Steady improvements in the fuel economy of new vehicles have stalled recently as consumers, buoyed by low gas prices, snap up lower-mileage trucks and sport utility vehicles. Credit Andrea Morales for The New York Times Barely a month after world leaders signed a sweeping agreement to reduce carbon emissions, the global commitment to renewable energy sources faces its first big test as the price of oil collapses. Buoyed by low gas prices, Americans are largely eschewing electric cars in favor of lower-mileage trucks and sport utility vehicles. Yet the Obama administration has shown no signs of backing off its requirement that automakers nearly double the fuel economy of their vehicles by 2025. In China, government officials are also taking steps to ensure that the recent plunge in oil prices to under $30 a barrel does not undermine its programs to improve energy efficiency. Earlier this month, the country’s […]