Less than a third of governments seeking a global climate agreement have submitted plans for reducing emissions, raising concerns over developing countries’ commitment to a deal months before talks are meant to culminate in Paris. As part of the latest international effort to stave off warming, nearly 200 countries agreed to present their own plans for curbing greenhouse-gas emissions to the United Nations body overseeing the talks. The national plans are meant to be folded into a broader accord aimed at putting the world on track to cap global average temperatures at no more than 2 degrees Celsius above preindustrial levels—a goal that U.N. officials now concede is unlikely in this year’s agreement. While the European Union, China, the U.S. and other big carbon emitters have submitted their reduction targets, many major economies haven’t—including Brazil, Indonesia, Saudi Arabia and India, the fourth-biggest source of carbon dioxide emissions. The EU’s climate czar said late last week that the silence from much of the world is threatening the global deal, which officials hope to wrap up in Paris in December. “The window of opportunity…is closing fast,” said Miguel Arias Cañete, the EU’s energy and climate commissioner. ENLARGE Previous climate accords—including the 1997 Kyoto Protocol—have put the responsibility for reducing emissions largely on advanced economies, which have burned large amounts of fossil fuels for years, as opposed to developing countries, which rely on increased energy consumption to fuel industrial growth and lift citizens out of poverty. But China and other fast-growing economies no longer fit neatly into those two categories. For the Paris agreement, all the countries agreed to develop individualized plans for curbing emissions after 2020, with the threat of international pressure if their commitments don’t compare favorably to others. The U.N.-brokered plan encouraged countries to submit their proposals, known as “intended nationally determined contributions,” or INDCs, by the end of March. A few did so, and others followed suit over the next few months. Submitted proposals now include countries responsible for an estimated three-fifths of global greenhouse emissions, but more than two-thirds of the countries haven’t offered plans. “They all agreed a long time ago to announce them earlier so we could have this review period afterward to see if they are enough collectively,” said Kyle Ash, senior legislative director at Greenpeace in Washington. “Lots of countries need pressure.” In Indonesia, a fast-growing economy that is a top coal producer and leading source of carbon emissions, officials are still working on the government’s proposal and expect to submit one before Oct. 1, the deadline for inclusion in the U.N. body’s report measuring the impact of the Paris agreement, said Nur Masripatin, climate chief at the Environment and Forestry Ministry. The government wants to “think carefully about promises” for the future after already committing to curbing emission through 2020 and halting the clearing of forests, she said. Brazil on Thursday reaffirmed many of the goals of the Paris climate accord during a meeting of its president, Dilma Rousseff, with Chancellor Angela Merkel of Germany, which has been a leader in green energy. “Both countries emphasize that highest ambition of all countries is needed, both in the short term and in the long term,” Brazil and Germany said in a joint statement. A spokesman for the Brazilian government said it also also plans to submit its emissions plan by Oct. 1. Other countries will likely come forward with plans in September, in time for the U.N. General Assembly in New York, where the climate talks are expected to attract increased attention, according to people following the talks. India, whose population and rapid growth make it the most closely watched country yet to submit a climate plan, is holding domestic consultations on the issue and is likely to publish its submission next month. Many countries are likely delaying because of domestic political concerns or to minimize the amount of global peer pressure they will face to cut emissions more deeply, environmental groups say. Poorer countries say they don’t want to commit to expensive shifts in energy policy until wealthier nations flesh out plans to finance green-energy transitions and climate-change preparedness to the tune of $100 billion a year. “In other countries there’s not a domestic constituency calling out for climate and action, and therefore you don’t see a lot of action in that part of the world,” Jennifer Morgan, director of climate and energy at the World Resources Institute, an environmental think tank in Washington. The U.S. has worked with smaller countries in putting together climate proposals. ‎”We have been actively engaging to encourage countries to come forward as soon as possible,” a U.S. official said. “‎Our strong hope is that we come into October with all the major economies.” President Barack Obama has made the issue a priority in recent bilateral meetings, including with Indian Prime Minister Narendra Modi, Ms. Rousseff of Brazil, and China’s President Xi Jinping, who announced Beijing’s climate target with Mr. Obama in November. Republicans lawmakers say the Obama administration doesn’t have the authority to conclude an international climate deal without congressional consent. “Other countries are catching on, which is reflected by the fact that such a small amount of countries have submitted intended nationally determined contributions with only a few months to go,” said Sen. Jim Inhofe (R., Ok.), who leads the Senate’s environmental committee.