WASHINGTON — The Earth is locked on an “irreversible” course of climatic disruption from the buildup of greenhouse gases in the atmosphere, and the effects will only worsen unless nations agree to dramatic cuts in pollution, an international panel of climate scientists warned Sunday.

The planet faces a future of extreme weather, rising sea levels and melting polar ice from soaring levels of carbon dioxide and other gases, the U.N. panel said. Only an unprecedented global effort to slash emissions within a relatively short time period will prevent temperatures from crossing a threshold that scientists say could trigger far more dangerous disruptions, the panel warned.

“Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts,” concluded the report by the United Nations’ Intergovernmental Panel on Climate Change, which draws on contributions from thousands of scientists from around the world.

The report said some effects of climate change will “continue for centuries,” even if all emissions from fossil-fuel burning were to stop. The question facing governments is whether they can act to slow warming to a pace at which humans and natural ecosystems can adapt, or risk “abrupt and irreversible changes” as the atmosphere and oceans absorb ever-greater amounts of thermal energy within a blanket of heat-trapping gases, according to scientists who contributed to the report.

“The window of opportunity for acting in a cost-effective way – or in an effective way – is closing fast,” said Michael Oppenheimer, a Princeton University geosciences professor and contributing author to the report.

The report is the distillation of a five-year effort to assess the latest evidence on climate change and its consequences, from direct atmospheric measurements of carbon dioxide to thousands of peer-reviewed scientific studies. The final document to emerge from the latest of five assessments since 1990, it is intended to provide a scientific grounding for world leaders who will attempt to negotiate an international climate treaty in Paris late next year.

In cautious and often technically complex language, the new report cites soaring emissions of carbon dioxide, methane and other greenhouse gases in the past 60 years as the cause of nearly all the warming seen so far. While carbon dioxide is a naturally abundant gas essential for plant respiration, it has been accumulating in the atmosphere at an unprecedented rate as a byproduct of the burning of fossil fuels by automobiles, power plants and factories.

Climate change is having profound impacts on “natural and human systems on all continents and across the oceans,” the panel concluded. It cited rising sea levels, more extreme weather events, warmer air and ocean temperatures, melting glaciers and vanishing sea ice.

And, since carbon dioxide remains in the atmosphere for 1,000 years or more, some effects are locked in, perhaps for centuries to come, the report warned.

Scientists and policymakers have set a goal of restraining the average global temperature increase to no more than 2 degrees Celsius, or 3.6 degrees Fahrenheit, on grounds that a higher increase would change the climate so dramatically that neither humans nor natural ecosystems could easily adapt. That would probably require keeping concentrations of key greenhouse gases in the atmosphere to under 450 parts per million, the panel said. Concentrations passed 400 parts per million for the first time in 2013.

Even with a rapid shift to renewable energy, the task of achieving such drastic reductions is daunting, IPCC Chairman Rajendra Pachauri said in a speech last week as panel members began final revisions to the report.

“May I humbly suggest that policymakers avoid being overcome by the seeming hopelessness of addressing climate change,” Pachauri said. “It is not hopeless. This is not to say it will be easy.”

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