The most recent GHG Emissions Inventory published by the EPA details the emissions from 1990 through 2003.  Any trend in these numbers between a select few years should be viewed in the context of the overall trend.  Overall, between 1990 and 2003, GHG emissions increased by 13%. 

Recently, claims have been made that between 2000 and 2003, total U.S. greenhouse gas emissions decreased by 0.8%.  This is true, but not representative of the overall trend.  2000 was a particularly high emissions year.  Additionally, all of this reduction occurred in the year 2001—in fact, emissions decreased by 2.1% that year—and is likely related to the economic recession and dramatic economic and travel effects of the September 2001 terrorist attacks.  In fact, since 1990, emissions have increased in every year except 1991 and 2001, both recession years.

While EPA figures for 2004 are not yet available, the EIA (within the Department of Energy) estimates that emissions of CO₂ (the dominant greenhouse gas) increased 1.7% from 2003-2004, which would indicate that even relative to 2000, emissions have increased, not decreased.

U.S. Greenhouse Gas Emissions 1990 - 2004