The United States on 4 November 2020 formally left the Paris Climate Agreement, three years after President Donald Trump announced his intention to undo what had been seen as a key achievement of his predecessor Barack Obama.

In December 2015, 195 countries signed an agreement to slow the process of global warming by making efforts to “hold the increase in the global average temperature to well below 2 degrees above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels”.

This basically means that the countries would try to limit the increase in global temperature rise. While poor countries and island states had requested a lower goal considering threats of droughts and sea-level rise, climate experts have said maintaining a 2 degrees increase will be a challenge in itself. The agreement came into force on 4 November 2016.

Another crucial point in this agreement was the decision to limit the amount of greenhouse gases emitted by human activities to a level that can be naturally absorbed by trees, soils and oceans. Nations have pledged “to achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century”. Climate experts told The Guardian that this meant attaining “net zero emissions” between 2050 and 2100. According to the UN’s climate science panel, net zero emissions must be attained by 2070 to avoid dangerous warming.

Developed countries were also told to provide financial resources to help developing countries in dealing with climate change and for adaptation measures. As part of a review mechanism, developed countries were also asked to communicate every two years the “indicative” amount of money they would be able to raise over the next two years, and information on how much of it would come from public financial sources. In contrast, developing countries have only been “encouraged” to provide such information every two years on a voluntary basis.

A key feature of the Paris Agreement has been the way the agreement reflects the principle of ‘common but differentiated responsibilities’ (CBDR), which has been invoked four times in the CBDR principle. Emerging nations stressed on the developed world to take greater responsibility for climate actions since they are largely responsible for emitting almost all of the greenhouse gases from about 1850 to the 1980s.

The agreement also includes a mechanism to address financial losses faced by less developed nations due to climate change impacts like droughts, floods etc. However, developed nations won’t face financial claims since it “does not involve or provide a basis for any liability or compensation”.

So, why did the US leave the Paris agreement?

During his 2016 presidential campaign, Donald Trump had described the Paris Agreement as “unfair” to US interests, and had promised to pull out of the agreement if elected. Trump had also sought to portray that election as a referendum on the policies of former President Obama, who had played a pivotal role in stitching together the complex and far-reaching agreement.

So in June 2017, months after his inauguration, Trump announced his government’s decision to quit the accord. Environmentalists fiercely criticised the move, saying that America’s exit would seriously jeopardise the agreement’s objective of keeping the global temperature rise to within 2 degrees Celsius from pre-industrial times, especially since the US was (and still is) the world’s second-largest emitter of greenhouse gases.

The US could not immediately exit the Paris Agreement, however, as United Nations rules permitted a country to apply for leaving three years after the accord came into force, i.e. November 4, 2019. The US formally applied to leave on that day and the departure automatically came into effect on 4 November 2020, at the end of a mandatory year-long waiting period.