A study of 11,000-year-old Antarctic ice has shown humans are responsible for releasing more climate changing greenhouse gases than previously thought.
An international team of scientists, led by the United States' University of Rochester, have spent six years analysing air trapped in the ancient ice. The frozen time capsules allowed them to measure how much methane was in the atmosphere thousands of years ago.
Publishing their findings in Nature journal on Thursday, they said they found there was much less escaping naturally from oil and gas fields than previously thought.
This meant human farming practices and the burning of fossil fuels since the Industrial Revolution were to blame for approximately 60 per cent of all methane in the atmosphere.
While the findings sound grim, New Zealand NIWA atmospheric scientist Dr Hinrich Schaefer, who took part in the studies, says there is an upside.
Because humans are responsible for releasing so much methane, it also gives countries plenty of opportunities to clamp down on emissions and reduce them.
"It gives us a warning of where we have to put in more effort and where we can make a difference," he said.
The scientists also found that during global warming at end of the last ice age there was not a great release of methane into the atmosphere as it became exposed by the melting of ice.
Dr Schaefer said scientists were hopeful this meant that if current global warming continued there would not be a spike in methane levels also.
NIWA praised the international scientific team's research, saying it had never been attempted before because it was so complex and laborious.