2007 VOL 315 SCIENCE www.sciencemag.org EFTA_R1_01521504 EFTA02444589 SPECIALSECTION IFS iry (144.tPGA Oninthowe Orsects l•Pct, PC at we Omar obt.off•• wnes Ite.3.n.a.1 *.ittl Cr ) .a Commeetsal Ng. 1. The complex system of energy Rows in the United States in 2005 (V. More than half of the energy