The Earth’s climate is changing and global warming is not a myth that can be taken lightly. The world must come together and fight the climate change or else within coming few centuries our planet will not be able to sustain life anymore.

To control and fight the climate change all the countries, especially the United States must curb its greenhouses gases.

If the Untied States pulls back from its pledge to cut carbon dioxide pollution, the planet is likely to hit more dangerous levels of warming even sooner, scientists said. That is because the Untied States contributes so much to the rising temperatures.

President Trump will soon decide whether America stays in or leaves the 2015 Paris climate change accord in which nearly every nation agreed to curb its greenhouse gas emissions.

During the high level security and economic meetings in Italy that began on Friday, all other global leaders urged Trump to say. Pope Francis already made the case with a gift of his papal encyclical on the environment

In an attempt to understand what could happen to the planet if the United States pulls out of Paris. The Associated Press consulted with dozens f climate scientists and analyzed a special computer model scenario designed to calculate potential effects.

Scientists said that the US pulling out will only worsen an already bad situation and make it far more difficult to prevent crossing a dangerous global temperature threshold.

According to the calculations, it could result in 3 billion tons of additional of carbon dioxide emission into the air a year. After few years, scientists said that it is enough to melt ice sheets faster, raise seas higher and trigger more extreme weather.

"If we lag, the noose tightens," said Princeton University climate scientist Michael Oppenheimer, co-editor of the peer-reviewed journal Climatic Change.

A expert group ran a worse case computer simulation that showed if the US did not curb emissions, but other nations do meet their targets, America would add as much as a degree of warning to the globe by the end of century.

Scientists are split on how reasonable and likely that scenario is.

Many scientists said that because of cheap natural gas that displaces coal and gowing adoption of renewable energy sources, it is unlikely that the United States would curb its carbon pollution. So the effect would could be smaller.

But other scientists said that it could be worse because other countries might follow a United States exit.

Another computer simulation team put the effect of the Untied States pulling out somewhere between 0.1 to 0.2 degrees Celsius.

While scientists disagreed on the computer simulations, but overwhelmingly agreed that the warming the planet is undergoing and it would be more faster and intense.

The world without United States efforts would have a more difficult time avoiding a dangerous threshold keeping the planet from warming more than 2 degrees Celsius above pre-industrial levels.

The planet has already warmed by just over half of that amount. With about one-fifth of the past heat-trapping carbon dioxide emissions coming from the US.

So the efforts are about preventing another 0.9 degrees from now.

Jennifer Francis, who is a climate scientist at Rutgers University said: "Developed nations - particularly the US and Europe - are responsible for the lion's share of past emissions, with China now playing a major role."

"This means Americans have caused a large fraction of the warming," he added.

Even with the United States its promises under the Paris agreement, the plant is likely to pass that 2 degree mark.

But the fractions of additional degrees the United States would contribute would mean passing the threshold faster.

National Center for Atmospheric Research's Kevin Trenberth said, “Ecosystems being out of whack with the climate, trouble farming current crops and increasing shortages of food and water."

Climate Interactive is a team of scientists and computer modelers who track the emission. It simulated that global emissions, if every country, but the United States reaches their individual goals to curb carbon pollution then what it would mean in global temperature, sea level rise and ocean acidification using scientifically-accepted computer models.

It would mean an extra 3 billion tons of carbon dioxide in the air a year by 2030. By the end of the century 0.3 degrees Celsius of warming.

The Climate Interactive co-director Andrew Jones said "The United States matters a great deal."

"That amount could make the difference between meeting the Paris limit of two degrees and missing it," he added.

A competing computer simulation team, Climate Action Tracker, put the effect of the United States pulling out somewhere between 0.1 to 0.2 degrees Celsius by 2100.

The team uses a scenario where United States emissions flatten through the century, while Climate Interactive has them rising.

The the director of the Potsdam Institute for Climate Impact Research, John Schellnhuber, is one of the scientists who downplay the harm of the Untied States possibly leaving the agreement  and the scientist credited with coming up with the 2 degree goal.

"Ten years ago a exit by the United States would have shocked the planet," Schellnhuber said. "Today if the United States really chooses to leave the Paris agreement, the world will move on with building a clean and secure future."

Katharine Hayhoe, who is a Texas Tech climate scientist said: "There will be ripple effects from the US choices across the world."

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