The move comes after calls for greater government focus on preparations for the Glasgow summit, which environmentalists regard as a make-or-break opportunity to rein in global warming by building on the Paris Accord of 2015.
In a sign of the prime minister’s ambitions for November’s UN summit, Mr Sharma will remain in the cabinet.
Postponed from 2020 because of the Covid crisis, Cop26 is expected to be the largest summit the UK has ever hosted, bringing together representatives from nearly 200 countries, including world leaders, experts, and campaigners.
Mr Sharma, who has stepped down as business secretary, will seek to persuade other countries to follow the UK’s lead in committing to reduce greenhouse gas emissions by at least 68 per cent by 2030, as part of the Paris target of keeping global temperatures lower than 2C above pre-industrial levels.
Mr Sharma was appointed president of the summit in February last year on a part-time basis, but Mr Johnson has come under increasing pressure to relieve him of departmental responsibilities to allow him to focus exclusively on making the meeting a success.
Former climate secretary Amber Rudd, who led the UK delegation at Paris, said that he would need to devote “100 per cent of his time, energy and persuasion” to Glasgow to make it a success.
Mr Sharma said: “The biggest challenge of our time is climate change and we need to work together to deliver a cleaner, greener world and build back better for present and future generations.
“Through the UK’s presidency of Cop26 we have a unique opportunity, working with friends and partners around the world, to deliver on this goal.
“Given the vital importance of tackling climate change I am delighted to have been asked by the prime minister to dedicate all my energies to this urgent task.”
Mr Kwarteng’s promotion comes after 18 months as second-in-command at the Department for Business, Energy and Industrial Strategy.
The 45-year-old Spelthorne MP previously served as a minister under Theresa May in the Department for Exiting the European Union.
Former international development secretary Anne-Marie Trevelyan takes his former role as minister for business, energy and clean growth.
The move was welcomed by Richard Black, senior associate at the Energy and Climate Intelligence Unit.
“Allowing Alok Sharma to focus full-time on his Cop26 role is a sensible decision, not least as it signals the government’s commitment to ensuring that the summit is a success,” he said.
“Being president of Cop26 needs a full-time focus, but Mr Sharma will also need the full backing of No 10 and other key parts of government, such as the Foreign Office.
“Although the pandemic makes a tough job even more challenging, the government should focus squarely on building diplomatic alliances as the French did ahead of the successful Paris summit, including with the smallest and least developed nations whose support will be critical for achieving a positive summit outcome.”