Arizona governor Janet Napolitano said western states “are particularly hard-hit by the effects of climate change,” with recent droughts and worse-than-usual fire seasons.

“In the absence of meaningful federal action, it is up to the states to take action to address climate change and reduce greenhouse gas emissions in this country,” said Napolitano, a Democrat.

Her Republican colleague, California governor Arnold Schwarzenegger, said a cap-and-trade program, which lets companies that can’t meet their emission reduction targets buy credits from those that reduce carbon dioxide, would provide “a powerful framework for developing a national cap-and-trade program. … This agreement shows the power of states to lead our nation addressing climate change.”

The agreement — called the Western Regional Climate Action Initiative — builds on earlier efforts by several states.