The performance of the European Union’s Emissions Trading System (EU ETS) to date cannot be evaluated without recognizing that the first three years from 2005 through 2007 constituted a "trial" period and understanding what this trial period was supposed to accomplish. Its primary goal was to develop the infrastructure and to provide the experience that would enable the successful use of a cap-and-trade system to limit European GHG emissions during a second trading period, 2008-12, corresponding to the first commitment period of the Kyoto Protocol. The trial period was a rehearsal for the later more serious engagement and it was never intended to achieve significant reductions in CO2 emissions in only three years. In light of the speed with which the program was developed, the many sovereign countries involved, the need to develop the necessary data, information dissemination, compliance and market institutions, and the lack of extensive experience with emissions trading in Europe, we think that the system has performed surprisingly well.

Although there have been plenty of rough edges, a transparent and widely accepted price for tradable CO2emission allowances emerged by January 1, 2005, a functioning market for allowances has developed quickly and effortlessly without any prodding by the Commission or member state governments, the cap-and-trade infrastructure of market institutions, registries, monitoring, reporting and verification is in place, and a significant segment of European industry is incorporating the price of CO2 emissions into their daily production decisions. The development of the EU ETS and the experience with the trial period provides a number of useful lessons for the U.S. and other countries.

• Suppliers quickly factor the price of emissions allowances into their pricing and output behavior.
• Liquid bilateral markets and public allowance exchanges emerge rapidly and the "law of one price" for allowances with the same attributes prevails.
• The development of efficient allowance markets is facilitated by the frequent dissemination of information about emissions and allowance utilization.
• Allowance price volatility can be dampened by including allowance banking and borrowing and by allocating allowances for longer trading periods.
• The redistributive aspects of the allocation process can be handled without distorting abatement efficiency or competition despite the significant political maneuvering over allowance allocations. However, allocations that are tied to future emissions through investment and closure decisions can distort behavior.
• The interaction between allowance allocation, allowance markets, and the unsettled state of electricity sector liberalization and regulation must be confronted as part of program design to avoid mistakes and unintended consequences. This will be especially important in the U.S. where 50 percent of the electricity is generated with coal.

The EU ETS provides a useful perspective on the problems to be faced in constructing a global GHG emission trading system. In imagining a multinational system, it seems clear that participating nations will retain significant discretion in deciding tradable national emission caps albeit with some negotiation; separate national registries will be maintained with some arrangement for international transfers; and monitoring, reporting and verification procedures will be administered nationally although necessarily subject to some common standard. All of these issues have had to be addressed in the trial period and they continue to present challenges to European policy makers.

The deeper significance of the trial period of the EU ETS may be its explicit status as a work in progress. As such, it is emblematic of all climate change programs, which will surely be changed over the long horizon during which they will remain effective. The trial period demonstrates that everything does not need to be perfect at the beginning. In fact, it provides a reminder that the best can be the enemy of the good. This admonition is especially applicable in an imperfect world where the income and wealth effects of proposed actions are significant and sovereign nations of widely varying economic circumstance and institutional development are involved. The initial challenge is simply to establish a system that will demonstrate the societal decision that GHG emissions shall have a price and to provide the signal of what constitutes appropriate short-term and long-term measures to limit GHG emissions. In this, the EU has done more with the ETS, despite all its faults, than any other nation or set of nations.