Powerful swells averaging 5m (16ft) washed across the capital of the Marshall Islands, Majuro, last week.

But President Hilda Heine said the Pacific nation had been fighting rising tides even before last week's disaster.

Political leaders and climate diplomats are meeting in Madrid for two weeks of talks amid a growing sense of crisis.

This conference of the parties, or COP25, was due to be held in Chile but was cancelled by the government due to weeks of civil disturbances.

Spain then stepped in to host the event, which will see 29,000 attendees over the two weeks of talks.

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School protesters are among those who have taken to the streets

The world's average surface temperature is rising rapidly because human activities release greenhouse gases such as carbon dioxide (CO2). These gases trap heat in the atmosphere, a bit like the glass roof of a greenhouse.

At the meeting, Ms Heine commented: "Water covers much of our land at one or other point of the year as we fight rising tides. As we speak hundreds of people have evacuated their homes after large waves caused the ocean to inundate parts of our capital in Majuro last week."

She added: "It's a fight to the death for anyone not prepared to flee. As a nation we refuse to flee. But we also refuse to die."

Ms Heine is not alone in the view that small nations like the Marshall Islands face an imminent existential threat. At the Madrid summit, ambassador Lois Young, from the Alliance of Small Island States (AOSIS), which represents low-lying coastal countries and small island nations, launched a rebuke to the world's big polluters.

"We are disappointed by inadequate action by developed countries and outraged by the dithering and retreat of one of the most culpable polluters from the Paris Agreement," she said.

"In the midst of a climate emergency, retreat and inaction are tantamount to sanctioning ecocide. They reflect profound failure to honour collective global commitment to protect the most vulnerable.

The hottest that this location has ever been...

"With our very existence at stake, COP 25 must demonstrate unprecedented ambition to avert ecocide."

The COP25 meeting will aim to step up ambition so that all countries increase their national commitments to cut emissions. The meeting follows on the heels of three UN reports which stressed the increased urgency of limiting dangerous climate change.

According to UN Secretary General António Guterres, "the point of no return is no longer over the horizon".

Speaking ahead of the meeting, he said political leaders had to respond to the imminent climate crisis.

"In the crucial 12 months ahead, it is essential that we secure more ambitious national commitments - particularly from the main emitters - to immediately start reducing greenhouse gas emissions at a pace consistent to reaching carbon neutrality by 2050.

"We simply have to stop digging and drilling and take advantage of the vast possibilities offered by renewable energy and nature-based solutions," Mr Guterres said.

Almost every country in the world has now signed and ratified the Paris climate agreement and under the terms of the pact they will all have to put new climate pledges on the table before the end of 2020.