Hillary Clinton's science adviser has ruffled the feathers of the anti-GM lobby, calling their arguments "tragically bad" and saying public fears risk blocking food from the needy when climate change hits.

Nina Fedoroff, science adviser to the United States Secretary of State, says people will starve if climate change cuts water supplies and raises temperatures while people remain too afraid to use genetically modified crops.

Echoing dire warnings by climate scientists, she said water shortages and rising heat could cut crop yields in the order of 10 per cent per 1C of warming this century but said countries were being blocked from using modern science to fight it.

Globally the population was predicted to swell 2-3 billion by mid-century, while the driest and most populous places got drier, potentially creating a surge of political instability and environmental refugees, she said.

"If there are more and more environmental refugees, they are going to end up on your doorstep too," she told a public gathering at Auckland University.

Her comments about the opposing lobby upset GE-free New Zealand head Claire Bleakley, who told Dr Fedoroff campaigners had pointed out genuine problems with trials here and overseas.

Last year, New Zealand lobbyists overturned a 10-year vegetable genetic modification trial by a Government-owned company when they discovered plants that should have been destroyed had instead been left to flower, exposing their GM pollen to the environment.

Dr Fedoroff said in 30 years of laboratory tests and 15 years' commercial production "nobody had documented so much as a headache".

"How many more decades of testing do you want?" she asked.

The US Government is among the biggest supporters of GM technology and many crops are owned by a US firm, Monsanto.

Other high-profile scientists have also recently called for greater use of GM. Earlier this month, Gordon Brown's science adviser, John Beddington, called for Britain to embrace GM crops.

Dr Fedoroff, a molecular biologist here as part of a delegation of US scientists to build stronger ties with New Zealand, said she knew of New Zealand's strong anti-GM movement. "So I throw myself in front of the train," she joked.

She said if climate change unfolded as predicted, tweaking existing farming practices would not be enough.

She predicted public attitudes would change when rising prices turned people towards cheaper, GM food. "Stay tuned ... dug-in positions can change quite rapidly," she said.