The Climate Change Bill aims to enable South Africa to meet its emissions reduction commitments under the Paris climate agreement, the presidency said in a statement on Tuesday.
South Africa, which is the world's most carbon-intensive major economy and among the top 15 greenhouse gas emitters, is on track to miss those targets because of to its heavy reliance on coal for electricity.
"This is very significant in that it's the first time that our climate change response is directly brought into domestic law," said Brandon Abdinor, a lawyer at South Africa's Centre for Environmental Rights, a non-profit organisation.
"A lot of work needs to be done, but this act puts the basic architecture in place for that to happen."
The presidency statement did not say when Ramaphosa had signed the law, which requires every province and municipality to assess climate change risks and develop a response plan.
Emissions targets will be set for each high-emitting government sector such as agriculture, transport and industry, and each relevant minister must adopt measures to achieve them.
The law also says the environment minister must allocate a carbon budget to large greenhouse gas-emitting companies, setting a limit on their emissions over a specified time.
The allocations have not yet been set, and the law does not make it an offence to exceed the limit although climate advocates had wanted this, said Abdinor. But emitters that exceed their budget are likely to have to pay a higher rate of carbon tax.
"With mandatory carbon budgets now in place, we expect to see significant emissions reductions from large companies," Harald Winkler, an expert on climate policy at the University of Cape Town, said on X.
"Transparency in annual reporting will be key," he added.
The bill is the latest sign that South Africa's new government might be more aggressive on climate change and renewable energy than its predecessors.
The new energy minister has vowed to speed up the transition to renewables, but few specific plans have emerged. Funding plans to support the new bill are also unclear.
Western donors are offering billions of dollars in loans to fund the transition, but South African officials say they barely scratch the surface of the finance needed.
