The Paris Agreement is an agreement within the United Nations Framework Convention on Climate Change, dealing with greenhouse-gas-emissions mitigation, adaptation, and finance, starting in the year 2020. As of September 2018, 195 UNFCCC members have signed the agreement, and 181 have become party to it.
Some key elements of the Paris Agreement are the following:
Governments agreed to reduce emissions: with a long-term goal of keeping the increase in global average temperature to well below 2°C above pre-industrial levels, and to aim to limit the increase to 1.5°C, since this would significantly reduce risks and the impacts of climate change.
Governments agreed to improve transparency and to a global stocktake: signatories agreed to come together every 5 years to set more ambitious targets as required by science; track progress towards the long-term goal through a robust transparency and accountability system.
Governments agreed to support climate action: developed countries intend to continue their existing collective goal to mobilise USD 100 billion per year by 2020 and extend this until 2025 to fund the reduction of emissions and the building of resilience to climate change impacts in developing countries.
On June 1, 2017, United States President Donald Trump announced that the U.S. would cease all participation in the 2015 Paris Agreement on climate change mitigation. Trump stated that "The Paris Agreement will undermine (the U.S.) economy," and "puts (the U.S.) at a permanent disadvantage." Trump stated that the withdrawal would be in accordance with his America First policy.
The effects of the US' withdrawal are unclear. In a commentary for Nature, Luke Kemp wrote that "withdrawal is unlikely to change US emissions" since "the greenhouse gas emissions of the US are divorced from international legal obligations." However, he added that it could hamper climate change mitigation efforts if the U.S. stops contributing to the Green Climate Fund. Kemp said the effect of a U.S. withdrawal could be either good or bad for the Paris agreement, since "a rogue US can cause more damage inside rather than outside of the agreement." Finally, "A withdrawal could also make the US into a climate pariah and provide a unique opportunity for China and the EU to take control of the climate regime and significantly boost their international reputations and soft power."
A previous question, How much global warming by 2100?, asked How much greater (in ˚C) will the average global temperature in 2100 be than the average global temperature in 1880?. This question asks How much less will the median prediction be to that same question be if the US resumes participation in the Paris Climate Accord?
If the US outlined its intention to resume participation in the Paris Climate accord, how much less will the median prediction to How much global warming by 2100? be in the 2-month period following the announcement?
An intention is outlined by either (a) the election of a US president with the clear stated position of re-entering the Paris accord, or (b) the announcement by an administration of re-entering it, whichever happens first (if either). The metric used will be a weekly average of the median prediction that will be generated for the 2-month period after the first announced outline. If the US does not announce its intention to resume participation in the Paris Climate Agreement, this question will resolve ambiguously.
This question asks how much less global warming if the US resumes participation in the Paris Agreement, so if you expect that the US resuming the Agreement will reduce global warming, you should predict a positive number.