OSLO (Reuters) – Norway’s $1.5 trillion sovereign wealth fund faces growing obstacles to earning a return on its investments amid persistent inflation, already-high market valuations and geopolitical tension, its CEO said on Tuesday. The Norwegian Government Pension Fund Global, the world’s largest sovereign wealth fund, invests proceeds from the country’s oil and gas industry in foreign stocks, bonds, real estate and renewable energy assets. “The biggest challenge is to generate return in a world which is becoming difficult,” CEO Nicolai Tangen of Norges Bank Investment Management, which oper…