Coal-fired power stations are a major contributor to South African emissions
South Africa has committed to reducing its carbon emissions by 34% by 2020, but says it will need financial aid from developed countries to do so.
The announcement was made as the world climate talks started in Copenhagen.
Environmental group Greenpeace said the announcement had made South Africa "one of the stars of the negotiations".
The country's greenhouse gases come mostly from the coal-burning power stations. The government says it is looking at other energy sources.
US-LED COPENHAGEN DEAL
No reference to legally binding agreement Recognises the need to limit global temperatures rising no more than 2C above pre-industrial levels Developed countries to "set a goal of mobilising jointly $100bn a year by 2020 to address the needs of developing
countries" On transparency: Emerging nations monitor own efforts and report to UN every two years. Some international checks No detailed framework on carbon markets - "various approaches" will be pursued
Updated: 13:47 GMT, 19 December
South Africa said it would lower its carbon emissions to 34% below current expected levels by 2020 and about 42% below current trends by 2025.
"This undertaking is conditional on firstly a fair, ambitious and effective agreement," a South African government statement said.
"And secondly, the provision of support from the international community, and in particular finance, technology and support."
The government said developing countries such as South Africa would need financial help from developed economies, with some of the aid being used to acquire the technology needed to reach its target.
The country's chief climate negotiator Alf Wills told Reuters the offer was the first time South Africa had given a specific target for reducing its carbon footprint.
AFRICA HAVE YOUR SAY
Climate change is a Western problem and at such a Western solution should be found
Laura Golakeh, Monrovia
The government said international finance has helped South Africa to build new solar and wind-powered plants.
But construction has already begun on what is believed to be the biggest coal-burning power plant in the country.
The plant is aimed at meeting the country's increasing energy needs and avoiding a repeat of last year's rolling blackouts, which cost the country millions of dollars.