(CNN) Two years ago this week, representatives from close to 200 countries gathered in the French capital and pledged to take decisive action on climate change.

The Paris Agreement pushed signatories to reduce their carbon output and halt global warming below two degrees Celsius by the end of the century.

The deal was heralded as "the end of the era of fossil fuels" and "a victory for all of the planet" over the days that followed.

Yet under 18 months later the United States, the world's largest economy and second biggest carbon emitter, confirmed it was pulling out of the agreement.

While former President Barack Obama described the Paris accord as "best chance we have to save the one planet that we've got," his successor, President Donald Trump, has been far from as complimentary.

The climate pact was shaped around voluntary commitments reviewed and reassessed every five years. But Trump has stated he sees the agreement as unfair to the US and bad for American jobs.

As things stand , the US will be the only country in the world not signed on to the accord when it completes the lengthy withdrawal process in 2020.

President Donald Trump has pulled the US out of the Paris Agreement on climate change.

How has the world responded?

Mark Lynas, a British author, journalist and environmental activist who focuses on climate change, says Trump's decision has only served to "galvanize" the rest of the world.

It's also left the stage clear for other leaders to come to the fore on the issue.

French President Emmanuel Macron invited scientists, entrepreneurs and NGO workers to move to his country shortly after Trump announced the US would be walking away from the Paris text.

Macron also vowed to " Make Our Planet Great Again ," a pointed play on Trump's "Make America Great Again" slogan.

Elsewhere, India's prime minister Narendra Modi said it would be a " morally criminal act " for the world not to do its part on climate change. Both the European Union and China, meanwhile, have vowed to push forward with the Paris Agreement.

Chinese President Xi Jinping even spoke of his country becoming a " torch bearer " for ecological issues at the Chinese Communist Party Congress in October.

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At the recent COP 23 event in Bonn, Germany, representatives from over 190 countries gathered to discuss the next stages of implementation of the Paris Agreement and how commitments could be increased

Cassie Flynn, a global climate change adviser at the UN Development Programme, says these developments show that "the momentum around the Paris Agreement certainly continues."

A lot of the world's smaller and less developed nations are also stepping up to the plate and pushing to lead on the issues, Flynn adds -- a fact emphasized by Pacific island nation of Fiji presiding over COP 23.

Is the world on track to cut emissions?

According to Climate Action Tracker , the world remains a significant way off meeting its emission reductions goals even with American cooperation.

The independent group of research bodies, which estimates the cuts countries need to make to prevent two degrees of warming, calculates a jump of 3.2 degrees before the end of the century when existing pledges are factored in.

The head of the UN Environment Agency, Erik Solheim, acknowledged as much last month when he wrote that current pledges "cover no more than a third of the emission reductions needed."

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Lynas says it has been "much more difficult to transition away from fossil fuels than anyone thought" while scaling up renewables has not happened as fast as envisioned.

This makes him concerned about the difficulties ahead in ensuring the two degrees target is met even with the political will to do so.

Flynn, however, is more optimistic. She believes Paris has provided the basic framework required for countries to work together. However, ambitions need to be increased "as quickly as possible ... (to) keep our emissions down and increase our resilience to climate change," she adds.

Why is leadership on the issue important in America's absence?

Some believe US withdrawal could still affect how the Paris pact develops.

Rob Bailey, research director on energy, environment and resources at the UK's Chatham House think tank, says one of the key reasons a meaningful agreement was struck in Paris was American and Chinese cooperation.

Chinese workers commute as smoke billows from a coal fired power plant on November 25, 2015 in Shanxi, China.

This made clear early on that the two biggest polluters in the world -- China accounts for 28% of global carbon emissions from fuel combustion and the US 15%, according to the Union of Concerned Scientists -- were on board.

With America gone, Bailey questions whether China can be as ambitious without the dynamic created by another major partner like the US.

He highlights the difficulties engulfing other potential partners such as the EU which is politically preoccupied with the likes of Brexit and the refugee crisis.

A Chinese man and his child wear masks to protest against pollution as they walk through a shopping area in heavy smog on December 8, 2015 in Beijing, China.

Lynas, however, believes that China has signaled it will "exploit its role as a global leader" on this issue and "would find support from the most of the rest of the world" should it do so.

Taking the lead on climate will also likely play well domestically for President Xi given pollution is a major issue in many cities , Lynas adds.

Cities and sub-state actors

Former President Obama recently described the leaders of cities, states and non-profits as the new leadership on climate change.

Obama was speaking at an event in Chicago where mayors from around the world signed on to a charter that looked to emulate the Paris agreement from a city rather than nation-state level.

Many American mayors and governors have rejected Trump's isolationism on the issue.

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Former mayor of New York City, Michael Bloomberg, and California governor, Jerry Brown, founded America's Pledge -- an initiative that aims to bring together states, cities, businesses, universities, and citizens to ensure the US delivers on its Paris Agreement goals.

Lynas says that cities in the US are "keep(ing) the flame alive" for the time being while Flynn also highlights the work done in other major cities like London and Paris as they aim to reduce emissions.

On top of that, she points to the realization among private firms and some of the world's biggest businesses that "addressing climate change is simply good business."

Even with major companies, cities and nation states on board, however, its clear the battle to meet the ambitious targets of the Paris Agreement is only just beginning.