Nations around the world still aren’t doing nearly enough to limit greenhouse gas emissions that cause global warming,?? ?? ??? a new report warns.

While progress is being made, a new United Nations report says that collectively countries aren't on track to contain global warming to the level set by leaders in the Paris Climate Agreement. We are currently on course to see between 3 and 3.2 degrees Celsius, or about 5.8 degrees Fahrenheit, of warming by the year 2100.

To put this another way, countries have only committed to about one-third of the emissions reductions needed to meet the Paris Agreement's temperature target, the report found.

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Such a rapid and sizable temperature increase would lead to dangerous changes in the climate, from the rapid melting of polar ice sheets, rising sea levels that could swamp coastal cities worldwide, to more frequent and extreme heat waves, wildfires, and heavy precipitation events.

The report cites some of 2017's calamitous events, including Hurricane Harvey, which caused the heaviest rainstorm in U.S. history, as harbingers of what may be to come around the world.

“One year after the Paris Agreement entered into force, we still find ourselves in a situation where we are not doing nearly enough to save hundreds of millions of people from a miserable future,” said Erik Solheim, head of the U.N. Environment Program, in a statement.

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“This is unacceptable. If we invest in the right technologies, ensuring that the private sector is involved, we can still meet the promise we made to our children to protect their future. But we have to get on the case now.”

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As Solheim suggests, countries have a short window of time during which they can narrow what the report calls a "dangerous gap" between agreed emissions cuts and what is actually necessary to meet the Paris targets. Unless sizable new emissions cuts are pledged by 2020, it's likely that a 1.5-degree Celsius, or 2.7-degree Fahrenheit, target would be impossible to meet after 2030, and the 2-degree target would be all but lost as well.

The gap itself, measured in billions of tons of carbon dioxide emissions per year, is not impossible to narrow or even close altogether, if the right tools are deployed. These include limiting deforestation, deploying more renewable energy installations while limiting the construction of new coal plants, and improving the energy efficiency of everything from automobiles to buildings.

According to the "Emissions Gap Report," published by the U.N. Environment Program and designed to inform diplomats at the upcoming climate summit in Bonn, Germany, the remaining emissions gap is between 11 to 13.5 billion tons of carbon per year compared to scenarios that have a good chance of limiting global warming to 2 degrees Celsius.

People evacuate their homes after the area was inundated with flooding from Hurricane Harvey on August 28, 2017 in Houston, Texas. Credit: Getty Images

The gap is larger, however, when looking at the more ambitious target in the Paris Agreement, which calls for holding warming to 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, above preindustrial levels.

Under the Paris Agreement, each country committed to taking particular actions to reduce their greenhouse gas emissions, with the hope that collectively, these commitments would add up to meeting the overall temperature target in the treaty. However, that's not yet the case.

"The gap between the reductions needed and the national pledges made in Paris is alarmingly high," the report said.

Many climate scientists have warned that the 2-degree target is unrealistic in light of continued increases in greenhouse gases in the atmosphere, and the climate's rapid warming during the past several decades. The year 2016 was the planet's warmest on record, and carbon dioxide levels increased at the fastest rate ever observed between 2015 and 2016.

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But other studies have shown that the climate may exceed the 2-degree target before global average temperatures are then reduced in subsequent decades. However, how long the climate exceeds this target will be crucial for determining the fate of the planet's ice sheets, and therefore, the viability of mega-cities like New York, Shanghai, and Mumbai.

The report notes that non-state actors, such as cities and regional coalitions, could help narrow the emissions gap as well, but it's not yet clear how sizable their contribution will be. Cities, in particular, have taken on an outsized role in the U.S. since the Trump administration announced in June that it intends to pull the country out of the Paris Agreement as soon as it is able to under the treaty.

“The Paris Agreement boosted climate action, but momentum is clearly faltering,” said Edgar E. Gutiérrez-Espeleta, the minister of environment and energy of Costa Rica and president of the 2017 U.N. Environment Assembly, in a statement. “We face a stark choice: up our ambition, or suffer the consequences.”

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