By Andrea Shalal WASHINGTON (Reuters) -U.S. Treasury Secretary Janet Yellen announced a $950 million loan to the Clean Technology Fund (CTF), a multilateral trust that helps developing countries accelerate their transition from fossil fuels to clean energy. The contribution, the first of its kind from the U.S. Treasury, makes good on a U.S. pledge made at the 2021 Group of Seven summit alongside other G7 countries, Treasury said. “We are committed to a net zero economy by 2050,” Yellen said in a speech at the Center for Global Development, calling climate change “an existential threat to our p…