Lisbon, Dec 2 (AFP) Swedish teen eco-warrior Greta Thunberg was nearing the Portuguese coast on Monday after crossing the Atlantic in a catamaran to attend a UN climate change summit in Madrid, her entourage said.

Thunberg, 16, has become the face of young peoples' demands for climate action and made a point of making the journey back from September's New York climate summit by sea rather than fuel-guzzling plane.

She had expected to be heading for Chile, but the South American nation passed the hosting of the COP25 summit meeting to Spain after suffering a spate of deadly anti-government protests.

Rather than besmirch her status as an environmental activist by taking a carbon emissions-heavy air trip, Thunberg instead set sail on the 14-metre (45-foot) La Vagabonde catamaran on November 13 from Hampton, Virginia to return to Europe.

Thunberg, British navigator Nikki Henderson and the Australian family who own the vessel were expected to arrive in Portugal's capital Lisbon at around 0800 GMT on Tuesday after a voyage of more than 5,500 kilometres (3,400 miles).

Lisbon mayor Fernando Medina was set to greet them along with young Portuguese environmental campaigners inspired by Thunberg.

Thunberg is scheduled to hold media interviews then take an overnight train to Madrid, Portuguese sources said.

The climate summit, which opened Monday and runs to December 13, brings together representatives of some 200 signatory nations to the 2015 Paris accord.

Having used her appearance in New York to denounce governments for failing to act with sufficient urgency on the environment, Thunberg attended weekly green protests in several US cities before embarking on her long trip home.

"In one way, lots of things have changed, and lots of things have moved in the right direction," she told AFP before setting off.

"But also in a sense we have gone a few more months without real action being taken and without people realising the emergency we are in." (AFP)

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