Alok Sharma will now concentrate on this year's UN COP26 climate conference full-time as COP26 president, with Kwasi Kwarteng appointed secretary of state for Business, Energy and Industrial Strategy (BEIS).
As COP26 president, Sharma will be based in the Cabinet Office, continuing as a full member of Cabinet, and will chair the Climate Action Implementation Committee to coordinate government action towards net zero by 2050 in the run up to COP26.
He 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."
Kwarteng, previously minister of state for Business, Energy and Clean Growth, is tasked with "leading and bringing together work on business, science and innovation to unleash investment and growth".
Anne-Marie Trevelyan assumes Kwarteng's previous role, taking forward climate and energy policy, including implementing plans in the Prime Minister’s Ten Point Plan for a Green Industrial Revolution.
She will also continue in her role as the UK’s International Champion on Adaptation and Resilience for the COP26 Presidency, supporting countries vulnerable to climate change to adapt to its impacts and build resilience.