minister Kevin Rudd facing a "very daunting task".

"The prospects as they seem to be emerging in Copenhagen are not totally reassuring, and it will pay for all of us to give Kevin (and Environment Minister Peter Garrett) ... all the encouragement we can, to be brave, to be courageous," he said.

"Because in the end, if knowledge can be disseminated, prejudices dispersed, then sensible and decent policy decisions can be made.

"And I deeply hope that even if we get rebuffed in Copenhagen - and that is a possibility - that we won't give up because the cause is too important."

Hawke was speaking at a celebration in Sydney to mark the 20th anniversary of his government's international campaign to prevent mining in Antarctica.

He said the achievement - which he named as one of his proudest moments - was an example of why we should use history as a lesson for the future.