CLIMATE activist Greta Thunberg has arrived by yacht in the port of Lisbon after a three-week voyage across the Atlantic Ocean from the US.

The Swedish teenager arrived in the port of the Portuguese capital on Tuesday, before heading to neighbouring Spain to attend the UN Climate Change Conference in Madrid.

She was met in Lisbon by local dignitaries and other activists.

Greta hitched a renewable-energy ride from the US, joining an Australian family on their 48ft catamaran.

She wanted a low-carbon form of transport to get to the climate meeting, which was switched at short notice to Spain from Chile due to unrest there.

The yacht, named La Vagabonde, leaves little or no carbon footprint when its sails are up, using solar panels and hydro-generators for electricity.