On October 5, 2016, when the agreement reached enough signatures to cross the threshold, U.S. President Barack Obama said, „Even if we achieve all the goals… we will only get to part of where we need to go. He also said that „this agreement will help delay or avoid some of the worst consequences of climate change.“ It will help other nations reduce their emissions over time and set bolder goals as technology progresses, all under a strong transparency system that will allow each nation to assess the progress of all other nations.  Although the agreement was welcomed by many, including French President Francois Hollande and UN Secretary-General Ban Ki-moon, criticism also emerged. James Hansen, a former NASA scientist and climate change expert, expressed anger that most of the agreement is made up of „promises“ or goals, not firm commitments.  He called the Paris talks a fraud with „nothing, only promises“ and believed that only a generalized tax on CO2 emissions, which is not part of the Paris agreement, would force CO2 emissions down fast enough to avoid the worst effects of global warming.  Under the Paris Agreement, each country must define, plan and report regularly on its contribution to warming mitigation.  There is no mechanism for a country to set an emission target for a specified date, but any target should go beyond the previous targets. The United States formally withdrew from the agreement the day after the 2020 presidential election, although President-elect Joe Biden said America would return to the agreement after his inauguration.  President Obama was able to formally enshrine the United States in the agreement through executive measures because he did not impose new legal obligations on the country. The United States already has a number of instruments on the books, under laws already passed by Congress to reduce carbon pollution. The country officially joined the agreement in September 2016, after submitting its request for participation.
The Paris Agreement was only able to enter into force after the formal accession of at least 55 nations representing at least 55% of global emissions. This happened on October 5, 2016 and the agreement came into force 30 days later, on November 4, 2016. While the enhanced transparency framework is universal and the global inventory is carried out every five years, the framework must provide „integrated flexibility“ to distinguish the capabilities of developed and developing countries. In this context, the Paris Agreement contains provisions to improve the capacity-building framework.  The agreement recognizes the different circumstances of some countries and notes, in particular, that the technical review of experts for each country takes into account the specific capacity of that country to report.  The agreement also develops a capacity-building initiative for transparency to help developing countries put in place the necessary institutions and procedures to comply with the transparency framework.  This 32-sided document provides a framework for comprehensive climate action, including climate change mitigation and adaptation, aid to developing countries, transparency of reporting and strengthening climate targets.