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They might be fluffy faced, buck-toothed little creatures, but two species of rodent have been identified the latest culprits to be contributing to climate change.

Researchers have found that the arctic ground squirrel and the beaver may be playing a far greater role in global warming than had previously been realised.

It means that scientists will in the future have to alter their theories around anthropogenic climate change to take account of 'rodentopogenic' influences.

Menace: Ground squirrels live in shallow burrows around the Arctic Circle but their incessant digging mixes the normally frozen soil, introducing oxygen and leading to the release of methane gas

The influence that these two species of rodents have on the climate were uncovered during separate studies of how their behaviour affects the environment.

Researchers studying permafrost in the Arctic found that ground squirrels there are hastening the release of greenhouse gases from the frozen soil where they build their burrows.

They found that by churning up the normally stable layers of soil, and fertilizing it with their faeces and urine, the little rodents are encouraging the decomposition of biological material that is usually locked in suspended animation by the permafrost.

This leads to methane gas and carbon dioxide locked within the frozen Tundra ground to be released into the atmosphere.

Permafrost is known to be an enormous store of carbon as molecules of methane are become locked inside ice crystals while organic matter from dead plants and animal are preserved in the ice.

Scientists estimate that the Arctic permafrost is a store of twice as much carbon than is currently in the atmosphere and fear that if the permafrost melts, it will release these huge reserves of greenhouse gases, leading to climate change.

Nigel Golden, an ecologist at the University of Wisconsin who took part in the research, said that by digging into the frozen soil, ground squirrels, which are also known as Parka in Alaska, increased the amount of carbon being released during summer melts.

He said the temperature of the ground around their burrows was higher than in the surrounding area.

Speaking to the BBC, he said: 'They are soil engineers. They break down the soil when they are digging their burrows, they mix the top layer with the bottom layer, they are bringing oxygen to the soil and they are fertilizing the soil with their urine and their faeces.

'We saw an increase in soil temperature in the soils where the arctic ground squirrels were occupying.

'This is a major component. As that permafrost begins to warm, now microbes can have access to these previously frozen carbons that were in the soil.

'And because they mix the soil layers, they are being exposed to warmer temperatures.'

Scientists estimate that more than 1,600 billion tons of carbon is locked in the Arctic permafrost and if released it could treble the levels of greenhouse gases in the Earth's atmosphere, driving global warming

Arctic ground squirrel, or parka, live in high numbers through out the arctic and climate scientists may now need to start taking account of their role in releasing greenhouse gases in future climate change models

It is not the first time that animals have been found to play a role in climate change - it is already widely accepted that livestock are major contributors to global warming through the methane they emit while digetsting their food.

However, the researchers belive that ground squirrels may be playing a far more important role in the release of carbon from the permafrost than had been appreciated.

Arctic ground squirrels are among the most numerous rodents in the arctic circle, found across North America and Siberia. With an average length of around 15 inches, they dig shallow burrows to shelter from the harsh conditions and can hibernate for around seven monoths of the year.

They feed on grasses and other plants that grow during the brief summer in the Arctic.

The research team, who presented their findings at the Fall meeting of the American Geophysical Union, also found that the nitrogen that squirrels were adding to the ground in their waste was having an impact.

Dr Sue Natali, an environmental scientist at Woods Hole Research Centre in Massachusetts, who led the work as part of the Polaris Project to study climate change at the poles, said: 'We know wildlife impacts vegetation, and we know vegetation impacts thaw and soil carbon.

Dam building by beavers is thought to have contributed 200 times more methane to the atmosphere than 100 years ago and the ponds they create in rivers now cover more than 16,200 square miles around the world

'It certainly has a bigger impact than we've considered and it's something we will be considering more and more going into the future.'

It is estimated that around 1,600 billion tons of carbon is stored in the Arctic permafrost.

However, the role of arctic ground squirrels is thought to be tiny compared to the melting of the permafrost caused by carbon dioxide released into the atmosphere by human activity.

However, a separate study has also found that another rodent, the beaver, is also playing a far greater role in the release of climate changing gases like methane than had been previously thought.

Numbers of these animals has increased in recent years in both North America and Europe as a result of conservation projects.

However, the shallow ponds that build up behind beaver dams produce methane as biological material builds up on the low oxygen environment on the beds of the ponds.

Scientists estimate that 200 times more methane is released from beaver ponds now than was being released in 1900.

Dr Colin Whitfield, from the University of Saskatchewan, Canada, estimated the size of global beaver populations and the amount of area covered by their ponds. Fur trade between the sixteenth and nineteenth century lead to beaver populations in many areas becoming extinct.

But now Dr Whitfield and his team have estimated that beaver numbers have grown dramatically to more than 10 million and estimate populations in Europe and Asia could increase by a further four million.

Beaver numbers have soared to more than 10 million globally since 1900 due to reintroduction projects

Ponds behind beaver dams are often less than five feet deep and as a result allow methane from decomposing biological material on bottom of the ponds to be released into the atmosphere rather than dissolved in water

They found that beavers have dammed up more than 16,200 square miles of ponds. The scientists, whose work is published in the journal AMBIO, claim that beavers are responsible for releasing around 881,000 tons of methane into the atmosphere each year.

This is about 15 percent of what wild cud-chewing animals, such as deer or antelope, are thought to contribute. 

Dr Whitfield said: 'The dynamic nature of beaver-mediated methane emissions in recent years may portend the potential for future changes in this component of the global methane budget.

'Continued range expansion, coupled with changes in population and pond densities, may dramatically increase the amount of water impounded by the beaver.

'This, in combination with anticipated increases in surface water temperatures, and likely effects on rates of methanogenesis, suggests that the contribution of beaver activity to global methane emissions may continue to grow.'