World leaders are lying to the public about the climate crisis and dismissing scientific evidence.

That was the stark warning from former US Secretary of State John Kerry who said the truth is not just being ignored but altered.

“Today we have public leaders who not only try to avoid the truth, but who try to alter it, through thousands of lies,” he said.

Mr Kerry was speaking after addressing a global oceans summit in Cork where he said the world and its climate do not have the time or space to deal with “presidents and prime ministers” who deny the truth about climate change.

However, he told delegates at the Our Ocean Wealth summit that the tide can be turned if governments face up to the truth and act faster.

Mr Kerry is leading a global effort to deliver more Marine Protected Areas but warned that humans are changing the chemistry of that oceans faster than it has been changed in the last 50m years.

“We can’t protect oceans without solving the problem of climate change and we can’t solve that without protecting the oceans — they go hand in hand,” he said.

“I believe we can do this. My frustration is that we are not doing what we know we can do. And time is not on our side.

“We know the enemy — the enemy is man-made. If it’s man-made it can be ‘man-solved’.”

The summit, sponsored by PwC, was also addressed by young Irish activist and youth ambassador Alicia O’Sullivan, 17, who described the realities of climate change as “terrifying” and challenged world leaders to act now to save her generation’s future.

Ms O’Sullivan said that, like other teenagers around the world, she is worried about school, exams and relationships.

“But I am worried about something far greater — my future,” she said.

“And I am not alone, with 1.6m young people from all over 123 countries scared. We are scared that we will not have what you had.”

The summit was attended by the leaders or political representatives of some 30 island state nations who have most to gain from the blue economy but who are also most at risk from the climate crisis.

Elizabeth Thompson, the permanent representative of Barbados to the UN, said her government, which oversees a landmass of 32sq km but 183,436 sq km of oceans, have appointed a ministry of the blue economy to help foster a sustainable blue economy.

A survey of attendees at the event, who represent leading voices in Ireland’s marine industry, showed that offshore wind and ocean energy in particular represent the greatest opportunity for the sector. with the committee up and running before the end of the year.

Mr Kerry’s warning comes as a new study shows more than 500 species of plants have disappeared in the past 250 years — more than twice the number of birds, mammals and amphibians recorded as extinct.

Scientists at the Royal Botanic Gardens, Kew, and Stockholm University carried out a groundbreaking global analysis of all plant extinction records to come up with the figure.

The research, published in the journal Nature, Ecology & Evolution found that 571 plant species have disappeared in the last two and a half centuries — four times more than the current listing of extinct plants.

The figure is also more than twice the number of birds, mammals and amphibians recorded as extinct — a combined total of 217 species.

Meanwhile, the Green Party made an immediate impact on Cork City Council last night after councillors agreed to their motion calling for the establishment of a climate action committee.

Its membership is expected to be decided over the coming weeks.