reported in Table 1. With that in mind, together with the fact that the numbers in Table 2 are generated from a model than does not include increasing returns to scale, imperfect competition, productivity enhancement or dynamics, the ‘Central’ scenario’s benefits (equal to 0.2 percent globally and 0.28 percent for developing countries) should be considered very much lower-bound estimates.

As for an upper bound on comparative static gains, the results in Table 1 suggest it could be as much as nine times greater, depending on the extent to which services trade and investment are also liberalized, on the strength of influence of imperfect competition and economies of scale, and on the extent to which the appropriate counterfactual in 2015 is not just current policies but rather moreprotectionist ones in the absence of a robust Doha agreement. To err on the conservative side, we choose an upper bound of five times the lower bound, or 1.0 percent of GDP globally (1.4 percent for developing countries). We also assume that those gains will accrue fully after an eight-year phase-in period from 2008, prior to which the gains will begin in 2008 at one-eighth the full amount as of 2015 and rise by a further one-eighth each year until 2015.

There are dynamic gains from trade to consider in addition to the above comparative static ones. The past experiences of successful reformers such as Korea, China, India and Chile suggest trade opening immediately boosts GDP growth rates by several percentage points per year for many years. A conservative estimate might be that reform boosts GDP growth rates – projected to 2015 by the World Bank (2006) to be 2.7 percent for high-income countries and 4.6 percent for developing countries and so 3.2 percent globally – by one-sixth or 0.45 of a percentage point for high-income countries and by one-third or 1.53 percentage points for developing countries, that is, to 3.15 and 6.13 percent, respectively, and hence from 3.2 to 3.73 percent globally through to 2015.<sup>17,18</sup> For the period after 2015, we assume the boost to growth rates diminishes linearly over time, petering out by 2025 in the low-gain case and by 2050 in the high-gain case. Thereafter there would be no further dynamic benefit in the absence of further reforms, just the continuing comparative static gain of 0.2 percent globally and 0.28 percent for developing countries. This is in line with the summary of the literature provided by Winters (2004), who argues that while the growth increments due to trade liberalisation will be temporary, they could last several decades.

In addition to these contribution to net global benefits, multilateral trade opening also can contribute to reducing inequality and poverty both between and within countries (Hertel and Winters 2006, Hertel et al. 2007). While those are benefits that cannot be incorporated in the standard benefit-cost metric used in this project, they can be thought of as positive externalities that reduce such things as inter- and intra-national social tensions, environmental degradation, malnutrition, and disease, thereby addressing several of the other challenges being considered by the Copenhagen Consensus project.

> 17 For years beyond 2015, we assume the developing country real GDP growth rate converges lineally from 4.6 percent to the current global average of 3.2 percent p.a. over the remaining 85 years (while high-income countries continue to grow at 2.7 percent).

> 18 Econometric support for the claim that this assumed increase in GDP growth rates is conservative is provided by Romalis (2007), who estimates that the elimination of just import tariffs, and only by highincome countries, would boost annual GDP growth in developing countries by up to 1.6 percentage points. In the model by Rutherford and Tarr (2002), their ten percentage point cut in tariffs led to a rise in the steady-state growth rate of 2 percent p.a. to 2.6 percent over the first decade and 2.2 percent over the first five decades (and even after fifty years their annual growth rate is 2.1 percent).

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