Professor Jim Skea was a professor in sustainable energy at Imperial College London before this year being elected the new head of the United Nations' Intergovernmental Panel on Climate Change (IPCC), which advises all UN governments on the latest climate science.

As the IPCC embarks on a new phase of work, its chair told journalists it must walk a "delicate tightrope", of communicating both the "urgency" of climate change and human "agency" to tackle it.

"We are in dire circumstances, there are threats to people in many parts of the world," said Prof Skea.

But "the human race has agency over that future and how it deals with these threats", he added.

Responding to a question from Sky News, he said using "nothing but apocalyptic language" can "undermine a sense of agency" and give people the sense "it's hopeless, we can do nothing about it".

"We can do things about it... that's the key message I would like to get across".

Asked if this put him at odds with UN chief António Guterres, whose warnings about being on a "highway to climate hell" have raised eyebrows, Prof Skea said: "the secretary general has an entirely different mandate from IPCC, so it is perhaps unsurprising that the language that is used is different."

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The role of a UN secretary general includes diplomacy and advocacy, especially for the poor and vulnerable.

However, Prof Skea also warned focusing only on solutions could lead to false optimism and "an underestimate of the risks, which are very, very serious, obviously".

The IPCC, currently deciding where to focus its attention over its next five to seven-year cycle of work, is considering a report on the science of science communication, he said, acknowledging the IPCC itself "hasn't got it perfect yet".

Sticking to IPCC policy not to comment on member states' policies, the chair could not be drawn on recent UK government decisions to delay some key climate targets or to champion new North Sea oil and gas developments.

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But he said it was not just the timing of the net zero target - which the UK and most of the developed world aims to reach by 2050 - but how we get there too.

"It is cumulative emissions of carbon dioxide over time, that is the main factor leading to a specific level of warming.

"Therefore, the path by which you get to net zero matters.

"If you put it off to the last minute, then you will find that warming would be larger than it otherwise would have been on. I think that's the global point I can make."