Moments before it became official, the most significant climate change action agreement in history looked doomed because of one seemingly inconspicuous word.

Thanks to the eagle eye of the United States’ legal team and an opportunistic Central American nation, weeks of work at the Paris climate summit were very nearly rendered useless and the world would’ve had to wait longer for a united approach to global warming.

And it all came down to a five-letter word.

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In previous draft agreements, the word “should” had been written in place of the word “shall”, however the latter appeared in the proposed final version.

But if “shall” was to sit in the wrong spot in the final agreement, some US legal advisors believed it would mean the deal would need congressional approval in the US – an almost impossible barrier to overcome because of the problem’s contentious nature there.

“Should” implied a moral obligation but did not compel a nation to do something, the advisers believed.  

“Shall” meant there would be a legal obligation to undertake action.

With the problem identified, it should have been a simple matter of switching the text – but not when there are 195 different nations involved.

Nicaragua, a country opposed to the deal, saw it as an opportunity to re-open negotiations and make gains on their grievances.

Things got so heated that US President Barack Obama, Cuban leader Raul Castro and influential Chinese representatives had to make calls to the Nicaraguans so they would back down.

Luckily for the 40,000 delegates and world leaders who had attended the two-week conference, the Nicaraguans relented and the deal went through, free of “shall”, with “should” in its place.

What was decided?

The world will aim to keep warming under 1.5C from pre-Industrial Revolution levels. Photo: AAP

Essentially, it is the first time almost every country in the world has settled upon binding ways and measurements to fight global warming together.

The main agreement reached in the document was to keep global warming to “well below” 2 degrees Celsius from pre-Industrial Revolution levels, but to strive for 1.5C if possible.

The world will also aim for climate-altering greenhouse gas emissions to peak “as soon as possible”, with “rapid reductions” thereafter.

By 2050, there must be a balance between the emissions from human activity, and the amount that can be captured by carbon-absorbing “sinks” such as forests or carbon storage technology.

It described climate change as “an urgent and potentially irreversible threat to human societies and the planet”.

The agreement was prefaced by the fact countries’ existing pledges to curb greenhouse gas emissions would fail to meet targets for stopping dangerous planetary warming.

In 2018, two years before the agreement is enforced, countries will take stock of the overall impact of what they are doing and revisit their carbon-curbing plans in 2020.

Once the agreement takes effect, the collective impact of countries’ efforts will be reviewed at five-year intervals from 2023.

The outcome will inform countries in “updating and enhancing” their pledges.

Rich countries must help poorer countries to finance emissions cutting schemes, and the wealthier nations are also being held to higher emissions cutting targets becuase their greater development meant they’d polluted more.

Leaders trumpet ‘incredible, pivotal’ deal

Julie Bishop and Canadian environment minister Catherine McKenna celebrate the agreement. Photo: Twitter

Many heavy-hitting figures in climate action joined in chorus to celebrate the deal.

Leading the charge was US President Barack Obama, who said his people could be “proud” of the nation’s role in the outcome.

“Today the American people can be proud because this historic agreement is a tribute to American leadership,” Mr Obama said.

“Over the past seven years, we’ve transformed the United States into the global leader in fighting climate change.”

Australian Foreign Minister Julie Bishop was more cautious about the nature of the agreement, although she acknowledged it was “pivotal”.

“Our work here is done and now we can return home to implement this historic agreement. This is a pivotal moment,” Ms Bishop said.

“No country would see this as the perfect outcome. Certainly it does not include everything that we envisaged. However, this agreement does give us a strategy to work over coming years and decade to build the strong and effective action the world needs.”

Professor Tim Flannery, the former chief commissioner of the Climate Council, described it as “incredible”.

“We have witnessed something incredible today. Finally, we can feel hopeful that we are on a path to tackling climate change,” he said.

“This is a watershed moment. All countries have acknowledged they have to act, and almost all are already doing so.”

– with ABC