This important provision states that the host of a CO2 reduction project « will benefit from mitigation measures that result in emission reductions that can also be used by another party to fulfill its national contribution. » This provision requires the « link » between different CO2 emission trading systems – since measured emission reductions must avoid « double counts, » the transferred mitigation results should be considered as a gain on emission units for one part and as a reduction in emission units for the other party.  Due to the heterogeneity of NDCs and national emissions trading systems, ITMOs will provide a format for global connections under the aegis of the UNFCCC.  This provision also puts pressure on countries to implement emission management systems – if a country wants to use more cost-effective cooperative approaches to achieve its NPNs, they need to monitor carbon units for their economies.  According to an analysis by the Intergovernmental Panel on Climate Change (IPCC), a carbon « budget » based on total emissions of carbon dioxide into the atmosphere (relative to the annual emission rate) to limit global warming to 1.5 degrees Celsius has been estimated at 2.25 trillion tonnes since 1870. This represents a significant increase from the initial estimates of the Paris climate agreement (out of a total of 2000 billion tonnes) to reach the global warming target of 1.5oC, a target that would be reached in 2020 for 2017 emission rates. [Clarification needed] In addition, annual CO2 emissions are estimated at 40 billion tonnes per year in 2017. The revised IPCC budget was based on the CMIP5 climate model. Estimate models using different reference years also provide other slightly adjusted estimates of a carbon « budget. »  Japan`s national policy to meet its Kyoto target includes the purchase of AAA sold under GIS.  In 2010, Japanese and Japanese companies were the main customers of AAUs. :53 In the international carbon market, AAE trade is only a small part of the total market value. 9 In 2010, 97% of trade on the international carbon market was fuelled by the European Union`s Emissions Trading Scheme (ETS). :9 Companies regulated under the EU ETS are not able to use APUs to meet their emission limits.  However, the Kyoto Protocol objectives are challenged by climate change deniers, who condemn strong scientific evidence of the human impact on climate change.
An eminent scholar believes that these climate change deniers are « good » in violation of Roussau`s idea of the social contract, which is an implicit agreement between members of a society to coordinate efforts in the name of general social utility. The movement to reject climate change is hampering efforts to reach an agreement on climate change as a global collective society.  But he says Carbon Brief that there will be limited private investment in Article 6.4 projects if the system « authorizes loans that are not credible. » This point is confirmed by IETA, which not only contains positive estimates of future carbon markets, but also notes that the Kyoto Protocol has implemented the UNFCCC`s goal of reducing global warming by reducing greenhouse gas concentrations in the atmosphere to « a level that would prevent dangerous anthropogenic interventions in the climate system » (Article 2). The Kyoto Protocol applies to the six greenhouse gases listed in Schedule A: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), hydrofluorocarbons (PFC) and sulphur hexafluoride (SF6).  In practice, it is very difficult to establish a clear link between the ability to purchase cheap emission credits and a country`s willingness to commit to strengthening climate protection.