In December 2015, after years of negotiations, 195 countries made a new commitment to work together to address global climate change.
This landmark agreement, signed in France's capital, Paris, and seen as a turning point for global climate policy, came into force on November 4, 2016.
As of June 2017, 195 UNFCCC (The United Nations Framework Convention on Climate Change) members had signed the agreement, and 148 have ratified it.
However, on Wednesday, President Donald Trump announced that the United States would withdraw from the accord and suggested he would seek a new deal, without offering any details.
"So we are getting out, but we will start to negotiate and see if we can make a deal that's fair," he said.
The withdrawal also includes the cancellation of all US contributions to the Green Climate Fund, which Trump said was "costing the US a vast fortune".
Trump's decision drew strong criticism both at home and abroad, with world leaders, leading scientists and activists calling the move "disappointing" and "regrettable".
It is an agreement within the UNFCCC dealing with greenhouse gas emissions mitigation, adaptation and finance starting in the year 2020.
The aim is to limit global temperature rise to two degrees Celsius above pre-industrial levels by 2100.
This level is considered a crucial tipping point, above which there will be serious consequences for global food production and more frequent and dangerous climate events, such as flooding and drought.
To achieve this, global greenhouse gas emissions will need to be cut by an estimated 40-70 percent by 2050, and by 2100 the planet must be carbon-neutral.
Under the Paris accord, each country must submit its own plan to reduce emissions of greenhouse gases and address the impact of climate change.
The agreement as a whole is not legally binding and does not penalise nations who fail to meet their commitments.
But it does impose an obligation on countries to implement their plans and includes a review process designed to pressure them into compliance and to increase the scope of their efforts every five years.
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Two of Trump's primary arguments against the accord is that it is "disadvantageous to the US" and that it gives "exclusive benefits of other countries".
The US president said he could not "in good conscience support a deal that punishes the US and that poses no punishment for the world's great polluters".
The US is the world's second-largest emitter of greenhouse gases, and when the agreement was signed in 2015, it was seen as "major leap for mankind".
World leaders, leading economists, scientists, and activists at the time admitted the deal was not "perfect", while some criticised it for not going far enough. Yet many called it a "turning point" for the world's fight against climate change.
Following Trump's decision to withdraw from the accord, the leaders of Germany, France and Italy said the agreement was "not renegotiable".
Many of the largest cities in the US pledged their support for the pact, regardless of Trump's decision.
Canadian Prime Minister Justin Trudeau called Washington's move "deeply disappointing", while Japan's foreign ministry said the decision was "regrettable".
Paris Mayor Anne Hidalgo said Trump's move "is a mistake with dramatic consequences".
The US would join Nicaragua and Syria as the only countries to have not signed on to the agreement.
Nicaragua declined to sign the deal in the first place, arguing that it was too weak.
The White House said it would stick to the UN rules for withdrawing from the agreement.
Under the provisions of the accord, the US cannot formally withdraw until 2020 because countries can only officially leave after three years of the agreement coming into effect and must give a one-year notice prior to withdrawing.
This means that the US can only submit its paperwork for withdrawal in November 2019. The formal withdrawal would not take effect until November 2020, after the next US presidential election.
Because the accord is non-binding, however, Trump could choose to simply ignore the accord's terms.
A quicker option for the US president would be to withdraw from the 1992 UNFCCC, which has nearly universal membership. That process would take about a year to complete.
It remains to be seen what direct impact Trump's decision will have on the accord itself.
Environmentalists and others have long worried a US withdrawal could create a domino effect, with other high carbon-producing countries following Washington's lead.
Many of those countries, however, have reaffirmed their commitment to the deal.
Chinese Prime Minister Li Keqiang said it was "in our interest ... to work step by step towards sustainable development" and environmental protection together with the international community.
One of the major tenets of the Paris agreement was to create a fair environment for all countries in their efforts to combat climate change. Many have argued that developing countries should not have to bear the same financial burden as more developed countries, which are among the world's top polluters.
To address this, the Green Climate Fund was created to aid and encourage developing countries to invest in cleaner energy. A number of countries have pledged $10.3bn to fund, including the US.
The Obama administration pledged $3bn, of which only about $1bn has been delivered.
Trump said that he will end the US contributions to the fund, prompting some to worry about the direct impact such a cut might have on developing countries such as India.
"Countries like India will obviously have to do a lot more by carrying the financial and technological burden," Sunita Narain, an environmentalist with the New Delhi-based Centre for Science and Environment, told Al Jazeera.
Others worry about the impact of the decision on US greenhouse gas emissions.
The Obama-administration had pledged to reduce greenhouse gas emission 17 percent below 2005 levels by 2020 and 26 to 28 percent by 2025.
While recent analyses suggest the US may still be on track to meet its 2020 goal, scientists and consultancy groups have said the withdrawal from the agreement, along with other steps taken by Trump to roll back Obama-era climate regulations, will likely produce a negative "prolonged effect".
The Associated Press consulted with more than two dozen climate scientists and analysed a special computer model scenario designed to calculate potential effects.
Scientists said the US pullout of the agreement would worsen an already bad problem and make it far more difficult to prevent crossing a dangerous global temperature threshold.
There is wide consensus within the scientific community that climate change is fueled by man-made greenhouse gas emissions.
The Intergovernmental Panel on Climate Change (IPCC) has said: "scientific evidence for warming of the climate system is unequivocal".
The temperature of Earth's air and the quantity of heat trapped in its oceans continue to increase, with 2016 declared the hottest year on record.
Climate change could lead to political instability, increased societal tensions and could place new burdens on economies and governments, a report by the American Association for the Advancement of Scientists (AAAS) found. Large numbers of people will likely be displaced due to famine and drought.
A NASA-funded study said that global industrial civilisation is headed for a collapse in the coming decades, blaming unsustainable resource use and increasing wealth inequality.
Source: Al Jazeera and news agencies