South Africa needs concrete action soon if it is to maintain momentum on an energy transition program backed by the United States and other countries, U.S. Treasury Secretary Janet Yellen said on Friday after visiting the coal mining region of Mpumalanga. Yellen said the United States is resolute in its commitment to ensuring South Africa’s transition to renewable energy does not leave its workers behind, but appealed to philanthropists and private sector officials to step up their support as well.