You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
He gave a public talk on climate change issues in Dunedin last night, hosted by the Otago Climate Change Network.
Mr McKibben, who founded the influential environmental group 350.org, said in an interview New Zealand's recent mixed track record on climate change issues was already putting the country's ''clean green'' international image at risk.
''I'm afraid that image is starting to change around the world.''
A staunch critic of the fossil fuel industry, he said New Zealand was ''starting to explore for offshore oil'', and warned about the huge oil spill which had occurred in the Gulf of Mexico in 2010 through a deep sea drilling accident.
''It would be good to have some countries that provided some leadership on climate [change], which is the greatest crisis the world has ever faced.
''This problem is getting much, much worse.''
Recent extensive melting of ice in the Arctic was ''not a good sign''.
''New Zealand needs to take some leadership here, from the bottom of the world - we need some real leadership.''
New Zealand had shown that leadership on nuclear issues.
And a few countries, including Germany, were already taking such a role over climate change issues.
He was glad to be back in Dunedin, having earlier visited the city about four years ago, when he enjoyed viewing wildlife on the Otago Peninsula, including yellow-eyed penguins coming ashore.
He had met Jinty MacTavish, a ''great'' young environmental activist, on his earlier visit and he was pleased she had since been elected to the Dunedin City Council.