To protect humanity from the threat of global warming, the Third Conference of the Parties to the United Nations Framework Convention on Climate Change, held in Kyoto, Japan, in December 1997, adopted the Kyoto Protocol, which aims to limit greenhouse gas emissions from developed countries in order to curb global warming.

  The Kyoto Protocol stipulates that by 2010, all developed countries must reduce their emissions of six greenhouse gases, including carbon dioxide, by 5.2% compared to 1990 levels.

  Specifically, the reduction targets that developed countries must meet from 2008 to 2012 are as follows: compared to 1990 levels, the European Union must reduce emissions by 8%, the United States by 7%, Japan by 6%, Canada by 6%, and Eastern European countries by 5% to 8%. New Zealand, Russia, and Ukraine may maintain their emissions at 1990 levels. The Protocol also allows Ireland, Australia, and Norway to increase their emissions by 10%, 8%, and 1%, respectively, compared to 1990 levels.

  The Kyoto Protocol requires ratification by at least 55 countries accounting for more than 55% of global greenhouse gas emissions to become a legally binding international treaty. China signed the Protocol in May 1998 and ratified it in August 2002. The European Union and its member states formally ratified the Kyoto Protocol on May 31, 2002. On November 5, 2004, Russian President Vladimir Putin signed the Kyoto Protocol, formally making it part of Russian law. As of August 13, 2005, 142 countries and regions worldwide had signed the Protocol, including 30 industrialized nations, with the populations of the ratifying countries accounting for 80% of the world’s total population.

  Although the U.S. population accounts for only 3% to 4% of the global population, its carbon dioxide emissions account for more than 25% of global emissions, making it the world’s largest emitter of greenhouse gases. The United States signed the Kyoto Protocol in 1998. However, in March 2001, the Bush administration announced its refusal to ratify the Kyoto Protocol, citing the excuses that “reducing greenhouse gas emissions would harm the U.S. economy” and that “developing countries should also bear the obligation to reduce and limit greenhouse gas emissions.”

  On February 16, 2005, the Kyoto Protocol officially entered into force. This marked the first time in human history that greenhouse gas emissions were legally restricted. To encourage countries to meet their greenhouse gas reduction targets, the Protocol permits the following four methods of emission reduction:

  1. “Emissions trading,” in which two developed countries can buy and sell emission allowances; that is, countries struggling to meet their reduction targets can purchase excess allowances from countries that have exceeded their targets.

  2. Calculating greenhouse gas emissions based on “net emissions,” which involves subtracting the amount of carbon dioxide absorbed by forests from a country’s actual emissions.

  3. The use of the Clean Development Mechanism (CDM) to encourage developed and developing countries to jointly reduce greenhouse gas emissions.

  4. The use of the “block approach,” whereby multiple countries within the European Union are treated as a single entity, with some countries reducing emissions while others increase them, to collectively meet the overall reduction target.