Most people know rainforests are vital in the fight against climate change, but now scientists say wetlands could be even more important.

Saltmarshes, mangrove swamps and wetlands can absorb carbon "four times faster than trees", according to the charity the Wildfowl and Wetlands Trust (WWT).

Celebrating 80 years since WWT's first wetland bird reserve was founded at Slimbridge, in Gloucestershire, the charity's leaders have called for one million hectares of wetlands to be restored across the world.

Sarah Fowler, CEO of WWT, said: "They are mood-boosting, flood-buffering, water-purifying, incredible habitats. But we have lost 85% of the world's wetlands."

WWT now runs 10 wetland bird reserves across the UK.

Many people come to enjoy the swans, geese, flamingoes and migrating wildfowl, but do not realise how powerful these habitats can be in soaking up carbon and slowing down climate change.

So how vital are wetlands for birds, and how powerful can they be in the fight against climate change?

In November 1946, a naturalist called Peter Scott came to a wild marshy area on the banks of the River Severn, near Slimbridge. He was drawn by the thousands of migrating geese and swans that flew thousands of miles from the Russian Arctic to spend the winter here on the mudflats and marshes.

Captivated, Scott settled in a small cottage and later built a house right on a lake, with a huge window to watch the wildfowl.

Over the years, the reserve grew and became home to thousands of ducks, swans , geese as well as the migrating wildfowl.

"He really was a pioneer in conservation," said Chris Moore, a historian of Slimbridge and author of Peter Scott and the Birth of Modern Conservation.

As well as creating a safe haven for endangered species, Scott was a vigorous campaigner for nature.

He led the fight to stop commercial whaling, presented some of the BBC's first natural history programmes called live from Slimbridge, and helped set up WWF, the World Wildlife Fund.

In 1973 Sir Peter Scott became the first person to be knighted for conservation work.

Moore explained: "Scott was talking about the impact that man was having on the natural world, long before we started talking about climate change and global warming.

"David Attenborough called him the Patron Saint of Conservation, and I think that is more than deserved," Moore added.

One of Scott's typically ambitious projects was to save the Hawaiian Goose, or Nēnē.

Unique to the Pacific islands, the Nēnē was hit hard by road building and development. By 1949 barely 24 birds remained.

Scott heard of its plight, and asked Hawaiian authorities to send a few geese to Slimbridge where he hand-reared them.

"Unfortunately they sent us two females," chuckled Enid Cole, a WWT volunteer at Slimbridge.

"Peter asked them for a gander - 'It would help', he said."

Nine chicks were later born, and hand-raised successfully to adulthood at Slimbridge.

Today there are more than 3,000 Nēnē geese, most of them living peacefully on Hawaiian golf courses. But a handful still live at Slimbridge, where Enid Cole and her friends hand feed them lettuce every day.

"It's a marvelous project, and typical of Sir Peter," Enid smiled.

Over the last 80 years, the teams at Slimbridge have hand-reared several other species, including the Common Crane and the world's rarest diving duck, the Madagascan Pochard.

It was while they were working to save the Madagascan Pochard that they realised how vital the wetland habitats were.

"We realised that to save that species, we had to bring the wetland back," explained Sarah Fowler, WWT's chief executive.

"And to bring the wetland back, we had to work with the whole community in Madagascar."

Ian Hollister, a volunteer warden at Slimbridge, said: "The wetlands are great at absorbing carbon, they're like a soggy secret weapon."

Scientists calculate that 85% of the world's wetland habitats have been lost as marshes drained for agriculture, and swamps cleared for construction as cities expand.

And yet, as Fowler explained, "40% of the world's species rely on wetland habitats for survival".

What started at Slimbridge has spread to 10 wetland reserves across the UK with the charity now working with local councils to restore wetlands, even in small city areas.

A scheme in Bristol has seen small floating islands of wetland plants moored in the city's harbour.

Across the world, they are campaigning to restore one million hectares of lost wetland, partly to provide safe habitats for endangered species but also because wetlands help absorb carbon far quicker than even forests.

"Salt marshes bury carbon," said Fowler.

"Every time the big tides go over them, the plants that have grown up in the salt marsh get buried. Those plants are full of carbon, so they are a massive carbon sink.

"And the brilliant thing about salt marshes is they do this four times faster than trees. Wetlands are vital in our fight against climate change, and we must restore them."

What started 80 years ago as a bird reserve on the banks of a river in Gloucestershire has grown into a global campaign to restore wetlands, which they call the "soggy secret weapon" against climate change.

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