Muckraker: Grist on Politics Today at the G8 summit, which began yesterday in Hokkaido, Japan, world leaders reached a landmark deal: agreeing to cut emissions in half by 2050.

The leaders agreed to “seriously consider” this goal last year, and six of the eight leaders have been trying desperately to get George Bush and Canadian Prime Minister Stephen Harper — who continued to resist mandatory cuts as of Monday — on board. That is, until a breakthrough today. Well, sort of: The Bush administration agreed to the 50-percent-by-2050 goal while still bucking at the idea of any shorter-term targets.

German Chancellor Angela Merkel praised the agreement as “a significant step forward” from last year’s meeting: “This means that the international community will no longer get off the hook.” Enviros, though, are concerned about the lack of near-term targets, and setting a “goal” of halving emissions is well short of the binding targets many would like to see.

Regardless, it is a significant step for an administration that has long resisted any effort to establish a global goal for emissions cuts.

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Via Reuters, here’s the statement G8 leaders agreed on:

22. We reconfirm the significance of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) as providing the most comprehensive assessment of the science and encourage the continuation of the science-based approach that should guide our climate protection efforts. We reaffirm our commitment to take strong leadership in combating climate change and in this respect, welcome decisions taken in Bali as the foundation for reaching a global agreement in the United Nations Framework Convention on Climate Change (UNFCCC) process by 2009. We are committed to its successful conclusion. Enhanced commitments or actions by all major economies are essential for tackling climate change. Therefore, we endorse the positive contribution of the Major Economies Leaders Meeting to the UNFCCC.

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23. We are committed to avoiding the most serious consequences of climate change and determined to achieve the stabilization of atmospheric concentrations of global greenhouse gases consistent with the ultimate objective of Article 2 of the Convention and within a time frame that should be compatible with economic growth and energy security. Achieving this objective will only be possible through common determination of all major economies, over an appropriate time frame, to slow, stop and reverse global growth of emissions and move towards a low-carbon society. We seek to share with all Parties to the UNFCCC the vision of, and together with them to consider and adopt in the UNFCCC negotiations, the goal of achieving at least 50% reduction of global emissions by 2050, recognizing that this global challenge can only be met by a global response, in particular, by the contributions from all major economies, consistent with the principle of common but differentiated responsibilities and respective capabilities. Substantial progress toward such a long-term goal requires, inter alia, in the near-term, the acceleration of the deployment of existing technologies, and in the medium- and long-term, will depend on the development and deployment of low-carbon technologies in ways that will enable us to meet our sustainable economic development and energy security objectives. In this regard, we emphasize the importance and urgency of adopting appropriate measures to stimulate development and deployment of innovative technologies and practices.

24. Making progress towards the shared vision, and a long-term global goal will require mid-term goals and national plans to achieve them. These plans may reflect a diversity of mitigation and adaptation approaches. Sectoral approaches are useful tools among others for achieving national emission reduction objectives. We look forward to discussing this issue with leaders of other major economies tomorrow and to continuing the discussions among the major economies and in the UNFCCC negotiations over the coming months. We recognize that what the major developed economies do will differ from what major developing economies do, consistent with the principle of common but differentiated responsibilities and respective capabilities. In this respect, we acknowledge our leadership role and each of us will implement ambitious economy-wide mid-term goals in order to achieve absolute emissions reductions and, where applicable, first stop the growth of emissions as soon as possible, reflecting comparable efforts among all developed economies, taking into account differences in their national circumstances. We will also help support the mitigation plans of major developing economies by technology, financing and capacity-building. At the same time, in order to ensure an effective and ambitious global post-2012 climate regime, all major economies will need to commit to meaningful mitigation actions to be bound in the international agreement to be negotiated by the end of 2009.

25. Sectoral approaches can be useful tools to improve energy efficiency and reduce GHG emissions through dissemination of existing and new technologies in a manner compatible with economic growth. We ask the IEA to enhance its work on voluntary sectoral indicators through improved data collection, complemented by business initiatives. We emphasize the importance of expeditious discussions in the International Civil Aviation Organization (ICAO) and the International Maritime Organization (IMO) for limiting or reducing GHG emissions in the international aviation and maritime sectors, bearing in mind the distinct processes under the UNFCCC toward an agreed outcome for the post-2012 period.