One argument in defense of George W. Bush’s lack of action on climate change is some variation of this: “Bill Clinton wasn’t any better … he never sent the Kyoto Protocol to the Senate.

This is true. But it also ignores one important fact.

The science of climate change has improved dramatically since the mid-’90s. In its 1995 report, the Intergovernmental Panel on Climate Change (IPCC) summarized our knowledge about climate change by saying …

… the balance of evidence suggests a discernible human influence on the climate …

This is weak brew, and given the mixed evidence connecting human activities with warming, it was not at all clear exactly how much action to address climate change was warranted.

Around the time George W. Bush took office, however, the IPCC’s 2001 report came out. In it, they concluded:

In the light of new evidence and taking into account the remaining uncertainties, most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations.

And recently, the IPCC’s 2007 report (PDF) concluded:

Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.

It is clear that our understanding of the climate has dramatically improved since Clinton was in office. Today, the evidence that humans are now in control of the climate is overwhelming.

Lack of action by the Bush administration has to account for a much stronger scientific consensus on climate change. There is, basically, no credible dispute on this question. Comparisons to Clinton, who was in office when our knowledge of the climate was much poorer, are not apt.