Four months after settling on a plan to stave off calamitous global warming, more than 160 nations gather in New York Friday to ink the pact whose execution demands a radical overhaul of the global economy.

After the Champagne moment when the world community sealed the hard-fought agreement in Paris on December 12, signing the document is an important step.

The next, and final, procedural phase will be ratification by individual governments. Only when 55 countries responsible for 55 percent of global greenhouse gases have done so can the agreement enter into force.

"First and foremost, it (Friday's signing) will serve a strong symbolic function," said Pascal Canfin, with green group WWF.

"But it also creates the political space to accelerate action and build on the dynamism" of the Paris conference, which concluded years of tough and complicated negotiations.

A total of 163 countries have said they will attend the high-level signing ceremony hosted by UN chief Ban Ki-moon.

About 60 heads of state and government will put pen to paper -- including France's Francois Hollande and Canada's Justin Trudeau.

The United States and China -- jointly responsible for 40 percent of greenhouse gases -- will not be represented at the highest level, but are sending Secretary of State John Kerry and Vice Premier Zhang Gaoli.

With so many countries present, "we should set a record for the signing of an international accord," French Environment Minister Segolene Royal, who presides over the climate forum, predicted before departing for New York.

"It is clear that decision-makers have taken the urgency of the climate threat to heart. It is a very good sign."

Countries which do not sign the document on Friday can do so in the year that follows.

- Far from the goal -

The agreement sets out broad lines of attack against climate change.

It defines the goal of limiting global warming to "well below" two degrees Celsius (3.6 degrees Fahrenheit) -- 1.5 C if possible.

It does not prescribe deadlines or targets for curbing planet-warming greenhouse gas emissions: these are described in further detail in non-binding pledges countries filed to shore up the pact.

"We are far from the 2 C goal," said France's top climate negotiator Laurence Tubiana, reiterating the need to "accelerate reform towards a low-carbon economy."

On current trends, scientists say, the world will warm by 4 C over benchmark pre-Industrial Revolution levels -- or 3 C if countries live up to their pledges.

There have been some hopeful signs since Paris.

According to the World Resources Institute (WRI) thinktank, global investment in renewable energy hit a record of $286 billion (252 billion euros) last year -- more than double the sum committed to fossil fuel power plants.

Energy-related carbon emissions stalled for the second year in a row, while renewable energy capacity grew a record 8.3 percent, according to the International Renewable Energy Agency (IRENA).

Peabody Energy, the largest US coal miner, filed for bankruptcy last week in the latest defeat for a sector battered by competition from cheap natural gas and a push for cleaner energy.

Number one carbon polluter China reported two consecutive years of falling coal consumption and invested a record $111 billion in clean energy in 2015, said the WRI.

Companies, investors, universities, governments, insurers, banks, even churches have been withdrawing investments in fossil-fuel projects.

- No magic wand -

Even so, the reality is that developing countries will continue to rely on cheap and abundant fossil fuels like coal and oil to power their fast-growing economies and populations in the years go come.

The Paris Agreement places an onus on rich nations to help poorer ones make the transition to a low-carbon economy.

"Paris created momentum to start to grapple with some of these issues, but it doesn't mean they are solved yet," said Union of Concerned Scientists climate analyst Alden Meyer.

"There is a lot of work to be done yet to adjust to the post-Paris reality" and draw up a workable plan of action.

Added Celia Gautier of the Climate Action Network NGO grouping: "We knew that the Paris agreement wouldn't be a magic wand that would make all the bad disappear. We must keep pushing governments to take action".

This could be through a tax or price on carbon emissions, pulling out of fossil fuel investments, imposing emissions standards for industry, subsidising renewable energy and protecting CO2-absorbing forests.

On Tuesday, global financial firms responsible for tens of trillions of dollars in investments urged the world's leading economies to sign the pact in New York.