WASHINGTON — When people think of potential solutions to global warming, they tend to visualize technologies like solar panels or electric cars. A new study published on Wednesday, however, found that better management of forests, grasslands and soils in the United States could offset as much as 21 percent of the country’s annual greenhouse gas emissions. At the high end of the projections, that would be roughly equivalent to taking every single car and truck in the country off the road. The paper, published in the journal Science Advances, identified a number of promising strategies, like replanting trees on degraded lands, changing logging practices to better protect existing forests and sequestering more carbon in farmland soils through new agricultural techniques.