Since the Kyoto Protocol came into force, the Clean Development Mechanism has been criticized because, in most cases, it has not brought significant emission reductions or benefits for sustainable development.  It has also suffered from low prices from Certified Emission Reductions (REFs), which has reduced project demand. These criticisms have motivated the recommendations of various interest groups who, through working groups and reports, have provided new elements that they hope to see in the MDS that will support their success.  Details of the governance structure, the terms of the project proposal and the comprehensive approach should be detailed at the conference of the parties to be held in Marrakech in 2016. [must update] Indeed, research shows that the cost of climate activity far outweighs the cost of reducing carbon pollution. A recent study suggests that if the United States does not meet its climate targets in Paris, it could cost the economy up to $6 trillion in the coming decades. A lack of compliance with the NPNs currently foreseen in the agreement could reduce global GDP by more than 25% by the end of the century. Meanwhile, another study estimates that achieving – or even exceeding – the Paris targets by investing in infrastructure in clean energy and energy efficiency could have great benefits globally – about $19 trillion. While the agreement has been welcomed by many, including French President Francois Hollande and UN Secretary-General Ban Ki-moon, criticism has 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.
 In 1992, President George H.W. Bush joined 107 other heads of state at the Rio Earth Summit in Brazil to adopt a series of environmental agreements, including the UNFCCC framework, which is still in force today. The international treaty aims to prevent dangerous human intervention in the planet`s climate systems in the long term. The pact does not set limits on greenhouse gas emissions from individual countries and does not contain enforcement mechanisms, but establishes a framework for international negotiations on future agreements or protocols to set binding emissions targets. Participating countries meet annually at a Conference of the Parties (COP) to assess their progress and continue discussions on how best to combat climate change. InDCs become CNDs – nationally determined contributions – as soon as a country formally adheres to the agreement. There are no specific requirements as to how or how many countries should reduce emissions, but there were political expectations about the nature and rigour of the targets set by different countries. As a result, the scale and ambition of national plans vary widely, largely reflecting each country`s capacity, level of development and contribution to emissions over time. China, for example, has committed to cleaning up its CO2 emissions by 2030 at the latest and reducing CO2 emissions per unit of gross domestic product (GDP) by 60-65% by 2030 from 2005 levels. India has set a target of reducing emissions intensity by 33-35% from 2005 levels by 2030 and producing 40% of its electricity from non-fossil fuels. While the United States has officially announced that it will leave the Paris Agreement in November 2020, a coalition of cities and states (particularly California) agreed in 2017 to comply with the Paris climate agreement and that U.S. emissions be 26 percent lower than in 2005 by 2025.