It is more then USA, its international:

Transmission lines resting on the bed of the Pacific and Atlantic oceans link all the world’s power grids. Though not known officially to the public, sometime between the years 1970 and 1990, millions of miles of high voltage cooper cable were placed on ocean floors. There are no maps currently available with the exact placing of said cables but it is believed that they run between the places listed below: (it is feared that they are more)

Alaska and Russia
North Eastern Canada to Greenland to Iceland to the United Kingdom
China to Western USA
Japan to China
Unsuccessful efforts were made to run cable from North Korea to USA

During Earth Hour, when global power consumption in low, the voltage stored in all local power grids, and consequently the international transmission lines will increase. This surplus of electricity will be used to power systems like HAARP. Also, by turning off electrical appliances that would otherwise malfunction during the spike in transmission from HAARP, it will give less indication of the general public for the transmissions. Meaning: we are powering their monster by turning off the devices that would detect their monster.