Ancient reserves of the greenhouse gas methane trapped in ice for millions of years in the Arctic Ocean are being released into the atmosphere, researchers claim.
The deposits of methane and other gases, dubbed hydrates, have previously been dubbed the 'sleeping giants of the carbon cycle'.
An international research team on a Russian ship spotted bubbles of the potent gas, which has a warming effect 80 times greater than carbon dioxide over 20 years, at the surface.
According to the scientists behind the preliminary findings, which have yet to be scrutinised by other scientists and published, this new source of greenhouse gas emissions could lead to a runaway sequence of events known as a feedback loop.
Other scientists are taking the claims with a pinch of salt and say it is highly unlikely the methane is finding its way into the atmosphere.
If further analysis confirms the methane is indeed seeping into the air, it could further accelerate the pace of climate change.
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A research team on a boat in the ocean has spotted bubbles of the potent gas, which has a warming effect 80 times greater than carbon dioxide over 20 years, being released (pictured)
In a Facebook post from last week, the team from the International Siberian Study Shelf Expedition say: 'This may be the first comprehensive observation of active release from methane hydrates on the Siberian-Arctic slope system.
'We believe these emissions at this stage have not yet had any large impact on global atmospheric methane and climate, yet these huge carbon/GHG [greenhouse gas] capacitors are clearly activated.'
The researchers found the methane leak in a remote corner of the Arctic Ocean near Russia while onboard the research vessel R/V Akademik Keldysh.
It was discovered over a 1,500 square km (580 square mile) patch of the Laptev Sea more than 600km (370 miles) from the shore.
Methane concentrations at a depth of around 300 metres (1,000 feet) reached up to 1,600 nanomoles per litre, 400 times higher than in a balanced system.
Levels of methane were up to eight times higher than expected at the surface and when this is combined with the visual bubbles, researchers believe the gas is being released into the atmosphere.
Örjan Gustafsson, of Stockholm University, told The Guardian he believes methane is now venting into the air from the water.
'At this moment, there is unlikely to be any major impact on global warming, but the point is that this process has now been triggered,' he said.
'This East Siberian slope methane hydrate system has been perturbed and the process will be ongoing.'
Gavin Schmidt, a climatologist and director of the NASA Goddard Institute for Space Studies, tweeted his skepticism at the findings. He said: 'This story is... unconvincing'
Scientists uncover the first active leak of METHANE from the sea floor in Antarctica
A methane leak was identified coming out of the Antarctic seabed in July, causing alarm among climate scientists and conservationists.
The stream of methane coming from 30ft below the surface and into the ocean is 'incredibly concerning', say scientists from Oregon State University which led the study.
Antarctica's seabeds are known to be a source of an enormous amount of methane.
It is thought ancient algae deposits are the original source of the methane which are trapped under sediments.
Researchers who had previously speculated about this event had hoped methane-devouring microbes in the water would feast on the gas and limit emissions.
However, the latest research, which documents the leak, also found these microorganisms avoided the gas for more than five years.
However, marine methane escaping into the atmosphere is a topic which is hotly debated among climate experts.
At the moment, while there is emerging evidence of methane being spewed into the water, there is no concrete proof of it subsequently entering the atmosphere.
Gavin Schmidt, a climatologist and director of the NASA Goddard Institute for Space Studies, tweeted his scepticism at the latest findings.
He said: 'This story is... unconvincing.
'First off it’s just two scientists (no publication), one of whom has made similar (unsupported) claims before & ignores the context that permafrost & methane have been degrading in this region since it was inundated in the early Holocene.'
And while the team of researchers 'believe they are the first to observationally confirm the methane release is already under way', according to The Guardian report, other scientists have dispelled such claims.
Martin Siegert, co-director of the Grantham Institute for Climate Change at Imperial College London, told The Times similar emissions have been found previously.
'But if the measurements show an increase then we should be concerned,' he adds.
'I suspect the work will provoke greater analysis of the problem and that is probably overdue. '
The Arctic is being harder hit by global warming than anywhere else on the planet.
Scientists analysing this anomalous weather concluded it was almost definitely caused by humans.
The researchers found the methane leak in a remote corner of the Arctic Ocean near Siberia while onboard the research vessel R/V Akademik Keldysh. It was discovered over a 1,500 square km patch of the Laptev Sea and more than 600km from the shore and concentrations reached up to 1,600 nanomoles per litre
A July study found Siberia's recent heatwave was made 600 times more likely due to human-induced climate change and would have been 'effectively impossible' without anthropogenic emissions.
The extreme weather saw a huge amount of wildfires raging across Siberia, releasing an average of 700 tonnes of carbon dioxide every minute up to September.
A total of 244 megatonnes of CO2 spewed into the air from the Arctic Circle wildfires, plaguing the world's northernmost region between January 1 and August 31.
While the Arctic has borne the brunt of the warming, the entire Northern Hemisphere has this year experienced its hottest summer on record.
From the start of June to the end of August, the average temperature north of the equator was 2.11°F (1.17°C) above the pre-industrial average.