In a speech to political leaders and delegates at the opening ceremony of the world leaders summit at the UN climate conference he is expected to urge countries to move from talk and debate to concerted real-world action.
He will call for action on phasing out coal power, protecting and restoring forests, providing finance for countries to tackle climate change and boosting electric vehicles.
The Prime Minister is also pledging an extra £1 billion in climate finance to support developing countries by 2025 if the economy grows as forecast and the UK’s aid budget returns to the 0.7% of GDP level.
The UK Government has faced criticism for cutting the aid budget, in the run-up to the talks where delivery of a long-promised 100 billion US dollars a year by 2020 for poorer countries to develop cleanly and cope with climate impacts is a key issue for developing nations.
Ahead of the Cop26 summit, a report revealed that developed countries would not mobilise the 100 billion dollar goal for public and private finance until 2023.
The UK doubled its promised climate aid to £11.6bn over five years in 2019 and the new announcement would bring that to £12.6bn if it is delivered.
Separately the UN has warned that plans by countries to cut climate-warming emissions in the next decade were not enough to put the world on track to limit warming to 1.5C, beyond which increasingly severe extreme weather, rising seas and damage to crops, health and wildlife will be felt.
Mr Johnson will say: “Humanity has long since run down the clock on climate change.
“It’s one minute to midnight and we need to act now.
“If we don’t get serious about climate change today, it will be too late for our children to do so tomorrow.”
He is also expected to say: “We have to move from talk and debate and discussion to concerted, real-world action on coal, cars, cash and trees.
“Not more hopes and targets and aspirations, valuable though they are, but clear commitments and concrete timetables for change.
“We need to get real about climate change and the world needs to know when that’s going to happen.”
More than 120 leaders are set to attend the world leaders summit where countries are under pressure to increase action in the next decade to curb dangerous warming and to deliver financial support for poorer countries least responsible for and most vulnerable to climate change.
There are also efforts to drive action by countries, regions, and businesses to curb emissions in sectors such as power with efforts to phase out coal, as well as finalise parts of the Paris climate accord agreed in 2015 to make it effective and operational.
But international tensions, political discord and the non-attendance of some key world leaders has cast a shadow over the summit with some experts predicting it will not lead to the vital changes needed to halt climate change.