A study of ancient Antarctic ice has found fossil fuel emissions may be having a greater effect on climate change than previously thought.
Scientists were able to study air nearly 12,000 years old in ice cores harvested from Taylor Glacier in Antarctica. The ice trapped tiny bubbles of air, like frozen time capsules.
It's an opportunity to glimpse into the past - a glimpse which has surprised scientists.
Methane levels in the past were much lower than expected - meaning it's likely fossil fuels have had a much larger impact on current levels than previously thought.
NIWA atmospheric scientist Dr Hinrich Schaefer, one of the researchers, told Newshub it's a significant discovery.
"The most recent increase is most likely caused by agricultural practices, but the historical impact on greenhouse gases is much larger from fossil fuels than we've previously assumed," he said.
"It means there's a lot more potential to clamp down and prevent leakage from wells and pipelines, and therefore bring down the global levels of methane in the atmosphere."
The methane levels from the past were three to four times lower than previously thought, containing methane solely from natural sources without any human activities.
Now, around 60 percent of current methane levels are caused by humans, the researchers say. This includes fossil fuel use, raising livestock and landfill.
"This means we have even more leverage to fight global warming by curbing methane emissions from our fossil fuel use," lead author Vasilii Petrenko, from the University of Rochester, said.
The research could mark a starting base for emission reductions, in the fight to keep global warming below 2degC as agreed in the Paris targets.
"It pays to target the most relevant sources, and our research shows the fossil fuel industry... is a major place to start," Dr Schaefer said - though he warned this doesn't mean agriculture, another key methane emitter, gets off scot-free.
"It's easy to get into a fight of, well if we do this, we don't have to do the other... Both of them have to be targeted to bring down methane levels."
Melting permafrost won't spike methane levels
Scientists have been concerned that as permafrost melts, methane levels will start to spike due to the gases in that ice being released.
But this new research suggests that may not be the case.
"We can show with our research that a time of rapid warming in the past, at the end of the last ice age, that did not happen, which makes us more hopeful that it will not happen with future climate change," Dr Schaefer said.
However he said the world was different at the time they were studying, with large ice sheets covering North America and Europe when the warming began.
"We have to be careful how far our analogy carries in that case," he said.
The study was published in Nature on Thursday (NZ time).