Final answer:
The United States and China are the most notable countries that have not signed the Kyoto Protocol, primarily due to concerns over economic impacts and growth hindrance respectively.
Step-by-step explanation:
The most notable country that has not signed the Kyoto Protocol is the United States. This international agreement aimed to reduce greenhouse gas emissions was largely shaped by representatives from the U.S. but was ultimately not ratified due to concerns that it would severely harm the U.S. economy. Another significant country that did not ratify the Kyoto Protocol is China, with concerns that it would hinder national growth. Despite this, the protocol was signed in 1997 in Kyoto, Japan, and committed various signatory countries to reduce emissions by 2012. While some countries met or exceeded their goals, the overall global effort to reduce greenhouse gas emissions has been more challenging, as countries have not been able to agree on a successor agreement with clear timelines and benchmarks.