The failure to limit global warming to 1.5 degrees Celsius is an emergency and nations must now "lead or be led to ruin", UN Secretary-General Antonio Guterres said as the COP30 climate conference got underway in Brazil's rainforest city Belem.

Scientists have confirmed the world is set to cross the 1.5C warming threshold around 2030, risking extreme warming with irreversible consequences.

"Too many corporations are making record profits from climate devastation, with billions spent on lobbying, deceiving the public and obstructing progress," Mr Guterres said in his speech.

"Too many leaders remain captive to these entrenched interests."

Countries are spending about $US1 trillion ($1.54 trillion) each year in subsidising fossil fuels.

Leaders have two clear options, Mr Guterres said:

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