Why was the Kyoto Protocol criticized for not binding China and the United States to emission limits?

The Kyoto Protocol was criticized primarily due to its structure, which imposed mandatory emission-reduction targets only on developed countries (Annex I signatories) while exempting developing nations.12

The criticism regarding China and the United States centered on these distinct factors:

• China: As a developing country, China was not required to restrict its emissions under the protocol. Critics argued that because China was the world’s leading emitter of greenhouse gases, its exclusion undermined the treaty's overall effectiveness in addressing global warming.1
• United States: Although the U.S. was the world’s second-largest emitter, it did not ratify the protocol. The U.S. government, notably under President George W. Bush, rejected the treaty specifically because it lacked compulsory emission reductions for developing countries, viewing this as an inequitable burden on industrialized nations.123

This tension was rooted in the principle of "common but differentiated responsibilities," which acknowledges that while all nations must act, developed countries should take the lead due to their historical contributions to environmental degradation. These concerns eventually led to the development of the Paris Agreement, which sought a more inclusive approach by requiring all major emitters to participate.2314