The U.N.'s environment program said Tuesday countries and industries need to do more to meet targets to trim emissions of greenhouse gases that experts say are contributing to global warming.

In its latest "Emissions Gap" report issued ahead of an important climate conference in Germany next week, the program takes aim at coal-fired electricity plants being built in developing economies and says investment in renewable energies will pay for itself — and even make money — over the long term.

Tuesday's report comes as U.N. officials are making a renewed push to maintain momentum generated by the Paris climate accord of 2015.

It aims to cap global temperature increases to 2 degrees Celsius (Fahrenheit) by the year 2100 compared to average world temperatures at the start of the industrial era.

"The Paris agreement boosted climate action, but momentum is clearly faltering," said Edgar Gutiérrez-Espeleta, Costa Rica's environment minister who heads the 2017 UN Environment Assembly. "We face a stark choice: up our ambition, or suffer the consequences."

A new round of U.N. climate talks known as COP 23 starts in Bonn, Germany, on Monday, when countries will take stock of their achievements and prepare more ambitious national goals.

In a summary of the report, UNEP says that current trends suggest that even if current national commitments are met, a temperature increase of 3-degrees Celsius by the end of the century is "very likely — meaning that governments need to deliver much stronger pledges when they are revised in 2020."

"Should the United States follow through with its stated intention to leave the Paris agreement in 2020, the picture could become even bleaker," the statement said, alluding to the Trump administration plans to withdraw the U.S. from the global climate pact.

On the upside, the agency highlights "rapidly expanding mitigation action" and says carbon-dioxide emissions have remained stable since 2014, thanks partly to renewable-energy use in China and India. It cautioned that other greenhouse gases like methane continue to rise, however.

UNEP trumpets the positive effects of investment in solar and wind energy and efficient appliances and cars, and efforts to preserve forests.