This “law” to de-fund Intergovernmental Panel on Climate Change is really an amendment to an omnibus continuing resolution appropriating money to fund the federal government from 4 March 2011 to 30 September 2011. As an omnibus continuing resolution, this bill starts with the default of continuing the same level of funding as that appropriated for the preceding fiscal year, 1 October 2009 to 30 September 2010. This vote here discussed therefore just excludes the funding for Intergovernmental Panel on Climate Change and related items from the spending bill for the balance of this fiscal year.
Association of Community Organizations for Reform Now (ACORN) is an ostensibly private entity that derives or at least derived funding through numerous line items in the federal budget, whereas Intergovernmental Panel on Climate Change (IPCC) is an entity of international diplomacy with a line item in the federal budget. The Congress did not appropriate money to ACORN but to bureaucratic agencies that in turn selected ACORN to receive grants. If eliminating funding for ACORN by name constituted a bill of attainder, then that logic does not apply to IPCC because the latter is essentially an entire government agency, not a private entity.