In December 2002, AGU Council voted to extend the lifetime of AGU's position statement, “Climate Change and Greenhouse Gases,” for one year until a new statement was prepared. A year later, Council voted unanimously to adopt a new statement, “Human Impacts on Climate,” that reflected advances in the relevant science since 1998 when the original statement was adopted (see Eos, 23 December 2003). The purposes of this article are to provide the rationale for this revision, and to explain the process for formulating and approving this new statement. Background material for this new AGU statement can be found in several sources. These include Ledley et al. , IPCC ,NRC ,and CSSP . The statement itself is available at http://www.agu.org/sci_soc/policy/climate_change_position.html.