The Paris Climate Agreement, also known as the Paris Agreement, is a landmark international treaty aimed at combating the global threat of climate change. It was adopted by 195 countries in December 2015 at the 21st Conference of the Parties (COP21) to the United Nations Framework Convention on Climate Change (UNFCCC) in Paris, France.

The agreement sets out a long-term goal of keeping the global temperature rise well below 2 degrees Celsius above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 degrees Celsius. To achieve this, each country has pledged to reduce its greenhouse gas emissions and regularly report on its progress towards meeting its targets.

The Paris Agreement officially entered into force on November 4, 2016, after it was ratified by at least 55 countries that together accounted for at least 55% of global greenhouse gas emissions. This threshold was reached much sooner than anticipated, indicating the strong global support for action on climate change.

Since its start, the Paris Agreement has faced various challenges, including the withdrawal of the United States, the second-largest emitter of greenhouse gases, under the Trump administration. However, President Biden has rejoined the agreement and has pledged to make climate change a top priority for the U.S. government.

In conclusion, the Paris Climate Agreement started in December 2015 and officially entered into force on November 4, 2016. It is a vital international agreement that aims to combat climate change by reducing greenhouse gas emissions and limiting the global temperature rise. Despite challenges, the agreement remains an essential tool in the fight against the existential threat of climate change.