Responding to concerns that human activities are increasing concentrations of "greenhouse gases" (such as carbon dioxide and methane) in the atmosphere and causing potentially damaging climate change and global warming, nearly all nations of the world joined together in 1992 to sign the United Nations Framework Convention on Climate Change (UNFCCC). The United States was one of the first nations to ratify this treaty. It included a legally non-binding, voluntary pledge that the major industrialized/developed nations would establish national action plans aiming to reduce their greenhouse gas emissions to 1990 levels by the year 2000, and that all nations would undertake voluntary actions to measure and report greenhouse gas emissions to the UNFCCC Secretariat. The parties to the UNFCCC hold annual meetings called Conferences of the Parties (COPs), at which unresolved issues are negotiated, rules of procedure are established or amended, and reviews of progress are considered. As scientific consensus grew that human activities are having a discernible impact on global climate systems, contributing to a warming of the Earth that could result in major impacts such as sea level rise, changes in weather patterns, and health effects—and as it became apparent that many major nations such as the United States and Japan would not be able to reduce their emissions to 1990 levels by 2000—parties to the treaty decided in 1995 that it would be necessary to move beyond voluntary measures and to enter into legally binding commitments. Negotiations began on a protocol to establish legally binding limitations or reductions in greenhouse gas emissions. It was decided by the parties that this round of negotiations would, in keeping with principles established in the UNFCCC, establish limitations only for the developed countries—the 38 nations listed in Annex I to the UNFCCC, including the former Communist countries, plus the European Union, and referred to as "Annex I countries." Developing countries are referred to as "non-Annex I countries." A basic principle established in the UNFCCC and continuing in negotiations on the Kyoto Protocol is that parties have "common but differentiated responsibilities" in dealing with climate change issues, and that first steps in reducing greenhouse gas emissions should be taken by the Annex I countries. Because developed countries have emitted the largest share of the greenhouse gases already in the atmosphere (carbon dioxide releases remain in the atmosphere for many decades), and because they are wealthier and more able to incur costs of any necessary changes in their economies, it was agreed by negotiators of the UNFCCC, and subsequently the Kyoto Protocol, that this principle would be a basic tenet of climate negotiations. The Kyoto Protocol negotiations were completed in late 1997. The protocol establishes legally binding, mandatory emissions reductions for the six major greenhouse gases . It requires that Annex I countries (listed again in Annex B of the Protocol) reduce their aggregate greenhouse gas emissions by 5% below 1990 levels (1990 is the baseline for carbon dioxide, methane, and nitrous oxide; 1995 is the baseline year for the other 3 gases), averaged over the "commitment period" of 2008 to 2012. Each country was assigned individually negotiated targets which differed according to their situations. The United States signed the Protocol in 1998. However, no country is subject to the provisions of a treaty until it has been ratified, which in the United States requires the consent of the U.S. Senate. Because the Senate was on record in mid-1997 in S.Res. 98 , objecting to a treaty that had no mandatory obligations for developing countries, President Clinton did not submit the Protocol to the Senate for advice and consent; therefore the United States did not ratify the Protocol during his Administration. Then in March 2001, soon after President George W. Bush took office, he rejected the Kyoto Protocol, and the United States declined further participation in Kyoto Protocol negotiations. After several years, the required number of Annex I countries had ratified, and the Protocol entered into force in February 2005. As of December 2007, following the announcement that Australia had ratified the Protocol, 175 nations plus the European Union had ratified it, representing over 62% of Annex I countries' 1990 greenhouse gas emissions. Since the United States has not ratified the Protocol, it is not subject to its terms. Negotiations continued after the 1997 treaty was finalized in order to put in place the detailed rules for how the Kyoto Protocol would operate and to establish procedures for how its provisions would be carried out. These negotiations were continued through two subsidiary bodies that address technical issues, and then decisions were made at the annual conferences of the parties (COPs) to the UNFCCC until February 2005 when the Kyoto Protocol had achieved the necessary ratifications to enter into force; the annual meeting is now a UNFCCC COP, combined with a "meeting of the parties (MOP)" to the Protocol. Thus the annual meetings are now referred to as COP/MOP meetings. The United States continues to participate in the discussions and negotiations of the COPs, but as it is not a party to the Kyoto Protocol, it does not participate in Kyoto-related (MOP) negotiations, attending those as an observer. In December 2007, COP-13/MOP-3 convened in Bali, Indonesia, and began the process of formulating an agreement that would succeed the Kyoto Protocol when its commitment period ends in 2012. As summarized below in the section on the Bali Action Plan, the negotiations at this meeting were closely watched for signs that the process agreed on would produce an outcome that would be sufficient to the challenge of mitigating and adapting to climate change. Final decisions on what the commitments of developing and developed countries would be were not expected at Bali, but the considerations to be included in negotiations toward these decisions are outlined in the "Bali Action Plan." The major commitments in the treaty on the key issues are as follows: The Kyoto Protocol calls on all Parties—developed and developing—to take a number of steps outlined in Article 10 to contribute to scientific research and monitoring of the climate system and greenhouse gases in their countries. They are also committed to formulate national and regional programs to improve local emission factors; carry out steps to promote and transfer environmentally sound technologies; strengthen national capacity building activities; and conduct national inventories of greenhouse gas emissions and sinks that remove these gases from the atmosphere. In keeping with the principle of common but differentiated responsibilities, the UNFCCC and the Kyoto Protocol recognize the relatively low per capita greenhouse gas emissions in developing countries, and the need to take into account the development activities of these countries that will require increased energy use. The Protocol does not impose any binding requirements on developing countries; the commitments in Article 10 are regarded as essentially voluntary. Obligations to reduce greenhouse gas emissions by Annex I countries are the focus of most of the Kyoto Protocol, which outlines the legally binding emissions reductions that the Parties to the treaty are to undertake, and provides for development of procedures and rules that apply to Parties as they move toward meeting these binding obligations. These are briefly summarized below. The Kyoto Protocol states that Annex I Parties are committed—individually or jointly—to ensuring that their aggregate anthropogenic carbon dioxide equivalent emissions of greenhouse gases do not exceed amounts assigned to each country in Annex B, "with a view to reducing their overall emissions of such gases by at least 5% below 1990 levels in the commitment period 2008 to 2012." Negotiations on the Kyoto Protocol included a nation-by-nation allocation of the percentage each Annex I country would be obligated to reduce its greenhouse gas emissions in order to collectively reach the overall 5% reduction agreed to in the Protocol. Annex B to the Kyoto Protocol lists 39 nations, including the United States, the European Union plus the individual EU nations, Japan, and many of the former Communist nations (the same countries as Annex I to the UNFCCC). The amounts for each country are listed in this annex as percentages of the base year, 1990 (except for some former Communist countries, which use a more recent year), and range from 92% (a reduction of 8%) for most European countries—to 110% (an increase of 10%) for Iceland. In negotiations on the Protocol, the United States agreed to a commitment on this list to 93%, or a reduction of 7% below 1990 levels. These commitments refer to averages that would be below each Party's 1990 levels for three major greenhouse gases, including carbon dioxide, (and below 1995 levels for the three other, man-made gases), averaged over the "commitment period" 2008 to 2012. (As noted above, only nations that ratify the Protocol are subject to its terms; the United States later rejected participation, and thus is not bound by it.) However, two of the most difficult issues unresolved in 1997 at Kyoto and still under discussion are related to counting emissions of a nation, specifically how to take into account: (1) emissions trading—specifically, how much of a country's obligation to reduce emissions can be met through purchasing credits from outside, vs. taking domestic action; and (2) the extent to which carbon sequestration by forests, soils and agricultural practices can be counted toward a country's emission reductions. These are discussed below. Emissions trading is one of three "flexibility" mechanisms contained in the Kyoto Protocol (article 17). Under the Kyoto Protocol, developed countries are given greenhouse gas emissions "budgets" (or emissions "caps") for the compliance period 2008-2012 based on a percentage of their 1990 or 1995 emissions levels (depending on the particular greenhouse gas). If a country determined that it would exceed its emissions limit during the compliance period, emissions trading would permit it to purchase emissions reductions "credits" from another country that determined it would achieve more emissions reductions than necessary to comply. With emissions trading, countries that can make relatively inexpensive emissions reductions have an incentive to reduce emissions below the level required by the Kyoto Protocol, and sell the extra credits to other countries whose emissions control costs are more expensive. Thus, both the seller and the buyer would have lower costs by virtue of the seller's profit and the buyer's savings.