The successful implementation of greenhouse gas mitigation options would need to overcome technical, economic, political, cultural, social, behavioral, and/or institutional barriers that prevent the full exploitation of the technological, economic, and social opportunities of these mitigation options (see Figure 7-1). The potential mitigation opportunities and types of barriers vary by region and sector, and over time. Most countries could benefit from innovative financing, social learning and innovation, and institutional reforms, removing barriers to trade, and poverty eradication. This is caused by a wide variation in mitigation capacity. The poor in any country are faced with limited opportunities to adopt technologies or change their social behavior, particularly if they are not part of a cash economy. Most countries could benefit from innovative financing and institutional reform and removing barriers to trade. In the industrialized countries, future opportunities lie primarily in removing social and behavioral barriers; in countries with economies in transition, in price rationalization; and in developing countries, in price rationalization, increased access to data and information, availability of advanced technologies, financial resources, and training and capacity building. Opportunities for any given country, however, might be found in the removal of any combination of barriers.

National responses to climate change can be more effective if deployed as a portfolio of policy instruments to limit or reduce net greenhouse gas emissions. The portfolio of national climate policy instruments may include -- according to national circumstances -- emissions/carbon/energy taxes, tradable or non-tradable permits, provision and/or removal of subsidies, land-use policies, deposit/refund systems, technology or performance standards, energy mix requirements, product bans, voluntary agreements, information campaigns, environmental labeling, government spending and investment, and support for research and development (R&D). The literature in general gives no preference for any particular policy instrument.