A climate summit of world leaders in 40 days' time will be the "turning point for humanity", PM Boris Johnson has said in a speech to the United Nations.

He warned that global temperature rises were already inevitable, but called on his fellow leaders to commit to major changes to curb further warming.

Four areas needed tackling - "coal, cars, cash and trees", he said.

Countries must take responsibility for "the destruction we are inflicting, not just upon our planet but ourselves".

"It's time for humanity to grow up," he added ahead of the UK hosting the COP26 summit in Glasgow.

The prime minister also said it was time to listen to the warnings of scientists. "Look at Covid if you want an example of gloomy scientists being proved right."

Setting the tone for November's meeting, he said countries must make "substantial changes" by the end of the decade if the world is to stave off further temperature rises.

"I passionately believe that we can do it by making commitments in four areas - coal, cars, cash and trees," he said.

Mr Johnson praised China's President Xi Jinping for his recent pledge to stop building new coal-fire energy plants abroad.

But he called on the country - which produces 28% of global greenhouse gas emissions - to go further and end its domestic use of coal, saying the UK was proof that it could be done.

The UK used coal to generate 25% of its electricity five years ago - but that is now down to 2%. Mr Johnson said it would be "gone altogether" by 2024.

The prime minister also said he did not see a conflict between the green movement and capitalism, saying that: "The whole experience of the Covid pandemic is that the way to fix the problem is through science and innovation, the breakthroughs and the investment that are made possible by capitalism and by free markets."

"We have the tools for a green industrial revolution but time is desperately short," he added.

Elsewhere, the prime minister made a series of calls for action to his fellow leaders, including:

to allow only zero-emission vehicles to be on sale across the world by 2040
for every country to cut carbon emissions by 68% by 2030, compared to levels in 1990
to pledge collectively to achieve carbon neutrality - or net zero - by the middle of the century
to end the use of coal power in the developing world by 2040 and in the developed world by 2030
to halt and reverse the loss of trees and biodiversity by 2030.

Amid the serious warnings, Mr Johnson also attempted to strike a humorous note at points, including saying Kermit the Frog had been wrong when he sang It's Not Easy Bein' Green.
'We missed our cue'

The prime minister reiterated that the world must curb the rise in global average temperatures to 1.5C - the stricter of the two targets set by the UN in the 2015 Paris agreement.

However, the world is already 1C hotter compared with pre-industrial levels.

"If we keep on the current track then the temperatures will go up by 2.7 degrees or more by the end of the century," Mr Johnson said.

"And never mind what that will do to the ice floes... we will see desertification, drought, crop failure, and mass movements of humanity on a scale not seen before, not because of some unforeseen natural event or disaster but because of us, because of what we are doing now.

"And our grandchildren will know that we are the culprits and... that we were warned and they will know that it was this generation that came centre stage to speak and act on behalf of posterity and that we missed our cue and they will ask themselves what kind of people we were to be so selfish and so short sighted."

Analysis box by Roger Harrabin, Environment analyst

Boris Johnson is fashioning himself as a leader on climate change.

He has set a benchmark by phasing out sales of most new conventional vehicles by 2030.

The international alliance he's formed to get rid of coal power is gathering support - though not yet enough.

And by setting aggressive targets to cut carbon emissions overall (78% by 2035) he is encouraging others to follow.

Yet, in his own backyard, the prime minister is stumbling.

He previously pledged "never to be lagging on lagging". But his plan for insulating homes is badly delayed - along with other vital initiatives on issues including aviation, farming and financing the low carbon revolution.

Recent research showed his government had imposed less than a quarter of the policies needed to clean up the economy.

And some policies - like not opposing a coal mine in Cumbria,cutting taxes on flying and building HS2 - will send emissions up when they are supposed to be going down.
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At COP26, leaders from 196 countries will be asked to agree action to limit climate change and its effects, like rising sea levels and extreme weather.

A recent report from UN scientists warned that global temperatures have risen faster since 1970 than at any point in the past 2,000 years.