The purpose of this is to reflect two things. One is that the state of our knowledge about climate change is always being added to by the scientific community, and if this is going to be a piece of living legislation, it always has to take into account the latest reports from the UNFCCC, for example. We can't be bound by last year's science if this year's science presents a stronger case for action. So that is one of the purposes of this.
The second purpose of this is that we locate our efforts within the context of what other countries do. This is an approach that the government itself has proposed. They have said that one of the ways in which we will judge our effort here is by what other major industrial polluters are doing--for example, China and India--so it is a judgment call by the government of the day, and the Parliament of the day, to look at what other large industrial emitters are doing and ask if this looks roughly responsible.
I think everybody accepts the fact that we are a privileged industrial power with greater capacity for adjustment than developing countries, that we're in a different situation. What “responsible” looks like is always going to be contextual. It will always be relative to what other countries are doing, whether they're developing countries or developed countries.
By the way, this is very much the European approach. The Europeans are saying that what they will do by 2020 is reduce their emissions by 20% vis-à-vis 1990, no matter what. If other large national governments have higher targets than are currently anticipated--such as the United States--they will then revise their targets upwards to 30%.
So this clause is designed to reflect our need to be competitive with other countries, because we wish to always be sure we are among the leaders in greenhouse gas reduction. What constitutes leadership will be an evolving story, depending on how other countries are doing, whether those countries are the United States, China, Russia, or whoever. This is designed to give both the government and Parliament the flexibility to take this legislation forward.