Next month, when Gov. Jerry Brown convenes the Global Climate Action Summit in San Francisco, it will be a chance to mark the huge strides he has made on behalf of the climate, and measure how much remains to be done. …But Governor Brown has the opportunity to make his biggest impact yet by harnessing the power of forests to reduce carbon dioxide pollution, the principal cause of global warming. Without protecting these forests, the world can’t cut emissions quickly enough to avoid the most dangerous impacts of climate change. …Though California is far away from the world’s vast tropical rain forests, the state is in a position to protect these rich carbon storehouses through its cap and trade market. …California should create credits for saving whole forest landscapes, across entire states or nations.