“Warning: This Is a Long Column,” writes PBS Ombudsman Michael Getler. It’s his second piece on viewers raising questions about the financial support of billionaire David H. Koch for Nova’s “Becoming Human” series. The issue is a complicated one, with Nova raising the ire of several letter writers by using a Smithsonian scientist to address the issue of climate change, when the Smithsonian’s David H. Koch Hall of Human Origins was founded by Koch — who is a skeptic that global warming is occurring.