In my testimony to a Subcommittee of the U.S. House of Representatives, I concluded that humans

“The human influence on climate is significant and involves a diverse range of first-order climate forcings, including, but not limited to the human input of CO2″.

Support for this perspective has come from a very distinguished scientist at the University of Virginia, Professor Jim Galloway, who was recently awarded the prestigious 2008 Tyler Environmental Prize.  The University of Virginia reported on this award (see) and wrote:

“The widespread use of nitrogen-based fertilizer in recent decades has introduced massive amounts of reactive nitrogen compounds into the environment. Few people know more about the problems this causes than U.Va. environmental sciences professor James N. Galloway, who has developed the “nitrogen cascade,” a flow chart demonstrating the pervasive effects of reactive nitrogen.”

and that

“‘We’re accumulating reactive nitrogen in the environment, and this is as much of a legacy as putting carbon dioxide in the atmosphere,”‘ Galloway says. “‘The public doesn’t know about nitrogen, but in many ways it’s as big an issue as carbon, and due to the interactions of nitrogen and carbon, makes the challenge of providing food and energy to the world’s peoples without harming the global environment a tremendous challenge.”‘

The conclusion by Professor Galloway that “in many ways it’s as big an issue as carbon” is one of the reasons that the human climate forcing “The influence of aerosol deposition (e.g., soot; nitrogen) on climate” was included in my House testimony.