Last week, the US President Donald Trump signed a dramatically sweeping executive order to roll back several policies on climate change initiated by his predecessor Barack Obama.

The order stifles the federal government’s enforcement of climate regulations by putting American jobs above addressing climate change.

Indeed, Trump reiterated that the order would put an end to the "war on coal” and "job-killing regulations”.

In a similar tone, President Trump said, after signing the order, that it will "eliminate federal overreach” and "start a new era of production and job creation.”

Specifically, the order rescinds at least six Obama-era executive orders aimed at curbing climate change and regulating carbon emissions, including Obama’s November 2013 executive order instructing the federal government to prepare for the impact of climate change and the September 2016 presidential memorandum that outlined the "growing threat to national security” that climate change poses.

This order ignited mixed reactions in the United States and around the world. In the United States, business groups, especially coal miners, have praised the Trump administration’s move but environmental campaigners have roundly criticised it.

Some environmental advocates have vowed to take legal action against the Trump administration.

Just a few days before signing the order in question, President Trump approved a permit for construction of the controversial Keystone XL pipeline, known as an oil pipeline system in Canada and the United States, which runs from Alberta to Illinois and Texas.

This project came to a greater prominence of attention due to obvious adverse environmental effects, and became a symbol of the battle over climate change and fossil fuels.

As widely known, in 2015, President Barack Obama flatly rejected to approve that project. Of course, this course of action is reminiscent of Trump’s campaign statement that the global warming is "a hoax.”

A fundamental question is: what does this mean to the implementation of the Paris Climate Change Agreement?

As a matter of fact, the United States is the second biggest carbon emitters, after China, in the world. And during the Obama administration, like many countries, the USA ratified the Paris Agreement and thus have an obligation to live up to it.

Reneging on its international obligations would set a bad precedent for other countries. From a legal perspective, states are bound to fulfill the commitments they undertake pursuant to a bilateral or multilateral treaty once it has been ratified and then enters into force.

This obligation stems from the principle of pacta sunt servanda, which means that every treaty in force is binding upon the parties to it and must be performed by them in good faith.

The duty to perform one’s solemn obligations is not something unique to international law and the law of treaties. A similar principle can be found in the contract law of many domestic legal traditions throughout the globe.

Every agreement of a legal nature, domestic or international, whether it is a contract between individuals or a treaty between states, presupposes that in concluding the agreement the parties acted with the intention to abide by its provisions.

The good faith element of this principle suggests that states should take the necessary steps to comply with the object and purpose of the treaty. States may not invoke restrictions imposed by domestic law as good reason for not complying with their treaty obligations provided the instrument was duly ratified by competent authorities and in accordance with constitutional and statutory requirements.

It is noteworthy that the Paris Agreement requires the State Parties to pursue domestic measures with the aim of achieving the objectives of the Nationally Determined Contributions (NDCs).

Moreover, the United States had expressed its intended nationally determined contribution. As such, they would provide information to facilitate the clarity, transparency, and understanding of the contribution.

More broadly, the United States is committed to reducing greenhouse gas pollution, thereby contributing to the objective of the Agreement. Once, this commitment is observed, the outcome would be the stabilisation of greenhouse gas concentrations in the atmosphere at level that would prevent dangerous anthropogenic interference with the climate system.

In fact, during the Obama administration, the United States had undertaken substantial policy action to reduce its emissions, taking the necessary steps to put the world on track to avoid dangerous climate change by limiting global warming to well below 2°C.

Furthermore, to me, one of the greatest achievements of Obama and Ban Ki-Moon was the signing, ratification and entry into force of the Paris Agreement. Both statesmen campaigned doggedly until the Convention became a breathtaking success.

If the United States, which is the biggest donor of the global indispensable activities, withdraws from its commitments, it will generally demotivate other countries towards their Nationally Determined Contributions (NDCs).

As is well known, developed countries have made commitments to provide financial resources to assist developing countries to be able to meet their commitments.

So, if the United States reneges on its pledge on climate change, it would be a major setback, if you like, to the implementation of the Paris Agreement.

The writer is an international expert