Greta Thunberg’s harsh reality check

THE global wave of school strikes for the climate over the past 12 months has "achieved nothing" because greenhouse gas emissions have continued to rise, Greta Thunberg told activists at United Nations climate talks in Madrid.

The 16-year-old Swedish climate activist said that calls for real action against climate change are still being "ignored" by political leaders - despite their continuous praise of the global environmental youth movement she helped create.

The teen joined an estimated 500,000 people in the Spanish capital, clutching her famed "school strike for climate banner" and taking to the streets to protest against the lack of progress in tackling the climate emergency.

Meanwhile, officials from more than 190 countries gathered at the UN climate conference, aiming to streamline the rules on global carbon markets and agree on how poor countries should be compensated for destruction largely caused by emissions from rich nations.

In the four years since the landmark Paris Accord agreement was signed, greenhouse gas emissions have risen by four per cent.

The talks this year are not expected to produce new commitments on carbon from the world's biggest emitters.

Thunberg was hopeful that the two-week round of annual climate negotiations - which commenced on Monday - would lead to "real action" and world leaders would grasp the urgency of the climate crisis.

But, flanked by three activists from Spain and Uganda, she told reporters: "We have been striking now for over a year, and still basically nothing has happened."

She said that although schoolchildren had been striking around the world - in cities from New York to Sydney - and they'd "achieved a lot, if you look at it from a certain point of view we have achieved nothing".

"We don't want to continue," Thunberg said.

"People are suffering and dying from the climate and ecological emergency today and we cannot wait any longer."

Thunberg, whose 2017 solo protest in Sweden snowballed into a global movement, said that asking children to skip school to protest inaction by governments on climate change was "not a sustainable solution".

Young people would continue to strike, but would stop if governments made credible promises and showed a willingness to act.

"I sincerely hope COP25 will reach something concrete and increase awareness among people, and that world leaders and people in power grasp the urgency of the climate crisis, because right now it does not seem that they are," she said.

An advocate for carbon-free transportation, the teen arrived in the city via train on Friday morning, having sailed across the Atlantic Ocean from the US by catamaran earlier in the week.

The march through Madrid's streets was scheduled to coincide with protests and youth climate strikes around the world.

In the US, democratic presidential candidate Bernie Sanders and actor Jane Fonda were among the politicians and celebrities planning to join in.

- with AAP