WASHINGTON — After several years of little growth, global emissions of heat-trapping carbon dioxide experienced their largest jump in seven years, discouraging scientists.World carbon dioxide emissions are estimated to have risen 2.7 percent from 2017 to 2018, according to three studies released Wednesday from the Global Carbon Project, an international scientific collaboration of academics, governments and industry that tracks greenhouse gas emissions. The calculations, announced during negotiations to put the 2015 Paris climate accord into effect, puts some of the landmark agreement’s goals nearly out of reach, scientists said.“This is terrible news,” said Andrew Jones, co-director of Climate Interactive, which models greenhouse gas emissions and temperatures but was not part of the research. “Every year that we delay serious climate action, the Paris goals become more difficult to meet.”The studies concluded that this year the world would spew 40.9 billion tons of carbon dioxide, up from 39.8 billion tons last year. The margin of error is about one percentage point on either side.The Global Carbon Project used government and industry reports to come up with final emission figures for 2017 and projections for 2018 based on the four biggest polluters: China, the United States, India and the European Union.The U.S., which had been steadily decreasing its carbon pollution, showed a significant rise in emissions — up 2.5 percent — for the first time since 2013. China, the globe’s biggest carbon emitter, saw its largest increase since 2011: 4.6 percent.