IPCC Report Missing Something

From http://www.msnbc.msn.com/id/18466213/:

Described as a road map for curbing global warming, a report was approved Friday by delegates from 120 countries that lays out what they said was an affordable arsenal of tools that must be rushed into place to avert a disastrous spike in temperatures.

But a U.S. official raised concern about the economic costs.

The report, a summary of a study by a U.N. network of 2,000 scientists, said the world has to make significant cuts in emissions through increasing the energy efficiency of buildings and vehicles, shifting from fossil fuels to renewable fuels, and reforming both the forestry and farming sectors.

The document made clear that nations have the technology and money to decisively act in time to avoid a sharp rise in temperatures that scientists say would wipe out species, raise ocean levels, wreak economic havoc and trigger droughts in some places and flooding in others.

...

Delegates said the approval of the report should conclusively debunk arguments by skeptics that combating global warming was too costly, that it would stifle development in poorer countries, or that the temperature rise had gone too far to change.

What I want to know is, how can the conclusions of scientists possibly debunk -- let alone do so conclusively -- fundamentally economic claims?

For crying out loud, this is economics: how can anything be conclusive anyway? Even if they were economists and not scientists? That they would even claim it is conclusive make me question their motives and judgment.