The world “listened, but did not hear” the extent of the dangers of the climate crisis, the head of the United Nations Environment Programme has said.

Inger Andersen criticised global leaders for “not acting strongly enough” and said a generation of politicians, business leaders and “conscious citizens” was needed to make “systematic changes”.

Her remarks came following the publication of a report by the Intergovernmental Panel on Climate Change (IPCC), which noted the “unequivocal” impact of humans on the environment.

Speaking at an IPCC press conference on Monday, Ms Andersen said: “You have been telling us for over three decades of the dangers of allowing the planet to warm.

“The world listened, but did not hear. The world listened, but it did not act strongly enough and, as a result, climate change is a problem that is here now.

“It’s time to get serious because every tonne of CO2 emission adds to global warming.”

Ms Andersen added people were “well aware of the drama” surrounding climate change, but reiterated that the “power is in our hands”.

“As citizens and businesses and governments, we are well aware of the drama,” she said.

“The drama exists and we have seen it and heard about it in every news bulletin, and that’s what we need to understand.

“What this excellent report does is it projects these scenarios outwards and tells us that if we do not take action what could be the potential outcomes.

“The power is in our hands at this point.

“Nobody is safe and it’s getting worse faster.”

It comes as Business Secretary Kwasi Kwarteng acknowledged that UK Government climate targets were “challenging” and that certain policies such as electric car rollout would not happen “overnight”.

Asked if the country was on track to hit net zero emissions by 2050, he told Sky News: “I think it’s challenging, but I think we are on track, I think we’re doing quite well.

“If you look since 1990 we’ve reduced our emissions by 45% and we’ve managed to grow the economy by 80%, this is a world-beating figure.”

“It’s 2021 now, I think there’s every chance we will hit the target. It’s a lot of work and I think we can do that … it is challenging, it’s not an easy thing, if it were an easy thing we wouldn’t be going on about it.”

He added: “It’s not something that’s going to happen overnight … I think the electric vehicle rollout is something that is actually very encouraging.

“I’m concerned about it but I don’t have the authority to write budgets or dictate tax policy.”

Mr Kwarteng also told the BBC Today programme the Government wanted to “try and help people make (the) transition” from gas boilers, when asked about the expense to consumers.

Ms Andersen told the press conference that G20 countries in particular had a “special responsibility” to tackle climate change as she urged world leaders to “live up to the facts on the table” at the upcoming Cop26 summit.

“Together they are nearly responsible for around 80% of all global emissions … and accordingly, therefore, have a unique opportunity to really help in reducing CO2 and greenhouse gases emissions,” she said.

“The G7 and the G20 … bear a special responsibility and we certainly urge them in their upcoming heads of state summit to live up to the facts that are on the table right now.”

She added: “We can’t undo the mistakes of the past, but this generation of political and business leaders, this generation of conscious citizens, can make things right.

“This generation can make the systemic changes that will stop the planet warming, help everyone adapt to the new conditions and create a world of peace, prosperity and equity.

“Climate change is here now, but we are also here now, and if we don’t act, who will?”

UK chief scientific adviser Sir Patrick Vallance said it was “easy to slip” with plans to tackle climate change and urged world leaders to set out clear, “practical” plans to address the crisis.

Addressing those due to attend the Cop26 climate summit, he said on Sky News: “Every government needs to develop an evidence-based roadmap setting out the technologies they require.

“That’s a really important practical step that governments need to take and each of us needs to hold ourselves to account for this because monitoring progress against those roadmaps is going to be crucial.

“It’s easy to slip and it’s easy to assume that something can happen later to rectify this.

“The message is ‘no, it has to happen now, the roadmap needs to be implemented now’ and we need to know when we’re off course and correct that as soon as possible.”