on a BAU trajectory and on a path towards stabilization at 550ppm $ CO_{2}e $ , the Stern Review estimated “the excess of benefits over costs, in net present value terms, from implementing strong mitigation policies this year, shifting the world onto the better path: the net benefits would be of the order of 2.5 trillion.”

The Stern Review also states that “innovation driven by strong policy will ultimately reduce the carbon intensity of our economies, and consumers will then see reductions in the prices that they pay as low-carbon technologies mature.”

The Stern Review, summarizing the results of analyses based on these three approaches, presented a simple conclusion: the benefits of strong, early action on climate change considerably outweigh the costs.

There is criticism of the Stern Review that the “discount rate” applied to economic model estimates has been set too low and this might have resulted in an overestimation of long-term impacts of climate change. Since many of the preceding economic analyses applied higher discount rates based on the observations of actual behaviors of people, certain researchers consider the Stern Review inappropriate. In contrast, in the Stern Review, Lord Stern argued that the discount rate should be set low and the long-term benefits should be given greater importance regarding the natural system affected by global warming and the human system that depends on the former for its subsistence.

Sources: Asia-Pacific Integrated Modeling (AIM) Team and the executive summary of the "Stern Review: The Economics of Climate Change" (translated by the National Institute for Environmental Studies)

## Section 3 Global Movement on Climate Change

Damage from Climate Change has already started emerging, and it is necessary to take appropriate measures for mitigation and minimize the cost of damage. But only Japan's efforts cannot halt climate change, even if it sets an ambitious reduction target. No country can deal with this problem alone. Persistent discussions are ongoing in international negotiations, where the short-term interests clash between developed and developing countries, among developed countries or among developing countries.

## 1 The International Community’s Responses So Far to Climate Change

The Kyoto Protocol adopted at the third session of the Conference of the Parties (COP3) to the United Nations Framework Convention on Climate Change (UNFCCC) in 1997 based on the UNFCCC committed developed countries to embark on international efforts to reduce greenhouse gas emissions and set numerical targets for greenhouse gas emission cuts by developed countries during the first commitment period (2008-2012). However, the Kyoto Protocol, which the United States does not ratify and developing countries are not subject to reduction targets, covers only about 28% of total global emissions of carbon dioxide from energy sources as of 2007. Global emissions of greenhouse gases are expected to continue to increase in tandem with economic development of developing countries with no reduction obligations. Under these circumstances, in order to reduce emissions of greenhouse gases effectively in the future, it is necessary to strive for measures to address climate change by the entire world, including the United States, which is yet to ratify the Kyoto Protocol, and China and other emerging economies whose energy consumption is expected to increase.

Regarding international negotiations on the post-2012 framework, the COP13 held in Bali, Indonesia, in December 2007 adopted the Bali Action Plan and decided to finalize the post-2012 framework by COP15 in 2009 with the participation of all parties to the UNFCCC.

Meanwhile, at the Group of Eight (G8) Hokkaido Toyako Summit held in 2008, the G8 leaders reached common understanding that they seek to share with all Parties to the Framework Convention on Climate Change the vision of, and together with them to consider and adopt in the UNFCCC negotiation, the goal of achieving at least 50% reduction of global emissions by 2050. At the G8 Summit in L'Aquila, Italy, in July 2009, the G8 leaders reaffirmed the goal of reducing global emissions by at least 50% by 2050, and as part of this, supported a goal of developed countries reducing emissions of greenhouse gases in aggregate by 80% or more by 2050 and also recognized the broad scientific view that the increase in global average temperature above pre-industrial levels ought not to exceed 2 degrees Celsius. Subsequently, then Prime Minister Yukio Hatoyama announced in a speech at the Summit on Climate Change in September 2009 that "For its mid-term goal, Japan will aim to reduce its emissions by 25% by 2020, if compared to the 1990 level, consistent with what the science calls for in order to halt global warming," which is premised on the establishment