Because while "warming" can be easily disproved by showing the temperature heading in the "wrong" (i.e. colder" direction). But "climate change" simply states that temperatures over time will be variable - something that is guaranteed to happen. However, more and more both proponents and skeptics are wondering if we know anything substantive about climate science and its causes.
Of course, this does NOT mean that we should not be looking to change our technologies to less-polluting versions
Should we do nothing about our consumption of petroleum? No, we should use this window of opportunity to decrease our reliance on petroleum; not because of "climate change," but to deprive the oil-producing nations of money too many of them use to underwrite terrorism. This should satisfy both the global warming disciples and deniers and make America and Europe less dependent on nations that wish to destroy our liberty. But threats to liberty are not limited to some oil-producing nations; they can also be found in the British Parliament and in the American Congress.Let's abandon quests for "philosophical purity" in the Copenhagen debate, and find common points of agreement like this.